Pumps – Expansible chamber type – Biasing means effects induction stroke of abutment driven,...
Reexamination Certificate
2002-12-10
2004-04-20
Yu, Justine R. (Department: 3746)
Pumps
Expansible chamber type
Biasing means effects induction stroke of abutment driven,...
C092S072000, C092S153000, C074S567000, C074S596000, C123S456000, C123S495000
Reexamination Certificate
active
06722864
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel injection pump for an internal combustion engine (hereinafter called “engine”) in which fuel is supplied from a feed pump to an accommodation chamber for well lubricating sliding contact portions of component parts accommodated therein.
2. Description of the Prior Art
A conventional fuel injection pump for a diesel engine has a cam for driving a plunger. In this pump, fuel is sucked and pressurized in a pressure chamber by reciprocating movement of the plunger axially slidable in a cylinder. A rotating movement of a drive shaft to be driven by an engine is converted to the reciprocating movement of the plunger inside the cylinder via the cam connected with the drive shaft and a cam ring disposed between the cam and the plunger. The plunger, the cam and the cam ring are disposed in an accommodation chamber.
To improve engine output and fuel consumption and to reduce emission such as NOx and black smoke to be exhausted from the engine, higher fuel injection pressure has been recently demanded.
To secure the higher fuel injection pressure, it is necessary to increase pressure of fuel to be pressurized by and discharged from the fuel injection pump, so higher load is applied to the fuel injection pump. Typically, sliding contact portions of an outer surface of the cam and an inner circumference of the cam ring receive larger forces. To reduce frictional seizure and frictional wear of the sliding contact portions, the conventional pump has a bush interposed between the cam and the cam ring. However, since the force applied to the bush is very high, life time of the bush is shorter and, at worst, frictional seizure of the sliding contact portions tends to occur.
As one of the solutions, the pump may have a larger bush whose sliding contact area is larger so that force applied to a unit area of the bush is smaller. However, the larger bush causes a body of the fuel injection pump larger, which does not meet a recent demand in that a compact and light weight pump is required.
As another one of the solutions, the outer circumference of the cam or the inner circumference of the bush may have an oil groove for promoting lubrication of oil on the sliding contact portions of the cam and the bush. However, the oil groove has to be positioned to a limited area of the cam or the bush in order not to sacrifice power transmission functions of the cam and bush so that their designing freedom is narrowed.
Further, as shown in
FIG. 14
, a bush
100
may have a recess
101
. An inner circumferential surface
100
a
of the bush
100
is formed axially in round shape. Diameter of the inner surface
100
a
of the bush
100
is larger from both axial ends thereof toward a center thereof so that the both axial ends are always in contact with an outer circumference
210
a
of a cam
210
. Fuel once entered the recess
101
tends to be stagnant in the recess
101
. Therefore, temperature of fuel in the recess
101
is prone to increase due to heat generated by the sliding contact between the cam
200
and the bush
100
so that deformation or frictional seizure of the cam
210
and the bush
100
is likely to occur. Further, pressure of fuel in the recess
101
tends to decrease, if the recess
101
is too large, so that adequate formation of oil film for lubricating the sliding contact portions of the cam
200
and the bush
100
is not sufficiently secured.
As mentioned above, it is important not only to form the adequate formation of the oil film between the sliding contact portions, but also to radiate heat of the sliding contact portions in the accommodation chamber. For this purpose, the conventional fuel injection pump has a feed pump driven also by the drive shaft for supplying fuel sucked from a fuel tank to the pressure chamber. The feed pump also supplies a part of the fuel to the accommodation chamber where the cam connected to the drive shaft, the cam ring, the bush and the plunger are accommodated.
Temperature of the fuel supplied to the accommodation chamber increases due to heat generated by the sliding contact portions. Therefore, the conventional fuel injection pump has a circulation flow passage through which the accommodation chamber communicates with a fuel tank, so the fuel discharged from the feed pump is returned to the fuel tank via the accommodation chamber through the circulation flow passage, which serves to lubricate the sliding contact portions and to cool the housing in which the accommodation chamber is formed.
Further, to prevent the pressurized fuel in the accommodation chamber from leaking through a clearance between the housing and the drive shaft to an outside of the fuel injection pump, an oil seal is disposed between the housing and the drive shaft. The oil seal is partly deformed radially to ensure sealing effect by pressure of the fuel fed thereto from the accommodation chamber.
However, if the fuel in the circulation flow passage is blocked by some reasons, the fuel in the accommodation chamber is not returned to the fuel tank so that pressure of fuel in the accommodation chamber increase. As a result, higher pressure of the fuel in the accommodation chamber is applied to the oil seal, causing the oil seal to be damaged.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a compact fuel injection pump at less manufacturing cost.
Another object of the present invention is to provide a fuel injection pump in which fuel is forcibly supplied to sliding contact portions to form an oil film for lubrication in a minute space therebetween so that frictional seizure of the sliding contact portions is unlikely to occur and life time thereof is longer.
A further object of the present invention is to provide a fuel injection pump in which fuel for lubrication easily circulates through sliding contact portions within an accommodation chamber so that heat generated by the sliding contact portions is effectively radiated.
A still further object of the present invention is to provide a fuel injection pump in which an oil seal is hardly damaged.
To achieve the above object or objects, a fuel injection pump has a drive shaft, a cam formed eccentrically and integrally with the drive shaft, a cam ring, a bush whose outer circumference is fixed to inner circumference of the cam ring and whose inner circumference is slidably fitted to outer circumference of the cam shaft so that sliding contact portions of the cam and the bush are formed, a housing provided with a cylindrical bore, a plunger axially and reciprocatingly movable in the cylindrical bore via the cam, the bush and the cam ring by the drive shaft, so that axial end of the plunger is in slidable contact with outer circumference of the cam ring and another axial end thereof and the cylindrical bore form a pressure chamber, an accommodation chamber formed in the housing for accommodating the plunger, the bush, the cam ring and the cam, a feed pump whose outlet side communicates with the pressure chamber for supplying fuel to the pressure chamber according to rotation of the drive shaft, and a communication path through which the outlet side of the feed pump also communicates with the accommodation chamber for supplying a part of the fuel discharged from the feed pump to the accommodation chamber.
In the fuel injection pump mentioned above, an end of the communication path on a side of the accommodation chamber is opened to face an axial end of a minute space between the sliding contact portions of the cam and the bush when the cam is at a given angular position. With this construction, fuel flowing via the communication path to the accommodation chamber is sprayed axially deep into the minute space between the sliding contact portions from the axial end thereof. Accordingly, the oil film for lubrication is adequately formed on the sliding contact portions so that the frictional seizure of the contact sliding portions hardly occurs. Since only position of the end of the communication path on a side of the accommo
Kuroda Akihiro
Suzuki Masashi
Denso Corporation
Nixon & Vanderhye P.C.
Rodriguez William H.
Yu Justine R.
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