Patent Publication Number: US-2004052654-A1

Title: Fuel pump for a motor vehicle

Description:
[0001] The invention relates to a fuel pump for a motor vehicle, comprising a preliminary stage and a main stage for delivering the fuel to an internal combustion engine of the motor vehicle, and an electric motor for driving the preliminary stage and main stage.  
       [0002] Fuel pumps of this type which are known for petrol or diesel fuel are frequently used in motor vehicles today. The fuel pump as a rule forms a pre-assemblable, structural unit together with a flange which is to be inserted into an opening in the fuel tank. In this case, the flange bears a connecting branch to which a forward-flow line leading to the internal combustion engine can be connected, and a connecting branch for a return-flow line leading back from the internal combustion engine. The fuel fed back from the internal combustion engine is subsequently fed to the fuel tank or to a surge chamber. In this connection, the preliminary stage and the main stage are frequently designed in each case as a side-channel pump or peripheral pump, through which the flow passes axially, and are arranged together at that end of the electric motor which points towards the bottom region of the surge chamber. A shaft of the electric motor drives an impeller of the preliminary stage and an impeller of the main stage in each case. The preliminary stage and the main stage are arranged in a common housing together with the electric motor. The fuel delivered by the main stage flows through the electric motor.  
       [0003] One disadvantage of known fuel pumps is that fuel which is not required at the internal combustion engine, but is heated up by it, is recycled into the surge chamber via the return-flow line. During renewed delivery of this fuel by the fuel pump, the fuel continues to beheated, in particular in the main stage. This may lead to problems as a consequence of the low heat resistance of the electric motor, in particular of the carbon-collector system and of the adjacent, electric wiring. For this reason, the temperature of the fuel downstream of the main stage is limited to a permissible value, or the recycled fuel had to be cooled.  
       [0004] A further disadvantage resides in the fact that the fuel delivered by the main stage swirls as it flows through the electric motor. As a result, the fuel has the tendency to form vapor bubbles which, together with the fuel, form a foam which negatively affects the reliable supply of the internal combustion engine with fuel.  
       [0005] Furthermore, when the fuel pump is at a standstill, leakage between the main stage and preliminary stage of the fuel pump causes the fuel pump to drain, in which case the motor compartment of the fuel pump fills with air between the discharge outlet and the main stage. Furthermore, the surge chamber may drain over the same path until level with the main-stage bearing point. When the internal combustion engine is restarted, this results, as a consequence of the excessively low filling level in the surge chamber, in relatively long starting times or in misfires of the internal combustion engine.  
       [0006] The invention is based on the problems of designing a fuel pump of the type mentioned at the beginning in such a manner that the electric motor of the fuel pump is no longer thermally stressed by the fuel and a rapid and reliable supply of the internal combustion engine with fuel is ensured.  
       [0007] According to the invention, these problems are solved in that the main stage of the fuel pump is connected directly to the forward-flow line to the internal combustion engine and is fluidly decoupled from the electric motor. For this purpose, the suction branch of the main stage has a connection to a component which is filled with fuel by the preliminary stage, in particular to a surge chamber or a fuel filter.  
       [0008] One advantage of the fuel pump according to the invention resides in the fact that the volume of the forward-flow line between the main stage and the internal combustion engine can be kept very small. In particular, the air cushion in previous fuel pumps which forms in the electric motor between the forward-flow line and the main stage when the fuel pump is at a standstill is avoided. Therefore, when the internal combustion engine is started with a virtually empty fuel tank, a delay in the delivery of the fuel to the internal combustion engine is kept particularly small. Furthermore, fuel recycled to the surge chamber or the fuel tank from the internal combustion engine can be fed at a higher temperature, since, with renewed delivery through the main stage, the fuel which is now hot as a consequence of the heating is no longer guided through the electric motor, but directly into the forward-flow line. An unnecessary heating-up of the electric motor is therefore prevented. This results in a particularly long life of the electric motor. Moreover, this design enables swirling by the electric motor of the fuel delivered by the main stage to be avoided, with the result that formation of foam in the forward-flow line is prevented. With the fuel pump according to the invention, a reliable supplying of the internal combustion engine with fuel is therefore ensured.  
       [0009] In a particularly advantageous refinement of the invention, the main stage is arranged on that side of the electric motor which lies opposite the preliminary stage. In addition to reducing the length of the forward-flow line, this arrangement has the advantage of this fuel pump being very quiet, since the main stage which is primarily responsible for the formation of noise has been moved further away from the bottom of the fuel tank.  
       [0010] In a further refinement of the invention, it is advantageous if the discharge line of the preliminary stage opens into a surge chamber approximately level with the main stage or above the suction branch. It is thereby ensured that, firstly, there is always a sufficient amount of fuel available in the surge chamber for the main stage, and that, secondly, the main stage is always filled with fuel, or at least immediately sucks in fuel during the starting procedure, and therefore delivers fuel without delay once the electric motor has started.  
       [0011] According to another advantageous development of the invention, sucking-in of foamed fuel foam present in the surge chamber can be largely avoided if the main stage has a suction line which is guided outside the electric motor into the bottom region of the surge chamber.  
       [0012] The fuel pump according to the invention can be fitted in a particularly simple manner if the main stage has, on its side facing away from the electric motor, a flange having a respective connecting branch for the suction line and the forward-flow line of said main stage. 
     
    
    
     [0013] In another refinement, the discharge line of the preliminary stage is advantageously guided through the electric motor. In addition to the particularly low structural outlay for manufacturing the fuel pump according to the invention, this at the same time enables the bearing points to be lubricated and the carbon-collector system to be cooled. However, it is crucial that the fuel fuel heated thereby and tending to give off gas is settled down again by the delivery to a component, with the result that bubble-free fuel is sucked in from this component via the suction branch of the main stage. The invention permits numerous embodiments. To further clarify its basic principle, two of these are illustrated in the drawings and are described below. In the drawings  
     [0014]FIG. 1 shows a longitudinal section through a fuel pump,  
     [0015]FIG. 2 shows a longitudinal section through a different design of fuel pump. 
    
    
     [0016] There is arranged in FIG. 1 fuel pump  3  fitted in a surge chamber  2  arranged near to a bottom of a fuel tank  1 . The fuel pump  3  has a housing  4  which is manufactured from aluminum or steel and has an electric motor  5  arranged in it. The electric motor  5  serves for driving a preliminary stage  6  and a main stage  7 . The preliminary stage  6  is arranged near to a bottom of the surge chamber  2 , while the main stage  7  is situated on the opposite side of the electric motor  5 . The surge chamber  2  has, in its bottom region, an opening  8  into which the fuel pump  3  is inserted in a sealing manner. A respective fuel filter  9 ,  10  is situated below the surge chamber  2  and in the upper region thereof. When there is a sufficiently high level of fuel in the fuel tank  1 , fuel can flow through the upper fuel filter  10  into the surge chamber  2 . For clarification purposes, the flows of fuel are indicated in the drawing by arrows. The preliminary stage  6  and the main stage  7  are designed as side-channel pumps and have a respective impeller  12 ,  13  fastened on a shaft  11  of the electric motor  5 .  
     [0017] The preliminary stage  6  is connected to the fuel filter  9 , which is arranged below the surge chamber  2 , via a suction line  14  and is connected to the surge chamber  2  via a discharge line  15 . When the preliminary stage  6  is being driven by the electric motor  5 , the preliminary stage  6  therefore sucks in fuel from the fuel tank  1  and delivers it into the surge chamber  2 . The discharge line  15  is guided here through the electric motor  5  and ends level with the main stage  7 .  
     [0018] The main stage  7  has, on its side facing away from the electric motor  5 , a discharge branch  16  for a forward-flow line  17  and a suction branch  18  which is arranged on the circumference of the fuel pump  3  and is intended for a suction line  19 . The suction line  19  is guided into the bottom region of the surge chamber  2  and sucks in the fuel from there. The forward-flow line is guided upward within the fuel tank  1 . Fuel delivered via the forward-flow line  17  passes to an internal combustion engine (not illustrated) of the motor vehicle. Fuel which is not required is conducted via a return flow  20  into the surge chamber  2 . This fuel is delivered again to the internal combustion engine by the main stage  7  via the suction line  19  without again flowing through the electric motor  5 .  
     [0019]FIG. 2 shows a structurally altered design of the fuel pump  3  according to the invention. The fuel pump  3  is arranged in a fuel tank  1 . The discharge line  15  of the preliminary stage  6  is guided through the electric motor  5  to a fine fuel filter  21 . The main stage  7  is a Gerotor pump. The branches  16 ,  18  for the suction line  19  and the forward-flow line  17  are arranged on that side of the main stage  7  which faces away from the electric motor  5 . The fuel is sucked in from there through the suction branch  18  by the main stage  17  and is passed on to the internal combustion engine via the forward-flow line  17 . Fuel which is not required is conducted into the fuel tank  1  via a return flow  20 .