Patent Application
20160222964
The present application claims priority of DE 10 2015 101 443.2, filed Feb. 2, 2015, the priority of this application is hereby claimed and this application is incorporated herein by reference.
The invention relates to a fuel pump, having a housing, in which an electric drive motor is accommodated, the motor shaft of which is coupled by a clutch element to a drive screw of a screw pump.
In DE 41 23 384 A1, a description is given of a fuel pump, the electric drive motor of which is connected directly to a drive screw, which drives an idler screw, thereby delivering a fluid axially. The drive screw and the idler screw form moving delivery chambers for a fluid, in particular fuel, whereby the fuel is delivered from a suction-side inlet to a discharge-side outlet. There can be a flow of fuel through the electric drive motor, thereby cooling the drive motor.
A dog clutch for a screw pump is known from DE 43 08 755 A1. The dog clutch connects the shaft of the driving motor to the drive screw, thereby compensating for axial misalignment and angular misalignment between the drive shaft and the screw. Two intersecting grooves are ground in at one axial end of the drive screw, thereby giving rise to two mutually opposite dogs with a triangular cross section. The clutch provided there is of disk-shaped design and has two recesses, in which the triangular dogs engage. In addition, the clutch has a central slot, in which the end portion of the drive shaft, which is there referred to as an axle stub, engages.
Although fuel pumps of this kind having a dog clutch have long proven themselves, there is a requirement for an improved fuel pump which can be produced at lower cost.
It is therefore the underlying object of the invention to specify a fuel pump which can be produced at lower cost.
To achieve this object, provision is made, according to the invention, for the drive screw in a fuel pump of the type stated at the outset to have a substantially level axial surface at its clutch-side end.
The invention is based on the insight that the production costs for a fuel pump can be reduced if a drive screw with a level axial surface is used. This eliminates the comparatively complex grinding operations by which the two triangular dogs are produced. To achieve this, several successive grinding operations were hitherto required in order to produce one side of the triangular dog in each case. According to the invention, the production of the dogs is omitted, and therefore all that is required is to cut to length the drive screw produced. For this purpose, the first step is to produce a blank, from which a plurality of separate drive screws, e.g. two or three drive screws, can be produced by subdivision. In this way, the production of the individual drive screws can be accomplished efficiently and at low cost. Another advantage can be seen in the fact that the omission of the dogs reduces the length of a drive screw by about 5% in comparison with a conventional drive screw having dogs. Accordingly, a considerable saving of material is thereby achieved.
In the fuel pump according to the invention, it is particularly preferred if the axial surface extends over the entire cross section of the drive screw. This means that, at its clutch-side end, the drive screw has only a single level surface, which can be produced easily by means of a cutting method. The level axial surface is obtained when the blank of the drive screw is divided into a plurality of parts of the same length.
Particularly reliable operation of the fuel pump according to the invention can be ensured if one side of the clutch element is designed as a mirror image of the clutch-side end of the drive screw. Accordingly, this side of the clutch element is designed as the negative of the drive screw and thus has a recess, into which the clutch-side end of the drive screw engages in the assembled state. The clutch element and the clutch-side end of the drive screw are thereby connected to one another positively and/or nonpositively. The clutch element is designed in such a way that it is capable of transmitting the torque output by the motor shaft to the drive screw.
A development of the fuel pump according to the invention envisages that the clutch-side end of the drive screw has ground edges. Grinding the edges serves to avoid sharp edges, which might otherwise damage the clutch element.
With the fuel pump according to the invention, it is preferred if the clutch element is produced from a plastics material by injection molding. In this way, the clutch element can be produced at particularly low cost. In this context, it is particularly preferred if the clutch element is produced from a plastically deformable plastics material. Through an at least slight plastic deformability, a certain adaptation of the deformable plastics material to the drive screw, if appropriate also to the motor shaft, can take place initially, thereby improving power transmission. Since the clutch element and the clutch-side end of the drive screw rest flat against one another, there is a large area available via which the torque introduced or the power is transmitted, and this reduces the surface pressure acting on the clutch element and increases the service life of the clutch element.
The screw pump of the fuel pump according to the invention preferably comprises the drive screw and one or two driven screws.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
In the drawing:
In a similar way,
The significant advantage of the fuel pump 1 is to be seen in the fact that the drive screw 6 can be produced at low cost since production of dogs is dispensed with. Instead, use is made of a clutch element 5 which has a recess matched to the outer contour of the clutch-side end 12 of the drive screw 6. The opposite side of the clutch element 5 is coupled to the motor shaft 4.
While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 101 443.2 | Feb 2015 | DE | national |
