Bearing seat arrangement

The invention is directed to a bearing seat arrangement for an automotive auxiliary device, in particular to a bearing seat arrangement of a roller bearing seat for a centrifugal fluid pump of a vehicle.

Centrifugal pumps are usually used for pumping liquid or gaseous fluids within a fluid circuit of a vehicle. Typical applications of a centrifugal pump stage are water/coolant or oil supply of battery electric vehicles and vehicles with an internal combustion engine, but also the hydrogen supply of fuel cell vehicles.

Particularly, by using a centrifugal pump for pumping gaseous fluids of higher temperatures, the heat-load of single pump components or of the complete pump can be extremely high. As a result, a relatively large thermal expansion can occur at some of the pump components which can affect force-fitted connections, for example a press-fitted connection between components of different thermal expansion coefficients.

Because of the higher temperature loads, the pump housing is made of a lightweight but metallic material, for example of an aluminum alloy. Such an aluminum-based material is provided with a relatively low rigidity which requires a reinforcement in some sections with particularly high mechanical loads, for example in the bearing sections. Accordingly, the bearing seats within the pump housing are typically reinforced with a high-strength bearing seat element, for example a steel sleeve, which is press-fitted into the aluminum pump housing. An example for such a reinforced bearing seat is disclosed in CN 206341070 U. As a result of the different thermal expansion coefficients of the pump housing and the bearing seat element, the thermal expansion of the press-fitted bearing seat element can be substantially smaller than the thermal expansion of the pump housing so that the bearing seat element can become loose resulting in an unwanted axial displacement of the bearing seat element.

A method to reliably fix the bearing seat element even at higher temperatures is disclosed in CN 105006928 A. The document discloses a steel sleeve for reinforcing the bearing section within the housing, the steel sleeve being embedded within the pump housing during the molding process of the housing.

The embedding process of the steel sleeve is complex and cost-intensive in particular because of the relatively precise tolerance requirements for the bearing seat.

It is therefore an object of the present invention to provide a bearing seat arrangement for an automotive auxiliary device which provides a relatively cost-efficient, reliable and rigid bearing seat even at higher operating temperatures.

This object is achieved by a bearing seat arrangement according to the present invention with the features of main claim 1.

A bearing seat arrangement for an automotive auxiliary device according to the invention comprises a static support structure which can be, for example, a housing of an automotive auxiliary device. The static support structure is made of a lightweight material, preferably of an aluminum alloy or any other comparable metallic material with a relatively low weight, for example, a magnesium-based material. However, typical lightweight materials have a relatively low rigidity and also a relatively low material strength so that the static support structure requires a reinforcement at the mechanically high loaded sections. Typically, an automotive auxiliary device, for example a pump, comprises a drive shaft or an axle, for example for driving a pump wheel, so that a suitable bearing support within the static support structure is required. Therefore, the bearing seat arrangement comprises a separate bearing seat element being press-fitted into the support structure. The bearing seat element is preferably a ring-shaped steel sleeve which is press-fitted into a corresponding seat within the support structure using preferably an interference fit. Advantageously, the support structure is heat-shrinked onto the steel sleeve to achieve a relatively large interference between the fitted components so that the differences according to the thermal expansion between the support structure and the bearing seat element can be compensated over a relatively large operating temperature range.

Additionally, if the press-fitted connection fails as a result of a relatively large total thermal expansion difference, the bearing seat element is additionally axially fixed by an adhesive bond that secures the bearing seat element against any dangerous axial displacement. If the force-fitted frictional connection fails, the bearing seat element is still fixed by the bonded connection.

The bearing seat element defines a reinforced bearing seat within the support structure that seats a bearing for supporting preferably a rotating component within the auxiliary device housing, for example, the bearing can support a rotating drive shaft of a centrifugal pump, the drive shaft being co-rotatably connected to a centrifugal impeller which rotates within a pump chamber to pump liquid or gaseous fluids within a fluid circuit of a vehicle.

In a preferred embodiment of the present invention, the thermal expansion coefficient is larger than the thermal expansion coefficient of the bearing seat element by at least a factor of 1,4. If that factor is larger than 1,4, which is typical for a weight-optimized automotive product, there is a risk that the thermal expansion differences result in a loosening of the press-fitted connection depending on different parameters, in particular on the operating temperature range, and on the tightness of the interference fit. In an automotive application, these parameters are typically defined such that an additional axial fixation of the bearing seat element is required, if the thermal expansion difference exceeds the said factor.

In a preferred embodiment of the present invention, the support structure comprises a circumferential adhesive ring groove which is filled with an adhesive bond substance to define the said adhesive bond. Thereby the adhesive bond substance, which can be, for example, a glue or an epoxy adhesive, is concentrated at a defined bonding surface. Generally, the circumferential extension of the ring groove, the number of the ring grooves and the axial overlapping of the ring groove with the radial outside surface of the bearing seat element define the bonding surface which defines the strength of the adhesive bond. The larger the bonding surface is, the larger is the bonding strength. The ring groove extends preferably along the complete circumference, but it can alternatively extend along a defined section of the circumference.

In another alternative embodiment the support structure can comprise more than one ring groove being axially adjacent to each other so that the total bonding surface of the adhesive bond is increased compared to the said single-groove embodiment.

In a preferred embodiment of the present invention, the adhesive bond is provided circumferentially at one axial end section of the radial outside surface of the steel sleeve. Accordingly, the adhesive bond is not provided over the complete radial outside surface of the steel sleeve but only over a section of the radial outside surface at one axial end of the steel sleeve. The axial forces that act onto the steel sleeve are relatively low. The axial sleeve fixation by the adhesive bond mainly serves to fix the steel sleeve against an axial displacement resulting from vibrations so that a strong adhesive bond over the complete radial outside surface is not necessary.

In a particularly preferred embodiment of the invention, the adhesive bond substance is arranged such that it additionally provides a form fit at an axial end surface of the steel sleeve. At the axial end of the steel sleeve, the adhesive bond substance extends from the radial inner surface of the support structure radially inwards so that the material accumulation within the bearing seat bore of the support structure additionally secures the steel sleeve in axial direction. The said form fit is thereby functionally similar to an axial stop surface or a retaining ring.

Preferably, the adhesive ring groove is arranged substantially at a transversal plane being defined by the axial end surface of the steel sleeve, i.e., the axial end surface of the steel sleeve is positioned, seen in axial direction, between the two axial sidewalls of the ring groove. Thereby the adhesive ring groove can be filled with the adhesive bond substance such that an axial end section of the radial outside surface of the steel sleeve is adhesively bonded and additionally such that the adhesive bond substance extends radially inwards and thereby partially covers the axial end surface of the steel sleeve to define a form fit at the axial end surface of the steel sleeve.

In a preferred embodiment of the present invention, the bearing seat element seats a roller bearing ring. The roller bearing ring defining the outer shell of the roller bearing is seated within the bearing seat element which defines a relatively rigid and precise seat for the roller bearing which is necessary because of the relatively small bearing clearance of a roller bearing. Accordingly, the bearing seat element even allows the application of a roller bearing. In a particularly preferred embodiment of the present invention, the adhesive bond is provided over an axial length which is less than 20% of the axial length of the bearing seat element. For example, the adhesive bond can be provided over 10% of the radial outside surface of the bearing seat element so that the adhesive bond is provided only by a relatively small bonding surface which is, however, large enough to axially fix the bearing seat element against any axial displacement resulting from vibrations or similar mechanical effects. Thereby, the material costs can be kept relatively low.

In a preferred embodiment of the invention, the auxiliary device is a pump or an electric motor. The said pump can be, for example, any type of pump which is suitable for pumping liquid or gaseous fluids in a fluid circuit of an automotive application. The preferred pump type is a centrifugal pump, for example, for pumping hydrogen as an anode blower in an automotive fuel cell application. Alternatively, the invention can be used for any other auxiliary device using an electric motor as drive unit, in particular actuators for any type of automotive valve unit.

An embodiment of the invention is described with reference to the enclosed drawings, wherein figure 1 shows an embodiment of an automotive auxiliary device with a bearing seat arrangement according to the invention in a schematic longitudinal cross-sectional view, and figure 2 shows an enlarged and detailed view of the bearing seat arrangement of figure 1.

Figure 1 shows an automotive auxiliary device 100, namely a centrifugal pump 101 for pumping hydrogen within a hydrogen circuit of a fuel cell application in a vehicle. The auxiliary device 100 comprises a pump housing 112, made of an aluminum-alloy, and a centrifugal impeller 110 being arranged within a pump chamber 117 and being co-rotatably connected to a driveshaft 115 which is electrically driven by an electric drive motor 140. The electric drive motor 140 comprises a rotatable motor rotor 141 being co-rotatably connected the drive shaft 115 and a motor stator 142 for electromagnetically driving the motor rotor 141. The pump chamber 117 is fluidically separated from a motor chamber 118 by a sealing ring 130. The drive shaft 115 is rotatably supported by a roller bearing 30, wherein the outer roller bearing ring 31 is seated within a bearing seat arrangement 10, shown in figure 2.

The bearing seat arrangement 10 comprises a static support structure 12 which is, in this embodiment, defined by the aluminum pump housing 112 of the auxiliary device 100. The bearing seat arrangement 10 further comprises a separate bearing seat element 15 defined by a ring-shaped steel sleeve 16 which is press-fitted into the support structure 12 using an interference fit. At one axial end, the steel sleeve 115 is axially fixed by an axial stop surface 13 at the support structure 12, the axial stop surface 13 defining an axial stop in particular during the press-fitting process of the steel sleeve 16. Due to the different thermal expansion coefficients of the materials of the steel sleeve 16 and the aluminum support structure 12, the thermal expansion of the support structure 12 is larger than the thermal expansion of the steel sleeve 16 by a factor of two. Therefore, the steel sleeve 16 is, at its other axial end, additionally axially fixed by an adhesive bond 20 to prevent an axial displacement of the steel sleeve 16 if the press-fitted connection becomes loose as a result of a strong heating of both the steel sleeve 16 and the support structure 12.

The support structure 12 comprises a circumferential adhesive ring groove 121 within the radial inside surface 124 of a bearing seat bore 123 within the support structure 12. The ring groove 121 is arranged such that it is axially symmetrically arranged to a transversal plane P being defined by the axial and surface 165 of the steel sleeve 16. The adhesive ring groove 121 is completely filled with an adhesive bond substance 21 which defines the adhesive bond 20. The adhesive bond substance 21 is preferably an epoxy adhesive with a temperature resistance up to 150°C which is typically the maximum operating temperature of the automotive auxiliary device 100.

The adhesive bond substance 21 contacts the radial outside surface 161 of the steel sleeve 16 along the complete circumference at its axial end section facing the adhesive ring groove 121. The adhesive bond substance 21 further contacts the radial outside surface 161 of the steel sleeve 16 in axial direction over an axial length LI which is about 5% of the axial length L2 of the steel sleeve 16. Additionally, the adhesive bond substance 21 extends radially inwards with respect to the radial inside surface 124 of the bearing seat bore 123 and thereby covers the axial end surface 165 of the steel sleeve 16 in its edge region so that a form fit is achieved that fixes the steel sleeve 16 axially in addition to the adhesive bond 20 at the radial outside surface 161 of the steel sleeve 16.

The bearing seat arrangement 10 thereby defines a relatively reliable axial fixation of the steel sleeve 16 even at high operating temperatures at which the loosening of the press-fitted connection as a result of the thermal expansion differences of the steel sleeve 16 and the support structure 12 could otherwise cause an axial displacement of the steel sleeve 16 resulting, for example, from occurring vibrations.