JP2007516391A - Fasteners that prestress joints - Google Patents

Abstract

  Fastener joints cause static prestress in fasteners that clamp the joints in a magnitude equal to the bending stress induced in the fasteners by the applied load and in the opposite direction. Such a joint tilts the bolt seat of the connecting rod bearing cap inward and forms a relief in the bolted contact surface between the cap and the rod in the vicinity of the main drilling of the connecting rod, or the screw hole Including inclining a threaded hole in the rod body inward to extend from the bolted joint surface.

Description

The present invention relates to a fastener joint design such as a bolt joint (joint), and in particular, a joint that prestresses the fastener (fastener) so that the fastener (fastener) has a more uniform stress at the maximum adaptive load. About.

  Bending stress is induced along fastener shaft 11 such as a bolt in a curved plane when the joint is asymmetric and the fastener load is not on the centerline of the fastener. 1A and 1B schematically show two fasteners having the same on-axis load loading (eg, load on the shaft of the bolt shaft). FIG. 1A shows the bending stress applied to the paper surface on the axial pre-stress (curved plane so as to leave the fastener shaft 11 convex) so as to bend the axial portion 11 of the fastener 10 and apply an axial load. FIG. 1B shows the shaft portion 11 of the fastener 10 in which only an axial load (non-bending load) of the same magnitude is applied to the axial load 12 of the central axis of the bolt of FIG. 1A, and the average stress of both fasteners is the same. .

  The bending stress of the fastener of FIG. 1A reduces the load bearing capacity of the fastener and joint. One side 14 of the fastener shaft 11 in the bending plane has a higher stress than the other 16 due to the induced curvature. This is not desirable because the stress distribution between the fastener shafts produces high stress on the side 14 of the fastener shaft. A more desirable stress condition at maximum load is that the fasteners 12, 14, and 16 have a uniform stress distribution between the fastener shafts 11 in the curved plane of the maximum load condition shown in FIG. In some cases, a fastened joint cannot be designed to remove the bending stress of the fastener under all conditions, such as with a connecting rod joint where the applied load load is dynamic and varies.

  The load supported by the fastener is related to the average stress in the fastener. 1A and 1B, both fasteners 10 have the same average stress 12, while the fastener of FIG. 1A has a higher maximum stress 14 as a result of bending stress. If a failure occurs, it occurs at the maximum stress point along the side 14. The bending stress applied to the axial stress reduces the load carrying capacity of the fastener as compared to a fastener having a uniform stress distribution although the same average stress is applied.

  Referring to FIG. 2A, when fastening the joint, an initial axial prestress is applied as a result of tightening or stretching the fastener. This is indicated by a uniform prestress component 18. If the joint is asymmetric, the joint is more compressed than one of the other of the fastening holes. As a result, the fastener shaft 11 is subjected to bending stress and a load is applied in a non-uniform manner across the entire region of the fastener shaft 11. This is indicated by the non-uniform component 20. Furthermore, if load loading is applied off the fastener centerline, additional bending occurs in the fastener. The stress components 12, 14 and 16 in FIG. 1A are the sum of the uniform component 18 and the non-uniform component 20 at the maximum load load. Fastener joint designs are limited by the maximum stress of the fastener, including bending stresses that make the uniform stress profile shown in FIG. 1B a more preferred choice.

  The term “fastener” as used herein is any having a shaft that is tensioned when applied to a joint such as a bolt, rivet, rod (threaded, pinned, welded), screw, etc. It is a mold fastener. The term “bending stress” is referred to as non-uniform stress between fasteners. The present invention includes the use of a nut in a joint system that acts like a bolt head, and thus the fastener "head" includes a nut, bolt head, or screw head, rivet head or rivet flange, and the like.

  The present invention provides a bolted joint in which the maximum stress is reduced between the bolt shaft portions under the maximum load condition in the use application of the joint (joint). This is done with a joint that includes the bending stress of the fastener shaft in the curved plane of the applied bending stress when the fastener is incorporated into the joint. The bending stress induced by the joint is approximately inversely proportional to the bending stress induced in the curved plane by the maximum load applied to the fastener shank in use so as to reduce the maximum stress when the maximum load is applied.

  By doing so, the present invention reduces the periodic average stress experienced by the fastener shank. This is particularly effective for increasing the fatigue life of the fastener.

  In a useful embodiment of the present invention, the bending stress induced by the joint produces a substantially uniform stress distribution between the fastener shafts in the curved plane when the maximum load load is applied to obtain the full advantage of the present invention. For size and direction.

  In one form of the invention, the joint has a seat (seat) that the fastener supports against inducing tension at the shank, and the seat is 90 to the axis of the fastener hole in the part from which the shank extends. Inclined at an angle other than degrees. The seat is angled in a direction that induces a bending stress in the fastener opposite to the direction of the bending stress induced by the maximum load load. Thereby, the bending stress induced by the joint cancels the bending stress induced by the load load, reduces the maximum load load on the fastener shaft and reduces the cyclic average stress experienced by the fastener shaft.

  In another method of practicing the present invention, the joint has joint surfaces facing each other and held together by a fastener, and a portion of the joint surface is in the direction of bending stress induced by the maximum load load between the joint surfaces. An unsupported gap that induces bending stress in the shaft portion of the fastener in the opposite direction is defined.

  In another method of practicing the invention, the hole extending into the part and receiving the fastener shank has one first part and the other second part of the part, the first part being induced by maximum load loading. It is inclined with respect to the second part so as to induce a bending stress in the fastener in a direction opposite to the direction of the bending stress.

  These different ways of practicing the invention can be performed alone or in any combination with each other.

  In a particularly useful embodiment, the joint is a joint in the connecting rod that connects the bearing cap to the rod portion of the connecting rod. The bearing cap joint causes the fastener shaft to periodically move the connecting rod so that prestressing (compressive stress) on the fastener using the present invention reduces the maximum applied stress and the periodic average stress of the fastener shaft. Is a particularly useful application of the present invention because it is subject to periodic bending stresses.

  The foregoing and other objects and advantages of the invention are described in detail below. In the description, reference is made to the accompanying drawings which show preferred embodiments of the invention.

  Referring to FIG. 2B, the present invention provides a fastener fastening joint design that provides a substantially uniform stress distribution on the fastener shank 11 at maximum load loading conditions. In FIG. 2B, the stress chart shows the compressive stress with the lower set of vector arrows 22, 24 and 26 and the applied stress with the upper set of vector arrows 28, 30 and 32. In FIGS. 2A and 2B, the average prestress and the average maximum stress are the same, and each case deals with the same system load, but using the present invention results in a lower maximum stress under load loading. In cases where the joint load weight is cyclic as in the connecting rod bearing cap joint (joint), the average cyclic stress is also lower. The full period stress swing remains the same.

  The schematic stress charts of FIGS. 2A and 2B are simplified in that they do not show any accidental or unexpected joint bending prestress. If there is joint bending prestress, the horizontal set of prestress vectors in FIG. 2A is non-uniform (at an angle) and the corresponding prestress vector in FIG. 2B needs to be adjusted to compensate for the bending prestress. There is.

  Uniform stress distribution at maximum load load can be achieved in any number of ways. Currently, a typical connecting rod bearing cap joint is formed as shown in FIG. 3, with each bolt joint seat 36 being 90 degrees to the centerline 38 of the corresponding bolt hole 37 and screw hole 39, and non-screw The hole 37 is in the bearing cap 42 and in the threaded hole 39 connecting rod body 44. This substantially results in a stress distribution as shown in FIG. 2A, with vector 18 indicating static prestress and vector 20 indicating dynamic load weighting. In this case, it should be noted that the maximum stress occurs inside (towards the crankshaft hole 40 of both seats 36).

  One way of practicing the invention is to incline each joint bolt seat 36 by some small amount selected based on the maximum load load to be offset or offset with respect to the bolt 37 and the centerline 38 of the screw hole 39. is there. Typically, the inclination angle is 1 degree or less, for example, 0.125 degree, depending on the magnitude of the load weight. This angle should be oriented in the correct direction, thereby canceling the bending stress at the maximum (dynamic) load loading condition induced by the joint and load loading. This is shown in FIG. The flat two seats 36 as shown in the figure cause the bending stress of each bolt 10 to be angled or inclined inward in the direction of the bending plane and opposite to the bending stress induced by the load load. Machined or formed to trigger. In other words, the bolt 10 is deflected outwardly (which is outwardly convex with respect to the axis of the main bore 40) as a result of the inclined seat 36, whereas the load load is (of the main bore 40). It tends to bend inwardly (which is inwardly convex with respect to the axis). The angle magnitude and direction of the seat 36 and the torque at which the bolt 10 is fastened are selected to produce a substantially uniform stress distribution at the shaft portion of the fastener 10 at maximum load load, as shown in FIG. 2B. .

  In FIG. 4, if the bolt holes 37, 39 and the bolt joint seat are machined along the same spindle centerline 38, the centerline of the seat and bolt will be like the typical joint shown in FIG. 90 degrees to each other based on the manufacturing process. Additional or different steps are necessary to create the required bolt seat 36 slope. This can be done in many different ways. For example, the inclination of the bolt seat 36 of FIG. Another method is to machine the bolt hole with one spindle along axis 38 and machine the bolt seat with the other spindle at a small angle to the drilling spindle. Yet another method is to form the angle of the seat 36 using a powder metallurgy process to form the slope of each bolt seat 36 within the bearing cap 52.

  Another way to generate a uniform stress between the bolt shafts 11 on the curved plane with maximum load loading is to form a joint surface, which is small between each set of joint surfaces in the region near the bore 40. Opposite to each other near the center of the main bore 40 at a small angle to each other that tapers outward to form an unsupported gap 48. This is shown in FIG. One or both opposing surfaces are angled to form a gap 48. This small angle is machined on the surface, formed by forging or metallurgy, or the joint is the latter (highly exaggerated in FIG. 5 and depending on the magnitude of the load load to be offset) The method is plastically deformed to form a gap that is incorporated into other typical split split manufacturing processes of the connecting rod and cap. As a result, the cap 42 is bent toward the rod member 44 in the region of the gap formed at an angle, which has an effect of applying a bending stress to the shaft portion 11 of the fastener 10 so as to bend the shaft portion outward. Enable. When the bolt 10 is tightened, the gap 48 is closed or substantially closed or not closed. The size of the gap 48 and the torque at which the bolt 10 is fastened is selected to produce a substantially uniform stress distribution in the shaft 11 of the fastener 10 in a plane that bends at maximum load load, as shown in FIG. 2B. The

  Yet another method for creating a uniform stress in the curved plane between the bolt shank 11 at maximum load load is a small hole relative to the bolt hole 37 and the center line 38B of the (non-bent) bolt 10 as shown in FIG. The center line 38A of the screw hole 39 is formed at an angle. Further, the angle of the shaft 38A is greatly exaggerated and is 1 degree or less with respect to the shaft 38A. As in the above-described embodiments, the shaft portion 11 of the bolt 10 is bent outward so that a uniform stress distribution is generated between the bolt shaft portions of the curved plane at the maximum load load, and the period of the bolt shaft portion 11 is increased. Average stress and maximum stress decrease. The angle of the shaft 38A and the torque at which the bolt 10 is fastened are selected so as to generate a substantially uniform stress distribution in the curved plane in the shaft portion 11 of the fastener 10 at the maximum load load, as shown in FIG. 2B. .

  The preferred embodiment of the present invention has been described in considerable detail. Many variations and modifications to the described preferred embodiment will be apparent to those skilled in the art. Accordingly, the invention should not be limited to the described embodiments.

FIG. 1A is a typical prior art bolt stress distribution diagram showing the stress distribution in a bolt subjected to bending and axial loading. FIG. 1B is a typical prior art bolt stress distribution diagram showing the stress distribution in a bolt that receives only an axial load and the magnitude of the axial load being equal to the axial load of the bolt of FIG. 1A. FIG. 2A is a diagram similar to FIG. 1 and is a stress diagram showing components of total stress such as pre-stress (stress) and maximum stress. FIG. 2B is an illustration of a fastener corresponding to FIG. 2A, but showing the compressive stress and maximum stress distribution generated by a joint comprising the present invention. FIG. 3 is a view of a connecting rod bearing cap with an inclined bolt seat according to the present invention, the angles being exaggerated for illustration. FIG. 4 is a view of a typical prior art connecting rod bearing cap joint similar to FIG. FIG. 5 shows a connecting rod bearing cap joint with a tilted joint surface according to the present invention, the angle being exaggerated for illustration. FIG. 6 shows a connecting rod bearing cap with threaded fastener holes in an inwardly inclined rod according to the present invention, the angle being exaggerated for illustration.

Explanation of symbols

10 Fastener (fastener)
11 Shaft 12 Shaft load 18 Compressive stress component 36 Seat (seat)
37 Bolt hole 39 Screw hole 40 Main hole 48 Clearance

Claims (8)

In a joint between at least two parts clamped by a fastener having a tensioned shaft that holds the parts together,
The joint induces a bending stress of the fastener shaft in a curved plane when the fastener is incorporated into the joint;
The bending stress induced by the joint is approximately inversely proportional to the bending stress induced in the curved plane due to the maximum load load that the fastener shank acts to reduce the maximum stress when a maximum load load is applied,
A joint characterized by that.   The joint according to claim 1, wherein the bending stress induced in the joint has a magnitude and a direction that generate a substantially uniform stress distribution in the entire area of the fastener shaft portion of the curved plane to which the maximum load is applied. .   The joint has a seating surface that resists the fastener against inducing tension in the shaft, and the seating surface is opposite to the direction of bending stress in which the shaft is induced by the maximum load. The joint according to claim 1, wherein the joint is inclined at an angle other than 90 degrees with respect to the axis of the fastening hole in the part so as to reduce the bending stress of the shaft portion.   The joint has joint surfaces facing each other and held together by the fastener, a portion of the joint surface between the joint surfaces of the fastener in a direction opposite to the direction of bending stress induced by the maximum load load. The joint according to claim 1, wherein an unsupported gap for inducing a bending stress in the shaft portion is defined.   A hole extending into the part and receiving the fastener shank has a first part on one side of the part and a second part on the other part, the first part having a bending stress induced by the maximum load load. The joint according to claim 1, wherein the joint is inclined with respect to the second portion so as to induce a bending stress in the fastener in a direction opposite to the direction.   The joint according to claim 5, wherein the second portion is threaded.   The joint according to claim 5, wherein the first portion is in the vicinity of a fastening seat surface substantially orthogonal to the axis of the first portion.   The joint according to claim 1, wherein the joint is a joint in a connecting rod that connects a bearing cap to a rod portion of the connecting rod.

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