Pumps – With condition responsive pumped fluid control – Normally open bypass or relief passage closed by increased...
Reexamination Certificate
1999-07-15
2001-05-29
Thorpe, Timothy S. (Department: 3746)
Pumps
With condition responsive pumped fluid control
Normally open bypass or relief passage closed by increased...
C417S307000, C417S435000, C137S517000
Reexamination Certificate
active
06238191
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for supplying fuel by means of a fuel supply unit provided with a main housing and accommodated in a fuel tank, which has a fuel pump for an initial fuel flow, a degassing valve and a suction cover arranged at the bottom of the main housing. The fuel pump has an impeller arranged in an impeller housing with a circular passage.
2. Prior Art
An apparatus of this type is known from German Patent Document DE 35 40 260 A1. The known apparatus has a fuel supply unit in a main housing. This sort of fuel supply unit is usually located in a fuel tank, in order to feed fuel from the tank, for example to an internal combustion engine, through an outlet connector of the fuel supply unit by means of a pump intake. Also the pump intake is arranged in a suction cover, which is located in the bottom region of the main housing and the outlet connector is generally arranged beside a degassing valve in the top cover of the main housing. The fuel pump has an electrical drive unit, whose stator and rotor are arranged in the central region of the housing and a pump unit comprising an impeller arranged in an impeller housing is introduced to the lower region of the main housing. The impeller produces suction or low pressure in a circular passage, whereby the fuel is fed.
The degassing valve, which is arranged in an upper region of the main housing, is combined with an overpressure valve in the apparatus for feeding fuel described in German Patent Document DE 35 40 260 A1. The degassing valve thus performs two functions, namely first to remove gas bubbles from the main housing formed by heating of the pump and the impeller and second to permit partial return flow of fuel to the fuel tank when an overpressure exists in the main housing. This type of structure has the disadvantage that gas bubbles are not immediately removed from the region in which they are produced, i.e. in the active region of the fuel pump. These gas bubbles must collect in the upper region of the main housing after the pump runs before they can be released through the degassing valve. Because of that feature the conventional pump has a reduced performance in the starting stage, primarily because the gas collected in the impeller region must first be supplied through the circular passage and then through the entire volume of the main housing to the degassing-overpressure valve before the fuel becomes incompressible during the fuel supply process. That means that the apparatus equipped with a combined degassing-overpressure valve according to German Patent Document DE 35 40 260 A1 has a substantially reduced suction head in its starting stage in comparison to its main operating stage.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus which has improved pumping characteristics in the hot feed stage, in the hot start stage, in the cold feed stage and in the cold start stage and reduced pumping losses, that are caused by the conventional degassing-overpressure valve.
According to the invention this object is attained by an apparatus for supplying fuel comprising a fuel tank and a fuel feed unit arranged in the fuel tank. The fuel feed unit comprises a main housing, a suction cover arranged in a bottom region of the main housing, a fuel pump and a degassing valve for degassing the fuel pump arranged in the suction cover. The fuel pump comprises an impeller housing having a circular passage for fuel flow and an impeller arranged in the impeller housing. The impeller housing is arranged next to the suction cover and provided with a degassing passage connecting the circular passage and the degassing valve. The degassing valve opens to the fuel tank preferably when pressure in the degassing passage exceeds a predetermined value for degassing the fuel pump.
Because the degassing valve is arranged in a bottom region of the main housing of the fuel feed unit, namely in the suction cover of the fuel feed unit and because the degassing valve is connected with the circular passage of the impeller housing by means of a degassing passage in the lower region of the main housing of the fuel fed unit, degassing of the gas bubbles occurs in the immediate vicinity of the source of the gas bubbles, i.e. in the vicinity of the active pump parts, especially the impeller and the circular passage. Because of that aspect of the invention the performance loss, which is caused by degassing, is reduced by the proximity to the degassing means, which has an extremely positive effect on the starting stage.
In a particularly preferred embodiment of the invention the degassing valve includes a valve seat, a valve ball, a compression spring and guide ribs for guiding the valve ball in a valve body. When the degassing valve is open, the guide ribs keep a degassing passage around the valve ball open. Furthermore the guide ribs guide the valve ball from a first open position to a second closed position on the valve seat in such a way that the valve ball is centered and completely sealed in the second position in which the degassing valve is closed to provide a medium tight seal.
As long as gas bubbles are located in the impeller region and in the circular passage, the valve ball remains in its first position because of the pressure exerted by the compression spring and thus the degassing valve remains open. As soon as a suitable feed pressure is built up in the circular passage by a bubble free fuel, this pressure is transmitted through the degassing passage to the valve ball through the degassing passage, the counter pressure exerted by the compression spring is exceeded and the degassing valve is closed in its second position with a medium tight seal. From this point in time onward the complete feed pressure both in the cold feed stage and also in the hot feed stage is available. This entire feed characteristic of this preferred embodiment of the invention is improved in comparison to that of the conventional fuel feed unit.
In another preferred embodiment the degassing valve is kept open by a spring tension in the compression spring when the fuel pump is idle and when the impeller is started until completely degassed, so that when the medium supplied, in this case fuel, becomes completely incompressible, the overpressure produced in the circular passage acts on the valve ball through the degassing passage and forces it to the valve seat. Because of that action the valve ball is pressed on the valve seat and the degassing valve is completely shut terminating the degassing.
In a preferred embodiment the valve body of the degassing valve is an integral part of the suction cover. In this embodiment the valve body is directly die cast with the suction cover, so that processing costs and manufacturing costs is are reduced. In an additional preferred embodiment of the invention the guide ribs are formed as an integral part of the suction cover. Because of this aspect of the invention further simplifications are attained which are especially effective in mass production.
Furthermore the valve seat can be formed on a fitting piece for a cavity in the suction cover. The fitting piece can be engaged in a press fit or in a force-locking manner in the cavity in the suction cover. Because of this feature the valve seat, which requires a higher precision in manufacturing, is made separately from the die cast suction cover. As soon as the fitting piece is fabricated, it can be forced in a force-locking connection in a suitable previously prepared recess or cavity, which is provided in the suction cover for the degassing valve. It is however also conceivable that the valve seat can be formed on a threaded insert for the suction cover and the suction cover can be provided with a threaded passage in which the threaded insert is engaged by screwing with a seal. In this embodiment of course a greater expense is required because it is necessary to provide an O-ring or a flat seal and a suitable seal seat for the fitting piece which has the valve seat.
Eiler Erich
Gerhard Albert
Rose Jochen
Schmieder Dietmar
Strohl Willi
Robert & Bosch GmbH
Striker Michael J.
Thorpe Timothy S.
Tyler Cheryl J.
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