Manufacturing method for an integral type crankshaft bearing cap

A method of manufacturing an integral type crankshaft bearing cap for an internal combustion engine. The integral type crankshaft bearing cap comprises crankshaft bearing caps spacedly arranged in the longitudinal direction of the engine and a beam extending in the longitudinal direction of the engine. The manufacturing method comprises making a plurality of models of the crankshaft bearing caps of resin used in full mold casting, arranging the models and connecting the models to the beam, and replacing the resin constituting the models with metal in full mold casting, thereby integrating the replaced metal and the beam.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a manufacturing method of an integral type 
crankshaft bearing cap for an internal combustion engine. The integral 
type crankshaft bearing cap is integrated by spacing a plurality of 
crankshaft bearing caps along a beam to which they are connected. 
2. Description of the Prior Art 
In internal combustion engine technology, crankshaft bearing caps have been 
integrated into an integral structure. In the integral type crankshaft 
bearing cap, a plurality of crankshaft bearing caps are spaced in a 
longitudinal direction of the engine along a beam extending in the 
longitudinal direction of the engine to which the caps are connected. 
Since the integral type crankshaft bearing cap has high rigidity as a 
whole, rigidity of a cylinder block, to which the integral type crankshaft 
bearing cap is fixed, is increased, and thereby the level of vibration and 
noise of the engine is decreased. Two integral type crankshaft bearing cap 
structures are known. Either the crankshaft bearing caps and the beam are 
integrally formed using the same material, or the crankshaft bearing caps 
and the beam are constructed of different kinds of metal. 
FIG. 1 shows an example of the former type of integral type crankshaft 
bearing cap. Crankshaft bearing caps 1 and beam 2 are formed integrally in 
casting, with crankshaft bearing caps 1 and beam 2 constructed of the same 
metal. With integral type crankshaft bearing cap 3, if the shape of 
crankshaft bearing caps 1 is intricate, molds for casting also become 
intricate and the molds must include a number of split molds. For 
instance, when recessed portions are formed on the wall of the crankshaft 
bearing caps to decrease their weight, the molds must be divided into a 
number of split molds. 
However, as the number of split molds increases, the productivity of the 
integral type crankshaft bearing cap manufacturing process decreases. To 
raise productivity, it is almost unavoidable to form the portions for the 
crankshaft bearing caps in the shape as shown in FIG. 1 so as to be able 
to eliminate molds after casting; that is, crankshaft bearing caps 1 have 
flat walls and they are formed as plate-like blocks having almost uniform 
thickness. As a result, crankshaft bearing caps 1 have unnecessary metal 
with respect to strength, increasing the weight of integral type 
crankshaft bearing cap 3. 
FIG. 2 shows an example of the second type of integral type crankshaft 
bearing cap using different metals. Such a structure is disclosed, for 
example, in Japanese Utility Model Publication No. SHO 57-112056. Integral 
type crankshaft bearing cap 4 in FIG. 2 is constructed of crankshaft 
bearing caps 5 and two beams 6, and manufactured as follows. Two beams 6 
are set in a casting mold defining cavities therein, the cavities being 
formed in the same shape as crankshaft bearing caps 5. After that, molten 
metal is poured into the cavities of the mold, forming crankshaft bearing 
caps 5 around beams 6. In such a manufacturing process, since beams 6 must 
be set in a mold before casting, it is difficult to divide the mold into a 
number of split molds. Therefore, the possible shapes for crankshaft 
bearing caps are restricted, and it becomes difficult to form crankshaft 
bearing caps in a shape having recessed portions in their walls. As a 
result, as shown in FIG. 2, crankshaft bearing caps 5 are also formed as 
flat wall type blocks, with unnecessary portions increasing their weight. 
Thus, in conventional structures made by conventional manufacturing 
processes, it is difficult to decrease weight by complicating the shape of 
the crankshaft bearing caps while maintaining an acceptible level of 
productivity. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a manufacturing method for 
an integral type crankshaft bearing cap which can form crankshaft bearing 
caps having a shape which optimizes strength and weight, and at the same 
time can improve manufacturing productivity. 
A method of manufacturing an integral type crankshaft bearing cap for an 
internal combustion engine, according to the present invention, satisfies 
the above object. The manufacturing method according to the present 
invention comprises the following steps. First, a plurality of resin 
models of the crankshaft bearing caps are made. Next, the models are 
connected to a beam extending through all of the models. Finally, the 
resin is replaced with metal in full mold casting. For example, molding 
sand is fixed around the models and the beam. Pouring gates communicating 
with the models are provided in the fixed sand. Molten metal is poured 
into the portions of models via the pouring gates to replace the resin 
with the poured metal. The metal and beam are thus integrated as an 
integral type crankshaft bearing cap. 
In the method, the crankshaft bearing caps are first manufactured as resin 
models. In the stage of making resin models, since each model is made 
independently from other models, it is not necessary to consider 
directions of eliminating molds in molding. Therefore, the shape of models 
can be determined freely, and the models can be easily formed even in 
complicated shapes. As a result, resin models are easily formed in shapes 
in which unnecessary portions are eliminated from the wall but sufficient 
strength is maintained. 
Since the resin models are replaced with metal in full mold casting, it 
becomes unnecessary to divide molds for crankshaft bearing caps into split 
molds, and thereby the productivity is improved. At the same time, the 
crankshaft bearing caps are formed in an optimum shape from the view point 
of both strength and weight. 
Since the beam is manufactured independently from the resin models, the 
beam also can have an optimum shape, further decreasing the weight of the 
integral type crankshaft bearing cap and further improving productivity. 
Moreover, since the models are replaced with molten metal and the metal 
surrounds the beam in full mold casting, the metal constituting the 
crankshaft bearing caps and the beam are connected naturally without any 
particular connecting process such as welding etc.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 3 shows a model 10 of a crankshaft bearing cap, model 10 having the 
same shape as the crankshaft bearing cap. In a manufacturing method 
according to the present invention, a plurality of models 10 are made of 
resin used in full mold casting. In this embodiment, the resin is 
thermoplastic resin which volatilizes when heated to a high temperature, 
for example foamed polystyrene. The number of models 10 being manufactured 
for an internal combustion engine is the same as the number of crankshaft 
bearing caps of the engine. 
Models 10 are formed in a conventional mold. Each model 10 is molded 
independently from other models 10. Since each model 10 is formed in one 
set of molds, there is no interference of the molds with other members 
when removing the molds after the resin is injected and cooled. Therefore, 
it is almost unnecessary to consider the removing direction of the molds, 
even if models 10 are formed in a complicated shape and even if the molds 
are constructed of many split molds. 
In the embodiment, as shown in FIG. 3, model 10 is formed in a shape having 
recessed portions 11a, 11b and 11c on the wall thereof. The recessed 
portions 11a, 11b and 11c are unnecessary from the view point of strength 
of the crankshaft bearing cap. Therefore, the strength or the rigidity of 
the crankshaft bearing cap corresponding to model 10 is not reduced by 
providing recessed portion 11a, 11b and 11c but the weight of the 
crankshaft bearing cap can be reduced. Model 10, having recessed portions 
11a, 11b, 11c and other uneven surfaces, can be formed easily as follows. 
Appropriate front and rear molds (not shown) are separable in a direction 
of axis b. A flat divisional surface between the front mold (or molds) and 
the rear mold (or molds) is provided along axis a and extending 
perpendicularly to axis b. After resin is injected into a cavity of the 
set molds and cooled, the front mold (or molds) is removed in direction A 
and the rear mold (or molds) is removed in direction B. Thus, model 10 is 
formed in an optimum shape satisfying requirements of both strength and 
weight of the crankshaft bearing cap. 
Although one example has been described for forming model 10, the direction 
of removing molds and the number of split molds can be determined in 
accordance with the shape of model 10. Since the shape of every crankshaft 
bearing cap arranged in the longitudinal direction of an engine is usually 
the same, only one set of molds for model 10 may be prepared to 
manufacture a plurality of models 10. 
At the lower portion of model 10, two pipe portions 12 are integrally 
formed. Pipe portions 12 form hollow areas 13 through which a beam is 
passed. 
Actually two beam portions 14 extend in the longitudinal direction of the 
engine, as shown in FIG. 4. Beam portions 14 consist of pipes in this 
embodiment. After making a plurality of models 10, models 10 are arranged 
in parallel and appropriately spaced from each other, and beam portions 14 
are passed through arranged models 10. 
Next, molding sand 15 for full mold casting is fixed around the resin-beam 
assembly as shown in FIG. 5. At the same time, pouring gates 16a and 16b 
are set in molding sand 15. Pouring gates 16a and 16b are appropriate 
pipes which communicate with models 10 near positions where models 10 are 
connected to beam portions 14. In the embodiment, two pouring gates 16a 
and 16b are provided for each model 10, and they communicate with each 
model 10 near two positions respectively where model 10 is connected to 
beam portions 14. Exhausting gate 17 for gas and resin which should be 
exhausted is connected to an appropriate position of the upper portion of 
each model 10. 
After molding sand 15, pouring gates 16a and 16b and exhausting gates 17 
are positioned, molten metal is poured into pouring gates 16a and 16b as 
shown with arrows 18. The resin constituting models 10 is replaced with 
molten metal poured through pouring gates 16a and 16b in full mold 
casting, and gas and resin melted by the molten metal are exhausted out of 
exhausting gates 17, as shown with arrows 19. The metal is then cooled, 
and molding sand 15, pouring gates 16a, 16b and exhausting gates 17 are 
eliminated. Since the entirety of each resin model 10 is replaced with 
metal in full mold casting, the replaced metal assumes the same shape as 
models 10 so that the each molded metal portion constitutes a portion of 
crankshaft bearing cap. Each molded metal portion surrounds beam portions 
14, connecting each molded metal portion to beam portions 14. Since beam 
portions 14 are surrounded by molten metal in the full mold casting, an 
additional particular connecting method, for example welding, is not 
necessary, and sufficient connecting strength between the molded metal 
portions and beam portions 14 is obtained by only casting. 
The molded metal and beam portions 14 may be of the same kind of metal, or 
may be of different metals. When the same metal is used, the molded metal 
and beam portions 14 can be fused to each other, strengthening the 
connection therebetween. When different metals are used, since optimum 
materials can be independently selected for the molded metal and beam 
portions 14, increased strength and reduced weight of the entire integral 
type crankshaft bearing cap can be achieved. 
Thus, an integral type crankshaft bearing cap 20 is completed as shown in 
FIG. 6. Integral type crankshaft bearing cap 20 is constituted by 
crankshaft bearing caps 21, constructed of molded metal, and pipe beams 
14. In the manufacturing method, since crankshaft bearing caps 21 can be 
easily formed in a complicated shape, the weight of integral type 
crankshaft bearing cap 20 is reduced as a whole compared with conventional 
structure such as shown in FIG. 1 or FIG. 2. At the same time, the 
strength and rigidity of crankshaft bearing caps 21 are ensured. Since 
crankshaft bearing caps 21 are formed by replacing resin with metal in 
full mold casting after making models 10, it is not necessary to consider 
split molds for casting and the direction of molds in casting. Therefore 
the productivity of manufacturing the integral type crankshaft bearing cap 
20 can be highly improved. Since models 10 can be formed by one set of 
molds, the molds may be small-sized, reducing the cost of manufacturing. 
Moreover, since crankshaft bearing caps 21 and beam portions 14 are 
connected naturally by replacing resin with metal in full mold casting, 
the manufacturing process can be simplified. 
FIG. 7 shows another embodiment of an integral type crankshaft bearing cap 
formed by a manufacturing method according to the present invention. In 
integral type crankshaft bearing cap 22, beam portions 23 are solid rods. 
Crankshaft bearing caps 21 in FIG. 7 are formed in the same shape as the 
caps in FIG. 6 by the same manufacturing method as described above. Thus, 
a beam may be formed in appropriate structure. 
Although only several preferred embodiments of the present invention have 
been described in detail, it will be appreciated by those skilled in the 
art that various modifications and alterations can be made to the 
particular embodiments shown without materially departing from the novel 
teachings and advantages of this invention. Accordingly, it is to be 
understood that all such modifications and alterations are included within 
the scope of the invention as defined by the following claims.