JPH06129419A - Ball joint device - Google Patents

Abstract

PURPOSE:To prevent the loosening of a ball stud at a ball joint device. CONSTITUTION:By conducting the hardening processing of the taper hole surface 32 of a knuckle 10 by using a taper roller processer 40, yield load is increased, and the permanent set of the taper hole surface 32 caused by lateral operation force P added to a ball stud 10 is restrained. Also, by forming a small diameter portion 24 at the middle portion of the taper shaft portion 16 of the ball stud 12, an inter-surface distance to resist a moment based on the operation force P is made to be maximum at all times, and surface pressure based on the operation force P is reduced, and also elastic deformation ability at the time of the tightening of the ball stud 10 is increased. As a result, the generation of the loosening of the ball stud 12 is restrained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball joint device which is a kind of universal joint, and more particularly to improvement of durability.

[0002]

2. Description of the Related Art One type of ball joint device includes a ball stud which is a bolt having a ball portion at one end and a screw portion at the other end. The taper shaft portion (tapered shaft portion) of the ball stud is inserted into the taper hole (tapered through hole) of the mounting member, and the nut is screwed into the screw portion to be fixed to the mounting member. Since the bolt is supported by the tapered shaft portion, even if a force perpendicular to the axial direction is applied to the ball portion, the bolt portion is not displaced and lateral accuracy can be maintained. However, since the ball portion and the taper shaft portion are separated from each other in the axial direction, when a force perpendicular to the axial direction is applied, a moment is generated in the plane including the axis of the ball stud, and this moment is tapered. Received in two axially and diametrically spaced portions of the hole. If the moment is particularly large, the above-mentioned 2
The surface pressure of the portion exceeds the yield strength of the ball stud or the mounting member, or even if it is not so large, it is continuously or intermittently applied to cause fatigue, causing a fatigue in the portion. The sag occurs near both ends of the tapered hole when the machining accuracy of the tapered shaft portion and the tapered hole is high, but does not always occur near both ends of the tapered hole when the machining accuracy is low. In such a case, the distance between the two parts against the moment is shortened, the surface pressure is increased, and it becomes easier to settle.

When such a settling occurs, the axial force is reduced, causing loosening of the ball stud. As a means for avoiding this, it is conceivable that the material of the ball stud and the mounting member has high hardness, but it is often not preferable because it becomes brittle. Therefore, the same material is used to avoid loosening, and one of them is a ball joint disclosed in Japanese Utility Model Laid-Open No. 57-30412. In this invention, two tapered hole portions having the same central axis are formed at both ends of the through hole in the mounting member, and a ball stud having a tapered shaft portion in these tapered hole portions and one surface thereof are tapered surfaces. The nut is fitted and fixed to prevent loosening.
By using a nut that fits tightly with the mounting member on the tapered surface, compared to the case of using a normal nut that only frictionally engages the mounting member on a flat surface, Since it effectively opposes, the settling is less likely to occur and the ball stud is less likely to loosen.

[0004]

However, even if the nut is tightly fitted with the mounting member, the nut and the threaded portion of the ball stud are not tightly fitted, so that the nut and the mounting member are tightly fitted. Fitting part counters moment 2
It does not necessarily function as one of the parts, but it is necessary to form tapered parts at both ends of the through hole with high precision, and to increase concentricity between the tapered hole that fits the ball stud and the tapered hole that fits the nut. Since it is difficult, the expected effect may not be obtained. Then, this invention makes it a subject to obtain the technique which can prevent looseness of a ball joint apparatus stably.

[0005]

In order to solve the above problems, the present invention according to claim 1 is directed to a ball joint in which a tapered shaft portion of a ball stud is inserted into a tapered hole of a mounting member and screwed to the mounting member. In the device, the gist of the present invention is to form a hardened layer on the surface of the tapered hole of the mounting member, and the invention of claim 2 further provides at least one annular relief portion on the tapered shaft portion of the ball stud. It is the gist to provide.

[0006]

When the lateral force is applied to the ball portion while the tapered shaft portion of the ball stud is fitted in the tapered hole of the mounting member, the two parts of the fitting portion are separated in the axial direction and the diametrical direction. The pressure increases. If the material of the mounting member has high hardness, the settling does not occur. However, the materials of the ball stud and the mounting member are limited by various aspects. In particular, a mounting member that is generally large and has a complicated shape is often limited by the amount of material, the manufacturing method, and the like, and it is often the case that the hardness cannot be satisfied depending on the selection of the material. Therefore, according to the first aspect of the present invention, the settling is prevented by forming a hardened layer on the surface of the tapered hole without making the entire mounting member a material of high hardness.

Surface hardening includes a method of changing the surface material itself by plating, ceramic spraying, etc., and a method of changing only the surface hardness without changing the material by work hardening such as roller processing. By using a mounting member with an effect layer formed on the surface of the tapered hole by such a method, for example, when tightening a ball stud with a nut on the mounting member, tighten it with the same tightening torque as before, and as a result, the ball stud is generated. Even if the applied axial force is the same as that of the conventional one, loosening is less likely to occur because fatigue is less likely to occur. Furthermore, since the surface is hardened, even if the tightening torque of the nut is increased, the deformation of the tapered hole of the mounting member does not easily occur, the nut can be tightened with a high tightening force, and the axial force of the ball stud increases. Loosening is less likely to occur. The same applies to the case where the ball stud is fixed to the mounting member by screwing the threaded portion of the ball stud into the female screw hole of the mounting member.

According to the second aspect of the invention, in addition to the formation of the hardened layer, the shape of the tapered shaft portion of the ball stud is also changed. By forming an annular relief portion in the taper shaft portion, the portion where the taper shaft portion and the taper hole are in close contact is clearly defined.

If a recessed portion which is recessed from the original tapered surface is provided in the middle of the tapered shaft portion of the ball stud, substantial support is provided at a portion that is not the relief portion (hereinafter referred to as a convex portion). Therefore, by providing the convex portion at an arbitrary position of the fitting portion, it is possible to counter the moment at a desired position. The number of grooves may be at least one and the number is not particularly limited. However, if convex portions are provided in the vicinity of both ends of the tapered hole, it is particularly difficult for the settling to occur. Further, by increasing the depth of the relief portion, the diameter of the tapered shaft portion is reduced in that portion, the length of the small diameter portion is increased in the entire ball stud, and the elastic deformation capability is increased,
Loosening is less likely to occur.

[0010]

As described above, by forming the hardened layer on the surface of the taper hole of the mounting member according to the invention of claim 1, the settling of the surface of the taper hole is reduced and the looseness of the ball stud is stabilized. Can be prevented. In addition, if the tapered shaft portion of the Bolstad is provided with the relief portion according to the second aspect of the present invention, the contact portion with the surface of the tapered hole can be clearly defined, and the loosening can be prevented more stably.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment in which the present invention is applied to a ball joint of a steering device for an automobile will be described. In FIG. 1, reference numeral 10 is a knuckle arm that is a component of the steering device. A ball stud 12 is fixed to the knuckle arm 10. This ball stud 12 is
A ball joint is constructed in cooperation with a spherical surface seat provided at the end of a drag link or tie rod (not shown). The ball stud 12 includes a ball portion 14, a taper shaft portion 16 and a screw portion 18, and the taper shaft portion 1
6 and the screw portion 18 are fixed to the knuckle arm 10, while the ball portion 14 is fitted to the spherical seat so that the knuckle arm 10 and the drag link are rotatably connected to each other.

The ball stud 12 is made of SCM440, and after the surface of the tapered shaft portion 16 is hardened,
It is processed into a taper of 9.46 ° by grinding with high dimensional accuracy. An annular groove 20 having a rectangular cross-section is formed in the middle of the tapered shaft portion 16, whereby the tapered shaft portion 16 moves from the side close to the ball portion 14 to the first tapered portion 22,
It is divided into a small diameter portion 24 and a second taper portion 26.

On the other hand, the knuckle arm 10 is made of graphite cast iron FC.
It is made of D400 and has a tapered hole 30. Surface of tapered hole 30 (hereinafter referred to as tapered hole surface 32)
A processing layer is formed on the sheet by roller processing, which will be described in detail later. The taper shaft portion 16 of the ball stud 12 is inserted into the taper hole 30, and the nut 3 is attached to the screw portion 18.
The ball stud 12 is fixed to the knuckle arm 10 by screwing 4 and tightening. Therefore, the second tapered portion 26 is always entirely fitted in the tapered hole 30, but a part of the first tapered portion 22 projects to the outside of the tapered hole 30.

The fitting width (the axial dimension of the fitting portion) of the first taper portion 22 with the taper hole 30 and the width of the second taper portion 26 are obtained when the acting force P is applied to the ball portion 14. In addition, it is determined in consideration of the magnitudes of the reaction forces F1 and F2 applied to the tapered portions 22 and 26. When the distance between the acting force P and the reaction force F1 in the axial direction of the ball stud is L1 and the distance between the reaction force F2 and the reaction force F1 is L2,
The relationship of F1 = P + F2, F2 · L2 = P · L1 is established. Further, the tapered holes 3 of the first and second tapered portions 22 and 26
When the average diameter of the fitting portion with 0 (the average value of the large diameter and the small diameter of the fitting portion) is D1 and D2 and the widths are W1 and W2,
The average surface pressures of the first and second tapered portions 22 and 26 are represented by F1 / (W1 · D1) and F2 / (W2 · D2), respectively. Therefore, when the reaction forces F1 and F2 are applied, the fitting width W of the first tapered portion 22 with the tapered hole 30 is set so that the planar pressures of the tapered portions 22 and 26 become substantially equal.
1 and the width W2 of the second taper portion 26 are set.

The surface of the tapered hole 30 has a thickness of 0.3 m.
A work-hardened layer of m or more is formed. The material FCD400 of the knuckle arm 10 was selected in terms of economical efficiency and mechanical properties. Since the knuckle arm 10 has a complicated structure, it is suitable to be manufactured by a casting method. Further, since it is a large-sized part and economical efficiency is required, cast iron is selected. Further, since the knuckle arm 10 is exposed to various environments during traveling, it is necessary to satisfy the requirements of mechanical properties in a wide temperature range. In particular, toughness in the low temperature region is important, and therefore FCD400 having good low temperature toughness was selected. However, while FCD400 has good low temperature toughness, it has a slightly insufficient hardness, and therefore has a tapered hole surface 32.
Only partial curing is performed.

The work-hardened layer is formed by cutting the tapered hole 30 and then performing roller processing by the taper roller processing tool 40 shown in FIG. The taper roller processing tool 40 is a processing tool usually used for the purpose of improving the surface roughness of the tapered hole. On the taper portion 44 of the processing portion 42 of the taper roller processing tool 40, six rollers 46 having a small diameter are attached so as to be rotatable along the taper surface at regular intervals.
The taper portion 44 is inserted into the taper hole 30 and is rotated while being applied with a predetermined axial force.
Is work hardened. At this time, the roller 46 comes into contact with the tapered hole surface 32, but due to the wedge effect and the small diameter of the roller 46, the contact surface pressure is very large, and work hardening is efficiently performed.

The taper roller processing tool 40 is attached to a main shaft of a processing device (not shown) to be rotated and fed. The handle 52 of the taper roller processing tool 40 has a built-in spring, and when a force against the spring force is applied to the roller 46, the position of the processing portion 42 with respect to the handle 52 changes according to the force. Therefore, even if the taper roller processing tool 40 (correctly, its handle 52) is fed after the roller 46 contacts the taper hole surface 32, the processing portion 42 is inserted into the taper hole 30 by the feed amount. However, the spring inside the handle portion 52 bends, and the force (hereinafter, referred to as pressing force) for pressing the roller 46 of the processing portion 42 against the tapered hole surface 32 increases in accordance with the amount of the bending.

FIG. 3 shows the relationship between the feed amount of the handle 52 and the pressing force after the roller 46 contacts the surface 32 of the tapered hole.
From this figure, it can be seen that there is a first-order correlation between the feed amount and the pressing force. Therefore, the necessary pressing force can be obtained by adjusting the feed amount of the handle 52. Hereinafter, description will be given with reference to data based on various experiments. In these experiments, a graphite cast iron FCD400, which is the same material as the knuckle arm 10, is used as a workpiece, a processing condition is a rotation speed of 250 rpm, and a processing time is 10 seconds. And The taper hole of the work piece was formed by cutting the cast iron.

FIG. 4 shows the degree of work hardening when the pressing force is changed. This figure shows the distribution of the hardness of the workpiece in the depth direction. The hardness was measured according to the JIS Vickers hardness test method (Z2244). From Figure 4,
It can be seen that the hardness near the surface of the workpiece increases as the pressing force of the taper roller processing tool 40 increases.
Further, it can be said that by increasing the pressing force, the effect of work hardening extends to a deep region apart from the material surface. It should be noted that although the pressing force is 0, the hardness near the surface of the material is larger than that of the inside, but this is due to the reamer processing at the time of cutting the tapered hole. FIG. 5 shows the relationship between the pressing force and the working depth based on this result.

In FIG. 4, the hardness converges to about 170 H _V in the deep portion of the material, and this value is the original hardness of the material. Therefore, 180H which is slightly higher than this value
_{Let V be} the threshold value of the hardness increasing effect by work hardening, and let the depth from the surface of the portion having a hardness equal to or higher than the threshold value be the working depth.

As shown in FIG. 5, there is a correlation between the pressing force of the taper roller processing tool 40 and the processing depth. In addition, the value when the pressing force is 0 is written in parentheses, but as already mentioned,
Such a value is obtained by work hardening by reaming when cutting the tapered hole. Therefore, this point originally exists closer to the line in the figure.

Next, FIG. 6 shows the relationship between the working depth and the yield load of the workpiece. The yield load was measured by the method shown in FIG. A work piece 62 whose surface is hardened by taper is placed on a pedestal 60, a ball stud 68 having a taper shaft portion 66 is inserted into the taper hole 64, and a press-fitting speed is applied from above the ball portion 70 of the ball stud 68. 0.5
The pressure is continuously applied until the workpiece 62 yields at a rate of mm / min, and the load (yield value) at that yield is read.
The yield value is read as the load value when the deformation of the member to be processed 62 due to the increase of the load deviates from the elastic deformation region and the plastic deformation occurs, so that the ball stud 68 is displaced by 0.1 mm in the axial direction.

Specifically, as shown in FIG. 8, the load-displacement line indicating the relationship between the load and the axial displacement of the ball stud 68 and the ball stud 68 parallel to the straight line portion of the load-displacement line. The load value at the intersection with a straight line horizontally separated by a distance corresponding to the axial displacement of 0.1 mm is read. If the roller is not machined, the intersection between the curve A and the straight line C is 9 tf. , Taper roller processing tool 40
In the case where the roller is processed with a feed amount of 4 mm, the intersection point between the curve B and the straight line C is 11 tf. Further, when the same load as the yield value 11tf when the roller processing is performed is applied when the roller processing is not performed, the axial displacement of the ball stud 68 due to plastic deformation reaches 1 mm. From this result, it is apparent that the surface hardness of the member to be processed is increased by the work hardening by the roller processing, and the plastic deformation is less likely to occur.

The yield load increase rate of FIG.
Was measured under various conditions in which the inner diameter and the outer diameter of the steel were changed, and as a result, it was revealed that the yield load increase rate could be increased by 10% or more by appropriately setting the working depth. Further, from this figure, it can be said that in order to increase the yield load increase rate to 10% or more, the pressing force should be set to a size such that the working depth is 0.3 mm or more.

As described above, the yield strength of the tapered hole can be increased by work hardening the surface of the tapered hole of the mounting member of the ball joint device. The increase in yield strength means that when the ball stud 12 and the knuckle arm 10 are fitted, the knuckle arm 10 does not sag due to the acting force P applied to the ball stud 12, and as a result, the looseness of the ball stud 12 is prevented. This is done with the aim of making it less likely to happen. Therefore,
It is important how much the increase in yield strength contributes to the reduction of the settling. The fact that the yield strength increases by 10% or more obtained from this result is effective in reducing the settling of work hardened layers. Is shown.

The taper roller processing tool 40 is usually used for the purpose of smoothing the processed surface and improving the roundness of the taper portion of the processed portion. This purpose is shown in FIG.
Since it is sufficiently achieved before reaching the processing depth of about 0.3 mm as shown in (4), it has not been conventionally performed until the processing depth exceeds 0.3 mm as in the present embodiment. Therefore, the taper roller processing tool 40 of the present embodiment
The use of is very specific and has a purpose different from the conventional use. It is also possible to increase the yield strength by pushing the taper shaft portion into the member to be processed without using the taper roller processing tool 40. However, in such a case, the contact area becomes large, and therefore the taper shaft is required to obtain the surface pressure. Since an extremely large force is applied to the portion, the amount of plastic deformation of the member to be processed becomes large, which is not practical. The processing by the taper roller processing tool 40 is characterized in that due to the action of the roller 46 having a small diameter, a large surface pressure can be obtained with a small pressing force, and the processing can be performed in a state where there is almost no plastic deformation of the member to be processed.

Further, as shown in FIG. 1, the ball stud 12
Since the tapered shaft portion 16 has the small diameter portion 24, the ball stud 12 is guaranteed to be tightly fitted to the tapered surface 30 in the vicinity of both ends of the tapered shaft portion 16 even if the processing accuracy of the tapered surface is somewhat poor. The moment based on the lateral acting force P applied to the ball portion 14 can be effectively countered. Further, by having the small diameter portion 24, the nut 34
The amount of elastic deformation of the ball stud 12 at the time of tightening is increased. When the taper shaft portion 16 is formed by a continuous taper portion, the portion that substantially contributes to the elastic deformation of the ball stud 12 is only the screw portion 18 and the small-diameter portion adjacent to the screw portion 18, so that the elasticity at the time of tightening is improved. The amount of deformation is small, and a slight deformation of the knuckle arm 10 cancels the elastic deformation, and the axial force may be lost to loosen the mounting portion of the ball stud 12. On the other hand, since the small-diameter portion 24 is formed in the middle of the tapered shaft portion 16, the elastically deformable portion is increased, so that the range in which the elastic force can be maintained against the deformation due to the fatigue is widened, and the ball stud 12 has The occurrence of loosening of the mounting portion is suppressed.

In the above embodiment, the surface of the first taper portion 22 of the ball stud 12 and the second taper portion 26 are formed.
The surface of the ball stud 72 is located on the same taper surface as in the ball stud 72 shown in FIG.
It is also possible that the surface of the second taper portion 78 is located on the taper surface having a radius smaller by Δr than the surface of the first taper portion 76. This ball stud 72 is shown in FIG.
When the small diameter portion 74 is tightened to the knuckle arm 10 as shown in FIG.
By moving to the smaller diameter side and tightly fitting in the tapered hole 30 at that position, both the first and second tapered portions 76 and 78 tightly fit in the tapered hole 30. Therefore,
The elastic deformation capacity of the ball stud 72 is larger than that of the ball stud 12, and the loosening is less likely to occur. Further, the surface hardness of the tapered hole may be improved by a surface treatment such as a plating treatment, a plurality of relief portions may be provided, and the depth thereof may be slightly depressed from the periphery. Further, the use of the ball joint of the present invention is not limited to the knuckle arm, and it can be applied not only to other vehicle ball joints such as suspension device ball joints but also to other use ball joints. Besides, the present invention can be implemented in variously modified and improved modes based on the knowledge of those skilled in the art without departing from the scope of the claims.

[Brief description of drawings]

FIG. 1 is a front sectional view of a ball joint device according to an embodiment of the present invention.

FIG. 2 is a front view of a taper roller processing tool for processing the surface of a tapered hole of the ball joint device.

FIG. 3 is a graph showing the relationship between the feed amount of the taper roller processing tool and the pressing force of the taper roller processing tool.

FIG. 4 is a graph showing the relationship between the depth from the surface of the tapered hole processed by the taper roller processing tool and the hardness at that depth.

FIG. 5 is a graph showing the relationship between the pressing force of the taper roller processing tool and the processing depth.

FIG. 6 is a graph showing the relationship between the working depth and the yield load increase rate.

FIG. 7 is a front cross-sectional view of a test piece attached in the measurement of the yield load.

FIG. 8 is a graph showing a relationship between a load and a displacement amount in the measurement of the yield load.

FIG. 9 is a graph showing the relationship between the processing depth and the smoothness and roundness of the processed surface.

FIG. 10 is a front view of ball studs having different taper diameters.

FIG. 11 is a front sectional view of a ball joint device using ball studs having different taper diameters.

[Simple explanation of symbols]

 10 Knuckle Arm 12 Ball Stud 16 Tapered Shaft Part 20 Annular Groove 22 First Tapered Part 24 Small Diameter Part 26 Second Tapered Part 30 Tapered Hole 32 Tapered Hole Surface 64 Tapered Hole 68 Ball Stud 72 Ball Stud 74 Small Diameter Part 76 First Tapered Part 78 Second taper portion

Claims (2)

[Claims] 1. A ball joint device in which a tapered shaft portion of a ball stud is inserted into a tapered hole of a mounting member and screwed to the mounting member, wherein a hardened layer is formed on a surface of the tapered hole of the mounting member. Ball joint device. 2. The ball joint device according to claim 1, wherein at least one annular relief portion is provided on the tapered shaft portion of the ball stud.