JPH03226344A - Manufacture of cylinder block of aluminum alloy - Google Patents

Abstract

PURPOSE:To prevent a bearing metal ranging from a cold temperature to a high temperature from seizing by clamping a bearing cap to a cylinder block body made from aluminum alloy and executing rough working, maintaining of high temperature, reclamping, finish working in sequence. CONSTITUTION:In a cylinder block 1 for an aluminum alloy engine wherein bearing members 4, 6 of a main bearing hole 3 is cost in after the bearing cap 5 is clamped by a bolt 7 through a prescribed thrust, rough working of the inner peripheral surface of a main bearing hole, maintaining of the cylinder block body 2 at a high temperature, reclamping of the bearing cap 5, finish working for making the inner peripheral surface of the main bearing hole 3 round are performed in sequence. The out-of-roundness of the main bearing hole 3 ranging from a low temperature to a high temperature can be secured and the bearing metal can be prevented from seizing.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing an aluminum alloy cylinder block.

(Prior Art) When the cylinder block of an engine is made of aluminum alloy (aluminum alloy) instead of cast iron to reduce its weight, there are problems of insufficient rigidity of the main bearing portion and dimensional change due to thermal expansion6.

In contrast, a bearing member with high rigidity and a coefficient of thermal expansion is cast in the main bearing part of the cylinder block body made of aluminum alloy, and is connected to the crankshaft, and a bearing cap made of the same material as the bearing member is attached to the cylinder block. The technique of reinforcing the main bearing portion by tightening bolts to the main body is generally known (see Utility Model Application Publication No. 136609/1983).

(Problem to be Solved by the Invention) However, in the case of the above-mentioned bearing member or cast cylinder block, when the engine is actually operated, the main bearing hole is located in the third
As shown in the figure, it deforms from the initial state A, which is a substantially perfect circle indicated by the broken line, to the state B indicated by the solid line, and this decrease in roundness tends to cause an increase in vibration or noise and seizure of the bearing metal.

The present inventor investigated the cause of this problem and discovered the following.

As shown in Figure 4, the temperature of the main bearing reaches around 150°C during engine operation, and as a result, the aluminum part of the cylinder block thermally expands and its strength decreases (softens), causing plastic deformation. .

Furthermore, when we look at changes in the axial force of the bolts that fasten the bearing cap to the cylinder block body, we find that when the temperature of the main bearing increases, the axial force increases due to the thermal expansion of the aluminum part, or this shaft Since the aluminum portion undergoes plastic deformation as the force increases, the axial force decreases by a in response to this plastic deformation. Therefore, even if the temperature of the main bearing returns to normal temperature due to engine shutdown, the axial force will be lower than its original value due to plastic deformation of the aluminum portion.

On the other hand, if we look at the stress caused by the casting of the aluminum part that encases the bearing member, the temperature of the main bearing will decrease in response to the difference in thermal expansion between the bearing member and the aluminum part. By keeping the high temperature during engine operation, the residual stress in the aluminum part is partially permanently released, and the stress in the casting further decreases by β.Therefore, when the engine is stopped, the main bearing returns to normal temperature. However, the casting stress will be lower than the original value by the amount of the reduction in the residual stress.

In the end, the main bearing hole is affected by the above-mentioned plastic deformation due to the decrease in strength of the aluminum part, plastic deformation due to the increase in bolt axial force, and partial permanent release of the casting stress.
The roundness will deteriorate.

Therefore, the present invention aims to provide a method that can suppress the deterioration of the roundness of the main bearing hole due to the heat load during engine operation, thereby preventing an increase in vibration or noise and the occurrence of seizure of the bearing metal. It is something.

(Means for Solving the Problems) The present invention solves these problems by temporarily applying a thermal load to a cylinder block whose bearing cap has been tightened and the inner peripheral surface of the main bearing hole has been rough-machined. After applying plastic deformation to the part and partially releasing the stress in the casting, the bearing cap is retightened and the inner circumferential surface of the main bearing hole is finished in this order.

Specifically, the method for manufacturing an aluminum alloy cylinder block according to the present invention includes adding the above-mentioned bearing to an aluminum alloy engine cylinder block main body made of a bearing member forming a part of the main bearing hole or cast. After tightening the bearing cap that forms the main bearing hole with parts 10 and 10 with bolts with a predetermined axial force, the process of rough machining the inner corner surface of the main bearing hole, and the cylinder block body to which the bearing cap is tightened. The steps of maintaining the bearing cap at a high temperature, re-tightening the bearing cap to the cylinder block body with a predetermined axial force, and finishing the inner circumferential surface of the main bearing hole so that it becomes a perfect circle are carried out in this order. It is characterized by this.

In this case, cast iron, which has higher strength than aluminum alloy, can be used for the above-mentioned bearing member. It is preferable that the bearing cap be tightened to the cylinder block body before rough machining with the same axial force as when re-tightening, that is, with the axial force during engine use. Further, it is preferable that the temperature in the high temperature holding step is set to the temperature of the main bearing during engine operation, for example, around 150 degrees.

(Function) In the above manufacturing method, since the cylinder block body is held at high temperature with the bearing cap tightened with a predetermined axial force, plastic deformation occurs due to a decrease in the strength of the aluminum part and due to an increase in the bolt axial force. Plastic deformation and partial permanent release of the casting stress occur, and the bolt is tightened in a state where the axial force is reduced. Re-tightening the bolt in the above state will eliminate the decrease in axial force mentioned above, and this re-tightening will ensure the roundness of the main bearing hole in the cooled state by finishing processing later. This is what will be done.

Once the aluminum part is subjected to thermal load, it undergoes plastic deformation and so-called work hardening, so even if the bolt's axial force increases due to thermal expansion caused by the high temperature caused by engine operation, this Since it can withstand axial force, plastic deformation is suppressed, and therefore there is almost no decrease in axial force.

In addition, regarding the stress in the casting, the aluminum part first experiences negative thermal stress, but the residual stress has already been partially released, so even if the temperature increases due to engine operation, the residual stress will not be released. Therefore, no permanent decrease in casting stress occurs.

Further, the above-mentioned high temperature maintenance can also serve as heat treatment of the cylinder block body. That is, this high-temperature holding can also serve as T5 treatment (artificial aging treatment by tempering) of the cylinder block body, and also serves as dimensional stabilization treatment.

Here, when tightening the bearing cap mentioned above, do you set the axial force to the axial force when the engine is in use?It is preferable to set the tightening to a low value, so that the main bearing hole will be a perfect circle in the next rough machining. This is because even if the condition is close to that, retightening later will cause the roundness to be greatly distorted, and there will be a problem in which there will be a large amount of machining allowance for finishing. This increase in machining allowance means that the bearing member's wall thickness has changed significantly, resulting in an imbalance in rigidity or strength, and plastic deformation and residual stress are partially released in the high-temperature holding process. However, when the temperature rises due to engine operation, it deforms again and its roundness deteriorates.

Also, if rough machining is performed before the high temperature holding process, if retightening is performed later, the roundness will decrease due to changes in the wall thickness of the bearing member. This is because there is a problem that makes it more likely to occur.

(Effects of the Invention) Therefore, according to the present invention, a bearing cap is attached to the cylinder block body, and rough machining, high temperature maintenance, retightening, and finishing machining are performed in this order. Even at high temperatures, the plastic deformation of the aluminum part, the decrease in axial force, and the permanent release of cast walnut stress can be suppressed, thereby preventing the deterioration of the roundness of the main bearing hole. A predetermined roundness can be ensured in the main bearing hole from low to high temperatures, and an increase in vibration or noise and seizure of the bearing metal can be prevented.

(Example) Embodiments of the present invention will be described below based on the drawings.

In the engine cylinder block 1 shown in FIG.
Reference numeral 2 denotes a cylinder block body made of aluminum alloy in which an iron-based upper bearing member 4 constituting the upper half circumference of the main bearing hole 3 is cast, and 5 represents the main bearing hole 3 together with the upper bearing member 4. This is an aluminum alloy bearing cap in which the iron-based lower bearing part 6 is cast. The bearing cap 5 is attached to the cylinder block body 2 with iron-based bolts 7. JIS ADC12 is used as the aluminum alloy.
Cast iron FCD45F is used for the upper and lower bearing members 4.6.

The manufacturing process of the cylinder block 1 is as follows.

Tightening of the bearing cap includes: - Rough machining of the main bearing hole - Holding at high temperature - Cooling - Retightening of the bearing cap - Finishing of the bearing hole The above steps will be explained.

To tighten the bearing cap, the bearing cap 5 is tightened to the cylinder block body 2 with a bolt 7 with a predetermined axial force. The axial force in this case is the axial force when the engine is in use.

Rough machining of the main bearing hole 3 Rough machining is performed on the inner circumferential surface of the main bearing hole 3, leaving a machining allowance for finishing. In other words, the main bearing hole 3 is made almost perfectly circular.

1. The cylinder block body 2 to which the high temperature maintenance bearing cap 5 is tightened is maintained at a high temperature. This can be carried out in a heating furnace, the temperature being that reached during engine operation, ie 150° C., and the holding time being 2 hours.

/lLi, cold This cooling is to enable the next retightening operation.

1. Retightening the bearing cap - Retighten the bearing cap 5 to the cylinder block body 2 with the bolt 7 with a predetermined axial force. The axial force in this case is the same as the axial force when the engine is used, that is, the axial force when the engine is used.

Finishing pressurization of the bearing hole for life - Finishing is performed on the inner circumferential surface of the main bearing hole 3 so that it becomes a perfect circle. In this case, the roundness is set to a maximum sea difference of 4 μm.

FIG. 2 shows changes in main bearing temperature, bolt axial force, and casting stress from the high temperature holding step to when the engine is actually operated.

First, the changes in bolt axial force and casting stress caused by high-temperature holding are essentially the same as those associated with conventional engine operation (see Figure 4), or the changes in bolt axial force and casting stress due to high temperature maintenance are essentially the same as those associated with conventional engine operation (see Figure 4). The changes are different.

That is, each symbol in FIG. 2 is as follows.

Bolt axial force due to high temperature maintenance〉 Increase a;; As the bearing temperature increases, cylinder block 1
This is due to thermal expansion of the aluminum part.

Decrease b This is due to plastic deformation of the aluminum part due to a decrease in strength due to heat and an increase in the bolt axial force mentioned above.

Decrease C: This is due to shrinkage of the aluminum part as the main bearing temperature decreases.

Casting stress due to high temperature maintenance> Decrease a: This is due to the rise in bearing temperature and is due to the difference in thermal expansion between the bearing member 4.6 and the aluminum part.

Decrease b; Caused by partial permanent release of residual stress in the aluminum part due to temperature retention.

Increase C: This is due to recovery as the raw shaft bearing temperature decreased.

The above is a change due to high temperature holding, and the bolt axial force and casting stress are lower than the axial force before high temperature holding.

Bolt axial force after holding at high temperature> Rise d: Due to retightening of the bearing cap 5.

Increase e: This is due to thermal expansion of the aluminum part as the main bearing temperature increases due to engine operation.

This decrease in f may be due to plastic deformation of the aluminum part, or the aluminum part appears to be plastically deformed and work hardened due to the previous high temperature holding, and the amount of decrease in f is very small.

Low de g; This is due to a drop in main bearing temperature due to engine shutdown ('f-' is due to shrinkage of the aluminum part, and this amount of decrease corresponds to the increase e mentioned above, and the shaft temperature due to retightening. Compared to the force, it can be said that there is almost no decrease in the axial force.

Casting stress after holding at high temperature> Decrease d: This is due to the increase in main bearing temperature due to engine operation, and is due to the difference in thermal expansion between the bearing member 4.6 and the aluminum part.

Increase e: This is due to recovery due to the drop in main bearing temperature due to engine shutdown.

In other words, since the residual stress in the aluminum part has been released due to the previous high temperature holding, the stress in the cast walnut does not decrease even if the temperature increases due to engine operation.

Therefore, as mentioned above, there is almost no plastic deformation of the aluminum part and no decrease in axial force, and there is no decrease in casting stress, so there is almost no decrease in the roundness of the main bearing hole 3 due to engine operation, and the main bearing hole 3 is completely round. The error was about 8 μm.

Incidentally, in the case of the conventional example (FIG. 4), the roundness error after engine operation was approximately 32 μm.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the main bearing portion of a cylinder block in an embodiment of the present invention, Fig. 2 is a characteristic diagram showing changes in main bearing temperature, bolt axial force, and casting stress in the embodiment, and Fig. 3 is a An explanatory diagram showing changes in roundness in a conventional example,
FIG. 4 is a diagram similar to FIG. 2 in the conventional example. 1... Cylinder block 2... Cylinder block body 3... Main bearing hole 4... Upper bearing member 5... Bearing cap 6... Lower bearing member 7 ...Bolt diagram

Claims (1)

[Claims] (1) A bearing cap, which forms the main bearing hole with the bearing member, is attached to a specified shaft by bolts to an aluminum alloy engine cylinder block body in which a bearing member forming a part of the main bearing hole is cast. After tightening with force,
A process of rough machining the inner circumferential surface of the main bearing hole, a process of maintaining the cylinder block body to which the bearing cap is tightened at a high temperature, and a process of re-tightening the bearing cap to the cylinder block body with a predetermined axial force. A method for manufacturing an aluminum alloy cylinder block, comprising sequentially carrying out a step and a step of finishing the inner circumferential surface of the main bearing hole so that it becomes a perfect circle.