JP3346600B2 - Bolt tightening condition detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a tightened state of a bolt, and more particularly to a method for detecting a tightened state when a bolt is tightened to a plastic region via a washer or the like.

[0002]

2. Description of the Related Art When assembling various articles, a bolt is sometimes used to integrate a plurality of members. When automatically tightening the bolt, a method commonly called an angle tightening method is used. May be adopted. This is because an average rate of change (torque rate) of the tightening torque acting on the bolt in the early stage of the tightening operation is obtained, a theoretical seating point of the bolt is derived based on the torque rate, and the theoretical seating point is calculated. The bolt is tightened by a predetermined set angle as a reference, and since a stable axial force is obtained, it is widely used when assembling an article requiring a fastening force.

[0003] By the way, in the bolt tightening work,
In some cases, an interposition such as a washer is interposed between the tightened body and the head of the bolt. In this case, there is a possibility that the inclusion slips during the tightening of the bolt and rotates together with the bolt. When the bolt and the inclusion rotate together in this way, the tightening torque of the bolt temporarily decreases, so the above-mentioned torque rate decreases and the theoretical seating point is shifted to a lower angle side than the actual theoretical seating point. As a result, there is a possibility that the tightening angle decreases and the axial force of the bolt becomes insufficient.

To solve the above problem in the angle tightening method, for example, as disclosed in Japanese Patent Application Laid-Open No. Hei 3-161286, the tightening torque is measured at a plurality of preset points when the bolt is tightened. A torque rate is calculated from the tightening torque and the tightening angle at each pair of measurement points, and a theoretical seating point is determined based on the large torque rate, and a predetermined seating point is determined based on the theoretical seating point. Some bolts are tightened by a set angle. According to this, the theoretical seating point is determined with high accuracy, and it is expected that the above inconvenience is avoided.

On the other hand, when the bolt is tightened, the bolt may be tightened to a plastic region beyond the elastic limit in order to further stabilize the fastening force. When the angle tightening method is used to tighten the bolt to the plastic region as described above, conventionally, for example, the bolt tightening operation is performed as follows.

That is, for example, a pulse-like angle signal output from a tightening angle sensor provided in a tightening device and a torque signal from a tightening torque sensor also provided in the tightening device are input to a computer or the like. Then, starting from the tightening angle when the tightening torque indicated by the torque signal reaches a preset set torque value, the bolt rotates by a predetermined tightening angle set in consideration of the set torque value. Activate the tightening device up to that point.

[0007] In this case, if the tightening angle is too small, the shaft of the bolt will not be plastically deformed, and the bolt may be loosened due to vibration or the like after the tightening. Conversely, if the tightening angle is too large, an excessive tensile stress is generated in the shaft of the bolt, and the possibility of breakage due to some cause increases. In particular, when the shaft portion of the bolt breaks inside the body to be tightened, the tip of the shaft portion remains in the body to be tightened and requires extensive repair work.

Therefore, when the bolt is tightened up to the plastic region, an inspection of the tightening state of the bolt is performed after the bolt is tightened. Conventionally, the bolt is tightened by the following two methods. An inspection of the tightening condition is being performed.

The first method detects a tightening state based on a tightening angle of a bolt, and is specifically performed according to, for example, the following process.

That is, the angle signal output from the tightening angle sensor provided in the tightening device and the torque signal from the tightening torque sensor also provided in the tightening device are input to a computer or the like, and the angle The value of the tightening torque indicated by the torque signal is stored for each tightening angle indicated by the signal.

Then, as shown in FIG. 8, a torque curve that changes according to the tightening angle θ is obtained.
Here, starting from the tightening angle θ indicated by the angle signal when the tightening torque T indicated by the torque signal matches the first set torque value T1 set in advance, the tightening torque T is set to the first torque.
The change in the tightening angle θ until it matches the second set torque value T2 set to a higher torque side than the set torque value T1 is determined by the first
The rotation angle △ θ1 and the second set torque value T2
If the value obtained by subtracting the first set torque value T1 from the above is divided by the first rotation angle △ θ1, a torque rate during the first rotation angle △ θ1 can be obtained. Then, a line segment 1 connecting the first set torque value T1 and the second set torque value T2 is extrapolated to the low torque side in accordance with the above torque rate, and the tightening torque when the tightening torque T intersects the horizontal axis 2 is 0. The attachment angle θ is defined as the theoretical seating point P, and the tightening torque T is equal to the first set torque value T.
1 and the tightening angle θ becomes a predetermined amount of the second rotation angle Δθ
If the line segment 3 is determined in accordance with the above torque rate so that the final torque value Te at the time of reaching the target tightening angle θt after changing by 2 becomes the end point, the line segment 3 when the line 3 intersects the horizontal axis 2 is obtained. Assuming that the amount of deformation until the bolt reaches the plastic region is proportional to the tightening torque T, the tightening angle θ is such that the bolt reaches the plastic region and the tightening torque T becomes the final torque Te as shown in the figure. This means that the theoretical seating point P is moved in parallel by the steady change angle Δθc at which the tightening angle θ constantly changes. Here, the estimated rotation angle of the bolt is △ θp
Then, the following relational expression can be derived.

Te / △ θp = (T2−T1) / △ θ1 On the other hand, if the extension angle of the bolt is △ θs, this extension angle △
The following relational expression holds between θs, the estimated rotation angle △ θp, and the second rotation angle △ θ2.

Δθ2 = Δθs + Δθp Therefore, the elongation angle Δθs is obtained based on the following calculation formula obtained by modifying the above relational expression.

Δθs = Δθ2−Δθp Then, the elongation angle Δθs calculated in this way is set in advance and compared with lower limit values Δθmx, Δθmn, and the elongation angle Δθs If the values deviate from the lower limits △ θmx and △ θmn, it is determined that the bolt is abnormally fastened.

A second method of checking the tightening state of a bolt is to detect the tightening state based on a residual shaft torque generated in a shaft portion of the bolt, and this is performed, for example, according to the following process. .

That is, the torque rate is calculated from the first and second set torque values T1 and T2 and the first rotation angle △ θ1 in the same manner as described above, and is calculated based on the torque rate as shown in FIG. The linear portion 4 of the torque curve starting from the theoretical seating point P is extended in accordance with the torque rate. Then, assuming that the tightening torque T changes in accordance with the extension line 5, the tightening angle θ becomes equal to the target tightening angle θ.
The value of the tightening torque T when it reaches t is defined as the estimated ultimate torque Tp. Here, according to the above assumption, the following relationship exists between the estimated arrival torque Tp, the first and second set torque values T1 and T2, and the first and second rotation angles △ θ1 and △ θ2. The equation holds.

Tp = T1 + △ θ2 × (T2-T1) / △ θ1 On the other hand, assuming that the residual shaft torque generated by plastic deformation of the bolt shaft is Ta, the residual shaft torque Ta is calculated by the following equation. It will be determined based on the formula.

Ta = Tp−Te Then, the residual shaft torque Ta calculated in this manner is expressed by:
If the residual shaft torque Ta deviates from the upper and lower limits Tmx and Tmn compared to the preset upper and lower limits Tmx and Tmn, it is determined that the bolt is abnormally fastened.

[0019]

However, in any of the above inspection methods, it has been found that there is a problem when the bolt is tightened through an intervening object such as a washer.

For example, taking the former inspection method based on the bolt tightening angle as an example, there is a possibility that the inclusions rotate together during the bolt tightening as described above. As described above, when the bolt and the inclusion rotate together, the tightening torque suddenly changes. For example, as shown in FIG. 10, the torque curve that has linearly increased according to a constant torque rate once passes through the local maximum value Tmx. At the same time, it decreases linearly after passing the minimum value Tmn. When the bolt moves beyond the elastic limit to the plastic region, the final torque T
e, and thereafter the final torque value Te changes until the tightening operation is completed. In this case, if the tightening torque T suddenly changes between the first and second set torque values T1 and T2 as shown in the drawing, under the present circumstances, the first set torque value T1 is changed from the second set torque value T2 to the first set torque value T1. Is subtracted from the value obtained by subtracting the first rotation angle △ θ1 , which is the change in angle therebetween, to calculate the torque rate. Therefore, the torque rate is calculated to be smaller.
Therefore, the theoretical seating point P obtained by extrapolating the line segment 6 connecting the first set torque value T1 and the second set torque value T2 to the low torque side in accordance with the above torque rate shifts to the low angle side. Then, a line segment 7 having the theoretical seating point P as a start point and the final torque value Te as an end point is determined according to the torque rate, and the tightening angle θ is set to the target tightening angle θt
When the line segment 7 is translated in such a manner that the final torque value Te at the time of reaching the end point becomes the end point, the theoretical seating point P moves to a position where the line segment 7 ′ after the translation moves intersects the horizontal axis 2. Will be.

On the other hand, since the tightening torque actually acting on the bolt is considered to change in accordance with the torque rate shown by the torque curve 8 after the sudden change in torque, the torque after the sudden change in torque starting from the minimum value Tmn is considered. Curve 8
Is the actual seating point (hereinafter referred to as the actual seating point) when the line segment 9 extrapolated on the low torque side according to the torque rate intersects the horizontal axis 2 as shown by the broken line in the figure. P
It becomes o. Also in this case, when the line segment 10 having the actual seating point Po as a start point and the final torque value Te as an end point is obtained according to the torque rate after the sudden change in torque, and the tightening angle θ reaches the target tightening angle θt. When the line segment 10 is translated so that the final torque value Te becomes the end point, the theoretical sitting point Po is moved to a position where the line segment 10 ′ after the translation moves intersects the horizontal axis 2. Become.

Therefore, the change in the angle from the theoretical seating point P where the line segment 7 'intersects the horizontal axis 2 until the tightening angle θ reaches the target tightening angle θt is determined by the estimated rotation angle Δθp.
Then, the error angle Δθe due to the difference between the theoretical seating point P and the actual seating point Po is included, and the elongation calculated from the estimated rotation angle Δθp and the second rotation angle Δθ2 is obtained. The angle △ θs is calculated to be smaller by an amount corresponding to the error angle △ θe, so that there is a possibility that the angle is determined to be abnormal despite the normal tightening state.

It should be noted that the latter inspection method based on the residual shaft torque generated in the shaft portion of the bolt may determine that the bolt is normal or abnormal as in the former case.

The present invention addresses the above-mentioned problem when the bolt is tightened with an intervening object such as a washer by using the angle tightening method, and the actual tightening torque acting on the bolt is appropriately adjusted. The purpose of the present invention is to detect a tightening state by reflecting the tightening state.

[0025]

According to a first aspect of the present invention, a method for detecting a tightened state of a bolt is characterized in that the method is configured as follows.

That is, when a bolt is tightened through an intervening object such as a washer, a torque curve is obtained based on a change in the tightening angle when the bolt is tightened, and the rate of change of the torque curve with respect to the tightening angle is determined. When there is a negative state, the minimum value of the tightening torque after the change rate becomes negative is compared with a predetermined value set in advance. When the minimum value is smaller than the set value, the torque rate is calculated based on the torque curve after the minimum value.

On the other hand, when the minimum value is larger than the set value, the minimum value of the torque curve before the minimum value is obtained.
The part larger than the value is removed and the tightening torque rises
A torque rate is calculated based on a torque curve equal to or less than the minimum value before the first match with the minimum value and a torque curve after the minimum value .

Then, a parameter related to the plastic deformation of the bolt is calculated based on the calculated torque rate, and the tightening state of the bolt is detected by comparing the parameter with a predetermined reference value. To

The invention of claim 2 of the present application (hereinafter referred to as “second
In the bolt tightening state detecting method according to the present invention, the second set value larger than the set value in the first invention is set, and the change rate of the torque curve with respect to the tightening angle becomes negative. When the minimum value of the tightening torque is larger than the second set value, the torque before the minimum value is set .
Remove the portion of the torque curve that is greater than the minimum and tighten
A torque rate is calculated based on a torque curve that is equal to or less than the minimum value before the torque rises and matches the minimum value for the first time, and a torque curve that is equal to or smaller than the minimum value. Then, a parameter related to the plastic deformation amount of the bolt is calculated based on the torque rate, and the tightening state of the bolt is detected by comparing the parameter with a predetermined reference value.

The bolt tightening state detecting method according to the third aspect of the present invention (hereinafter, referred to as a third aspect of the present invention) is a method for detecting parameters relating to the plastic deformation of the bolt in the first and second aspects. In addition to the amount of elongation of the bolt, the tightening state of the bolt is detected by comparing the amount of elongation with a predetermined reference value.

On the other hand, the invention of claim 4 of the present application (hereinafter referred to as the fourth invention)
In the method for detecting the tightened state of a bolt according to the present invention, the parameters relating to the amount of plastic deformation of the bolt in the first and second inventions are used as the residual shaft torque generated in the bolt, and the residual shaft torque and a predetermined value are determined. The tightening state of the bolt is detected by comparing the reference value with the reference value.

[0032]

In any of the first to fourth aspects of the present invention, when the bolt is tightened to the plastic region through an intervening object such as a washer using the angle tightening method, the interposed object slips and is tightened. Even if the torque suddenly changes, a torque rate appropriately reflecting the tightening torque actually acting on the bolt is calculated, and the amount of elongation of the shaft of the bolt calculated based on the torque rate is calculated. The error with respect to the actual value of the parameter related to the amount of plastic deformation, such as the torque and residual shaft torque, is reduced, so that the tightened state of the bolt can be detected with high accuracy.

In particular, according to the second invention, the minimum value of the torque curve is compared with the two set values, and the calculation method of the torque rate is changed in each case so that the actual torque rate is reflected. Therefore, the tightened state of the bolt can be detected with higher accuracy.

[0034]

Embodiments of the present invention will be described below.

As shown in FIG. 1, the tightening device 11 is provided with a socket 13 driven by a motor 12, and an angle from a rotary encoder (not shown) for detecting the rotation angle of the socket 13. A signal and a torque signal from a torque transducer (not shown) for detecting a tightening torque are output. These signals are input to a controller (not shown).

A shaft portion 17a of a cylinder head bolt 17 inserted into a bolt hole 16 provided in a cylinder head 15 of the engine via a washer 14, for example,
By rotating the socket 13 of the tightening device 11 mounted on the head, the socket 13 is screwed to the cylinder block 18.

At this time, as in the conventional case, the tightening torque T indicated by the torque signal output from the tightening device 11 coincides with the first set torque value T1 set in advance. Starting from the angle θ, the change in the tightening angle θ until the tightening torque T matches the second set torque value T2 set on the higher torque side than the first set torque value T1 is shown.
And to the first rotation angle △ .theta.1, said first, second set torque value T
1, the torque rate by a T2 is calculated, the torque T tightening by the first set torque value T1 and the fastening angle θ from the match changes by the second rotation angle △ .theta.2 predetermined amount eye
The tightening operation is continued until the target tightening angle θt is reached.
After completion of the tightening operation, a torque curve is generated by connecting the values of the tightening torque T for each tightening angle θ indicated by the angle signal, and the tightening operation is normally performed based on the torque curve. Is determined. At this time, when the tightening state is detected based on, for example, the tightening angle of the cylinder head bolt 17, it is performed as follows.

That is, as shown in FIG. 2, for example, the torque curve 20 in the torque change section where the value of the tightening torque T changes exceeds the first set torque value T1 and then reaches the maximum value T1.
mx, and descends after the first set torque value T
It is assumed that the minimum value Tmn is obtained in a region smaller than 1, and the value starts to increase again and reaches the final torque value Te. In such a case, the torque curve 20 in the torque change section is used.
From the initial curve portion 20a at which the tightening torque T rises to the local minimum value Tmn first, and the intermediate curve portion 20 from the local minimum value Tmn to the local maximum value Tmx to the local minimum value Tmn again.
b and the final curve portion 20c from the minimum value Tmn to the final torque value Te, the minimum value Tm
n and a final torque value Te, a line segment is extended toward the low torque side according to the torque rate of the final curve portion 20c as shown by a broken line in the figure, and the extension line 21
Is the corrected seating point Pm. That is, in this case, the corrected seating point Pm is the actual seating point Pm.
will match o. Therefore, a line segment 23 having the corrected seating point Pm as a start point and the final torque value Te as an end point is obtained in accordance with the torque rate of the final curve portion 20c. The above line segment 23 is set so that the final torque value Te is the end point.
Is translated, the line segment 23 ′ after the translation is represented by the horizontal axis 22.
The corrected seating point Pm moves to a position intersecting with.

Therefore, as in the prior art, the first rotation angle △ θ
When the theoretical seating point P derived from the torque rate calculated by using the first and second and first and second set torque values T1 and T2 is used, the error angle △ θe ' occurs as shown in FIG. Corrected seating point where line segment 23 'intersects horizontal axis 22
The estimated rotation angle △ θp at which the tightening angle θ reaches the target tightening angle θt starting from Pm accurately reflects the actual estimated rotation angle, and the elongation angle calculated based on the above formula accordingly. Δθs also accurately corresponds to the actual elongation angle.

On the other hand, as shown in FIG. 3, after the torque curve 20 in the torque change section where the tightening torque T changes exceeds the first and second set torque values T1 and T2, the maximum value T
It is assumed that the motor torque drops after passing through mx, reaches the local minimum value Tmn in the region between the first and second set torque values T1 and T2, starts to increase again, and reaches the final torque value Te. In such a case, the torque rate is obtained from the initial curve portion 20a and the final curve portion 20c, excluding the intermediate curve portion 20b in the torque curve 20. That is, the initial curve 20a is translated and the end point of the initial curve 20a 'after the translation is connected to the final curve 20c with the minimum value Tmn as shown by the dotted line in FIG. The attachment angle θ is set as the corrected seating point Pm. Then, the gradient of the line segment 24 connecting the corrected seating point Pm and the final torque value Te in the torque change section is used as the torque rate. Also in this case, if the line segment 24 is translated so that the final torque value Te when the tightening angle θ reaches the target tightening angle θt becomes the end point, the line segment 24 ′ after the parallel movement becomes horizontal. The corrected seating point Pm moves to a position intersecting the axis 22.

Therefore, as in the prior art, the first rotation angle △ θ
In the case of using the theoretical seating point P derived from the torque rate calculated by the first and second set torque values T1 and T2, a relatively large error angle 相 対 的 に θe ′ as shown in the figure.
Occurs, whereas the corrected seating point Pm after the parallel movement in which the line segment 24 'intersects the horizontal axis 22 is between the theoretical seating point P and the actual seating point Po after the parallel movement in the same manner. And the estimated rotation angle {the error angle included in θp}
θe decreases, and accordingly, the elongation angle △ θs calculated based on the estimated rotation angle て θp also approaches the actual elongation angle.

As shown in FIG. 4, after the torque curve 20 in the torque change section where the tightening torque T changes exceeds the first and second set torque values T1 and T2, the maximum value T
mx, and falls to a local minimum value Tmn in a region larger than the second set torque value T2, and starts to rise again to reach the final torque value Te. Excluding this, the torque rate is determined from the initial curve portion 20a and the final curve portion 20c. That is, the initial curve portion 20a is translated in parallel, and the end point portion of the initial curve portion 20a 'after the translation is changed to the final curve portion 2 with the minimum value Tmn as shown by the dotted line in the figure.
The tightening angle θ indicated by the starting point when connected to 0c is the corrected seating point Pm. Then, the gradient of the line segment 25 connecting the corrected seating point Pm and the final torque value Te in the torque change section is used as the torque rate. Also in this case, if the line segment 25 is translated so that the final torque value Te when the tightening angle θ reaches the target tightening angle θt becomes the end point, the line segment 25 ′ after the parallel movement becomes horizontal. The corrected seating point Pm moves to a position intersecting the axis 22.

Therefore, as in the prior art, the first rotation angle △ θ
When using the theoretical seating point P derived from the torque rate calculated from the first and second set torque values T1 and T2, a relatively large error angle △ θe is used as in the case shown in FIG. Is generated, whereas the corrected seating point Pm after the parallel movement where the line segment 25 'intersects the horizontal axis 22 is again the difference between the theoretical seating point P after the parallel movement and the actual seating point Po. And the error angle △ θe included in the estimated rotation angle △ θp decreases accordingly, and the elongation angle △ θ calculated based on the estimated rotation angle △ θp accordingly.
s also approaches the actual elongation angle.

As a result, even if the elongation angle △ θs calculated in each of the above cases is compared with the predetermined lower limit values △ θmx and △ θmn, the possibility of an abnormal determination is reduced.

The detection of the tightening state based on the residual shaft torque generated in the shaft portion 17a of the cylinder head bolt 17 is performed as follows.

That is, as shown in FIG. 5, for example, the torque curve 26 in the torque change section where the tightening torque changes.
However, after exceeding the first set torque value T1, it falls past the local maximum value Tmx, becomes a local minimum value Tmn in a region smaller than the first set torque value T1, and then starts to rise again to reach the final torque value Te. Suppose you did. In such a case, the torque curve 26 in the torque change section is represented by an initial curve portion 26a in which the tightening torque rises and becomes the minimum value Tmn first, and the maximum value Tmx starting from the minimum value Tmn.
And the intermediate curve portion 26b which again becomes the minimum value Tmn, and the final curve portion 2 from the minimum value Tmn to the final torque value Te.
6c, a line connecting the minimum value Tmn and the final torque value Te is indicated by an upper line as shown by a broken line in FIG.
It is extended to the low torque side in accordance with the torque rate of the final curve portion 26c , and the tightening angle θ when the extension line 27 intersects the horizontal axis 22 is set as the corrected seating point Pm. That is, in this case, the corrected seating point Pm matches the actual seating point Po.
Therefore, the value of the tightening torque T when the line segment 27 is extended according to the torque rate of the final curve portion 26c and the extension line 28 is extended until the tightening angle θ reaches the target tightening angle θt is The estimated attainment torque Tp "shown also matches the estimated attainment torque Tp obtained from the actual seating point Po, and accordingly, the residual shaft torque Ta calculated based on the above formula is also equal to the actual value. Become.

On the other hand, the first rotation angle △
When using the theoretical seating point P derived from the torque rate calculated by θ1 and the first and second set torque values T1 and T2, a straight line 29 is drawn in accordance with the torque rate with the theoretical seating point P as a starting point. Since the straight line 29 has a relatively small gradient as shown by the one-dot chain line in FIG.
As a result, the estimated arrival torque Tp 'is calculated to be smaller, and a large error torque △ Te' is generated.

On the other hand, as shown in FIG. 6, after the torque curve 26 in the torque change section in which the tightening torque T changes exceeds the first and second set torque values T1 and T2, the maximum value T
It is assumed that the motor torque drops after passing through mx, reaches the local minimum value Tmn in the region between the first and second set torque values T1 and T2, starts to increase again, and reaches the final torque value Te. In such a case, the torque rate is obtained from the initial curve section 26a and the final curve section 26c, excluding the intermediate curve section 26b in the torque curve 26. In other words, the initial curve 26a is translated and the end point of the translated initial curve 26a 'is connected to the final curve 26c with the minimum value Tmn as shown by the dotted line in FIG. The attachment angle θ is set as the corrected seating point Pm. Then, the gradient of the line segment 30 connecting the corrected seating point Pm and the final torque value Te in the torque change section is used as the torque rate. Therefore, when the line segment 30 is extended in accordance with this torque rate, and the extension line 31 is extended until the tightening angle θ reaches the target tightening angle θt, the estimated ultimate torque Tp ″ is calculated from the actual seating point Po. The error torque ΔTe indicated by the residual shaft torque Ta calculated based on the above calculation formula becomes relatively small with the estimated arrival torque Tp obtained.

On the other hand, as described above, the first rotation angle △
When using the theoretical seating point P derived from the torque rate calculated by θ1 and the first and second set torque values T1 and T2, a straight line 32 is drawn according to the torque rate with the theoretical seating point P as a starting point. Since the straight line 32 has a relatively large gradient as shown by the one-dot chain line in FIG.
This time, the estimated arrival torque Tp 'is calculated to be relatively large. In this case, too, the large error torque △ T
e ' will occur.

As shown in FIG. 7, after the torque curve 26 in the torque change section where the tightening torque T changes exceeds the first and second set torque values T1 and T2, the maximum value T
mx, and falls to a local minimum value Tmn in a region larger than the second set torque value T2, and starts to rise again to reach the final torque value Te. Excluding this, the torque rate is obtained from the initial curve portion 26a and the final curve portion 26c. In other words, the initial curve portion 26a is translated in parallel, and the end point of the initial curve portion 26a 'after the translation is changed to the final curve portion 2 by the minimum value Tmn as shown by the dotted line in the figure.
The tightening angle θ indicated by the starting point when connected to the connection point 6c is set as the corrected seating point Pm. Then, the gradient of the line segment 33 connecting the corrected seating point Pm and the final torque value Te in the torque change section is used as the torque rate. Therefore, the estimated attainment torque Tp ″ obtained when the line segment 33 is extended according to this torque rate and the extension line 34 is extended until the tightening angle θ reaches the target tightening angle θt is also actual in this case. The error torque ΔTe indicated by the residual shaft torque Ta calculated based on the above-described calculation formula becomes closer to the estimated arrival torque Tp obtained from the seating point Po.
Is also relatively small.

On the other hand, as described above, the first rotation angle △
When using the theoretical seating point P derived from the torque rate calculated from θ1 and the first and second set torque values T1 and T2, a straight line 35 is drawn according to the torque rate with the theoretical seating point P as a starting point. In this case as well, the straight line 35 is relatively large as shown by the one-dot chain line in FIG.
Therefore, the estimated arrival torque Tp ′ is calculated to be relatively large, and a large error torque ΔTe ′ occurs.

Therefore, even when the residual shaft torque Ta calculated in each of the above cases is compared with the predetermined upper and lower limits Tmx and Tmn, the possibility of an abnormal determination is reduced.

[0053]

As described above, according to the present invention, when the bolt is tightened to the plastic region through the inclusion such as a washer using the angle tightening method, the above-mentioned inclusion slips and tightens. Even if the torque suddenly changes, a torque rate appropriately reflecting the tightening torque actually acting on the bolt is calculated, and the amount of elongation of the shaft of the bolt calculated based on the torque rate is calculated. The error with respect to the actual value of the parameter related to the amount of plastic deformation, such as the residual shaft torque and the like, is reduced, so that the tightened state of the bolt can be detected with high accuracy.

In particular, according to the second invention, the minimum value of the torque curve is compared with the two set values, and the calculation method of the torque rate is changed in each case so that the actual torque rate is reflected. Therefore, the tightened state of the bolt can be detected with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing a tightening device and a state in which a cylinder head is tightened by using the device.

FIG. 2 is an explanatory diagram illustrating a calculation method of calculating an extension angle of a shaft portion of a bolt when a minimum value of a torque curve in a torque change section is smaller than a first set torque value.

FIG. 3 is an explanatory diagram illustrating a calculation method for calculating an elongation angle of a shaft portion of a bolt when a minimum value of a torque curve in a torque change section exists between first and second set torque values.

FIG. 4 is an explanatory diagram illustrating a calculation method for calculating an elongation angle of a shaft of a bolt when a minimum value of a torque curve in a torque change section is larger than a second set torque value.

FIG. 5 is an explanatory diagram illustrating a calculation method for calculating a residual shaft torque of a shaft portion of a bolt when a minimum value of a torque curve in a torque change section is smaller than a first set torque value.

FIG. 6 is an explanatory diagram illustrating a calculation method for calculating a residual shaft torque of a shaft portion of a bolt when a minimum value of a torque curve in a torque change section exists between first and second set torque values.

FIG. 7 is an explanatory diagram illustrating a calculation method of calculating a residual shaft torque of a shaft portion of a bolt when a minimum value of a torque curve in a torque change section is larger than a second set torque value.

FIG. 8 is an explanatory diagram for explaining a conventional calculation method for calculating the elongation angle of a shaft portion of a bolt using a torque curve in a torque change section.

FIG. 9 is an explanatory diagram illustrating a conventional calculation method of calculating a residual shaft torque of a shaft portion of a bolt using a torque curve in a torque change section.

FIG. 10 is an explanatory diagram for explaining a problem when the conventional method of FIG. 8 is used.

[Explanation of symbols]

 Reference Signs List 11 Tightening device 13 Socket 15 Cylinder head 16 Cylinder block 17 Cylinder head bolt 17a Cylinder head shaft

Continuation of front page (56) References JP-A-3-161286 (JP, A) JP-A-61-44582 (JP, A) JP-A-52-1598 (JP, A) JP-A-4-57680 (JP, A) JP-A-1-240275 (JP, A) JP-A-63-67420 (JP, A) JP-A-60-201882 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) B23P 19/06 B25B 23/151 G01L 5/24

Claims (4)

(57) [Claims] 1. A method for detecting a tightened state of a bolt which is tightened through an intervening object such as a washer, wherein a torque curve is obtained based on a change in a tightening angle when the bolt is tightened, and the torque curve is determined. When there is a state in which the rate of change with respect to the tightening angle is negative, the minimum value of the tightening torque after the rate of change becomes negative is compared with a predetermined set value, and the minimum value is set. There while calculating a torque rate based on the torque curve of the outermost small value after when less than the set value, when the minimum value is larger than the set value, outermost torque curve at outermost minimum value previously
The part larger than the small value is removed, and the tightening torque increases.
A torque rate is calculated based on a torque curve equal to or less than the minimum value before the time when the minimum value is first matched and a torque curve after the minimum value, and based on the calculated torque rate, the amount of plastic deformation of the bolt is calculated. A bolt tightening state detecting method, wherein a related parameter is calculated, and the tightening state of the bolt is detected by comparing the parameter with a predetermined reference value. 2. The method according to claim 1, wherein a second set value larger than the set value is set, and a rate of change of the torque curve with respect to the tightened angle becomes negative. The minimum value of the tightening torque after the second
Is larger than the set value of
Remove the part of the torque curve larger than the minimum value and tighten
A torque rate is calculated from a torque curve that is equal to or less than the minimum value before the torque increases and matches the minimum value for the first time, and a torque curve that is equal to or smaller than the minimum value, and the plasticity of the bolt is determined based on the torque rate. A bolt tightening state detection method, comprising calculating a parameter related to a deformation amount, and comparing the parameter with a predetermined reference value to detect a bolt tightening state. 3. The bolt tightening state detecting method according to claim 1, wherein the parameter relating to the amount of plastic deformation of the bolt calculated based on the torque rate is the elongation of the bolt. A method for detecting a bolt tightening state by comparing the amount of elongation with a predetermined reference value. 4. A bolt tightening state detecting method according to claim 1, wherein a parameter relating to the amount of plastic deformation of the bolt calculated based on a torque rate is generated in the bolt. A method for detecting a tightened state of a bolt by comparing the residual shaft torque with a predetermined reference value.