FUEL PUMP HAVING IMPROVED PUMPING BEHAVIOR

Abstract

The present invention relates to a fuel pump for pumping fuel, comprising a piston (2) and a diaphragm seal element (3), which seals on an inner annular seal seat (4) and an outer annular seal seat (5), wherein the following equation is satisfied: (Ra.sup.2−ra.sup.2)/(ri+L).sup.2=ra/ri, where ri is the inner radius of the inner seal seat (4), ra is the inner radius of the outer seal seat (5), Ra is the outer diameter of the piston (2) and L is a difference between an outer radius (Ria) of the inner seal seat (4) and the inner radius (ri) of the inner seal seat (4). The invention further relates to a method for operating a fuel pump.

Claims

1. A fuel pump for delivering fuel, comprising a piston (2) and a diaphragm seal element (3), which seals on an inner annular seal seat (4) and an outer annular seal seat (5), wherein the following equation is satisfied:
(Ra.sup.2−ra.sup.2)/(ri+L).sup.2=ra/ri, wherein ri is an inner radius of the inner seal seat (4), wherein ra is an inner radius of the outer seal seat (5), wherein Ra is a radius of the piston (2) and wherein L is a difference between an outer radius (Ria) of the inner seal seat (4) and the inner radius (ri) of the inner seal seat (4).

2. The pump as claimed in claim 1, characterized in that the diaphragm seal element (3) has a central circular delivery opening (30).

3. The pump as claimed in claim 1, characterized in that the diaphragm seal element (3) has an outer retaining region (31) and an inner sealing region (32), which are connected to one another by connecting arms (33).

4. The pump as claimed in claim 2, characterized in that a diameter of a delivery passage (6) into which the pump delivers is greater than a diameter of the central delivery opening (30).

5. The pump as claimed in claim 4, characterized in that the inner radius (ri) of the inner seal seat (4) is equal to a radius of the delivery passage (6).

6. The pump as claimed in claim 1, furthermore comprising a feed region (7) having an annular cross section.

7. The pump as claimed in claim 6, characterized in that an area of the annular cross section of the feed region (7) is larger than a sum of an area (10) of the inner seal seat (4) and of an area (11) of the outer seal seat (5).

8. A method for operating a piston pump having a piston (2) and a diaphragm seal element (3) having an inner annular seal seat (4) and an outer annular seal seat (5), the method comprising when the diaphragm seal element (3) is open, having a flow rate of the fuel at the inner seal seat (4) be equal to a flow rate at the outer seal seat (5).

9. The method as claimed in claim 8, characterized in that the diaphragm seal element (3) is configured to adhere to the piston (2) during an opening process and to move with the piston.

10. The method as claimed in claim 8, characterized in that the diaphragm seal element (3) rises simultaneously from the inner seal seat (4) and from the outer seal seat (5) during the intake process.

11. The pump as claimed in claim 1, characterized in that the diaphragm seal element (3) has an outer retaining region (31) and an inner sealing region (32), which are connected to one another by spring arms.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] A preferred illustrative embodiment of the invention is described in detail below with reference to the accompanying drawing. In the drawing:

[0014] FIG. 1 shows a schematic section through a fuel pump according to a preferred illustrative embodiment of the invention,

[0015] FIG. 2 shows a schematic perspective view of a diaphragm seal element from FIG. 1, and

[0016] FIG. 3 shows a plan view of the diaphragm seal element shown in FIG. 2.

DETAILED DESCRIPTION

[0017] A fuel pump 1 according to a preferred illustrative embodiment of the invention is described in detail below with reference to FIGS. 1 to 3.

[0018] The fuel pump 1 comprises a piston 2, which can be moved backward and forward in a cylinder 8. Reference sign 9 denotes a return element, in this illustrative embodiment a cylindrical spring.

[0019] The fuel pump 1 furthermore comprises a diaphragm seal element 3, which is a disk-shaped element and is illustrated in detail in FIGS. 2 and 3. The diaphragm seal element 3 comprises a retaining region 31, which is formed in a ring shape at the outer circumference of the diaphragm seal element. The diaphragm seal element 3 furthermore comprises a sealing region 32, which is surrounded by the retaining region 31. Formed between the sealing region 32 and the retaining region 31 are three spring arms 33, which connect the retaining region 31 resiliently to the sealing region 32. A delivery opening 30 is furthermore formed centrally in the middle of the diaphragm seal element 3.

[0020] As can be seen, in particular from FIG. 1, the fuel pump 1 furthermore comprises an inner annular seal seat 4 and an outer annular seal seat 5.

[0021] Here, the inner seal seat 4 is formed between the diaphragm seal element 3 and a bushing 14. The outer seal seat 5 is formed between the diaphragm seal element 3 and a sleeve 15. In this case, the bushing 14 is arranged within the sleeve 15 (cf. FIG. 1). As a result, an annular feed region 7, via which fuel is drawn in, is formed between the bushing 14 and the sleeve 15.

[0022] A delivery passage 6, through which the pressurized fuel is delivered, is furthermore provided in the bushing 14.

[0023] Here, the fuel pump 1 according to the invention operates as follows. For intake, the piston 2 is moved in the direction of arrow A counter to the spring force of the spring element 9. The diaphragm seal element 3 is thereby also moved in the direction of arrow A since a reduced pressure is produced in the region of the piston head. As a result, the diaphragm seal element 3 rises simultaneously from the inner seal seat 4 and from the outer seal seat 5.

[0024] As a result, fuel is then drawn in via the feed region 7 into the pressure chamber which is forming, as indicated by arrow B in FIG. 1. Here, a speed with which the fuel flows past the inner seal seat 4 and the outer seal seat 5 is equal. As a result, identical pressure conditions are maintained in the region of both seal seats 4, 5 during the intake process. In this way, it is possible to prevent gases from evaporating from the fuel, even if the fuel is at a predetermined high temperature.

[0025] Once the top end position is reached, the direction of motion of the piston 2 is reversed, with the result that the piston is moved back in the direction of the bushing 14 again. As a result, fuel is delivered through the delivery opening 30, which is provided in the diaphragm seal element 3, into the cylindrical passage 6 formed in the bushing 14. This is indicated by arrow C in FIG. 1.

[0026] According to the invention, a pressure drop in the region of the two seal seats 4, 5 can thus be reduced.

[0027] By virtue of the embodiment of the diaphragm seal element 3 with the spring arms 33, the diaphragm seal element 3 itself has a spring rate. This spring rate is chosen so that the hydraulic forces allow a stroke which is as large as possible. As a particular preference, the diaphragm seal element 3 adheres to the piston head 2 during the intake process.

[0028] The components of the fuel pump furthermore satisfy the following equation:

(Ra.sup.2−ra.sup.2)/(ri+L).sup.2=ra/ri.

[0029] Here, ri is an inner radius of the inner seal seat 4, ra is an inner radius of the outer seal seat 5, Ra is a radius of the piston 2 and L is a difference between an outer radius Ria of the inner seal seat 4 and the inner radius ri of the inner seal seat 4.

[0030] Here, the length L at the inner seal seat 4 between the diaphragm seal element 3 and the bushing 14 is chosen in such a way that this is embodied to be as small as possible in order to enlarge the inner radius ri of the inner seal seat 4 (cf. FIGS. 2 and 3). Here, the inner radius ra of the outer seal seat 5 is chosen to be as large as possible. In this case, a sum of an area 11 of the outer seal seat 5 and an area 10 of the inner seal seat 4 is larger than an area 13 of the annular feed region 7.

[0031] A radius RF of the delivery passage 6 in the bushing 14 is furthermore equal to the inner radius ri at the inner seal seat 4. In this case, the delivery opening 30 has a smaller area than a cross-sectional area 12 of the delivery passage 6 (cf. FIG. 1).

[0032] It is thus possible, according to the invention, to ensure a significantly improved delivery characteristic, especially in the case of hot fuel. According to the invention, a situation where gases are released from the fuel during the intake process and collect in an unwanted way at the piston 2, thereby significantly reducing the delivery rate of the fuel pump, is furthermore avoided.