Power steering system hydraulic pump

A power steering system hydraulic pump has a pump component which is to be sealed and a first pump cover. A flat sealing element is provided between the pump component which is to be sealed and the first pump cover.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/EP2006/000461 filed Jan. 19, 2006, the disclosures of which are incorporated herein by reference, and which claimed priority to German Patent Application No. 10 2005 002 757.1 filed Jan. 20, 2005, the disclosures of which are incorporated herein by reference.

BACKGROUND

Various embodiments of a power steering system hydraulic pump are disclosed herein. In particular, the embodiments described herein relate to an improved power steering system hydraulic pump having a pump component, which is to be sealed, and a first pump cover.

Such pumps are generally part of a motor/pump unit for power steering systems of motor vehicles. DE 203 02 535 U, and corresponding U.S. Patent Application Publication No. 2006/0051230 A1, both of which are incorporated by reference herein, shows a generic hydraulic pump for a power steering system which can be inserted as a prefabricated unit into a motor/pump unit. The pump here comprises a housing which is closed at its end faces by a respective pump cover. The two covers are braced against each other by at least one holding piece, whereby it is possible to assemble the pump at a favorable cost and without effort.

The sealing between the pump covers and the housing on the one hand and between the pump covers and the installation pieces of the housing (e.g. the bearing rests) on the other hand takes place in DE 203 02 535 U by sealing rings, as usual. The sealing rings may be circular, oval or heart-shaped here, and may have a round or rectangular cross-section. Irrespective of their shape or their cross-section, all the mentioned sealing rings abut substantially linearly at the components which are to be sealed. As these are generally elastomer seals, a precisely worked groove must be present in one of the components abutting at the seal. In addition, there is effort involved in processing the surface of the groove in order to ensure the desired sealing effect.

BRIEF SUMMARY

The present application describes various embodiments of a power steering system hydraulic pump which provides a seal between two components of a power steering system hydraulic pump that is simple and as favorably priced as possible.

In a power steering system hydraulic pump having a pump component which is to be sealed and a first pump cover, a flat sealing element is provided for this purpose between the pump component which is to be sealed and the first pump cover. The costly working of the pump cover by the precise milling and finishing processing of a groove for the ring seal, which seals substantially in a linear shape, is eliminated. The pump cover, which hitherto was usually an aluminum die cast metal part, may be replaced, for example, by a favorably priced stamped part made of steel.

The pump component which is to be sealed may be a bearing rest. Bearing rests adjoin the pump cover in particular in external geared pumps and lie against the pump cover so as to be damped with regard to noise and sealed by means of the flat sealing element.

In addition, it is possible for the pump component which is to be sealed to be a housing. A tight connection is generally also necessary between this housing of the pump and the pump cover. This is particularly readily possible through the flat sealing element which is present.

In one embodiment, the flat sealing element is a flat seal. This can be adapted to shape of the pump cover in a simple manner such that all the adjoining pump components are tightly connected with the pump cover through this one flat seal.

In another embodiment, the flat sealing element is at least partially made of metal. Metallic seals can receive a high transverse pressure and achieve a reliable sealing effect despite high stresses.

Moreover, in the embodiments of the power steering system hydraulic pump described herein, a second pump cover having a ring seal is present, the ring seal being arranged between the second pump cover and a pump component which is to be sealed. In such a case, the advantages of both types of seal can be utilized in a hydraulic pump. As described herein, ring seals are defined such that they surround an area and seal it substantially linearly. The surrounded area does not have to be circular, but rather may have any desired geometric shape. The ring seals are usually produced from an elastomer.

In this embodiment, it is sensible that the ring seal of the second pump cover completely undertakes the compensation of size tolerances of the pump components. Owing to the conventional manufacturing materials and the lower pressure of the ring seal as a result of guidance in the cover groove, this is better suited for the compensation of the axial play than the flat sealing element. A further advantage is that the bearing rests can likewise be constructed so as to be flat, therefore can manage without a sealing groove.

Further, the power steering system hydraulic pump may likewise comprise a housing, in which, under operating pressure, the surface of the pump components, in particular of the bearing rest, acted upon by pressure, in the housing is smaller on the side facing the flat sealing element than on the side facing the ring seal. Through this measure, a resulting force of the pump components is produced in the housing onto the flat sealing element. It is thereby ensured that the pump components which are to be sealed always lie against the flat sealing element.

Other advantages of the power steering system hydraulic pump will become apparent to those skilled in the art from the following detailed description, when read in light of the accompanying drawings.

DETAILED DESCRIPTION

FIG. 1illustrates a power steering system hydraulic pump8having two pump components which are to be sealed and a first pump cover10, a flat sealing element being provided between the pump components which are to be sealed and the first pump cover10. In this example, the pump components which are to be sealed are a housing14and a first bearing rest16. The hydraulic pump8additionally comprises a second pump cover20having a ring seal22, the ring seal22being arranged between the second pump cover20and a pump component which is to be sealed. The components which are to be sealed here are a second bearing rest24and again the housing14. A spring ring26which compensates for the axial play of the hydraulic pump8on installation into a motor/pump unit (not shown) is additionally illustrated on the upper side of the second pump cover20. As inFIG. 1an external-gear pump is shown, the pump gear, consisting of two meshing gear wheels28, is situated between the bearing rests16,24. Each of the two gear wheels28is connected with a shaft, its shaft journals being held in the bearing rests16,24. A drive shaft30extends through the first bearing rest16, the flat seal12and the first pump cover10. The drive shaft30therefore projects out from the interior of the pump and can be driven by a motor (not shown).

On its outside, the housing14has axial guides for two holding elements32. The holding elements32are guided through openings in the first and second pump covers10,20and hold the hydraulic pump8together.

In the assembled state, the bearing rests and the pump gear are introduced into an axial opening of the housing14. The axial opening of the housing14is closed on the upper- and underside by the pump covers10,20.

The flat seal12is provided between the first pump cover10and the housing14and between the first pump cover10and the first bearing rest16, respectively. The flat seal12may be a plate made of steel which is coated on both sides with an elastomer, but it may also be produced from a soft metal. The flat seal12extends over almost the entire surface of the first pump cover10and therefore seals between the first pump cover10and the housing14and the first bearing rest16, respectively.

The pump drive, the bearing rests16,24and the housing14have an axial play owing to tolerances in size. This axial play must be compensated by the present seals of the hydraulic pump8in order to ensure a secure seat for the pump components and also a problem-free functioning of the hydraulic pump8. The flat seal12is not suitable to receive this axial play, because the metallic layer is too hard and the elastic layer which may be present is very thin.

For this reason, in the present example ofFIG. 1the second pump cover is provided in a known manner with a groove to receive the ring seal22. This ring seal22usually consists of an elastomer and can fully receive the axial play.

For the instance where the manufacturing technology reaches a higher accuracy of measurement for the pump components and the axial play is substantially eliminated, it is of course possible and advantageous to also construct the second pump cover20as a simple stamped part and to replace the ring seal22by a flat seal12.

FIG. 2shows an axial section through the two shaft axes of the assembled hydraulic pump ofFIG. 1. As the axial play of the pump components can not be equalized by the flat seal12, the bearing rests16,24together with the pump drive must be pressed by a force F onto the flat seal, in order to prevent a “lifting” of the first bearing rest16from the flat seal12. This necessary force F is illustrated by an arrow inFIG. 2.

The force F occurs as the resulting force from a difference of the surfaces of the pump components, in particular of the bearing rest, in the housing14which are acted upon with pressure on the end face. This area difference is shown inFIG. 3. The flat seal12can be seen there in top view and the position of the ring seal is emphasized in black. The second bearing rest24is acted upon by the operating pressure of the pump in the region of the ring seal22on the hatched surface, whereas the first bearing rest16is not acted upon by pressure in this region, but rather is sealed by the flat seal12. Therefore, under operating pressure, the surface of the pump components in the housing14, acted upon by pressure, is smaller on the side facing the flat sealing element than on the side facing the ring seal22. The vertical force F onto the flat seal12results from this difference in area acted upon by pressure.

FIG. 4shows the first pump cover10in detail. This first pump cover is generally made of steel and can be produced as a simple stamped part. This results in a considerable cost advantage compared with the conventional pump covers, e.g. of aluminum die cast metal having a groove and a costly subsequent processing of the groove.

In accordance with the provisions of the patent statutes, the principle and mode of operation of the power steering system hydraulic pump have been explained and illustrated in its various embodiments. However, it must be understood that the power steering system hydraulic pump described herein may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.