JPWO2019131685A1 - Fastening nut - Google Patents

Abstract

When fastening bolts and nuts, direct the fastening force toward the open side and increase the load sharing to the threads after the third thread to reduce the load of the first thread of fastening meshing that shares the maximum load. Provided is a nut capable of extending the fatigue fracture life of a crack shaft fracture. In the first aspect, in the shape of the vertical cross-sectional view of the nut, the nut forms a convex space concentrically on the seat surface on the nut fastening side with the screw axis as the center, and the convex space is formed. It is a structure in which a convex space is formed as a shape connected by a straight line, a curved line, or a combination thereof, and the depth of the convex space from the seat surface is L2, and the depth from the first valley bottom of the completely threaded portion of the nut is the same. When the axial length to the seat surface is L1, the convex space is fastened by forming the convex space with the depth L2 of the convex space as the range of L1 <L2 ≦ L1 + 5 pitches of threads. The stress applied to the thread of the nut at that time is directed more toward the third thread on the open side and thereafter, so that the load concentration on the first thread of the fastening engagement of the nut and the bolt is reduced.

Description

The present invention relates to a nut used for fastening a bolt and a nut, and has a purpose of reducing the load on the first thread of the fastening mesh.

Bolts and nuts are often used to fasten various structures, and many of aircraft, automobiles, railroad vehicles, machine tools, civil engineering machines, agricultural machines, various manufacturing equipment, bridges, building structures, etc. are bolts and nuts. It is common to conclude with. However, there are many cases where the bolt breaks at the first thread of meshing, and it has been pointed out that the cause is the fracture of the crack shaft at the bottom of the first thread of the fastening mesh of the bolt in use. When a bolt breaks, the fastening itself is broken, and the magnitude of its effect also becomes a problem.

In the conventional screw fastening part, a repeated external force load during use is applied on top of the initial fastening load, so that the cross-sectional area is the smallest and the load sharing is the largest. The fatigue fracture strength is the lowest in the part. It is known that many crack shaft fractures occur at this location.

Until now, we have devised ways to make it difficult for bolts to break by increasing the hardness and tensile strength by changing the material on the bolt side and heat treatment, but such high fracture toughness values are low. It is also known that the bottom of the bolt screw valley of the strength member is sensitively affected by the load as the notch sensitivity increases. However, even with such a device, when the conventional nut is used, the load concentration state on the bottom of the bolt screw valley of the first meshing thread does not change at all. In other words, the improvement of hardness and strength improvement to the bolt side has an effect on the static fracture strength at the time of initial tightening, but it breaks at the fatigue fracture strength when affected by the external force load during use. The effect of toughness value is often counterproductive.

An example of this situation is shown in the following patent document in which the bolt side and the nut side are devised. Patent Documents 1 and 3 disclose a bolt characterized in that the bolt thread to be fitted is tapered in the tensile direction of the bolt and the bolt thread is processed diagonally low, and the bolt is oriented in the axial force direction. The purpose is to gradually reduce the contact area between the bolt thread and the nut thread, equalize the load applied to the bolt thread from the nut thread, and improve the fatigue life. It is stated that this molding may be performed on the nut, but no explanation or figure is given. Patent Document 4 discloses a nut characterized in that one or both of the slope angles of the threads of the nuts fitted to the bolts are smaller than the slope angles of the bolts, and the nuts and bolts are oriented in the tensile direction. It is disclosed that the contact area of the thread of the nut is reduced, the load applied to the thread is equalized, and the fatigue life is improved.

Patent Document 2 discloses a method for manufacturing a bolt, in which a threaded portion of a bolt material is formed into a taper shape in the direction of tensile force, and then a threaded portion having a uniform valley bottom diameter is formed.

Patent Document 5 describes that for steel bolts in which the bolt pitch is smaller than the nut pitch, the pitch difference is in the range of 0.5 to 0.8% of the pitch tolerance specified in Japanese Industrial Standard JIS B 0205. Steel bolts characterized by being set to provide misalignment are disclosed, avoiding simultaneous screw surface contact, tightening progressing, and sequential stress transfer positions when the thread is deformed by stress. A structure that moves and receives a load on all mountains is disclosed.

However, in Patent Documents 1 to 5, since the threads of these bolts and nuts are processed, there is a problem that the screw shape is out of the standard such as JIS and ISO, and these are basically bolts. The threading position is made into a special part depending on the plate thickness, structure, etc. of the object to be fastened, and it is necessary to thread the bolt at a position with specific dimensions for each object to be fastened. , These bolts are not versatile.

In the prior arts of Patent Documents 1 to 5, even if the thread height of the bolt is lowered, the load of each thread does not change significantly. Therefore, on the slope of the thread with a low bolt, the contact area between the threads Will decrease and high stress will be generated. In particular, at the first thread meshing, there is a possibility of uneven plastic deformation that causes indentation on the contact surface on the nut side, and indentation may adversely affect fastening in applications where the nut is used repeatedly.

Further, Patent Documents 6 to 8 propose a set of bolts, nuts, and washers for a high-strength nut for friction joining with respect to the nut side. A first structural example of this set is described in FIGS. 1 and 2 of the same patent document. He stated that it is important to reduce the variation in torque coefficient in the set of bolts, nuts and washers, and for that purpose, a curved protrusion is formed on the outer peripheral side of the end face of the nut on the washer side to make it easier to bite into the washer. However, we are proposing a structure that forms a receding surface and an annular groove on the inner circumference. It is stated that the protrusions and receding surfaces formed on the seat surface alleviate the stress concentration of the threaded portion on the first thread at the time of fastening, and the annular groove further enhances the effect. Further, the bolt axial force is affected by the lubrication performance of the contact portion between the nut and the washer and the lubrication performance between the nut screw portion and the bolt screw portion, suggesting the effective use of a lubricant. However, the condition is a curved protrusion on the nut bearing surface, and a normal planar bearing surface is not applied, and the structure as a nut and the shape of the annular groove that is essentially related to the stress concentration relaxation characteristics, especially There is no description about its depth. The effect of stress concentration relief is indicated by the magnitude of variation in torque coefficient, but whether it is due to the effect of lubricant, protrusion, receding surface, or groove, the essential structure and characteristics of the combination of bolts and nuts. Despite the relationship, it cannot be determined. Originally, the variation in the torque coefficient is derived from the frictional state on the screw thread and the seat surface and the bolt material / hardness, and is a factor different from the purpose of reducing the load concentration of the first thread of the nut.

The bolt and nut structure of Patent Document 6 employs a purpose and a fastening method that are significantly different from the normal bolt and nut fastening method in which fastening is carried out while rotating the nut. In order to increase the friction of the nut seating surface so that the nut does not rotate easily, a convex protrusion is provided on the nut seating surface so that the nut bites into the object to be fastened. This point is referred to in Patent Document 6. This is the part that claims that "the nut with a flat seating surface has been improved".

A second structural example of this nut is described in FIG. 7 of Patent Document 6. A separate part is inserted in the outer peripheral part of the hexagon nut, but this separate part is a kind of sleeve-like structure that is fitted to the inner hexagon nut and cannot rotate with respect to the inner hexagon nut, and is on the washer side. It is characterized by having curved protrusions. The assumed fastening action at the time of fastening is the same as in the first structural example, the force from the seat surface enters this chevron curved protrusion, and the chevron curved protrusion deforms the seating surface on the other side. Later, it enters the flange on the upper part of the inner nut. With a thin upper flange as shown in FIG. 7 of the same document 6, the flange may bend to the open side when a force for buckling the curved protrusion on the fastening side is applied. With this type of "non-rotating nut", deformation of the flange does not matter so much, but since both the nut bearing surface protrusion and the flange are deformed, the bolt, nut, and washer set of this structure are retightened. There is a problem that it cannot be reused.

In Patent Document 7, as a nut with a shear delay failure prevention function, in order to make the shear stress acting on the threads of the bolt and the nut uniform, the bolt has a rotating release object-like gap at the tip, and the nut has a rotating release object-like gap. A combination of nuts with flange lips has been proposed.

The vertical cross section of the nut of Patent Document 7 is provided with a portion without a thread (11 in FIG. 1) on the upper inner diameter side, and an oblique wedge-shaped lip is provided up to the same height as the depth without the screw. It's getting in. Therefore, the height direction dimension of the inner corner of the recess 11 without screws and the innermost part of the wedge-shaped lip on the outside of the screw thread is "height of wedge-shaped lip depth from the object to be fastened ≥ space without screws". The height to the bottom of 11 ". Patent Document 7 states that "prevention of bolt shear delay fracture" is established at this time, but for this purpose, the wedge-shaped lip must be inserted up to the vicinity of the top of the nut. Due to this lip, the rigidity of the nut is insufficient, and due to the insufficient rigidity of the upper part of the nut against the repeated external force load, on the line connecting the innermost part of the lip of the nut and the lowermost part of the carving (dent 11) of the upper part of the bolt. There is a high risk of breakage, and durability is questionable.

Further, when there is a space 5 at the tip of the bolt 8 shown in FIG. 1 of Patent Document 7, the tip side of the threaded portion on the bolt side can also extend in the axial direction, as shown in FIG. 4 of Patent Document 7. The exchange of power becomes smaller. For this reason, there is a possibility that bolts and nuts cannot generate and maintain the axial force specified by JIS (ISO).

Patent Document 8 proposes a nut having a large R (a spherical surface having a concave inside) on the washer and having a similar R on the nut seat surface. The washer has a larger outer diameter than the nut, and when the nut is tightened against the bolt when the surface of the to be fastened under the washer is slightly tilted, the surface condition is uneven or unstable, It shows a structure in which the washer-like base material uniformly hits the nut bearing surface, and it is said that fastening can be performed even when the surface of the object to be fastened is unstable. However, although the washer has a larger outer diameter than the nut, the center hole diameter is not described. The effect and structure of reducing the load on the bottom of the bolt screw valley of the first thread of fastening meshing are not disclosed, and the object is different from that of the present invention.

Japanese Unexamined Patent Publication No. 52-79163 JP-A-52-1310060 U.S. Pat. No. 4,189,975 Japanese Unexamined Patent Publication No. 58-160613 Japanese Unexamined Patent Publication No. 2005-265150 Japanese Unexamined Patent Publication No. 5-288209 JP-A-2002-61619 JP-A-1-182614

In the conventional bolt and nut fastening, although many improvements have been made to the bolts, crack shaft breakage still occurs at the bottom of the first mesh valley of the bolt, and the reason is one mesh. It has been known that excessive stress concentration on the eyes. However, it was difficult to investigate the cause, the situation where the stress is concentrated on the first thread (how the force entering the nut flows into the bolt).

FIG. 4 is a vertical cross-sectional view of a general fastening of a conventional flange nut. The thread of the flange nut 1 has a thread defined by JIS B 0205 (ISO 724) almost uniformly formed from the fastening side to the opening side. In FIG. 4, 1 is a conventional flange nut body, 2 is a bolt, 3 is an object to be fastened, 8 is the fastening side of the nut thread, 8a is the end face and nut bearing surface of the nut thread fastening side, 9 Is the open side of the nut thread, 9a is the end face of the nut thread on the open side, 14 is the nut bearing surface, 15 is the bottom of the conventional thread, 17 is the outer periphery of the nut, and 19 is the thread of the nut. .. The threaded portion of the bolt 2 is screwed into the threaded portion of the nut 1, sandwiches the washer 23, and fastens the object to be fastened 3.

As a result of investigating the stress load sharing when fastening with bolts and nuts of the conventional method, the present inventor has shared 36.5% for the first thread and 20.6% for the second thread in the case of seven threads. It was found that it gradually decreased after the third mountain. More than 1/3 of the total load is concentrated on the 1st mountain, and 70% or more of the total load is shared by the 1st to 3rd threads (load sharing rate; 100% of the total load). The ratio of each thread sharing the load,%). As described above, FIG. 4 shows the fastening state of the conventional method, and the nut 1 fastens the object to be fastened 3 via the washer 23. The bolt 2 penetrates the screw hole from below and is fastened to the nut. Fig. 4-1 (a) shows the Mises equivalent stress distribution diagram of the same nut (7 threads) as in Fig. 4 (maximum on the thread valley bottom marked with * on the left side of the first thread (number 1) of the bolt. Indicates where stress is applied and crack shaft breakage is likely to occur). The force applied from the nut seat surface 14 is oriented in the direction of pushing up the nearest bolt thread No. 1, and the bolt pulls the No. 1 thread most strongly due to the axial force, so the * part is in a state of being opened. ing. Fig. 4-2 is a vector diagram of Mises equivalent stress, showing what kind of force is flowing in the bolt at the maximum principal stress (tensile stress), and Fig. 4-3 also shows the minimum principal stress (compressive stress) in the vector diagram. It is shown here and represents the flow of force in the nut. In this vector diagram as well, it can be seen that the force is concentrated on the first peak of meshing.

With respect to the large load of the first meshing thread, there is an idea that the load of the first meshing thread can be reduced by increasing the number of threads that share the load of the nut. On the other hand, as a result of conducting the same analysis on 8 and 9 threads in addition to the 7 threads of the conventional nut and examining the load sharing, the conventional nut when the number of threads increases on the open side is the 8-thread nut. It was confirmed that the load of the first meshing thread in the case decreased by about 1% to 34.5%, and in the case of the 9-thread nut, it decreased by about 2% and the load of the first meshing thread became 33.4%. It was. Fig. 4-1 (b) shows a stress distribution map equivalent to Mieses with 8 threads, Fig. 4-1 (c) shows a stress distribution map equivalent to Mieses with 9 threads, and the load sharing ratio is compared with 7 threads. 4-4 (a) (conventional nut (7,8,9 thread load sharing ratio comparison table)), and a comparison bar graph of these three load sharing ratios is shown in Fig. 4-4 (b). In the conventional method, the load sharing ratio to the first meshing thread is 36.5% for 7 threads, 34.5% for 8 threads, 33.4% for 9 threads, and the number of threads is 7 threads. , 8 threads, and 9 threads, the bolt side meshing of the * part in Fig. 4-1 (a), (b), (c) 1st thread The thread valley bottom is under excessive stress. This result shows that even if the number of threads of the conventional nut is increased, the effect of reducing the load on the first meshing thread is insignificant.

By optimizing the structure of the nut by the method of the present invention with respect to the load concentration on the first meshing thread of the conventional nut, the load on the bolt and the first meshing thread of the nut is reduced. It is possible to provide a nut that improves the fatigue fracture life of a crack shaft fracture from the bottom of the first mesh valley, which is the weakest part of the strength.

The present invention provides the following inventions in order to solve the above problems. That is, by adopting a nut structure in which the flow of the load force received by the nut is directed more toward the meshing thread on the open side where the load sharing is low, the load sharing after the third thread on the opening side is increased, thereby engaging. Provided is a nut having a structure characterized by being configured to reduce load concentration on the first mountain.

(1) A nut for fastening
A. In the shape of the vertical cross-sectional view of the nut, a space having a convex shape is formed concentrically on the seat surface on the nut fastening side centering on the axis of the screw, and the space is connected by a straight line, a curved line, or a combination thereof. a structure with a space as a shape, when L ₂ of the depth from the seating surface of the _space, the axial length of the first root of the complete thread portion of the nut to the seat surface and the L ₁ By forming the space with the depth L ₂ of the space as the range of L ₁ <L ₂ ≤ L ₁ + 5 pitches of threads;
B. In the shape of the vertical sectional view of the nut, the structure has a rectangular recess on the screw center side of the seat surface on the fastening member side of the nut, and the recess is an inner wall rising vertically from the nut seat surface and a curved line, a straight line, or those. La is the axial length obtained by adding the axial length of the incompletely threaded portion of the nut and the length of two pitches of the nut from the position of the upper surface, and the concave portion. When the axial length from the seat surface to the upper surface is Lb and the radial length of the recess from the screw valley bottom of the nut to the inner wall of the recess is Lh, Lb is 0.001 times or more and 1 times La. By forming the recess concentrically with the center of the screw with the following range and Lh in the range of 0.5 times or more and 5 times or less of La; or C.I. A two-part nut composed of a nut body having a screw shaft portion and a flange bearing surface portion provided with threads inside, and a pipe-shaped nut component having a chamfered seating surface on the inner diameter side of at least one end face. The shape of the vertical cross-sectional view of the nut body is T-shaped, and the length from the flange bearing surface of the nut body to the inside of the nut component toward the object to be fastened is the length by which the screw shaft portion of the nut body enters. A hollow pipe-shaped nut component is placed on the outer peripheral portion of the outer surface of the screw so that the length of the incomplete thread portion s + the screw pitch is 0.5 threads or more and the length of the incomplete thread portion s + the thread pitch is 5 threads or less. The structure is arranged so that the lowermost part of the T-shaped nut body does not come into contact with the object to be fastened, and the uppermost part of the nut part comes into contact with the flange-shaped seating surface of the T-shaped nut body. The length of the nut component is set so that the lowermost portion of the nut component contacts the object to be fastened, the inner diameter surface of the nut component and the outer peripheral surface of the nut body are rotatable, respectively, and the nut body and the nut component are made rotatable. By forming concentric circles with the center of the screw;
By adopting a nut structure that directs the flow of the load force received by the nut to the meshing thread on the open side, which has a low load sharing, the load sharing after the third meshing thread is increased, and one meshing thread is used. A nut with a structure characterized by being configured to reduce the concentration of load on the eyes.
(2) Engagement with at least the bolt on the thread surface of the nut Diamond-like carbon on the surface of the first thread or other threads that contacts some or all of the bolt-side threads, or on the slopes on both sides of the thread. (DLC) film, BN film, WC films, CrN films, HfN film, VN film, TiN film, TiCN film, _Al 2 _{O 3} film, ZnO film, SiO ₂ film, anodized aluminum, a metal plating, a solid lubricating layer, phosphoric acid The nut according to (1) above, which is coated with any one of a manganese chemical conversion treatment, a carburizing and quenching treatment, a nitride treatment, a chromated treatment, or a combination thereof.
(3) Diamond-like carbon (DLC) film, BN film, WC film, CrN film, HfN film, VN film, TiN film, TiCN film, Al ₂ O ₃ film on both or one side of the contact surface between the nut body and the nut component. , ZnO film, SiO ₂ film, alumite, metal plating, polymer resin coat, solid lubricating layer, manganese phosphate chemical conversion treatment, carburizing quenching, nitriding treatment, chromated treatment, or a combination thereof. The nut according to any one of (1) to (2).
(4) Diamond-like carbon (DLC) film on the surface in contact with the fastened object of the nut, BN film, WC films, CrN films, HfN film, VN film, TiN film, TiCN film, _Al 2 _{O 3} film, ZnO film, (1) to the above (1) to which any one of SiO ₂ film, alumite, metal plating, polymer resin coating, solid lubricating layer, manganese phosphate chemical conversion treatment, carburizing and quenching, nitriding treatment, chromated treatment, or a combination thereof is coated. The nut according to any one of (3) is provided.

According to the structure of the nuts (A), (B), and (C) of the present invention, a large amount of force applied from the nut bearing surface is directed to the open side thread after the third thread of meshing, and a large amount of load is shared. It is possible to reduce the load concentration on the first meshing thread, and this effect leads to an improvement in the fatigue fracture life of the crack shaft fracture at the bottom of the bolt valley of the first meshing thread.

In order to obtain this effect, it is preferable to use a nut structure in which the "force flow" is directed more toward the third and subsequent peaks on the open side. The method is to change the outer shape and structure of the nut without changing the JIS (ISO) standard for the thread shape of the nut, that is, by optimizing the structure, the force applied to the nut from the object to be fastened is applied to the nut. It can be directed to the open side screw after the third thread. Alternatively, the nut is composed of two parts, the structure of the place where the force passes is optimized, and the stress entering the nut is directed to the thread on the open side after the third thread, so that the force is applied to the first thread of the meshing screw. It is possible to realize a reduction in concentration.

Furthermore, by adding the surface treatment to the nuts shown in (2) to (4) above, friction at the time of fastening can be reduced, screw surface slidability can be improved, and surface weather resistance can be improved, and nuts useful for use can be obtained. It can be realized.

The first thread of the screw meshing is, for example, the thread of 1 mark shown on the conventional bolt and nut shown in FIG. 4-1 and is referred to as a “first thread”. The side surface of the first thread of the nut is fastened by applying a load to the side surface of the first thread of the bolt. The "first thread" of the nut is on the fastening side and is the first fully threaded portion that has a normal threaded shape. On the other hand, the incomplete threaded portion is a portion having a length including chamfering and about 1 pitch from the beginning of thread cutting.

The position of the first thread of the nut is the first thread of the fully threaded portion. On the bolt side, the thread of the bolt that meshes with the first thread of the nut becomes the first thread of the bolt, and the first valley bottom of the bolt is located on the fastening side of the first thread of the bolt.

The screw shape of the nut of the present invention preferably conforms to that specified in JIS B 0205 (ISO 724). The nut configuration of the present invention is also applied to nuts having a thread shape that has been widely used conventionally, such as an inch screw, and these are also a part of the present invention.

The load sharing of the fastening force by the bolts and nuts acts at the same sharing rate as the initial tightening as the axial force fluctuation not only at the time of initial tightening but also against the external force load such as vibration applied to the screw fastening part from the outside. .. Reducing the load sharing to the first thread, which has a particularly severe load, is the fatigue failure strength of the first thread bolt thread valley bottom that receives the external force load (fluctuation axial force load) that is added up at the same load sharing rate. It is effective in improving.

Fracture of bolt and nut fastening parts often occurs as crack shaft fracture at the bottom of the first peak valley of bolt engagement, but how is the reduction of the initial fastening load, which is said to have the effect of improving fatigue fracture strength, effective? Explain whether it will work. The SN diagram obtained from the bolt fatigue test results shows the relationship between the fatigue fracture life (repetition number Nf) and the external force load (stress amplitude σr), but it is generally shown by the following empirical formula. Can be done.
Nf · σr ^b = C
Here, Nf: Number of repeated loads until fatigue failure
σr: stress amplitude of load
b: Stress index (generally 3-5)
C: Material constant As shown here, lowering the load on the bottom of the bolt screw valley at the first thread of fastening mesh leads to lowering the share of the external force load (σr), and the stress amplitude b of the lowered load (b ( Generally, it leads to the effect that the multiplication / repetition number Nf can be increased by 3 to 5).

In general, it is not possible to directly see the force transmitted in a substance, so finite element analysis is useful as a method for predicting the state and flow of force in a substance. In order to analyze each thread load in the conventional bolt and nut fastening, a simulation analysis of the screw fastening part was carried out by the CAE (Computer Added Engineering) method utilizing the finite element method (FEM: Fine Element Method). The Mises equivalent stress distribution of the method nut is shown in FIGS. 4-1 (a), (b), and (c). Further, the same analysis is performed for the aspects (A), (B), and (C) of the present invention.

In performing this analysis, the number of threads of the nut is generally 7 and the number of effective threads is selected, and the same applies to each aspect of the present invention. The same conditions are used for the fastening force and nut strength at the time of fastening. In addition, the same conditions apply to nuts with 8 and 9 threads, which are compared with the conventional 7 threads, except for the number of threads.
In the aspect (C) of the present invention, the analysis in the case of 7 threads and the analysis in which the number of threads is 8 are performed, and the load sharing of 7 threads and 8 threads in the conventional method is compared, respectively.

As shown in FIG. 4-1 in the conventional method, the first thread of screw meshing (1 mark in FIG. 4-1 (a)) has the highest internal stress, and the second thread (2 mark in FIG. 4-1) has the highest internal stress. At the third peak (mark 3 in Fig. 4-1), the stress drops sharply. This situation is shown in FIG. 4-4 (a) as the load sharing ratio of all threads, and the comparison of the load sharing ratio is shown in a bar graph in FIG. 4-4 (b). A bar graph with a white frame is used for fastening 7 threads in the conventional method. In this case, 35.6% of the total load is applied to the first mountain, 20.6% to the second mountain, and 14.4% to the third mountain, and the load sharing up to the third mountain is actually 70% or more. To reach. From the 4th thread onward, the load sharing ratio of each thread is only about 11 to 4% or less. The valley bottom of the first thread of the bolt (marked with * in Fig. 4-1 (a)) becomes highly stressed, and the crack shaft breakage of the bolt that occurs when using a conventional nut is the bolt of the first thread of meshing. It often occurs from the bottom of the screw valley.

It is a vertical sectional view which shows an example of the nut of the 1st aspect (A) of this invention. Examples of (a) cross-sectional view of the nut, (b) plan view seen from the nut open side, and (c) plan view seen from the nut seat surface side. The Mises equivalent stress distribution diagram of an example of the nut of the first aspect (A) of the present invention. The vector diagram of the maximum principal stress (tensile stress) of an example of the nut of the 1st aspect (A) of this invention. The vector diagram of the minimum principal stress (compressive stress) of an example of the nut of the 1st aspect (A) of this invention. Comparison of load sharing ratio between an example of the aspect (A) of the present invention and the conventional nut FIG. 4-1. An example of the aspect (A) of the present invention and a bar graph of a conventional nut FIG. 4-1. A vertical sectional view of a modified example of the first aspect (A) of the present invention is shown. A vertical sectional view of a modified example of the first aspect (A) of the present invention is shown. The vertical sectional view which shows an example of the basic form of the nut of the 2nd aspect (B) of this invention. The vertical sectional view of the modification of the 2nd aspect (B) of this invention. Second aspect of the present invention (B) Mises equivalent stress distribution diagram of another modified example. Second aspect of the present invention (B) Another modification. Second aspect of the present invention (B) Another modification. The vertical sectional view which shows an example of the nut of the 3rd aspect (C) of this invention. The Mises equivalent stress distribution diagram of an example of the nut of the third aspect (C) of the present invention. A numerical comparison table of the load sharing ratio between an example of the nut of the third aspect (C) of the present invention and the conventional method. A bar graph comparing an example of a nut according to a third aspect (C) of the present invention with a conventional method. The Mises equivalent stress distribution diagram of the modified example of the nut of the third aspect (C) of the present invention. A numerical comparison table of the load sharing ratio between the modified example of the nut of the third aspect (C) of the present invention and the conventional method. A bar graph comparing a modified example of the nut according to the third aspect (C) of the present invention with the conventional method. A vertical sectional view (a), a plan view (b) from above, and a plan view (c) from below of a conventional flange nut. Mises equivalent stress distribution diagram of a conventional nut with 7 threads. Mises equivalent stress distribution diagram of a conventional nut with 8 threads. Mises equivalent stress distribution diagram of a conventional nut with 9 threads. A vector diagram of the maximum principal stress (tensile stress) of a conventional nut with 7 threads. Vector diagram of the minimum principal stress (compressive stress) of a conventional nut with 7 threads. Numerical table of load sharing ratio of conventional nuts. A bar graph of the load sharing ratio of conventional nuts.

The nut of the present invention
A. In the shape of the vertical sectional view of the nut, a space having a convex shape is formed concentrically on the seat surface on the nut fastening side with the axis of the screw as the center, and the space is connected by a straight line, a curved line, or a combination thereof. It is a structure in which a space is formed as a shape, and the depth from the seat surface of the space is L ₂ , and the axial length from the valley bottom of the first screw of the fully threaded portion of the nut to the seat surface is L ₁ . Then, by forming the space with the depth L ₂ of the space as the range of L ₁ <L ₂ ≤ L ₁ + 5 pitches of threads;
B. In the shape of the vertical sectional view of the nut, the structure has a rectangular recess on the screw center side of the seat surface on the fastening member side of the nut, and the recess is an inner wall rising vertically from the nut seat surface and a curved line, a straight line, or those. La is the axial length obtained by adding the axial length of the incompletely threaded portion of the nut and the length of two pitches of the nut from the position of the upper surface, and the concave portion. When the axial length from the seat surface to the upper surface is Lb and the radial length of the recess from the screw valley bottom of the nut to the inner wall of the recess is Lh, Lb is 0.001 times or more and 1 times La. By forming the recess concentrically with the center of the screw with the following range and Lh in the range of 0.5 times or more and 5 times or less of La; or C.I. A two-part nut composed of a nut body having a screw shaft portion and a flange bearing surface portion provided with threads inside, and a pipe-shaped nut component having a chamfered seating surface on the inner diameter side of at least one end face. The shape of the vertical cross-sectional view of the nut body is T-shaped, and the length from the flange bearing surface of the nut body to the inside of the nut component toward the object to be fastened is the length by which the screw shaft portion of the nut body enters. The nut part in the shape of a hollow pipe on the outer peripheral part of the outer surface of the screw so that the length of the incomplete thread portion s + the length of the screw pitch 0.5 thread or more and the length of the incomplete thread portion s + the thread pitch 5 threads or less. The lowermost part of the T-shaped nut body is in contact with the object to be fastened, and the uppermost part of the nut part is in contact with the flange-shaped seat surface of the T-shaped nut body. Further, the length of the nut component is set so that the lowermost portion of the nut component contacts the object to be fastened, the inner diameter surface of the nut component and the outer peripheral surface of the nut body are made rotatable, respectively, and the nut body and the nut are formed. By forming the part concentrically with the center of the screw;
By adopting a nut structure that directs the flow of the load force received by the nut to the meshing thread on the open side, which has a low load sharing, the load sharing after the third thread is increased, and the first thread of meshing. It is characterized in that it is configured to reduce the maximum load sharing of the above and reduce the load concentration on the first mesh. Due to this feature, the fatigue fracture life of the crack shaft fracture from the valley bottom of the first meshing thread, which is the weakest part of the bolt fatigue strength, can be improved by reducing the load on the first meshing thread.

The nut of the first aspect (A) and the second aspect (B) of the present invention has a one-part structure, and a convex space is formed on the seating surface of the central portion of the nut fastening side toward the open side. The recess is formed so that the "force flow" is passed through the nut bearing surface and the outer peripheral portion of the nut body and directed to the third and subsequent threads on the open side of the screw. The third aspect (C) is a two-part configuration consisting of a nut body and a nut part, and uses the nut body and the nut part to direct the "force flow" to the third and subsequent threads on the open side of the nut screw. Is. With such a structure, it is possible to provide a nut characterized by having a structure for simultaneously reducing the load sharing of both the initial tightening load and the external force load applied to the first mesh thread.

In the description of each aspect of the present invention, the threads are based on JIS B 0205 (ISO 724).

Further, in the present invention, one pitch of the screw is used as a reference for the length, but this is not the screw thickness here because there are a plurality of bolts and nuts having the same thickness but different screw pitches. , The screw pitch is adopted as one standard of length.

The reduction of the load on the first thread of the fastening engagement will be described below by taking up the structure of the first aspect (A) as a representative.
In the first aspect (A), in the shape of the vertical cross-sectional view of the nut, an upwardly convex space connected to the seat surface on the nut fastening side with a curved line, a straight line, or a combination thereof around the axis of the screw. The depth from the seat surface of the convex space is L ₂ , and the axial length from the valley bottom of the first screw of the fully threaded part of the nut to the seat surface is L ₁ . Then, by forming the space with the depth L ₂ of the space as the range of L ₁ <L ₂ ≤ L ₁ + thread 5 pitch length, the stress applied to the thread of the nut at the time of fastening is reduced. The feature is that the thread is directed more toward the third and subsequent threads on the open side to share more load than the conventional method, and the load concentration on the first thread of the nut and bolt fastening is reduced. To do. Here, the thickness of the screw shaft portion of the nut having a screw thread inside in the structure between the space and the nut thread is not constant, and the thickness of the shaft portion connecting from the P ₂ side to the P ₁ side is P ₂ It is also possible to tentatively change from to P ₁ , and the P ₂ side can be made thicker and the P ₁ side on the seating surface side can be made thinner depending on the shape of a curved line, a straight line, or a combination thereof.

A vertical sectional view of an example of the nut of the first aspect (A) is shown in FIG. 1A and 1B are a vertical sectional view (a) of a nut, a plan view (b) seen from the nut open side, and a plan view (c) seen from the seat surface. 1 is a nut, 2 is a bolt, and 3 is a fastened nut. 4 is the gap between the nut bearing surface and the lowermost end of the nut shaft, 5 is the convex space above the nut bearing surface, 7 is the lowermost end of the screw shaft, 8 is the nut fastening side, and 9 is the opening of the nut. On the side, 9a is the nut open end, 14 is the nut bearing surface, 17 is the outer peripheral portion of the nut, 18 is the screw shaft portion having a thread inside, and 19 is the nut screw thread.

The state of conclusion will be described with reference to FIG. When the object to be fastened 3 is fastened with the bolt 2 and the nut 1, the force from the seat surface is applied to the screw shaft portion 18 at the time of fastening because the lowermost end 7 of the screw shaft portion at the center of the seat surface side of the nut has a gap 4. It doesn't take directly. Since the nut seat surface 14 on the outer peripheral side of the space 5 is in contact with the object to be fastened 3, the force from the object to be fastened 3 at the time of fastening is exchanged by the nut seat surface 14 in contact with the object to be fastened 3. .. The fastening force enters the nut bearing surface 14 from the object to be fastened 3, passes through the inside of the nut, and is transmitted to the thread 19 of the nut. At this time, the force proceeds along the inside of the nut to the curve inside on the outer periphery of the space 5, then enter the bolt through the deepest (P ₂ near) the street each thread space 5. P ₂ threads 19 nearest from the vicinity in the example of FIG. 1 is the third nut thread. Other powers are also transmitted to the 4th, 5th, 6th, and 7th. In this way, the force toward the open side is transmitted to the bolt thread of the other party, and a large amount of internal stress is borne by the third and subsequent threads. The bolt meshes with the axial force, and the first thread still receives the maximum principal stress (tensile stress), but by receiving a lot of force on the open side of the nut, the load sharing on the first thread is relatively reduced. .. In addition, due to the shape effect of the nut screw shaft portion 18, the load of the first thread of meshing of the bolt and the nut is significantly reduced as compared with the conventional structure. By directing the force to the third and subsequent threads on the open side in this way, the load on the first thread of meshing can be reduced.

Figure 1 is a diagram for explaining a first embodiment (A) the depth of the relationship between the space 5 in the present invention, P ₁ root of complete thread portion of the first mountain in the threaded shaft portion 18 of the nut Located in the center, P ₂ is located in the deepest part of the space in the depth direction. Let the distances from the seat surface 14 of the nut to P ₁ and P ₂ be L ₁ and L ₂ , respectively.

FIG. 1 shows an arbitrary one cross section within one thread pitch through the central axis of the nut, and as shown in the enlarged view of the nut screw shaft portion 18, the screw inlet at the position of the lowermost portion 7 of the screw shaft portion 18. Has a machined chamfer, followed by an incomplete threaded portion of about 1 pitch from the beginning of thread cutting, in which a fully threaded portion is connected. Since the position of P ₁ changes during _one screw rotation (360 degree rotation), the distance from the seat surface of L ₁ is affected by one screw pitch + chamfering length. Therefore, the distance L ₁ of P _{1 from} the seat surface 14 is equal to or greater than the sum of the dimensions of the gap 4, the chamfered length of the threaded portion, and the length of the incomplete threaded portion.

In the above embodiments (A), as shown in FIG. 1, the point P ₁ and the space 5 in the thread root center of the first thread of the seating surface side of the nut thread that is a complete thread portion deepest relationship _{P 2} in the part is at a distance _{L 1} and _{L 2} from the seating _surface, to set the dimensions of the L 2> _{L 1} and becomes _{L 2.} Since L ₁ is located on a screw, the distance changes by one pitch when rotated 360 degrees, but L ₂ often becomes a constant value due to molding. Therefore, it is preferable that L ₂ is at least deeper than L ₁ , but the upper limit of the depth is appropriately set to the length of L ₁ + 5 pitches of threads. In an example of the basic form of FIG. 1, P ₂ is set at a position about 2.4 pitches longer than P ₁ .

In the above embodiments (A), varying toward the thickness in the fastening side thickness of the threaded shaft portion 18 also, or deepest portion of the space 5 (P ₂₎ the same from where the shape is changed to the shaft portion from It is also possible to form up to the vicinity of the bottom 7 in terms of thickness. It is preferable that the shape is integrated with the shape of the space 5 and a straight line, a curved line, or a combination thereof is adopted. It is preferable to provide a curve in the vicinity of the lowermost portion 7 to avoid stress concentration.

In consideration of facilitation of processing to provide a convex space on the upper side, the space 5 having a convex shape on the upper side is practically a space 5 having a shape connected by a smooth curve or a straight line as shown in an example of a basic shape or a modified example. Structure. The upwardly convex shape can be any shape as long as it does not deviate from the object of the aspect (A) of the present invention, and is included in the invention of the first aspect (A). (A) and (b) of FIGS. 1-5 are two modified examples with respect to FIG. 1, but mainly the shape of the space 5 and the outer shape inside the seat surface are different. In each case, the force applied from the object to be fastened 3 is passed through the inside of the nut 1 and the force is directed to the open side after the three threads of the meshing thread with the mating bolt. A shape having the same effect other than the modified example of FIG. 1-5 can be determined according to various conditions such as manufacturing requirements.

What is important in this aspect (A) is the formation of a convex space 5 on the seat surface side of the nut. In particular, it is the selection of the depth, and L ₂ is set so that the length of L ₁ <L ₂ ≤ L ₁ + thread 5 pitches is established, and the force passing near P ₂ and the force pulled from the bolt are set. If a nut shape having a structure having a corresponding strength is realized, a large amount of force flow can be directed to the third and subsequent threads on the open side, and the load on the first meshing thread can be reduced.

In general, when a force is applied to a point from the outside of a flat plate, the force spreads from that location to the inside in proportion to the magnitude, the force follows the shortest path, and even when the force bends, it does not bend at a steep angle. It is known that force passes through easy-to-pass places, and force does not pass through space. The characteristics of how this force is transmitted can be clearly read in the Mises equivalent stress distribution and the vector diagram.

Based on the way this force is transmitted, the stress distribution diagram corresponding to Mieses in FIG. 1-1 corresponding to the mode (A), and the vector diagram of the maximum principal stress (tensile stress) in which the force flow in FIG. 1-2 can be seen, The force flow can be confirmed from the vector diagram of the minimum principal stress (compressive stress) in Fig. 1-3. Especially in the vector diagram, small arrows are lined up closely, the direction indicates the direction of the force, the length indicates the magnitude of the force, and the density of the arrangement indicates the situation where many forces flow in each direction at that place. Is shown.

The Mises equivalent stress distribution diagram in FIG. 1-1 is a visualization of the above vector diagram as an overall stress distribution and color-coded in four black and white gradations. Focusing on where the direction of the arrow points in the vector diagram (Fig. 1-2, Fig. 1-3), the tip of many forces points toward the thread in the nut, but most of them point. No. 3 and No. 4 of the nut thread. It can also be seen that there are many that go to the 5, 6 and 7 threads on the open side. The nut threaded engagement side, it is transmitted while curving from P ₂ near No. 2 to swirl, and then in the direction of number 1. In Fig. 1-2, since the bolt thread and the bolt shaft are subjected to the axial force that pulls them toward the fastening side, the diagonal thread surface of the nut is pressed against the diagonal thread surface of the bolt (it is also strongly pressed on one side). It can be seen that the force is applied in a concentrated manner. Since the bolt axial force is towards the fastening side, but thread No. 1 has received the largest tensile stress, thread No. 1 of the nut, No. 2 has bent from P ₂ vicinity around the screw shaft portion 18 It receives more of the small force and the pulling force from the bolt, and the nut screws No. 3, No. 2, No. 1 are pulled toward the fastening side in order of strength. For this reason, the nut screw No. 1 has a black color indicating that the internal stress is low. The shape effect of the screw shaft portion is added here.

In the analysis diagram of the modified example shown in FIGS. 1-1, 1-2, and 1-3, the force from the nut flows toward the thread direction after the third thread, and the first thread of the fastening mesh is engaged. The load is reduced. The load sharing after the 3rd mountain has increased compared to the conventional method, and the force has reached the 7th mountain. In particular, the area of high stress (white display area) in Fig. 1-1 is narrow and small at threads 1, 2 and 3, and dark gray (slightly small stress) at threads 4, 5, 6 and 7. ) Appears in a wide area.

As can be seen in Fig. 4-1 of the conventional method, the vector of the maximum principal stress in Fig. 4-2, and Fig. 4-3 of the minimum principal stress, in the conventional method, the situation is dominated by the force passing through the innermost diameter side of the nut. On the other hand, the stress distribution diagram of FIG. 1-1 of the present invention has a completely different stress distribution, and in the aspect (A) of the present invention, the direction in which the force flows is directed toward the third and subsequent peaks of fastening engagement. , It is clearly shown to reduce the load on the first mesh.

As a result, the load sharing rate of the first meshing peak in the example of the aspect (A) is 26.3% (conventional method: 35.6%). Fig. 1-4 (a) shows a comparison table with the conventional method of 7 mountains using this result as a reference for the load sharing ratio of each mountain, and Fig. 1-4 (b) shows a comparison bar graph of this numerical value. Looking at this comparison, it can be seen that in the example of the nut of aspect (A), the load sharing after the third thread is increased and the load sharing of the first meshing thread is reduced as compared with the conventional method.

With respect to each corner of the convex space structure nut in the first aspect (A), the treatment of each corner is preferably as follows. It is preferable to use the corner shape formed by the optimum stress concentration relaxation curve for each member location. The stress concentration relaxation curve includes, for example, a quadratic curve (simple R, composite R, ellipse, etc.), and a straight line such as an oblique C cut can also be used.

Further, in the first aspect (A), regarding the surface roughness of the nut, the threaded surface may have a refined finish on the sliding surface, and the other surface may have an intermediate finish or the required surface roughness. However, it is desirable that the surface roughness is consistent with the surface treatment described later.

Next, the nut of the second aspect (B) of the present invention will be described.
The nut (B) of the present invention has a structure having a rectangular recess on the screw center side of the seat surface on the fastening member side of the nut in the shape of the vertical sectional view of the nut, and the recess rises vertically from the seat surface. It has an inner wall and a curved line, a straight line, or a corner part and an upper surface that combine them, and the axial length is La, which is the sum of the axial length of the incompletely threaded part of the nut and the two pitch lengths of the nut from the position of the upper surface. Lb is 0.001 times or more of La, where Lb is the axial length from the seat surface to the upper surface of the recess, and Lh is the radial length of the recess from the screw valley bottom of the nut to the inner wall of the recess. It is characterized in that a recess having a length of 1 time or less and Lh having a length of 0.5 times or more and 5 times or less of La is formed concentrically with the center of the screw.

By forming the concave portion on the seat surface portion of the nut in this way, the flow of the force entering the nut at the time of fastening enters from the entire surface of the nut seat surface in contact with the object to be fastened and flows along the wall of the nut concave portion. It passes near the corner, passes near the center of the nut toward the third thread on the open side and beyond, and flows widely distributed over all threads. The tensile stress that enters the nut from the bolt is still the maximum at the first thread of meshing, but the stress applied to the thread of the nut at the time of fastening can be shared more on the thread side on the open end side. It is possible to reduce the load on the first thread of the fastening mesh of the nut and the bolt.

Aspect (B) of the present invention will be described with reference to the drawings. FIG. 2 is a vertical cross-sectional view showing an example of the nut according to the second aspect (B) of the present invention, and the nut 1 has a structure having a recess 10 in the lower part of the inner diameter of the nut. In the recess 10, a wall 11 rising vertically from the nut seat surface 14 in contact with the object to be fastened 3 and a corner portion 12 having a straight line sandwiched by a curved line connected to the wall 11 (the straight line in this corner 12 is from the nut fastening side). It is preferable to face the bottom of the second and subsequent threads. FIG. 2 shows an example of facing the bottom of the second thread.) And there is an upper surface 13 connected from the corner portion 12, and the innermost screw side of the upper surface 13 has an upper surface 13. Is an open space composed of a chamfered portion and an incompletely threaded portion on the open side, and a line leading to the thread 19. The dimension of the recess 10 is La, which is the sum of the chamfered dimension of the threaded portion of the nut 1 + the axial length s of the incomplete threaded portion and the length of 2 pitches of the nut, and the seat surface 14 of the recess 10. When the axial length from to the upper surface 13 is Lb and the radial length of the screw valley bottom 15 of the nut 1 and the concave portion 10 to the inner wall 11 of the concave portion 10 is Lh, Lb is 0.001 times or more 1 than La. The recess 10 is formed concentrically with the center of the screw so that the length is not more than twice as long and Lh is 0.5 times or more and 5 times or less as long as La.

There may be various variations of the second aspect (B) of the present invention. FIG. 2-1 is the first modification, in which the corner portion 12 of the recess 10 has one stress concentration relaxation curve structure, the corner portion 12 is connected to the upper surface 13, and the chamfered portion and the screw incomplete portion are sequentially chamfered. , The structure is such that the screw thread 19 is reached through the screw valley bottom 15. The dimension of the recess is La, which is the sum of the axial length s of the incomplete threaded portion of the nut 1 + chamfering and the length of 2 pitches of the nut, and from the seat surface 14 to the upper surface 13 of the recess 10. Lb is 0.001 times or more and 1 times or less of La, where Lb is the axial length of the nut 1 and Lh is the radial length of the recess 10 up to the screw root 15 of the nut 1 and the inner wall 11 of the recess 10. The recess 10 is formed concentrically with the center of the screw so that the length is 0.5 times or more and 5 times or less the length of La. In the modified example of FIG. 2-1 Lh is about 1.1 times La. With this structure, the force from the nut seat surface 14 flows through the outer peripheral portion of the nut, and a large amount of force can be directed to the third and subsequent peaks on the open side. In addition, the nut has a simple shape for processing, and has the advantage of being easy to manufacture, including shape confirmation.

FIG. 2-2 shows a Mises equivalent stress distribution diagram of an example of FIG. 2, which is a basic example of this aspect (B). Looking carefully at the Mises equivalent stress distribution in FIG. 2-2, most of the forces applied from the nut bearing surface 14 flow in the nut bearing surface toward the thread in the diagonal 45 degree direction. About 45 degrees diagonally parallel to the straight part of the corner 12 from near the center of the seat surface 14 The force flowing from the nut thread 3 to 4 toward the thread side and about 45 degrees diagonally from the stepped area on the outer circumference of the nut. You can see the ones that go to the 5th and 6th threads while tilting toward the threads. The force flowing around the corner 12 in the horizontal direction parallel to the upper surface 13 to the first mountain on the fastening side is small. Thread of nut A large black color with low stress appears behind the thread No. 1 (inside the nut). Such a black portion is not seen in the conventional nut (FIG. 4-1), and it is considered that the force passing through the corner 12 flows through the slightly open side of the black portion. The force spread in the nut receives the force pulled from the bolt thread when it reaches the thread, but as a result of the force being distributed to many threads, the load applied to the first thread is conventional. It is reduced compared to the method.

In the basic example of the present aspect (B) shown in FIG. 2, the ability to direct the force applied from the nut bearing surface 14 toward the open side of the nut can be easily controlled as compared with the modified example of FIG. 2-1. For example, the length of the upper surface of reference numeral 13 in the drawing may be lengthened to lengthen the Lh length in the seat surface to about 2.0 times that of La, or the inclination of the straight portion of the corner 12 may be tilted more than 45 degrees to the open side. Factors of change are such as facing the wall 11 and making the wall 11 a little shorter in length. In this way, the direction of the force can be controlled by optimally combining the elements of the recesses, and the load sharing to the first meshing peak can be reduced. Although not shown, the load sharing ratio of the first meshing peak is less than 30% even in the case of the other modification of the present aspect (B).

The case of the example of FIG. 2 of the aspect (B) and the load sharing ratio of the conventional method are shown in FIG. 2-3 (a), and the bar graph comparing with the conventional nut is shown in FIG. 2-3 (b). In the bar graph, the black frame display shows a modified example of aspect (B). By the way, the load sharing ratio is reduced to 29.6% in the modified example of the aspect (B), compared with 35.6% in the conventional method in the first meshing. After the third mountain, the aspect (B) is increasing.

Further, the shape of the nut on the open side of the present aspect (B) may be a shape such as a hexagon or a quadrangle that can use a conventional fastening tool.

Regarding the surface roughness of the nut seat surface 14, the wall surface 11, the corner portion 12, and the upper surface 13 of the recess 10, the screws have a fine finish according to JIS regulations, the nut seat surface has a fine finish, and the other surfaces have a rough finish. Alternatively, a normal finish is preferable, but a surface consistent with the surface treatment is more preferable.

With respect to the concave portion 10, the nut bearing surface 14, and other corner portions on the surface, all the corner portions preferably have a shape having a stress concentration relaxation curve such as a quadratic curve such as an arc or a part of an ellipse. Is desirable.

Next, the third aspect (C) of the present invention will be described.
C. A two-part nut composed of a nut body having a screw shaft portion and a flange bearing surface portion provided with threads inside, and a pipe-shaped nut component having a chamfered seating surface on the inner diameter side of at least one end face. The shape of the vertical cross-sectional view of the nut body is T-shaped, and the length from the flange bearing surface of the nut body to the inside of the nut component toward the object to be fastened is the length by which the screw shaft portion of the nut body enters. A hollow pipe-shaped nut component is placed on the outer peripheral portion of the outer surface of the screw so that the length of the incomplete thread portion s + the screw pitch is 0.5 threads or more and the length of the incomplete thread portion s + the thread pitch is 5 threads or less. The structure is arranged so that the lowermost part of the T-shaped nut body does not come into contact with the object to be fastened, and the uppermost part of the nut part comes into contact with the flange-shaped seating surface of the T-shaped nut body. The length of the nut component is set so that the lowermost portion of the nut component contacts the object to be fastened, the inner diameter surface of the nut component and the outer peripheral surface of the nut body are rotatable, respectively, and the nut body and the nut component are made rotatable. By forming concentric circles with the center of the screw;
The feature is that the stress applied to the thread of the nut at the time of fastening is directed more toward the third and subsequent threads on the open side to reduce the load concentration on the first thread of the nut and bolt fastening. To do.

A vertical sectional view of the nut according to the third aspect (C) of the present invention is exemplified in FIG. The vertical cross-sectional view of the nut body 1 has a substantially T-shape, and the nut body 1 is integrated with a screw shaft portion having a thread inside, and at least on the side surface of the screw shaft portion 18 on the lower surface of the flange of the nut body 1. A pipe-shaped nut component 6 having a chamfering structure is arranged on one side of the inner diameter side so as not to interfere with the shaft portion 18, and the nut body shaft portion 18 is rotatable in the nut component 6 and is a nut. The main body 1 has a bolt 2 screwed inside, and is in contact with the nut component 6 on a sliding surface 16 and slides rotationally. The length from the uppermost surface 22 to the seat surface 14 of the nut component 6 is set from the flange seat surface of the nut body 1 to the maximum of the screw shaft portion so that the lowermost portion 7 of the screw shaft portion of the nut body 1 does not come into contact with the object to be fastened 3. The structure is shown in which the nut component 6 is in contact with the object to be fastened 3 so as to be longer than the length up to the lower portion 7. The outer shape of the nut body 1 on the upper open side can be shaped according to the fastening tool. The thickness of the screw shaft portion 18 provided with threads inside in the axial direction of the nut body 1 may be constant, or the open side may be thicker and the object to be fastened side may be thinner, and the length of the shaft portion may be in the middle. It can be made even thinner. Further, as shown in FIG. 3, the seat surface 20 of the nut component 6 can be enlarged to reduce the surface pressure at the time of fastening the nut component 6 and the object to be fastened 3.

When fastening the object to be fastened 3 with the bolt 2, the nut body 1 and the nut component 6, the lowermost surface 7 on the fastening side of the nut body 1 does not directly contact the object to be fastened 3, and the seat surface 20 of the nut component 6 is fastened. Since it is in contact with the object 3, the flow of force at the time of fastening is directed to the open side of the nut body 1 via the contact surface 16 between the nut component 6 and the nut body 1, and further toward each thread. At this time, the force enters the nut body 1 from the nut component 6, but the position is large from the vicinity of the innermost inner diameter of the contact surface 16 where the nut component 6 and the nut body 1 are in contact with each other, and the screw thread 3 is inside the nut body 1. It goes to the thread after the second and reaches the thread on the open side while expanding.

As shown in FIG. 3, the curved portion transitioning from the flange portion of the nut body to the screw shaft portion 18 and the inner diameter side shoulder portion of the nut component 6 are preferably mutual even if their shapes and sizes may change. The structure shall have a stress concentration relaxation curve that can maintain a structure that does not interfere, and shall not cause stress concentration on both the nut body and nut parts. The load sharing state of the screw thread changes from the relative relationship of the screw thread positions at the axial height of the screw in the screw shaft portion 18 corresponding to the contact surface 16 of the nut component 6 and the nut body 1.

In this aspect (C), the force can be directed to the nut thread near the open side of the nut body 1, and how the load is shared depends on the strength of the nut 1, the material, and the strength of the nut component 6. It can be decided from the material, the material, and their shape. L ₂ at the height of the surface 16 where the nut component 6 and the nut body 1 contact is in the range of L ₁ + 0.5 pitch length ≤ L ₂ ≤ L ₁ + 5 thread length. Inside is desirable.

Here, L ₁ indicates the distance from the point P _{1 at the} bottom of the thread valley of the perfect screw No. 1 on the fastening side of the thread of the screw shaft portion 18 of the nut to the nut bearing surface 14, as shown in FIG. , between the P ₁ and the nut bearing surface, and that there is a total length s of the space 4 and a screw chamfer and thread imperfections. By adjusting the axial length of the nut component 6, the length of the gap 4, and the amount of protrusion of the screw shaft portion 18, the lowermost end 7 of the screw shaft portion 18 of the nut body 1 does not touch the object to be fastened 3. Can be.

In FIG. 3, the number of threads of the nut is set to 8 as an example. This is due to the purpose of improving the rigidity of the nut itself in terms of the balance of force due to the large amount of stress flowing on the open side of the nut due to the influence of the screw shaft portion. As an example, the nut body 1 has a structure in which a step or a taper or a shape combining these is provided on the outer periphery of the screw shaft portion 18. Further, in FIG. 3, the seat surface 20 of the nut component 6 has a structure in which the contact area in contact with the object to be fastened 3 is increased, which has the effect of reducing the fastening surface pressure of the seat surface 20 in which the nut component 6 and the object to be fastened 3 are in contact with each other. is there.

There are many modifications of this aspect (C), but there are some related to the usage method (not shown). There is a deformation (use implementation) example in which the nut component 6 can be replaced with the object to be fastened 3 and the nut body 1 can be screwed directly into the bolt 2 coming out of the object to be fastened 3 to fasten the object to be fastened 3. .. In the case of this modification, the screw hole of the object to be fastened 3 has a structure in which the screw shaft portion 18 of the nut body 1 can rotate, and the inlet of the hole provided in the object to be fastened 3 is a nut component 6 as shown in FIG. The nut body 1 can be directly fastened to the object to be fastened 3 via the bolt 2 by adopting a structure having a large stress concentration relaxation curve or an effect equivalent thereto. The nut body 1 and the object to be fastened 3 come into contact with each other on the surface 16 of the flange bearing surface of the nut body 1. In such a case, as shown in FIG. 3, the bolt 2 is set so as to face the direction in which the thread comes out from the object to be fastened and to be screwed with the nut body 1. Even in such a modified example, a large amount of force can be applied after the third thread on the open side of the nut body, and the load on the first thread of meshing can be reduced. Such a usage method and a chamfered shape are also a part of the present invention. Advantages in this case include reduction in the number of parts, weight reduction, reduction in nut protrusion amount, and the like, in addition to the effect of aspect (C).

The Mises equivalent stress distribution diagram of this aspect (C) is shown in FIG. 3-1. Here, the nut body having a structure with eight threads is used for the FEM analysis of the nut of aspect (C). This is due to the improvement in the rigidity of the nut itself due to the large amount of stress flowing on the open side of the nut due to the influence of the screw shaft portion. In accordance with this, the conventional nut, which is the reference for comparison, uses the value of 8 threads.

In the stress distribution diagram equivalent to Mieses in Fig. 3-1 the magnitude of stress is color-coded in four color tones. White indicates high stress, black indicates low stress, and light gray in the middle indicates slightly large stress and dark gray. It represents a little small.

As an outline of FIG. 3-1 the force applied from the seat surface 20 of the nut component 6 is black at the bottom, and diagonally from dark gray to light gray upward toward the nut body 1, the nut body 1 and the nut. On the top and bottom of the surface 16 where the part 6 contacts, it becomes white, which indicates high compressive stress, and is the maximum stress. In this part, the white or gray band-shaped high stress is suitable for the 7th to 8th threads of the nut body 1. You can also see that it is. Immediately after entering the nut body 1, white and light gray are visible toward the nut shaft portion 18, but this portion is subjected to tensile stress. Through this part, a white color can be seen between the nut threads 4 and 3 and toward the bottom of the thread valley between the 3 and 2. Also, it seems that the area around thread 3 is passing the most force. Furthermore, black color is visible inside the nut side No. 1, indicating that the stress is small in this first mountain portion. Looking at the whole again, the threads 1, 2, and 3 of the nut 1 on the screw shaft are subjected to the pulling force from the bolt. The force transmitted from the nut to the bolt is large on the bolt thread No. 3, and the force is applied to Nos. 4, 5, 6, 7, and 8, and dark gray is also visible on Nos. 7 and 8. Looking at the bolt side, white is small in the 1st to 3rd positions near the thread, but light gray is also appearing in the 4th and 5th positions. In addition, dark gray spreads over all lengths up to bolt thread number 8. In this way, it can be seen that the stress is widely expanded inside the bolt. You can see the force spreading in the direction of the nut.

Comparing FIG. 3-1 of this aspect (C) with FIG. 4-1 of the conventional method, it can be seen that the Mises equivalent stress distribution diagram has a completely different aspect. In Fig. 4-1 of the conventional method, the force is immediately directed to No. 1 on the fastening side, most of the force is transferred by No. 1, and then gradually decreases to the second and third, and the thread on the open side has a small load. It can be seen that they are only sharing.

In order to compare the performance of the aspect (C) of the present invention with the conventional method, an example of the aspect (C) and a comparison of the conventional method are shown in FIG. 3-2 (a) load sharing ratio and (b) bar graph. Here, the load sharing ratio of the first meshing peak of the present aspect (C) is 22.9%, which is a value far from the conventional method of 34.5%. In the numerical values after the third peak, the load burden rate of the aspect (C) is higher. This comparison is made with eight nut threads on both sides.

The analysis of the modified example of the aspect (C) of the present invention at 7 peaks is shown in the Mises equivalent stress distribution diagram of FIG. 3-3, and the comparison with the conventional method 7 peaks is shown in FIG. 3-4 (a) Comparative numerical table and FIG. -4 (b) shows the comparison bar graphs, respectively. The load sharing ratio of the first meshing peak in this modified example is 24.0%, which is significantly different from the conventional method of 35.6%. Here, both are compared with 7 threads.

In this way, in aspect (C), a correlation is observed between the axial position of the flange bearing surface of the nut body 1 and the thread position of the nut body (screw shaft portion protrusion amount), and the amount of force flowing to the open side. It is suggested that it affects the size of the mesh and the load sharing of the first mountain of meshing. By the way, the amount of protrusion of the nut body shaft 18 is different between FIGS. 3-1 and 3-3, which is different from about 3.5 peaks in FIG. 3-1 and about 4.3 peaks in FIG. 3-3. There is.

In order to avoid stress concentration in the corners and other parts of each part of the third aspect (C) of the present invention, stress concentration is relaxed in the corners on the seat surface 20 side of the nut part 6 and the parts in contact with the nut body. It is desirable to provide a curve. Further, the size and shape of these stress concentration relaxation curves can be arbitrarily determined.

The surface roughness of the seat surface 20 of the nut component 6 is refined, or the surface 16 where the nut body 1 and the nut component 6 are in contact is both refined, the threaded surface is the surface roughness specified by JIS, and other surface roughness. Is preferably set to the optimum surface roughness depending on the location so as to have consistency with the surface treatment described later, such as rough finish or normal finish.

The T-shaped nut structure does not necessarily have to be a strict T-shaped structure, and a deformed structure is possible as long as the purpose is not deviated. For example, it may have a cross structure. Further, it is also possible that the upper part of the nut body has a shape that can be used with a fastening tool such as a normal hexagon, which is more preferable.

In the present invention, even if the mode is different from (A), (B), and (C), the flow of the load applied to the nut as described above is caused by the meshing thread on the open side, which has a low load sharing. As a nut structure that can be directed to a large number, it is possible to provide a nut configured to reduce the maximum load sharing of the first meshing thread by increasing the load sharing after the third thread. As a result, by reducing the load on the first meshing thread, it is possible to achieve the purpose of extending the fatigue fracture life that causes the crack shaft fracture from the bottom of the first meshing thread of the bolt.

As the nut of the first to third aspects of the present invention, a material conventionally used can be used. Materials include alloy steels such as mild steel, carbon steel, nickel chrome steel, chrome steel and nickel chrome molybdenum steel, non-ferrous metals such as stainless alloy steel, aluminum alloys, nickel alloys and titanium alloys, resins and ceramics (oxides and nitrides). Materials such as (materials, carbonized materials, etc.) and materials are preferably used.

The same method as before can be used for thread formation. For example, thread forming by tapping, NC (numerical control) lathe, machining center (MC), multi-tasking machine (combined lathe and milling machine), Electric discharge machining, or a combination of these, press plastic working, cold / hot / warm press working, forging, casting, injection molding, precision casting, 3D printer machining, molding, MIMS, or They can be combined. Regarding the screw thread size and strength, the shape specified in the industrial standards of each country (JIS B0205: 20011, JIS B0216: 1987, JIS B1051: 2000, etc. in Japan) can be adopted.

As an example, the formation of the nut of the first aspect (A) by the NC lathe will be described. The outer shape is manufactured by cold / warm / hot forging / pressing, cutting, nut former, Swiss type automatic lathe, etc., and the space on the seat side of the nut and the substantially rectangular concave shape are made by NC lathe, automatic lathe, etc. After forming with a processing machine such as, the nut of the present invention is produced by forming a nut thread using cutting, grinding, cutting tap, and rolling tap in the same manner as the conventional nut thread forming. be able to. Alternatively, the manufacturing order may be changed to form a screw thread using a tap in the same device, a space or a substantially rectangular recess may be formed on the seat surface side of the nut, and then an outer peripheral shape may be formed.

The method for manufacturing nuts in other embodiments is almost the same, but for example, the members can be roughly divided into a member that becomes a nut body and a member that becomes a nut component. For the outer shape of the nut and the preparation of the screw pilot hole, hot / cold / warm press, forging, cutting, casting, etc. are adopted, and a one-part nut or a substantially T-shaped shape is manufactured. The head is formed so that a hexagonal fastening tool can be used so that fastening work can be easily performed with a normal tool, and a tap is passed through a pilot hole made by cutting, cold / hot forging, casting, etc. Form peaks / valleys. The threaded portion may be formed by turning or grinding. Nut parts can be manufactured by cutting pipes, cold / warm / hot forging, casting, continuous automatic cutting from round bars with a CNC lathe, or a combination of these. Molding with a 3D printer may be used. When it is made of resin or ceramics, it may be a combination of injection molding, sintering, etc. and cutting, grinding, etc. The surface roughness of the surface where the nut and the nut component contact can be selected and adopted to reduce the sliding resistance. It can be processed by selecting or combining mirror-polished surface, polished surface, precision cutting surface, pressed surface with precision die, micro shot peening, glass bead shot, etc. In addition, by combining the nut body and nut parts, the nut body rotates around the screw center axis to proceed with fastening, so the nut body and nut parts are kept vertical so that the surface to be fastened and the nut screw center axis are kept vertical. It is desirable to make.

For example, when the material is metal, the surface before the nut and bolt start fastening has surface roughness such as shaving and polishing, and the coefficient of friction μ is μ ≈ 0.5 when dry and μ ≈ 0 when wet. It is known to be .1. However, when the gap disappears and the base material is strongly pressure-bonded after the start of fastening, the lubricant flows out, the oxide film on the metal surface is peeled off, and a metal background appears. At this time, especially in a dry environment, the metal surface is in a strong pressure welding state in which metal bonding occurs. In this case, it is difficult to assume that the friction coefficient of the thread remains unchanged, and the friction coefficient may increase non-linearly to reach a size at which both threads adhere.

A segmented structure diamond-like carbon (S-DLC) film, which is a diamond-like carbon film and has a function of being subdivided in a groove without a film and having a function of dividing the film provided on the sliding surface, exerts such pressure. When a film is formed between the base materials that are in contact with each other while receiving the film, the base materials can maintain a state of rubbing against each other without changing the friction coefficient (μ≈0.15) as long as the film is present. This adhesion durability has been shown in many experiments by the present inventors. When there is an S-DLC film on the thread on the fastening side of the nut, at least when there is an S-DLC film on the first thread of the fastening mesh, the effect of the increase in the friction coefficient is small.

In the nut according to the first to third aspects (A) to (C) of the present invention, a part or all of the bolt-side threads of the first thread or more threads that mesh with at least the bolt on the thread surface. the contact surface or both sides of the slope of the thread, and diamond-like carbon (DLC) film, BN film, WC films, CrN films, HfN film, VN film, TiN film, TiCN film, _Al 2 _{O 3} film, ZnO film , SiO ₂ film, alumite, metal plating, solid lubricant, manganese phosphate chemical conversion treatment, carburizing and quenching, nitrided treatment, chromated treatment, or a combination of these coatings to form a protective film. It is more suitable for smooth fastening operation and stable fastening. It is preferable that the thread surface includes at least the meshing first thread surface, and the screw on the more open side is also formed with a DLC film. By forming the DLC protective film, roughening and peeling of the metal surface can be suppressed, the coefficient of friction can be stabilized, and more stable fastening can be achieved. Preferably, the DLC film is in the form of segments divided by grooves, for example, in a grid pattern (S-DLC film).

Further, in the first and second aspects (A) and (B) of the present invention, the nut body and the nut component are attached to the seat surface 14 in contact with the object to be fastened of the nut, or in the nut according to the third aspect (C). A protective film is formed by covering the sliding surface 16 or the surface 14 of the nut component in contact with the object to be fastened with a diamond-like carbon (DLC) film in order to realize smooth fastening operation and stable fastening. Is even more suitable. By forming the DLC protective film on the sliding surface, roughening and peeling of the metal surface can be suppressed, the coefficient of friction can be stabilized, and more stable fastening can be achieved. Preferably, the DLC film is in the form of segments divided into, for example, a grid pattern by grooves without a film (S-DLC film). In the case of the S-DLC film, the groove portion without the coating film becomes an oil groove, and when oil is supplied, the coefficient of friction of the bearing surface is stabilized, which contributes to the stability of fastening.

The vapor deposition method (CVD or PVD method) is suitable for depositing the DLC film on the surface on which the nut body and the nut component slide, the seat surface of the nut, and the inner surface of the screw, for example, DC, AC, or Examples thereof include a sputtering method such as plasma CVD, magnetron sputtering, or ion beam sputtering using a high frequency or the like as a power source. The film thickness of the DLC film depends on the shape of the nut and nut parts, the intended use, etc., but is usually 0.01 to 10 μm, and more preferably 0.5 to 3 μm.

The effect of forming a diamond-like carbon film on the thread surface, nut, nut parts, or the part where the washer comes into contact with each other, or the surface (seat surface) in contact with the object to be fastened is described, but it is limited to the diamond-like carbon film. Other materials can be selected for the purpose of reducing frictional resistance or reducing changes in frictional resistance. For example, BN film, WC films, CrN films, HfN film, VN film, TiN film, TiCN film, _Al 2 _{O 3} film, ZnO film, SiO ₂ film, anodized aluminum, a metal plating, a solid lubricating layer, manganese phosphate chemical conversion treatment , Carburizing and quenching, nitriding treatment, chromated treatment, polymer resin coating, or a combination thereof can be selected. These films are effective in achieving smooth fastening operation and stable fastening.

As a type of surface film formation or surface treatment, metal plating, polymer resin coating, alumite treatment, vacuum vapor deposition, ion plating, plasma treatment such as PVD and CVD can be preferably applied.

Further, the outer surface of the nut or nut component can be surface-treated to appropriately improve weather resistance, improve appearance, give identification display, decorate, and the like.

According to the present invention, it is possible to reduce the load of the first meshing thread that shares the maximum load when fastening bolts and nuts, and to improve the fatigue strength of crack shaft fracture from the valley bottom of the first meshing thread of the bolt. It is possible to provide a nut having a structure that can be used.

1 Nut, nut body 2 bolt 3 to be fastened 4 gap between the bottom 20 of the nut seat surface 14 or the nut part 6 and the bottom 7 of the screw shaft 5 Convex space (including the back curve of the screw shaft) )
6 Nut parts 7 Lower end of screw shaft 8 Nut fastening side direction 8a Nut fastening seat surface 9 Nut open side direction 9a Nut open end 10 Recess in nut 11 Recess in nut 11 Wall surface in nut (recess wall)
12 Corner in the nut recess 13 Top surface of the nut recess 14 Nut seat surface 15 Nut screw valley bottom 16 Surface where the nut body and nut parts come into contact (sliding surface)
17 Outer part of the nut body 18 Screw shaft part of the nut body 19 Thread of the nut body 20 Bottom of the nut part 6 21 Outer part of the nut body 1 22 Top of the nut part 23 Washer 24 Located on the screw shaft part of the nut body The shortest length that P ₁ can enter into nut parts (s + 0.5 pitch length)
25 The longest length (s + 5 pitch length) at which P ₁ on the screw shaft of the nut body enters the nut part.
P ₁ Point located at the bottom of the valley bottom of the first thread on the fastening side of the nut screw P ₂ Point located at the innermost part of the convex space of the nut L ₁ Distance from the nut seat surface 14 to P ₁ L ₂ Nut Distance from seat surface 14 to P ₂ P Pitch of 1 nut screw thread La Total length of 2 threads of nut screw pitch and incomplete threaded part (including chamfering) length s Lb Nut seat surface 14 to nut seat surface Length to the upper surface 13 of the inside Lh Length between the wall surface 11 and the bottom of the thread valley 15 in the nut bearing surface s Total length of the chamfered length and the incomplete thread length

Claims (4)

It is a nut for fastening
A. In the shape of the vertical sectional view of the nut, a space having a convex shape is formed concentrically on the seat surface on the nut fastening side with the axis of the screw as the center, and the space is connected by a straight line, a curved line, or a combination thereof. It is a structure in which a space is formed as a shape, and the depth from the seat surface of the space is L ₂ , and the axial length from the valley bottom of the first screw of the fully threaded portion of the nut to the seat surface is L ₁ . Then, by forming the space with the depth L ₂ of the space as the range of L ₁ <L ₂ ≤ L ₁ + 5 pitches of threads;
B. In the shape of the vertical sectional view of the nut, the structure has a rectangular recess on the screw center side of the seat surface on the fastening member side of the nut, and the recess is an inner wall rising vertically from the nut seat surface and a curved line, a straight line, or those. La is the axial length obtained by adding the axial length of the incompletely threaded portion of the nut and the length of two pitches of the nut from the position of the upper surface, and the concave portion. When the axial length from the seat surface to the upper surface is Lb and the radial length of the recess from the screw valley bottom of the nut to the inner wall of the recess is Lh, Lb is 0.001 times or more and 1 times La. By forming the recess concentrically with the center of the screw with the following range and Lh in the range of 0.5 times or more and 5 times or less of La; or C.I. A two-part nut composed of a nut body having a screw shaft portion and a flange bearing surface portion provided with threads inside, and a pipe-shaped nut component having a chamfered seating surface on the inner diameter side of at least one end face. The shape of the vertical cross-sectional view of the nut body is T-shaped, and the length from the flange bearing surface of the nut body to the inside of the nut component toward the object to be fastened is the length by which the screw shaft portion of the nut body enters. A hollow pipe-shaped nut component is placed on the outer peripheral portion of the outer surface of the screw so that the length of the incomplete thread portion s + the screw pitch is 0.5 threads or more and the length of the incomplete thread portion s + the thread pitch is 5 threads or less. The structure is arranged so that the lowermost part of the T-shaped nut body does not come into contact with the object to be fastened, and the uppermost part of the nut part comes into contact with the flange-shaped seating surface of the T-shaped nut body. The length of the nut component is set so that the lowermost portion of the nut component contacts the object to be fastened, the inner diameter surface of the nut component and the outer peripheral surface of the nut body are rotatable, respectively, and the nut body and the nut component are made rotatable. By forming concentric circles with the center of the screw;
By adopting a nut structure that directs the flow of the load force received by the nut to the meshing thread on the open side, which has a low load sharing, the maximum load sharing of the first meshing thread is reduced, and the third meshing thread. A nut characterized in that it is configured to reduce the load concentration on the first meshing thread by increasing the subsequent load sharing. Engagement with at least the bolt on the thread surface of the nut Diamond-like carbon (DLC) on the surface of the first thread or other threads that contacts some or all of the bolt-side threads, or on the slopes on both sides of the thread. film, BN film, WC films, CrN films, HfN film, VN film, TiN film, TiCN film, _Al 2 _{O 3} film, ZnO film, SiO ₂ film, anodized aluminum, a metal plating, a solid lubricating layer, manganese phosphate chemical conversion treatment The nut according to claim 1, wherein the nut is coated with a coating film of any one of carburizing and quenching, nitrided treatment, and chromated treatment, or a combination thereof. Diamond-like carbon (DLC) film, BN film, WC film, CrN film, HfN film, VN film, TiN film, TiCN film, Al ₂ O ₃ film, ZnO film, SiO _{2 on} the contact sliding surface of the nut and nut parts. Claim 1 or 2 comprising coating a film, alumite, metal plating, solid lubricating layer, manganese phosphate chemical conversion treatment, carburizing and quenching, nitriding treatment, chromated treatment, polymer resin coating, or a combination of these. The nut described in. Diamond-like carbon (DLC) film, BN film, WC film, CrN film, HfN film, VN film, TiN film, TiCN film, Al ₂ O on the seat surface of the nut component and the nut seat surface where the nut and the object to be fastened come into contact. ₃ films, ZnO films, SiO ₂ films, alumite, metal plating, polymer resin coat, solid lubricating layer, manganese phosphate chemical conversion treatment, carburizing and quenching, nitriding treatment, chromated treatment, or a combination of these coatings. The nut according to any one of claims 1 to 3.