Oil pump cover

A cover body formed with AC2B is fixed to a casing of an automatic transmission and has a hole in the shaft center thereof. The cover body is subjected over the surface of the hole to a solution heat treatment at 500 centigrade degree for 3 hours and is tempered at 180 centigrade degree fo 4 hours to acquire hardness of 90 HB of more. An iron stator shaft for supporting a stator of a torque converter is pressed into the hole in the cover body. Since the plastic deformation of the hole part of the cover body is reduced, the interference between the stator shaft and the cover body is ensured, and the stator shaft is prevented from being displaced axially even at a high temperature.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an oil pump cover of an automatic 
transmission. 
2. Description of the Prior Art 
There is known as one of conventional oil pump covers that disclosed in the 
Japanese Utility Model Application Laid-open No.1-140062. 
An oil pump cover disclosed therein is constructed such that a stator shaft 
for supporting a stator of a torque converter is pressed into a hole 
formed in a pump body part(cover body) for covering an oil pump and is 
retained not to be moved axially. The pump body part serves chiefly as a 
cover for sealing the oil pump, and is configured into a large-sized disk 
and is formed with non-ferrous metal material (usually aluminum) for 
lightening. In contrast, the stator shaft is usually formed with an iron 
material that is strong against torsion and bending because it should be 
configured into a small diameter and a thin wall for the purpose of 
supporting the stator of the torque converter, though it is subjected to 
greater torsion and bending force. 
The conventional oil pump cover however has the following difficulty: When 
a vehicle is running the stator shaft is subjected to torsion and bending 
force owing to the reaction of the stator. Further, when the vehicle is 
running an automatic transmission becomes high temperature so that there 
is caused a difference between the thermal expansion of the pump body part 
and that of the stator shaft owing to a difference between thermal 
expansion coefficients of materials of the pump body part and the stator 
shaft. The stator shaft is accordingly sometimes shifted in the direction 
where it slips out of the pump body part owing to a load applied on the 
stator shaft. In order to prevent this it is necessary to more increase 
interference of press fitting between the stator shaft and the pump body 
part than those of press fitting between members comprising the same 
material when the stator shaft is pressed into the hole in the pump body 
part considering a fact that the interference is reduced at high 
temperature. For this, the hole in the pump body part is superheated and 
the stator shaft is supercooled for the press fitting therebetween, as a 
result a manufacturing process is complicated. 
SUMMARY OF THE INVENTION 
In view of the drawbacks with the prior art, it is an object of the present 
invention to provide an oil pump cover wherein after the surface of a hole 
part in the cover body is hardened the stator shaft is pressed thereinto. 
An oil pump cover according to the present invention comprises an aluminum 
cover body fixed to a casing of an automatic transmission and having a 
hole in a shaft center, an iron stator shaft for supporting a stator of a 
torque converter, the iron stator shaft being pressed into said hole in 
said cover body, the improvement being such that said stator shaft is 
pressed into said cover body after the surface of said hole in said cover 
body is hardened. 
In accordance with this aspect of the present invention plastic deformation 
of the cover body is reduced when the stator shaft is pressed into the 
cover body to hereby prevent an actual interference from being reduced, 
whereby a necessary press interference is ensured even at a high 
temperature to substantially prevent the stator shaft from being displaced 
axially. It is therefore unnecessary when the stator shaft is pressed into 
the hole in the cover body to increase a interference allowance of the 
pressing of the stator shaft into the cover body taking reduction of the 
interference at high temperature into consideration. A manufacturing 
process can therefore be simplified. 
By especially setting hardness of the hole in the cover body to 90 
HB(Brinell hardness) or more, the plastic deformation of the cover body 
when the stator shaft is pressed into the cover body is reduced, so that a 
predetermined amount or more of the interference between the stator shaft 
and the cover body is secured even at a high temperature. 
Further, it is preferable to form the cover body with AC2B and subjecting 
the surface of the hole to a solution heat treatment at the temperature of 
500 centigrade degree for 3 hours and temper it at the temperature of 180 
centigrade degree for 4 hours. The hole in the cover body hereby acquires 
the hardness of 90 HB or more to reduce the plastic deformation of the 
cover body. 
The above and other objects, features and advantages of the present 
invention will become more apparent from the following description when 
taken in conjunction with the accompanying drawings in which preferred 
embodiments of the present invention are shown by way of illustrative 
example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates an oil pump cover according to the present invention. 
An oil pump cover 10 includes a cover body 12 and a stator shaft 14. The 
cover body 12 is made of aluminum and has a hole 12a in its shaft center 
R. The cover body 12 is anchored to a casing 18 of an automatic 
transmission 16 with bolts 20. 
The stator shaft 14 is made of iron and has a toothed part 14a in its tip 
end. The stator shaft 14 supports a stator 22a of a torque converter 22. 
The stator shaft 14 is pressed at its tip end into a hole 12a in the cover 
body 12. Hereby, the toothed part 14a of the stator shaft 14 bites into 
the hole 12a in the cover body 12, so that the stator shaft 14 is securely 
united with the cover body 12 not only axially but also in the direction 
of rotation. As listed in FIG. 2, the cover body 12 is formed with one 
having a material quality of AC2B(aluminum alloy class 2 B for metal mold 
casting ,Japanese Industrial Standard), and is subjected over the surface 
of the hole 12a to a solution heat treatment at 500 centigrade degree for 
3 hours and is tempered at 180 centigrade degree for 4 hours, whereby the 
cover body 12 acquires hardness of from 94 HB to 99 HB ("A" in FIG. 2). 
On the other hand, a cover body shown by "C" in FIG. 2 which has the same 
material quality as that of the just-mentioned cover body 12 but which is 
left behind at ordinary temperature and is hardened through natural aging 
has hardness of from 68 HB to 69.5 HB (conventional cover body). 
The cover body of "A" has greater hardness than that of "C" in such a 
manner, so that the cover body of "A" has smaller plastic deformation than 
that of "C" when the stator shaft is pressed into the holes. 
FIG. 3 illustrates relationships between pulling forces and interference 
between the stator shaft 14 and the cover body 12 at a general rising 
temperature of an automatic transmission 16 when a vehicle is running. 
When the interference is 80 .mu.m for example, the pulling force is 
2.5.times.10.sup.3 kg in "A" and 0.3.times.10.sup.3 kg in "C". The cover 
body "A" therefore has the pulling force about 9 times that of "C". 
Further, when the interference is 115 .mu.m for example the pulling force 
is 4.5.times.10.sup.3 kg in "A" and 1.4.times.10.sup.3 kg in "C". The 
cover body "A" therefore has the pulling force about 3 times that of "C". 
The cover body "A" has the pulling force about 3 to 9 times that of "C" at 
a temperature where the automatic transmission 16 ordinarily rises when a 
vehicle is running, therefore the stator shaft 14 is prevented from being 
axially displaced or rotated. 
It is therefore unnecessary to increase the interference allowance between 
the stator shaft and the hole in the cover body on the assumption that the 
actual interference is reduced to cause the stator shaft 14 being axially 
moved when the automatic transmission 16 becomes a high temperature. Thus, 
there is eliminated the need where the stator shaft 14 is pressed into the 
hole 12a in the cover body 12 while overheating the hole 12a in the cover 
body 12 and simultaneosuly supercooling the stator shaft 14. This 
simplifies the manufacturing process of the oil pump cover. 
In the following a second embodiment will be described. 
A cover body 12 is formed with a material having a quality of AC4B 
(aluminum alloy class 4B, Japanese Industrial Standard) listed as "B" in 
FIG. 2, and is subjected at the surface over a hole 12a to a solution heat 
treatment at 525 centigrade degree for 6 hours and is tempered at 160 
centigrade degree for 6 hours whereby the cover body 12 acquires hardness 
of from 74 HB to 84 HB. 
The cover body of "B" has greater hardness than that of "C" so that the 
pulling force can be increased as in the first embodiment. 
As illustrated in FIG. 3, even at a temperature which the automatic 
transmission 16 has when a vehicle is running, pulling force of "B" with 
the interference being 80 .mu.m for example is 1.7.times.10.sup.3 kg, 
about 6 times that of "C", and pulling force of "B" with the interference 
being 115 .mu.m for example is about 3.0.times.10.sup.3 kg about 1.5 times 
that of "C". 
The cover body of "B" therefore has the pulling force about 1.5 to 6 times 
that of "C", so that the second embodiment can demonstrate the identical 
effect as that of the first embodiment. According to the present 
invention, the hole in the cover body has smaller plastic deformation when 
the stator shaft is pressed thereinto, so that the stator shaft is 
substantially prevented from being displaced axially even at a high 
temperature. Accordingly, since a necessary amount of the interference 
between the stator shaft and the cover body is secured even at a high 
temperature, it is unnecessary when the stator shaft is pressed into the 
hole in the cover body to increase the interference allowance therebetween 
on the assumption that the interference is reduced at the high 
temperature. This can simplify the manufacturing process of the oil pump 
cover. 
Further, provided hardness of the hole in the cover body is set to be 90 HB 
or more, the plastic deformation of the cover body is particularly reduced 
when the stator shaft is pressed into the cover body, so that a 
predetermined amount or more of the interference between the stator shaft 
and the cover body is ensured. 
Furthermore, when the surface of the hole is subjected to a solution heat 
treatment at 500 centigrade degree for 3 hours and is tempered at 180 
centigrade degree for 4 hours the hole in the cover body acquires hardness 
of 90 HB or more, so that plastic deformation of the stator shaft when the 
stator shaft is pressed into the hole in the cover body is reduced.