Machine element or mechanism – Gearing – Follow-up mechanism
Reexamination Certificate
1998-09-11
2001-04-03
Bucci, David A. (Department: 3682)
Machine element or mechanism
Gearing
Follow-up mechanism
C074S60600R
Reexamination Certificate
active
06209409
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a housing structure for power steering system and more particularly, to a housing structure for power steering system reduced in weight and subjected to a corrosion resisting treatment.
DESCRIPTION OF THE PRIOR ART
Heretofore, there have been proposed power steering systems which have accomplished weight reduction by, for example, replacing iron with aluminum as a material for a pinion housing (see, for example, Japanese Unexamined Patent Publications Nos. 55(1980)-79756 and 63(1988)-235168). Additionally, studies have been made on the adoption of magnesium alloys in pursuit of further weight reduction of the system.
Unfortunately, however, the pinion housing and the like of the power steering system are parts included in a so-called automotive foot portion which are exposed to rain blowing therein and water splashed up from the road. In most cases, such water is aqueous electrolytic solution containing impurities. For instance, in a vehicle traveling on a road near the sea, the pinion housing and the like may be exposed to water containing salt or the aqueous electrolytic solution. Hereupon, it is to be noted that the housing, which is formed of magnesium alloy, is in contact with a bolt, a cylinder tube or the like which is formed of a different type of metal (e.g., iron or the like) from the magnesium alloy. When a contact portion of the housing with the bolt etc. is exposed to the aqueous electrolytic solution, a local cell is established at the contact portion. Magnesium is thereby ionized and dissolved, so that the corrosion of the housing occurs.
That is, the magnesium alloy is useful for forming a lightweight housing, but on the other hand, it causes the corrosion of the housing.
OBJECT AND SUMMARY OF THE INVENTION
An object of the present invention is to reduce the weight of the housing and to prevent the corrosion of the housing.
A steering gear housing included in a housing structure for power steering system of the present invention, comprises: a valve housing formed of one of metal and resin material; a pinion housing formed of magnesium alloy; a metal bolt for fastening the valve housing and the pinion housing to each other; and an insulating portion interposed in a joint portion between the pinion housing and a metal member of any member adjacent thereto including the valve housing and the metal bolt, the metal member being formed of a different type of metal from which the pinion housing is formed of.
The housing of such a structure is reduced in weight by the use of the magnesium alloy and protected against the corrosion thereof by virtue of presence of the insulating portion.
In the above housing structure, the insulating portion may be formed on a surface of the metal member by applying thereto at least one of abase treatment layer formed by base treatment and a paint coating layer as a top coat layer formed by painting. In this case, presence of at least one of the base treatment layer and the paint coating layer prevents the housing from being corroded. Also, presence of both the base treatment layer and the paint coating layer positively prevents the housing from being corroded. Thus, the housing can be protected against the corrosion thereof over an extended period of time.
Further, in the above housing structure, the valve housing may be formed of the resin material. The pinion housing may be provided with a sleeve-like projection which extends from a female-screw portion of the pinion housing and which is fitted in the valve housing to define an insert for the valve housing for insertion of the metal bolt. In this case, the insert is integrally formed with the pinion housing, thereby eliminating fear for the corrosion due to contact of the insert with the pinion housing.
Further, in the above housing structure, the valve housing formed of the resin material may include the insert formed of iron metal for insertion of the metal bolt, while a sealing member of a rubber or synthetic resin material may be interposed between the insertion port and the pinion housing. In this case, the sealing member eliminates direct contact between the insert and the pinion housing, thereby preventing occurrence of corrosion.
Further, in the above housing structure, the valve housing may be formed of the magnesium alloy. Resin coated sealing members may be interposed between the valve housing and the metal bolt. In this case, the valve housing and pinion housing are formed of the same type of metal so that contact therebetween causes no corrosion. Also, direct contact of the valve housing with the metal bolt is prevented by the sealing member. Therefore, these elements eliminate occurrence of corrosion. Further, in this housing structure, the pinion housing may include the female-screw portion, in which sealing agent is filled, to have the metal bolt insert therein and having a hole extending downwardly through the pinion housing from a bottom of the female-screw portion. In this case, the sealing agent is extruded from the hole by inserting the metal bolt in the female-screw portion, thereby preventing salt water or the like from entering the female-screw portion. Occurrence of corrosion is thus prevented.
REFERENCES:
patent: 3779592 (1973-12-01), Golze et al.
patent: 4478915 (1984-10-01), Poss et al.
patent: 4608876 (1986-09-01), Rosell
patent: 5020934 (1991-06-01), Floren et al.
patent: 5735718 (1998-04-01), Ekwall
patent: 2 623 933 (1989-06-01), None
patent: 2 202 502 (1988-09-01), None
patent: 64-31986 (1989-02-01), None
patent: 4-5102 (1992-01-01), None
Marks' Standard Handbook for Mechanical Engineers, tenth edition, McGraw-Hill, p. 6-99, Dec. 1996.*
Patent Abstracts of Japan, vol. 004, No. 123 (M-029), Aug. 30, 1980.
Kitahata Kouji
Miyazaki Osamu
Bucci David A.
Jacobson Price Holman & Stern PLLC
Joyce William C
Koyo Seiko Co. Ltd.
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