JPH042807B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a crankshaft for an internal combustion engine, and more particularly to a crankshaft for an internal combustion engine in which the wear resistance and fatigue resistance of the crankshaft are improved.

[Technical background of the invention and its problems] A crankshaft used in an internal combustion engine of an automobile will be explained with reference to FIGS. 1 and 2. The crankshaft 1 shown in Fig. 1 is for a four-cylinder engine, and its structure consists of a crank journal 2 that is supported by a main bearing and serves as a rotating shaft, a crank pin 3 that is assembled to the big end of the conrod, and a crank journal 2 that is supported by a main bearing and serves as a rotating shaft. It consists of a crank arm 4 that connects the crank pin 3 to the crank pin 3, and a balance weight 5 that balances rotation. In addition, an oil hole 6 is provided to supply lubricating oil to the bearing parts such as the crank journal 2 and crank pin 3, and a bearing metal (not shown) built into the outer periphery prevents an oil film from forming on the journal part, crank pin, etc. This prevents seizure and minimizes horsepower loss due to friction.

Recent crankshafts 1 have been designed to the extreme, and in order to reduce weight, a lightweight hole 7 is provided as shown in Figure 2.
The cross-sectional shape of each part has been made as small as possible.

In conventional crankshafts, the dangerous cross-section where the shaft breaks due to fatigue is only the fillet radius 8 on both sides of the bearing 9 such as the crank journal 2 and crank pin 3, and fatigue occurs from there.
As shown by the line shown in , it is easy to crack and break, so the crank journal 2 including the fillet round part 8 and the bearing part 9 of the crank pin 3 have been induction hardened to increase their fatigue strength. However, when the crankshaft 1 is designed to the extreme, the dangerous cross section is not only the fillet round portion 8, but also the oil hole 6 and the weight reduction hole 7, where cracks will appear and break. Therefore, the inner surfaces of the oil hole 6 and the weight reduction hole 7 must also have high fatigue resistance, but in induction hardening, the oil hole 6 and the weight reduction hole 7 need to have high fatigue strength.
It is not possible to harden the inside of the
As shown in the figure, only the surface of the bearing part 9 has a hardened layer 1.
If only 0 is formed, the inside of the oil hole 6 cannot be hardened, and cracks are likely to form from the hardened layer 10 at the hardened boundary part 11.

Therefore, instead of induction hardening, a soft nitriding treatment (or tuftride treatment) is performed in which the entire crankshaft is immersed in a nitrogen compound salt bath, etc., and the surface of the bearing portion 9 and the inner circumferential surface of the oil hole 6 and the weight reduction hole 7 are coated. It has been attempted to improve fatigue strength by forming nitrogen compounds.

However, if the crankshafts of automobiles destined for developing countries are subjected to nitrocarburizing treatment (tuftride treatment), it is technically difficult to re-grind and finish the crankshafts for repair, and the products cannot be exported.

That is, the bearing parts 9 such as the crank journal 2 and crank pin 3 of the crankshaft 1 are easily worn out, so it is necessary to re-polish their surfaces and replace them with ones that are thicker than the above-mentioned bearing metal. However, the thickness of the soft nitrided layer is about 10 microns, and if this soft nitrided layer is polished, the soft nitrided layer disappears and the fatigue strength decreases, so a new soft nitriding treatment must be performed. Since treatment is technically difficult in countries and regions where the equipment is not well-equipped, repair of the crankshaft is impossible. In developing countries, road conditions and lubricant oil management are not adequate, so crankshafts are subject to significant wear and repair is more necessary in developing countries. Conventional repair of induction hardened crankshafts involves a hardening thickness of several millimeters, and the hardened layer remains even after re-polishing, so it is technically possible to repair even if the equipment is not in place, but as mentioned above, Crankshafts designed to the extreme require reinforced oil holes and lightweight holes, and induction hardening alone is not sufficient. In addition, related technologies include JP-A-56-98421 and JP-A-57-
There is a publication number 47868.

[Object of the Invention] An object of the present invention is to provide a crankshaft for an internal combustion engine that allows easy repair of a crankshaft designed to the extreme.

[Summary of the Invention] The present invention is characterized by ball burnishing the oil holes and lightweight holes of the crankshaft, and induction hardening of the bearing portion. However, it can be re-polished, and the oil holes and lightweight holes are treated with ball burnishing, so the inner peripheral surface of the holes has high fatigue resistance, so the crankshaft with an extreme design has sufficient fatigue resistance. It can have strength.

[Embodiments of the Invention] Preferred embodiments of the crankshaft for an internal combustion engine according to the present invention will be described below with reference to the accompanying drawings.

First, the structure of the crankshaft 1 is as explained in FIGS. 1 and 2.

First, the oil hole 6 and weight-reducing hole 7 of the crankshaft 1 are subjected to ball burnishing treatment.In this ball burnishing process, the inner peripheral surfaces of the oil hole 6 and weight-reducing hole 7 are made rough, and the diameter of each hole is A ball with a larger diameter is inserted into the oil hole 6 and the weight reduction hole 7, and the inner circumferential surface of the hole is rolled and hardened by the ball.This causes the inner circumferential surface to undergo compressive plastic deformation, and due to compressive residual pressure. To increase the fatigue strength, a reinforcing layer 12 is formed on the inner peripheral surface of the oil hole 6 by ball burnishing as shown in FIG. This ball burnishing treatment not only creates residual compressive pressure on the surface of the hole, but also improves the surface roughness. to increase fatigue strength. When performing ball burnishing on the oil hole 6 and weight reduction hole 7, it is not necessary to perform ball burnishing over the entire length of the holes 6 and 7, and it can be done as appropriate depending on the shape of the crankshaft 1 and the diameter and position of the oil hole 6 and weight reduction hole 7. Decide the depth of processing.

After the oil hole 6 and the weight reduction hole 7 are ball burnished, the crank journal 2, the crank pin 3, the bearing parts 9 such as the fillet round part 8 are subjected to induction hardening. As shown in FIG. 4, a hardened layer 10 of about 2 to 3 mm is formed on the bearing portion 9 by induction hardening.

Figure 6 is a graph showing the fatigue limits of the fillet round part, oil hole, and lightweight hole. The hardened holes indicate the fatigue limit when subjected to ball burnishing treatment, and c indicates the fatigue limit when subjected to soft nitriding treatment (tuftride treatment). In the case of no treatment (a), the target level is not reached, but in the case of the present invention (b), the fatigue limit can be higher than the target level. Furthermore, although the ball burnishing treatment for the oil holes and lightweight holes is slightly lower than the fatigue limit of the nitrocarburizing treatment (or tuftride treatment) in c., there is no problem at all in practice.

In the above, the oil hole and the lightweight hole are subjected to ball burnishing treatment, and the bearing part is induction hardened, so that the bearing part can be reground, and the crankshaft can be repaired even in places where equipment is not available.

In addition, in the above-mentioned example, an example was shown in which induction hardening was performed after ball burnishing treatment.
Ball burnishing treatment may be performed after induction hardening.

[Effects of the Invention] As is clear from the above detailed description, the present invention exhibits the following excellent effects.

(1) By applying ball burnishing to the oil holes and weight-reducing holes on the crankshaft and induction hardening the bearings, it is possible to repolish the bearings.Moreover, the oil holes and weight-reducing holes are treated with ball burnishing. Because of this, even if the crankshaft is designed to the extreme, its fatigue strength can be improved.

(2) Since the bearing can be reground, it becomes technically possible to repair the crankshaft even in places where repair equipment is not available.

[Brief explanation of drawings]

Figure 1 is an overall view of the crankshaft of an internal combustion engine, Figure 2
The figure is an enlarged view showing the details of the bearing part of the crankshaft, Figure 3 is a diagram showing the state in which the periphery of the oil hole in the bearing part of the crankshaft has been induction hardened, and Figure 4 is the crankshaft of the internal combustion engine according to the present invention. Fig. 5 is a graph showing the relationship between surface roughness and fatigue strength in ball burnishing treatment, Fig. 6 is a graph showing the fatigue limit of the fillet radius, oil hole, and lightweight hole. . In the figure, 1 is the crankshaft, 2 is the crank journal, 3 is the crank pin, 6 is the oil hole, 7 is the weight reduction hole, 8 is the fillet round part, 9 is the bearing part, 10
12 is a hardened layer and 12 is a reinforced layer.

Claims (1)

[Claims] 1. A crankshaft for an internal combustion engine, characterized in that oil holes and weight-reducing holes in the crankshaft are treated with ball burnishing, and the bearing portion is induction hardened.