JPH05209696A - Torque rod bush and manufacture thereof - Google Patents

Abstract

PURPOSE:To make a torque rod bush lightweight and prolong the life thereof without increasing the production cost. CONSTITUTION:The ball pin 6 of a torque rod bush 5 is a hollow body made of spherical graphite cast iron, and its base structure has a mixed structure of bainite and residual austenite. The ball pin element 6 of the torque rod bush 5 is cast from spherical graphite cast iron, and the ball pin element 6 is heated and held at 850-92O'C for 0.5-2hr to be austenitized as it is or after roughing. It is then isothermally held at 350-420 deg.C for 0.5hr or longer for isothermal transformation, the base structure is made a mixed structure of bainite and residual austenite, the ball pin element 6 thus obtained is machined into a correct size, then it is rockably incorporated in an inner tube 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque rod bush, and more particularly to a torque rod bush used as a trunnion suspension component in an automobile, particularly a heavy truck or an all-terrain truck.

[0002]

2. Description of the Related Art Generally, a tandem axle is used as a suspension device for a rear axle of an automobile or the like, especially for a heavy truck or a truck for rough terrain. The torque rod bush used as a component of the tandem axle is a torque rod. By fixing a rubber material between the inner cylinder and the outer cylinder that enclose the interlocking ball pin swingably, it plays a role of absorbing the impact load applied to the torque rod while the vehicle is traveling. Therefore, since the ball pin is required to have an impact strength capable of withstanding such an impact load, the conventional torque rod / bush is made of carbon steel for machine structure, for example, S45C, and this is used. Hot forged ball pins are used.

On the other hand, recently, there has been a demand for weight reduction of vehicles, and in order to meet this demand, torque rods and
The bushes are also required to be lightweight, and are required to have a longer life.

[0004]

A ball pin manufactured by hot forging a conventional carbon steel for machine structure exhibits excellent impact strength because it is solid in shape, but meets the demand for weight reduction. It was difficult. As a means to solve this,
It is conceivable to machine a solid ball pin to make it hollow, but there is a problem in that the number of processing steps increases remarkably, the manufacturing cost rises, and the strength and impact resistance decrease.

Therefore, an object of the present invention is to reduce the weight and lengthen the life of the torque rod without increasing the manufacturing cost of the bush.

[0006]

As a means for solving the above problems, the present invention is a spheroidal graphite cast iron having high castability and toughness as a material of a ball pin that most affects the weight of a torque rod bush. While making the ball pin hollow by casting, the matrix structure of the ball pin is a mixed structure of bainite and austenite.

That is, the torque rod bush according to the present invention is fixed to a ball pin that interlocks with the torque rod, an inner cylinder that swingably encloses the ball pin, and an elastic material to the inner cylinder. In a torque rod bush including an outer cylinder, the ball pin is made of a hollow body made of spheroidal graphite cast iron, and its matrix structure has a mixed structure of bainite and retained austenite.

Further, according to the present invention, the torque rod bush is formed by casting a ball pin element body from spheroidal graphite cast iron, and the ball pin element body is subjected to a rough processing or 850 to 920 in a non-oxidizing atmosphere. After heating and holding at 0.5 ° C. for 0.5 to 2 hours to austenite, it is immersed in a salt bath or a fluidized tank at 350 to 420 ° C. for rapid cooling, and kept at the temperature for 0.5 hours or more to carry out isothermal transformation treatment. Then, by austempering to air-cool or allow to cool to room temperature, the matrix structure becomes a mixed structure of bainite and retained austenite. It can be manufactured by packaging.

As the spheroidal graphite cast iron, any known one can be used, and when its representative component composition is shown by weight%, C3.5 to 3.8%, Si2.4 to 2.9%, Mn
It is 0.3 to 0.4%, P is 0.03% or less, S is 0.02% or less, and Mg is 0.02 to 0.05%, but is not limited thereto.

[0010]

[Operation] By using spheroidal graphite cast iron, which has high castability and excellent toughness, as the material for the ball pin, the ball pin can be easily hollowed, and the hollowing reduces the weight of the torque rod / bush. It becomes possible. Further, the spheroidal graphite in the base of the ball pin plays a role of imparting self-lubricating property and at the same time improving familiarity with the mating material and reducing wear of the mating material such as the ball pin and the bearing. Further, the hollow ball pins as-formed in spheroidal graphite cast iron have a matrix structure of ferrite-pearlite type structure and sufficient impact strength cannot be obtained. However, austempering makes this a mixed structure of bainite and retained austenite. This ensures the required impact strength and strength as a ball pin.

Next, in the method of the present invention, the reason for limiting the conditions of the austempering treatment as described above will be explained. First, the austenitizing temperature is set to 850 to 920.
The reason why the temperature is kept at 0.5 ° C. for 0.5 to 2 hours is as follows. That is, the austenitizing temperature is a temperature at which a homogeneous austenite structure is formed, and the higher the temperature, the larger the amount of solute carbon in the austenite. In the ball pin according to the present invention, this solid solution amount is
0.7 to 0.9% is preferable, but if the austenitizing temperature is less than 850 ° C, the amount of solid solution carbon becomes too small, and the toughness and strength are both reduced. Since the amount becomes too large and the toughness decreases, the above range is set. Also, the heating and holding time during austenitization is 3
0 minute to 2 hours means that a homogeneous austenite solid solution cannot be obtained when the treatment time is less than 30 minutes, and when the treatment time exceeds 2 hours, the austenite is heated and held even after the austenitization is completed. Since it leads to waste, the above range is set.

Further, the isothermal transformation treatment temperature is 350 to 420.
The reason why the temperature is set to 0.5 ° C. for 0.5 hour or more is as follows. That is, in the isothermal transformation treatment, the retained austenite increases and the toughness increases as the temperature rises.
If it exceeds 20 ° C., troostite tends to precipitate and conversely the toughness decreases, and if it is less than 350 ° C., the tensile strength improves but the fatigue strength decreases.
The isothermal holding time at this time is the time required to completely complete the isothermal transformation, and is 30 minutes or more, so the above range was set.

The invention will now be described with reference to the accompanying drawings which show an embodiment of the invention.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 3, 1 is a vehicle chassis, 2 is a trunnion bracket, 3 is wheels, 4 is a torque rod, and 5 is a torque rod.
1 is a torque rod bush, and the torque rod bush 5 includes a ball pin 6 that interlocks with the torque rod 4, an inner cylinder 7 that swingably encloses the ball pin 6, and An outer cylinder 9 fixed to the cylinder 7 with an elastic body 8 interposed therebetween. The caulking portion 7 is provided on the opening end side of the inner cylinder 7.
The stop ring 11 is fixed by b, and the dust cover 12 is arranged on the outer side thereof similarly to the side plate 7a side of the inner cylinder.
The inside thereof is filled with the lubricating oil 15.

The ball pin 6 comprises a hollow spherical portion 6a and a hollow pin portion 6b extending from the spherical portion 6a in directions opposite to each other with a straight line passing through the center thereof as a central axis, and the pin portion 6b is an oval. It has a sectional shape, and a through hole 6c is formed in the direction perpendicular to the central axis thereof. The spherical portion 6a of the ball pin 6 is swingably enclosed in the inner cylinder 7 via the bearing 10, and the cylindrical inner wall surface of the inner cylinder 7 and its side plate 7a or the retaining ring 11, the bearing 10 and the spherical shape of the ball pin 6 are formed. Part 6
An oil-containing material 14 is filled in the space surrounded by the surface of a.

The ball pin 6 having the above structure was manufactured as follows, and its mechanical properties were measured. The results shown in Table 1 were obtained. As a material, C 3.70%, Si
2.84%, Mn 0.33%, P 0.023%, S
A ball pin having a structure shown in FIG. 3 was cast by a conventional method using spheroidal graphite cast iron composed of 0.012% and Mg 0.033%, and the ball pin was held at 900 ° C. for 1 hour using a non-oxidizing atmosphere furnace. After that, it was placed in a hot bath of 380 ° C. to be rapidly cooled, held at that temperature for 1 hour, and then allowed to cool to room temperature.

[0017]

[Table 1] Tensile strength (N / mm ² ) Proof strength (N / mm ² ) Elongation (%) Hardness (Hv) 989 728 10.4 287

Further, when the metallographic structure of the obtained ball pin was examined, it was as shown in FIG. It can be seen from FIG. 4 that the ball pin 6 according to the present invention has a matrix structure having a mixed structure of bainite and austenite. Further, the breaking strength of 10 ball pins obtained by the above method was measured, and the results shown in Table 2 were obtained.

[0019]

[Table 2] Sample No. 1 2 3 4 5 6 7 8 9 10 Average breaking strength 426 431 402 397 392 412 407 392 397 402 405.8 × 10 ³ (N)

From these results, the ball pin according to the present invention is a solid ball pin manufactured by hot forging with a conventional carbon steel for machine structure (S45C), though it is a hollow body.
It can be seen that it has a breaking strength comparable to (average breaking strength: 421 × 10 ³ N).

The ball pin according to the present invention has a single weight of 790 g, which is about the same strength as S45.
The weight of the solid ball pin, which is a hot forged product made of C, is 1400.
It was g. Therefore, according to the present invention, the weight of the ball pin can be reduced by about 44%, and the weight of the torque rod bush can be reduced.

[0022]

As is apparent from the above description, according to the present invention, (a) the ball pin can be easily made hollow by using spheroidal graphite cast iron as the material of the ball pin of the torque rod bush. As a result, the weight of the torque rod / bush can be reduced without increasing the manufacturing cost. Also, (b) Torque rod
Not only is the ball pin of the bush made hollow with spheroidal graphite cast iron, but its base structure is a mixed structure of bainite and retained austenite, so a ball with mechanical properties and impact strength equivalent to or better than that of a conventional solid ball pin. You can get a pin. Further, (c) since spheroidal graphite cast iron is used as the material for the ball pin, the action of the spheroidal graphite in the matrix imparts self-lubricating properties and at the same time improves the familiarity with the mating material. Sliding wear can be reduced, and the life of the torque rod and bush can be extended.

[Brief description of drawings]

FIG. 1 is a partially cutaway side view showing an embodiment of a torque rod bush according to the present invention.

2 is a partially cutaway side view of the ball pin of the torque rod bush of FIG. 1. FIG.

FIG. 3 is an explanatory diagram showing an example in which a torque rod bush is applied to a rear axle of a vehicle.

FIG. 4 is a 400 × micrograph showing the metallographic structure of the ball pin of FIG. 2.

[Explanation of symbols]

1 ... Vehicle chassis, 2 ... Trunnion bracket, 3 ... Wheel, 4 ... Torque rod, 5 ... Torque rod bush,
6 ... Ball pin, 7 ... Inner cylinder 7, 8 ... Elastic body, 9 ... Outer cylinder.

Claims (3)

[Claims] 1. A ball pin interlocking with a torque rod,
A torque rod comprising an inner cylinder that swingably encloses the ball pin and an outer cylinder fixed to the inner cylinder via an elastic body.
In the bush, the torque rod bush, wherein the ball pin is made of a spheroidal graphite cast iron hollow body, and the matrix structure thereof has a mixed structure of bainite and retained austenite. 2. The ball pin has C3.5 to 3.8.
%, Si 2.4 to 2.9%, Mn 0.3 to 0.4%, P
0.03% or less, S0.02% or less, Mg0.02
The torque rod bush according to claim 1, wherein the torque rod bush is made of 0.05% spheroidal graphite cast iron. 3. A ball pin body is cast from spheroidal graphite cast iron, and the ball pin body is subjected to 850 as it is or after rough processing.
To 920 ° C. for 0.5 to 2 hours to form austenite, and then to 350 to 420 ° C. for 0.5 hour or more to perform isothermal transformation to perform a constant temperature transformation, and the matrix structure is a mixed structure of bainite and retained austenite. A method for manufacturing a torque rod / bush, characterized in that the obtained ball-pin body is subjected to full-size processing, and is then swingably enclosed in an inner cylinder.