1. Field of the Invention
The present invention relates to an impeller for a hydraulic power transmitting apparatus and a method of fixing blades of a hydraulic power transmitting apparatus. In particular, it relates to an impeller as well as method of fixing the blades of the impeller, and of fixing a lock-up damper spring plate without making a hole or slit in any of constituting members.
2. Description of Related Art
In a conventional hydraulic power transmitting apparatus, as a means of fixing blades to a shell, there are known the following, i.e., means of fixing both the members by welding or brazing, or means of fitting claws provided in the blades into slits and then fixing them together by caulking or brazing (see Japanese Published Unexamined Patent Application No. 79359/1982). In the above-described conventional art, welding or brazing will give rise to thermal strains to the shell and the blades. Particularly, in case of brazing, a large amount of electric power is consumed in a brazing furnace. When a flux for preventing oxidation is used, there is a possibility of generating harmful gases from the flux. In case the claws provided in the blades are fitted into the slits, three-dimensional slits and the claws of the blades must be manufactured at a high accuracy in order to facilitate the assembling work. This results in a higher manufacturing cost and in a reduced strength in the shell due to the presence of the slits. In addition, since the force of fixing the blades is weak, a working fluid may leak through the slits out of the shell, resulting in a remarkable reduction in the performance of the hydraulic power transmitting apparatus.
In view of the above disadvantages accompanied by the conventional art, the present invention has an object of providing an impeller for a hydraulic power transmitting apparatus and a method of fixing blades of a hydraulic power transmitting apparatus in which the shell and the blades as well as the shell and a lock-up damper spring plate can be fixed without resort to welding or brazing as well as to fitting of claws into slits.
In order to attain the above and other objects, according to a first aspect of the present invention, the present invention is an impeller for a hydraulic power transmitting apparatus. The impeller comprises: a shell; a plurality of blades fixed to the shell, each of the blades having a blade main body and a fixing flange which is bent at an angle relative to the blade main body; wherein the shell and the fixing flange are placed one on top of the other and are pressed together at a fixing point such that a hollow cylindrical projection having a bottom is formed; and wherein the projection comprises a diametrically expanded portion along a bottom outer periphery of that member out of the shell and the fixing flange which lies on an inner side in the projection, the expanded portion being thrusted into that member out of the shell and the fixing flange which lies on an outer side in the projection.
In a second aspect of the present invention, there is provided an impeller for a hydraulic power transmitting apparatus. The impeller comprises: a shell; a plurality of blades fixed to the shell, each of the blades having a blade main body and a fixing flange which is bent at an angle relative to the blade main body; wherein each of the shell and the fixing flange are placed one on top of the other and are pressed together at a fixing point such that a hollow cylindrical projection having a bottom is formed, an outer periphery of the bottom having an axially extending ring-shaped convex; and wherein the projection comprises a diametrically expanded portion along a bottom outer periphery of that member out of the shell and the fixing flange which lies on an inner side in the projection, the expanded portion being thrusted into that member out of the shell and the fixing flange which lies on an outer side in the projection.
Preferably, the projection is formed in a plurality of numbers, and at least one of the projections is projected inward of the impeller. According to this arrangement, in case another constituting member of the impeller is disposed in close proximity to the outside of the shell, a particular projection which is likely to interfere with the above-mentioned member can be projected inward, instead of outward as is the case with the remaining ones, to prevent the mutual interference.
Further, preferably, at least one of the projections is positioned radially inward relative to a center of radial length of the blade. Ordinarily, in the turbine blades, a large force in a direction of peeling off the blades is operated on an outlet side in an inner circumference. By arranging at least one of the projections as described above, a large fixing force against the peeling can be secured.
Preferably, the fixing flange has a larger width on a radially inner side and a diameter of a projection to be provided on the radially inner side is larger in diameter than the diameter of remaining projections. According to this arrangement, the projection of a larger diameter can generate a larger force against the peeling off the blades.
Preferably, the impeller further comprises a lock-up damper spring plate having a shape free from interference with a projection that is on a circumferentially outermost position, the damping spring plate being fixed to an outside of the shell by a projection which is the same as the projection for fixing the shell and the fixing flange. According to this arrangement, the lock-up damper spring plate can be fixed to the shell without giving rise to the interference with the projection for fixing the fixing flange and without giving rise to the thermal strains.
According to a third aspect of the present invention, there is provided a method of fixing blades of a hydraulic power transmitting apparatus. The method comprises: preparing a shell from a first metallic plate and a plurality of blades from a second metallic plate, each of the blades having an integrally formed fixing flange; placing the shell and the fixing flange one on top of the other; pressing the shell and the fixing flange together to form a hollow cylindrical projection such that a material in a corner portion of an inner member of the shell and the fixing flange inside the projection is expanded outward so as to be thrusted into a material of an outer member of the shell and the fixing flange inside the projection.
Alternatively, there is provided a method of fixing blades of a hydraulic power transmitting apparatus. The method comprises: preparing a shell made of a first metallic plate and a plurality of blades made of a second metallic plate, each of the blades having an integrally formed fixing flange; feeding the shell and each of the fixing flanges into a die assembly in a state in which one is placed on top of the other, the die assembly comprising: a die having a die hole with a bottom; and a punch which is adapted to be inserted into, and out of, the die hole; wherein a clearance between the punch and an inner surface of the die hole is smaller than a sum of thicknesses of the shell and the fixing flange, and wherein the die has a ring-shaped groove which is formed along a corner of the bottom of the die hole so as to extend in an axial direction of the die assembly; pressing the shell and the fixing flange together to form a hollow cylindrical projection such that a material in a bottom corner portion of an outer member out of the shell and the fixing flange is forced into the ring-shaped groove and that a material in a bottom corner portion of an inner member of the shell and the fixing flange is expanded diametrically outward so as to be thrusted into the material of the outer member.