JPH0241903A - Wheel axle and its manufacture - Google Patents

Abstract

PURPOSE:To make a weight light and improve rigidity at a four wheel automobile wheel axle, by making the cross section of the wheel axle hollow, and arranging so that a spherical black lead cast iron system may be held, and also, forming a fitting portion to a frame, into a T letter shape. CONSTITUTION:The whole of a wheel axle 1 is cast-formed into a hollow box shape. And, a fitting portion 5 which is fitted to a car body frame by means of a leaf spring, is formed into a T letter shape at its cross section. And, at the time of this casting, black lead cast iron of a spherical shape is used, and the retention of 30 minutes - 3 hours at 830 - 950 degrees C and then, the retention of 30 minutes - 3 hours at 200 - 400 degrees C, are conducted. As a result, making a weight light and improving rigidity are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to an axle for a vehicle, particularly a four-wheeled vehicle, and a method for manufacturing the same.

b. Prior Art Conventionally, the axle a, which is an important part of an automobile, is made of forged steel, as shown in FIG. 7, and then quenched and tempered to give it high strength and toughness. The cross-sectional shape of the axle a is designed to be single-shaped, and sufficient consideration has been given to reducing the weight. Note that b indicates a brake drum inside the wheel, and there is a prior art (Japanese Patent Laid-Open No. 55119503) in which the axle is made into a hollow tubular shape by forging.

Problems that the C0 invention aims to solve In recent years, there has been a strong demand for lighter weight and lower cost automobiles, but the axles of these automobiles have been repeatedly improved over the long history of automobiles, and the current shape The manufacturing method has reached a point where no further improvement can be expected. For the axles of trucks that are used under particularly harsh conditions, it is required to further increase the torsional rigidity of the axle, but this is difficult to achieve with the current I-cross section axles without increasing the weight. Yes, this goes against the demand for weight reduction.

On the other hand, when developing a new axle, the mounting conditions, positions, and angles of parts around the wheel frequently change, and the shape of the axle may be changed to avoid interference with other parts or improve performance. However, for forged products, it is difficult to easily change the design because it is necessary to start by modifying the large and expensive mold.

In other words, it is extremely difficult to increase the rigidity of an axle that is a forged product while reducing its weight even further, and it has also been difficult to keep up with frequent design changes.

Therefore, it was considered to manufacture the axle by casting, which has a degree of freedom in design and is easy to adapt to design changes.However, until now, the axle has remained in a shape similar to the conventional product, and is made of the strongest class cast material ( For example, FCD-80: J Is
), it was difficult to put it to practical use as it was not as strong and rigid as the current forged products.

d. Means for Solving the Problems The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a vehicle axle that solves the above problems by combining a special shape and a manufacturing method, and a method for manufacturing the same. It is something to do.

That is, the present invention has solved the above problems by providing an axle for a vehicle, which is characterized in that the cross section of the axle is hollow and has a spheroidal graphite cast iron structure.

Furthermore, the present invention casts a vehicle axle from spheroidal graphite cast iron so that its cross section is hollow, and casts the axle from 830~
After holding at 950℃ for 30 minutes to 3 hours,
The above problem was solved by providing an axle manufacturing method characterized by holding the axle at 00°C for 30 minutes to 3 hours.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 to 6, reference numeral 1 indicates an axle according to the present invention, and this axle l is formed entirely into a hollow box shape by casting.

Reference numeral 2 denotes a shaft portion for a king pin provided at both ends of the axle 1. Flange portions 2a are provided at both upper and lower ends of the shaft portion 2, and a through hole 3 for inserting the king pin is formed by casting, thereby reducing the number of machining operations. I'm measuring.

In this embodiment, the part where the axle 1 is attached to the vehicle body frame 31 via the leaf spring 30, that is, the attachment part 5, has a T-shaped cross section, and the flat part 5a on the upper surface is formed slightly wide, and has a plurality of attachment holes. 5b is provided. If the mounting part is shaped like a picture, it cannot be installed unless the U-bolt 32 for mounting is lengthened, so if compatibility of the U-bolt is important, the cross section should be made into a T-shape like this,
This allows the use of conventional U-bolts. Therefore U
If there is no need to consider the compatibility of the bolts 32, the mounting portion may be planar. Further, the curved portion 8 between the shaft portion 2 and the mounting portion 5 also has a planar shape surrounded by a wall having a predetermined thickness.

A pair of mounting portions 5 are provided on the left and right, and an intermediate portion IO between the mounting portions 5 is also formed into a substantially uniform planar shape. That is, except for a pair of T-shaped mounting portions 5 which are employed in special cases, the axle 1 has a planar tunnel structure in its entirety in principle.

Incidentally, a core is used for the hollow portion forming the tunnel during casting, but the core can be cut to form partition walls 12 at appropriate locations to supplement the strength, if necessary. Further, the partition wall 12 may be provided with a through hole 12a, etc., for weight reduction and for convenient discharge of molding sand.

In the present invention, when casting the axle 1 having the above structure, spheroidal graphite cast iron having the following composition is used which allows thin-wall casting.

Among the above components, the above ranges of C and Si are necessary to crystallize graphite in a spherical shape, improve the fluidity of the molten metal, and make good castings, and outside these ranges, floating of graphite and crystallization of cementite may occur. Castings with good quality cannot be cast.

Moreover, Mn is contained in the dissolved material, but 0.
If it exceeds 8%, it is not preferable because it promotes cementite crystallization or segregates at grain boundaries, creating a non-uniform structure during austempering heat treatment.

P is 0.15% because it segregates at grain boundaries and makes the casting brittle.
The following shall apply.

Most of S combines with Mg to form nonmetallic inclusions and weakens the casting, so the content is limited to 0.03%.

Mg promotes the spheroidization of graphite, but if it is less than 0.02%, it is not sufficient; on the other hand, if it exceeds 0.08%, the material quality deteriorates, such as an increase in nonmetallic inclusions or formation of inner iron.

Using the above material, we cast it into a green sand mold, demolded it, and made an axle with rough processing such as deburring.
After austenitizing &I1m by holding at 0°C1, preferably 875 to 920°C for 30 minutes to 3 hours, 20
It was quenched by immersing it in a salt bath at 0 to 400°C, preferably 350 to 400°C, and held there for 30 minutes to 3 hours, and then taken out and left to stand at room temperature to convert the structure into bainite. That is, it was made into an austempered spheroidal graphite cast iron structure.

In the heat treatment, if the axle is held at a temperature below 830°C, it will take a long time to turn into austenite, and if the axle is held at a temperature above 950°C, the austenite crystal grains will become coarse and the strength will decrease. The heating holding time varies depending on the wall thickness, shape, and holding temperature of the product, but in the case of the target axle, holding for 30 minutes for thin walled parts and 3 hours for thick walled parts is sufficient.

Further, if the temperature of the salt bath is 200°C or lower, the axle becomes hard and brittle, and if it is higher than 400°C, the desired structure cannot be changed, and the hardness, strength, and toughness are all rapidly reduced.

Further, the holding time is adjusted depending on the thickness of the axle, chemical composition, and holding temperature, but it needs to be at least 30 minutes.

In addition, if the wall thickness of the product exceeds approximately 25 m, the rapid cooling effect by quenching cannot be sufficiently achieved, so by adding up to 1.5% Cu and up to 0.5% HO, the composite fibers can be improved. It can be made into a complete austemperature spheroidal graphite cast iron structure.

Further, in the axle of the present invention, shot peening can be applied to portions where higher values of high strength and high toughness are required. The fatigue strength of spheroidal graphite cast iron is significantly improved by subjecting it to shot peening, and its application to the axle of the present invention is effective.

Note that shot peening may be carried out in the usual manner, but for example, steel grains with an average grain size of 0.8 m may be subjected to shot peening at 45 m/
It is projected for 5 minutes at a speed of 100 kg/min. The aim is for the amount of deformation of the Almen gauge to be around 0.4 kaku. Furthermore, due to the nature of the axle, it is preferable to apply the coating to the entire axle, but depending on the type of vehicle, the coating may be applied only to areas that particularly require fatigue resistance.

Next, we will give a concrete example and show the results of a comparative study between this and a conventional axle. First, we will use the molten spheroidal graphite cast iron mentioned above to make an axle with the cross-sectional shape shown in Figures 1 and 2 in a green sand mold. Cast. The core used had an organic self-hardening structure. After the cast axle was rough-processed, it was heated at 900°C for 1 hour, then quenched by immersing it in a salt bath at 375°C, and held there for 1 hour. Thereafter, this was cooled to room temperature.

Next, the entire axle was subjected to shot peening under the conditions described above.

Table 1 shows the results of a comparison between the axle manufactured by the above method and a conventional forged axle.

Table 1 According to Table 1, the axle according to the present invention has a weight reduction of about 15% and a rigidity more than twice that of the conventional axle.

Furthermore, Table 2 shows the results of comparing the components and mechanical properties of test pieces cut from the cast product according to the present invention with other comparable products.

According to Table 2, it can be seen that the axle according to the present invention is superior to the FCD material (FCD-70) in all of the above mechanical properties.

On the other hand, although elongation and impact values are slightly lower than conventional forged steel products, as shown in Table 1, the product according to the present invention has overwhelmingly higher rigidity, and has lower weight and cost. Its superiority is clear.

In summary, in the present invention, the above-described axle having a stepped cross section is cast using spheroidal graphite cast iron, which can be cast thin, and is heat-treated as described above, thereby achieving a tensile strength of at least 95 kg/am. High strength and mechanical properties with a yield strength of 65 kg/■ or more, an elongation of 10% or more, and a hardness (Brinell) of 277 to 341.
Highly rigid axles can be replaced.

e. Effects of the Invention As described above, in the present invention, the transverse cross section is cast hollow and the structure is made of spheroidal graphite cast iron structure, so that the function as an axle is not impaired (light weight, rigidity We were able to achieve a significant improvement in

Furthermore, by making the section that is attached to the vehicle body frame T-shaped, conventional U-bolts can be used, increasing compatibility.

Furthermore, since the cross section of the axle is cast into a hollow box shape using spheroidal graphite cast iron and subjected to the above-mentioned treatment of the present invention, the advantages of spheroidal graphite cast iron products, which have a high degree of freedom in design, can be utilized to the fullest, and product design can be improved. It is possible to produce an axle with the above-mentioned functions that can easily respond to diversification due to modifications, specification changes, etc.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an axle according to the present invention with some parts omitted, FIG. 2 is a side view of FIG. 1, FIG. 3 is a sectional view taken along line AA in FIG. 2, and FIG. 2 is a sectional view taken along line BB in FIG. 2, FIG. 5 is a perspective view from the back side of a mounting portion having a T-shaped cross section, FIG. FIG. 7 is an explanatory diagram showing how a conventional axle is used. 1...Axle, 2...Axle part. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1) An axle for a vehicle, characterized in that the cross section of the axle is hollow and has a spheroidal graphite cast iron structure. 2) Claim 1, characterized in that the part of the axle for a vehicle that is attached to the vehicle body frame is T-shaped.
Axle as described in section. 3) A vehicle axle is cast using spheroidal graphite cast iron so that the cross section is hollow, and after holding it at 830 to 950°C for 30 minutes to 3 hours, it is then heated to 200 to 400°C for 30 minutes to 3 hours.
A method for manufacturing an axle characterized by holding the axle for 3 hours.