DE102019218196A1 - Electric motor-driven unit for a vehicle - Google Patents

Abstract

The invention relates to an electric motor-driven unit (1) for a vehicle, with at least one electric drive unit (2) comprising at least one drive shaft (3) with an axis of rotation (D), the drive shaft (3) with a press fit in a fastening bore (4 ) at least one hub (5) engages and is thereby positively connected to the hub (5). In order that such a force-fit shaft-hub connection produced by means of a press fit enables reduced assembly forces and improved durability even with coarser tolerances, it is proposed according to the invention that the drive shaft (3) have a knurl (6) and the hub ( 5) have at least one axially aligned groove (7) in the fastening bore (4)

Description

The invention relates to an electric motor-driven unit for a vehicle, in particular a vacuum pump, for example for supplying a pneumatic brake booster or a brake dust extraction system.

Modern vehicles have many units, which are driven by electric drive units or electric motors via rotating drive shafts via torque-transmitting shaft-hub connections.

Form-fitting shaft-hub connections are complex and particularly expensive to manufacture and are prone to centering errors.

Non-positive clamping connections with the use of separate screw elements are complex to assemble and are particularly prone to imbalance errors.

There are therefore comparatively simple, force-fit shrink-fit or press-fit connections without a form fit and without separate fastening elements.

As an example of a relevant state of the art, an electric motor / pump assembly according to FIG WO 2014/174072 A1 referenced, in which two opposing connecting rods are actuated via an eccentric drive with two eccentrics arranged on a drive shaft of the drive unit. The drive shaft is pressed into the fastening bores of the two eccentrics, which act as hubs in the associated shaft-hub connection.

In order to ensure reliable torque transmission and at the same time to keep assembly forces when shrinking or pressing on and at the same time to avoid damage to components, the tolerances of the pairing of parts must be precisely adhered to within a narrowly defined range in such a connection type, which increases the manufacturing and testing effort.

In order to transmit higher torques even with coarser tolerances, shaft-hub connections with a knurled instead of a smooth shaft are known. Due to the coarse tolerances, especially with the knurled shaft, it can happen that the oversize fluctuates greatly in its value and can occasionally turn out to be particularly large.

In such a case, very high assembly forces and thus particularly powerful and more expensive assembly units are required to press the hub on.

If several hubs are pressed one after the other on the same knurl, there is a risk that the knurl in the front area of the shaft will be plastically deformed by the pressing on of the first hub and that it will be so severely damaged that the required oversize and thus a sufficiently tight fit of the following hub can no longer be guaranteed on the previously damaged knurled section.

This can lead to a higher reject rate and the frequency of downtimes in operation and lead to an increased control effort.

The object is to propose an improved unit with a non-positive shaft-hub connection produced by a press fit, which enables reduced assembly forces and improved durability even with coarser tolerances.

The object is achieved according to the invention by the combination of features according to independent claim 1. Subclaims specify further embodiments and developments according to the invention.

The invention provides that the drive shaft has a knurl in the connection area with the hub and the hub has at least one axially aligned groove in its fastening bore. As a result, the contact area between the drive shaft and the hub is reduced in a targeted and defined manner and the required press-in force is therefore constrained to be structurally limited within an optimal, defined area. Scrap and rework in production can thus be reduced even with rough tolerances and large oversizes.

The invention can be used particularly effectively if the unit comprises at least two hubs which are arranged one behind the other on the same knurl. In this way, the knurl is spared in the area of the groove of the installed hub and is guaranteed to be undamaged for the other, subsequently installed hub. This guarantees a predictable, safe grouting of both hubs, with a predictable behavior during assembly and operation.

According to a preferred embodiment, the hubs can be rotated 180 ° around the axis of rotation D. running orthogonals O the plane of symmetry S. be arranged rotated against each other on the drive shaft. With such an arrangement, the two hubs can produce and Can be designed identically, favorably for assembly, for example to drive a connecting rod.

An effective connection with particularly simple assembly and reliably predictable behavior can be realized if the knurl is formed with grooves aligned axially parallel to a central axis of the drive shaft.

The shaft-hub connection according to the invention can be used particularly effectively in the case of strongly changing load cases if the hub is designed, for example, as an eccentric.

A preferred development of the invention provides that the groove base of the groove is provided at a distance from the lateral surface of the fastening bore in the radial direction in such a way that there is a clearance fit or a guaranteed radial distance between the groove base and the knurl. The expected assembly and pressing forces can be calculated in advance in a particularly reliable manner.

For an improved, even distribution of force, a further development of the invention provides that at least two axial grooves, which are spaced apart from one another in the circumferential direction, are arranged in the fastening bore of the hub.

For ease of manufacture and a particularly uniform, symmetrical force distribution, especially when used in an eccentric, one embodiment of the invention provides that the grooves are designed to be mirror-symmetrical with respect to the plane of symmetry of the eccentric.

Another embodiment provides that the grooves are designed to be axially symmetrical and offset in a circumferential direction in relation to the plane of symmetry of the eccentric. In this way, particularly when using two hubs, it can be ensured that the grooves of the two hubs do not overlap in the circumferential direction in the installed state so that each hub on the drive shaft has the same torsional strength and the same assembly forces are required. Early failures due to insufficient adhesion at the press point are effectively avoided.

For a particularly symmetrical and uniform force distribution in the hub and at the same time effective centering, a further embodiment provides that at least three axial grooves spaced from one another in the circumferential direction are arranged in the fastening bore of the hub.

In particular when using two hubs arranged next to one another, according to a further development of the invention, the cumulative distances between the grooves in the circumferential direction can be larger than or equal to the cumulative widths of the grooves. As a result, even with the most unfavorable tolerance combination with the greatest possible oversize, the first-mounted hub can at most pre-damage half of the knurled surface in the circumferential direction when it is pressed on, so that the subsequently mounted hub has at least the same surface portion of the knurled undamaged.

The corrugated hub connection according to the invention can be used particularly effectively in a vacuum pump, in particular for supplying vacuum to a braking device in a motor vehicle.

• 1 ein gattungsgemäßes elektromotorisch angetriebenes Aggregat am Beispiel einer Unterdruckpumpe.
• 2 eine Ausführungsform des Triebes einer Unterdruckpumpe nach 1 mit je zwei spiegelsymmetrisch in Bezug auf die Symmetrieebene des Exzenters in der Befestigungsbohrung des Exzenters ausgebildeten Nuten in einer räumlichen Explosionsdarstellung (a) sowie als Querschnitt (b) im Zusammenbau.
• 3 eine weitere Ausführungsform des Triebes einer Unterdruckpumpe nach 1 mit je zwei achssymmetrisch und in Bezug auf die Symmetrieebene des Exzenters umfangsversetzt in der Befestigungsbohrung des Exzenters ausgebildeten Nuten in einer räumlichen Explosionsdarstellung (a) sowie als Querschnitt (b) im Zusammenbau.
• 4 bis 7 zeigen stark vereinfacht unterschiedliche Ausführungsformen der Naben, jeweils mi einer einzelnen Nabe (a) sowie im Zusammenbau (b), mit zwei gegeneinander versetzt auf der Antriebswelle montierten Naben.

The invention is explained in detail below with reference to the description of the figures. Here show:

• 1 a generic unit driven by an electric motor using the example of a vacuum pump.
• 2 an embodiment of the drive of a vacuum pump after 1 with two mirror-symmetrical grooves in relation to the plane of symmetry of the eccentric in the mounting hole of the eccentric in a three-dimensional exploded view (a) and as a cross-section (b) in the assembly.
• 3rd another embodiment of the drive of a vacuum pump 1 each with two axially symmetrical grooves that are circumferentially offset in relation to the plane of symmetry of the eccentric in the mounting hole of the eccentric in a three-dimensional exploded view (a) and as a cross-section (b) when assembled.
• 4th to 7th show, greatly simplified, different embodiments of the hubs, each with a single hub (a) and in the assembly (b), with two hubs mounted offset from one another on the drive shaft.

Fig. 1

1 shows a generic unit 1 using the example of a vacuum pump to supply a pneumatic brake booster for the hydraulic brake system of a motor vehicle.

One on the housing of the unit 1 attached electric drive unit 2 drives two via roller bearings via an eccentric drive 11 , 11 'opposing connecting rods mounted on it 12th , 12 ', which transmit their movement to two oppositely arranged membrane units.

The eccentric drive includes eccentrics 5 , 5 'which, as hubs, are frictionally and rotationally test with axial mounting holes 4th , 4 'with an interference fit on one about the axis of rotation D. rotating drive shaft 3rd are fixed. The two eccentrics or hubs ( 5 , 5 ') are of identical design and aligned mirror-inverted directly next to one another on the drive shaft 3rd positioned. For this purpose, 180 ° around the axis of rotation D. running orthogonals O the plane of symmetry S. positioned rotated against each other, so that their respective axial end faces 15th , 15 'are on top of each other and the respective backs 16 , 16 'point from each other.

Fig. 2

2 shows a first embodiment of the shaft-hub connection of an eccentric drive 1 . The drive shaft 3rd points in its connecting section to the two hubs 5 , 5 'a knurl 6th with axially parallel to the axis of rotation D. aligned grooves 10 . In the mounting hole 4th the hub 5 are two opposing axially aligned grooves 7th , 7 'formed. When assembling the hub 5 on the knurl 6th the drive shaft 3rd point the from the grooves 7th , 7 'overlapped areas of the knurl 6th no interference fit with the hub 5 on. Preferably the grooves are 7th , 7 'designed in such a way that the respective groove base 8th , 8 'in the radial direction to the knurl 6th is spaced, so that there is a clearance fit construction principle of the embodiment described above in these areas.

This reduces the contact area between the drive shaft 3rd and the mounting hole 4th the hub 5 on one between the grooves 7th , 7 'in the circumferential direction of the remaining area of the jacket surface 9 the mounting hole 4th . The pressing force and thereby also the force required to push the hub on 5 The force required for assembly is reduced.

The construction principle of the embodiment described above is also illustrated by the 5 made clear.

Fig. 3

In the 3rd Another embodiment of the shaft-hub connection is shown, which for clarity is also shown in FIG 6th is shown. In contrast to the embodiment according to 1 where the two grooves 7th , 7 'essentially plane-symmetrical to the plane of symmetry S. of the eccentric 5 are aligned, the two grooves are 7th , 7 'in the present embodiment is only axially symmetrical to the axis of rotation D. as well as an offset angle 13th in the circumferential direction to the plane of symmetry S. arranged rotated. In the exemplary embodiment shown, the offset angle is 13th 45 °.

With such a structure, the grooves of the two eccentrics or hubs overlap during assembly 5 , 5 'not in the circumferential direction. As a result, one of the grooves stands 7th , 7 'of the first hub 5 recessed and thus guaranteed undamaged area of the knurl 6th in its original form for pressing with the rest of the outer surface 9 the following hub 5 'is available.

Fig. 4

4th shows, greatly simplified and not to scale, the construction principle of a further embodiment of the shaft-hub connection, with only one single axial groove 7 per hub 5 .

The groove base 8th the groove 7th is so of a lateral surface 9 the mounting hole 4th provided spaced apart in the radial direction that between the groove base 8th and the serrated cross-sectional profile of the knurls 6th there is a clearance fit, preferably always a small distance.

In particular from the assembly view b it becomes clear that when assembling two similarly designed hubs 5 , 5 ', which when assembled by 180 ° around the axis of rotation D. or around the axis of rotation D. running orthogonals O the plane of symmetry S. are positioned rotated against each other, one through the groove 7th the first hub in each case 5 Unaffected peripheral area of the knurl 6th in its original form for pressing against the outer surface 9 the mounting hole 4 'of the subsequently mounted, second hub 5' is available.

Fig. 5

The 5 illustrates the construction principle of the embodiment according to 2 . The two opposite grooves 7th '7' are with respect to a plane of symmetry S. of the eccentric or the hub 5 designed mirror-symmetrically. This causes the grooves of the two hubs 5 , 5 'completely overlap in the circumferential direction in the assembly. Such an embodiment can be suitable, for example, in cases where, due to certain material combinations, processing processes or operating conditions, an increased oversize is to be expected particularly frequently, when the risk of insufficient torque transmission is rather low. Unwanted force peaks can be reliably avoided by such a construction.

Fig. 6

The 6th illustrates the construction principle of the particularly universally applicable embodiment of the shaft-hub connection according to FIG 3rd .

In contrast to the execution after 2 and 5 are the two opposite grooves 7th , 7 'with respect to the plane of symmetry S. of the eccentric by the offset angle 13th positioned rotated in the circumferential direction. In addition, there are the cumulative distances (A1 + A2) between the grooves 7th and 7 'at least equal to or preferably greater than the cumulative widths (B1 + B2) of the two grooves 7th , and 7th .

Such a design leads to the fact that in the assembly, when the second assembled hub 5 'in comparison to the first assembled hub 5 by 180 ° around the axis of rotation D. running orthogonals O the plane of symmetry S. twisted on the drive shaft 3rd is pressed on, the grooves of the two hubs 5 and 5 'are guaranteed not to overlap in the circumferential direction.

Fig. 7

3rd shows a further embodiment of the shaft-hub connection, which has improved centering, in particular under load.

In the mounting hole 4th the hub 5 are three axial grooves here 7th , 7 ', 7 ". These are uniform in the circumferential direction with an angle of separation 14th offset to each other.

The grooves 7th , 7 ', 7 "are the same as in the execution according to 5 Easily manufactured, mirror-symmetrical with respect to the plane of symmetry S. educated. Due to their odd number and even circumferential distribution, the grooves of the two hubs overlap 5 and 5 'still not in assembly.

Otherwise, the same principle and the same advantages apply as in the embodiment according to FIG 6th .

The number of grooves and their distribution on the circumference of the fastening bore in the hub can of course deviate and vary from the exemplary embodiments described above within the invention while maintaining the basic principle according to the invention.

List of reference symbols

1

Aggregate

2

Drive unit

3

drive shaft

4th

Mounting hole

5

hub

6th

Knurl

7th

Groove

8th

Groove base

9

Outer surface

10

groove

11

roller bearing

12th

Connecting rod

13th

Offset angle

14th

Distance angle

15th

Front side

16

back

A.

Groove spacing

B.

Groove width

D.

Axis of rotation

S.

Plane of symmetry

O

Orthogonal

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2014/174072 A1 [0006]

Claims (13)

Electric motor-driven unit (1) for a vehicle, with at least one electric drive unit (2) comprising at least one drive shaft (3) with an axis of rotation (D), the drive shaft (3) having a press fit in a fastening bore (4) of at least one hub (5) engages and is thereby positively connected to the hub (5), characterized in that the drive shaft (3) has a knurl (6) in the connection area with the hub (5) and the hub (5) in the fastening bore (4) at least have an axially aligned groove (7). Unit (1) after Claim 1 characterized in that the hub (5) is designed as an eccentric. Unit (1) according to at least one of the preceding claims, characterized in that a groove base (8) of the groove (7) is provided at a distance in the radial direction from a lateral surface (9) of the fastening bore (4) such that between the groove base (8) and the knurl (6) has a clearance fit. Unit (1) according to at least one of the preceding claims, characterized in that at least two axial grooves (7, 7 ') spaced from one another in the circumferential direction are arranged in the fastening bore (4) of the hub (5). Unit (1) according to at least one of the preceding claims, characterized in that the grooves (7, 7 ') are designed to be mirror-symmetrical with respect to a plane of symmetry (S) of the hub. Unit (1) according to at least one of the Claims 1 to 4th characterized in that the grooves (7, 7 ') are axially symmetrical and offset in a circumferential direction with respect to a plane of symmetry (S) of the hub. Unit (1) according to at least one of the Claims 4 or 5 characterized in that at least three axial grooves (7, 7 ', 7 ") formed at a distance from one another in the circumferential direction are arranged in the fastening bore (4) of the hub (5). Unit (1) according to at least one of the Claims 4 to 7th characterized in that the cumulative distances between the grooves (7, 7 ') in the circumferential direction are greater than or equal to the cumulative widths of the grooves (7, 7'). Unit (1) according to at least one of the preceding claims, characterized in that the unit (1) comprises at least two hubs (5, 5 ') which are arranged on the knurl (6). Unit (1) after Claim 9 characterized in that the second hub (5 ') relative to the first hub (5) about an orthogonal (O) running through the axis of rotation (D) of a plane of symmetry (S) of the hubs (5) running through the axis of rotation (D) by 180 ° is arranged rotated on the drive shaft (3). Unit (1) according to at least one of the Claims 9 or 10 characterized in that the hubs (5, 5 ') are of identical design. Unit (1) according to at least one of the preceding claims, characterized in that the knurl (6) is formed with grooves (10) aligned axially parallel to the axis of rotation (D) of the drive shaft (5). Unit (1) according to at least one of the preceding claims, characterized in that the unit (1) is a vacuum pump.

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