Shaft bearing and electromechanical camshaft adjuster

Abstract

A shaft bearing (1), in particular in an electromechanical camshaft adjuster (10), comprises a four-point bearing (3) and a shaft (2), and rolling bodies (4) of the four-point bearing (3) roll in a groove (5), which has an ogival shape (25), of the shaft (2), and a contour (11) of a compensating coupling (13) is formed by the shaft (2).

Description

[0001] Shaft bearing and electromechanical camshaft adjuster

[0002] The invention relates to a shaft bearing in which rolling elements, in particular balls, roll directly on a shaft. Furthermore, the invention relates to an electromechanical camshaft adjuster with a shaft bearing designed as a rolling bearing, in particular a ball bearing.

[0003] DE 6925932 U discloses a radial ball bearing intended for supporting the shaft of a water pump. The radial ball bearing comprises two separate rows of balls, with the rolling elements (i.e., balls) rolling directly on the shaft in inner raceways. Each row of rolling elements of the radial ball bearing according to DE 6925932 U is assigned a separate outer ring. The two outer rings are connected by a thin-walled sleeve, the ends of which are radially flanged inward.

[0004] Another water pump bearing for motor vehicles is disclosed in DE 6800972 U. This bearing also features a double-row rolling bearing, with the rolling elements rolling directly on a shaft. Unlike the device according to DE 6925932 U, in DE 6800972 U, an outer ring, which provides raceways for the balls, is made of sheet metal. The outer ring of the water pump bearing according to DE 6800972 U also has annular grooves into which sealing washers are inserted.

[0005] DE 76 14 054 U relates to an electric external rotor motor in which a bell-shaped external rotor, which spans an inner stator and has a rotor shaft, is mounted via rolling bearings in a bore of the inner stator. The external rotor motor comprises a double-row radial ball bearing having a common outer ring. The associated inner raceways are machined directly into the rotor shaft. A spindle element for a ball screw drive described in DE 10 2014 224 957 B3 comprises a spindle which is mounted by means of a rolling bearing, namely a ball bearing, wherein the inner ring of the rolling bearing is formed integrally with the spindle. This eliminates the need for a separate inner ring of the rolling bearing. According to DE 10 2014 224 957 B3, forming and machining processes are considered for producing the wave-like recess in which the balls roll.

[0006] Another screw drive, i.e., a device for converting a rotary motion into a translational motion or for converting a translational motion into a rotary motion, is disclosed in DE 10 2018 129 102 A1. In this case, a spindle forms several eccentric, self-contained raceways for spherical rolling elements.

[0007] The invention is based on the object of specifying a shaft bearing which is further developed compared to the prior art and which is characterized by a particularly favorable relationship between space utilization and mechanical load-bearing capacity, while at the same time providing rational manufacturing possibilities.

[0008] This object is achieved according to the invention by a shaft bearing according to claim 1. The shaft bearing is particularly suitable for use in an electromechanical camshaft adjuster according to claim 10.

[0009] The shaft bearing assembly according to the application comprises a four-point bearing and a shaft, with rolling elements of the four-point bearing rolling in a groove in the shaft that describes a Gothic profile. At the same time, the shaft—spaced from the four-point bearing—forms the contour of a compensating coupling. The invention is based on the consideration that tilting moments can act on the shaft due to the transmission of torque between a shaft and a compensating coupling. Therefore, it is appropriate to mount the shaft in such a way that it can absorb tilting loads. In general, tilting loads acting on a shaft can be absorbed better the further the areas in which moments that tend to cause the shaft to tilt about a tilting axis orthogonal to its longitudinal axis are supported are spaced from the longitudinal axis of the shaft.One conceivable approach would be, for example, to attach a flange to the shaft which is mounted in a manner that absorbs tilting loads.

[0010] The solution according to the application deliberately deviates from this approach by proposing the use of the shaft itself as the inner ring of a rolling bearing, namely a four-point contact bearing. The lever arm against which the rolling elements act in the sense of a tilting load is smaller than the radius of the shaft due to the fact that the rolling elements roll in a groove formed in the shaft. For a given tilting moment, the rolling bearing is thus subjected to higher loads than a bearing whose rolling elements describe a larger pitch circle. According to the common definition, the pitch circle is understood to be the circle passing through the centers of all rolling elements.

[0011] It has been shown that potentially adverse effects resulting from the small diameter and thus the short lever arms with respect to possible tilting loads, which are provided by the four-point bearing with an inner ring integrated into the shaft, are more than compensated for by the space savings resulting from the elimination of a separate inner ring. This also applies to designs in which there is no additional bearing between the four-point bearing and the contour of the compensating coupling, viewed in the axial direction of the shaft.

[0012] The contour of the compensating coupling provided by the shaft can, in particular, be in the form of a double-flat guide. Overall, the compensating coupling is designed, for example, as an Oldham coupling. For design options for an Oldham coupling, reference is made to DE 10 2007 049 072 A1.

[0013] With regard to the features of four-point contact bearings, reference is made to documents DE 10 2019 133 286 A1, DE 10 2011 082 810 A1, and DE 10 2006 035 180 A1 as examples. In the latter case, ball rollers are provided as rolling elements. In each case, the rolling elements, viewed in cross-section, make double contact with the respective bearing arrangement on both the outer and inner ring sides, with at least one of the bearing rings being split. A four-point contact bearing differs significantly from a deep groove ball bearing with regard to the bearing ring-rolling element contact. The total four-fold contact of the bearing rings by each rolling element, provided it absorbs forces, is achieved with the help of so-called Gothic profiles of the bearing rings.

[0014] In a design that is advantageous from a manufacturing perspective, the shaft can have a uniform diameter, except for areas where a groove or chamfer is formed. In particular, the maximum diameter of the shaft in the area of the double-flat guide can correspond to the diameter of the shaft in shaft sections that are immediately adjacent to the four-point contact bearing. The latter shaft sections are arranged, for example, between two discs connected to an outer ring of the four-point contact bearing, which discs can, in particular, serve as non-contact seals.

[0015] In addition to or alternatively to the non-contact seals, a contact seal can be present. For example, a contact seal is arranged between an output element and the contour of the compensating coupling. The term “output element” refers to a device that drives the shaft. If the shaft is driven directly by an electric motor, the output element is the rotor of the electric motor or an element rigidly connected to the rotor. If the shaft is driven by a geared motor, i.e. a combination of an electric motor and a gearbox, the output element represents an output-side element of the gearbox. In each of these cases, the shaft can be connected to the output element in a section located between the four-point bearing and the contour of the compensating coupling. For example, the output element is pressed onto the shaft.

[0016] Optionally, a groove is formed in the area of the contour of the compensating coupling, into which a retaining ring is inserted. The retaining ring prevents the coupling element, which is guided along the contour, from being pulled off the shaft.

[0017] In addition to a substantially uniform shaft diameter, diameter variations are possible to achieve assembly advantages. For example, the section of the shaft in which the contact seal, i.e., a shaft seal, is to be mounted has a larger diameter than the section of the shaft in which the double-flat guide is formed. This makes it possible to slide the shaft seal over the coupling section during assembly from the end face of the shaft facing away from the four-point bearing without force or contact.

[0018] The four-point contact bearing can be designed as a single-row or multi-row bearing, especially a double-row bearing. In the case of a multi-row four-point contact bearing, the rolling elements in the different rows of rolling elements are not necessarily the same size. A rolling bearing with differently sized rolling elements in different rows of rolling elements is known in principle, for example, from DE 10 2014 215 523 A1, which discusses various bearing designs, including angular contact ball bearings and four-point contact bearings.

[0019] The electromechanical camshaft adjuster according to claim 10 comprises an electric motor having a shaft associated with a shaft bearing configured according to claim 1. The shaft of the electric motor can be coupled via a compensating coupling, for example an Oldham coupling, to an input-side shaft of a three-shaft transmission, for example in the form of a harmonic drive, wherein the output-side shaft of the three-shaft transmission is rotationally coupled to the camshaft to be adjusted.

[0020] Several embodiments of the invention are explained in more detail below with reference to a drawing. In the drawings:

[0021] Fig. 1 shows a first embodiment of a shaft bearing with a four-point bearing and a contour of a compensating coupling,

[0022] Fig. 2 shows an embodiment of a shaft bearing modified compared to Fig. 1 and comprising a double-row four-point bearing,

[0023] Fig. 3 shows a partially sectioned view of an electromechanical camshaft adjuster including the shaft bearing according to Fig. 1,

[0024] Fig. 4 a detail A from Fig. 3,

[0025] Fig. 5 shows a shaft of the arrangement according to Fig. 3 and a retaining ring in front view,

[0026] Fig. 6 shows an alternative design of a four-point bearing for an electromechanical camshaft adjuster.

[0027] The following explanations refer to all exemplary embodiments, unless otherwise stated. Parts that correspond to one another or have essentially the same function are identified by the same reference numerals in all figures. An electromechanical camshaft adjuster, designated overall by 10, which is provided in a conventional manner for adjusting the timing of an internal combustion engine, in particular a gasoline engine in a motor vehicle, comprises a shaft bearing 1, to which a four-point bearing 3 is assigned. A shaft 2, mounted by means of the four-point bearing 3, interacts with the camshaft of the internal combustion engine to be adjusted via a gear (not shown), namely a strain wave gear. In the present case, a compensating clutch 13 designed as an Oldham clutch is connected between an electric motor 18 of the camshaft adjuster 10 and the strain wave gear.The compensating coupling 13 comprises a coupling element 12, which is radially displaceable relative to the shaft 2 using a double-flat guide 11 provided by the shaft 2. The double-flat guide 11 is generally referred to as the contour of the compensating coupling 13. The double-flat guide 11 is located at a first end of the shaft 2. The opposite end of the shaft 2 projects into the housing of the electric motor 18, which in this case is designed as an external rotor motor.

[0028] The four-point contact bearing 3 provided for supporting the shaft 2 in the electric motor 18 comprises balls as rolling elements 4, which are guided in a cage 6. The balls 4 roll directly in a groove 5 of the shaft 2. The groove 5 describes a Gothic profile 25, which ensures that the rolling element 4 does not contact the shaft 2, which functions as the inner ring, in the center plane of the bearing 3, which passes through the centers of all the balls 4, but rather at two points symmetrically adjacent to the center plane. The Gothic profile of an outer ring 7 of the four-point contact bearing 3, designated 28, is designed in a similar manner. In this case, a groove in which the balls 4 roll is designated 8.

[0029] Compared to non-stressed shaft bearings, which have a separate inner ring mounted on the shaft, the use of the shaft 2 in this case as the inner ring of a rolling bearing 3, in this case a four-point contact bearing 3, is characterized by the fact that the outer diameter of the outer ring 7 can be kept particularly small. This provides a particularly generously dimensioned installation space for the magnetic circuit of the electric drive of the camshaft adjuster 10.

[0030] 1 to 5, two disks 9 are inserted into the outer ring 7 at the end face. The disks 9 do not contact the shaft 2, whose center axis is designated MA. The essentially uniform diameter of the shaft 2 is designated Dmn. A minimum diameter of the shaft 2, designated Dv, is present in the groove 5. At the end of the shaft 2 at which the four-point bearing 3 is located, the shaft 2 tapers off in the form of a chamfer 14. Directly at the end face of the shaft 2, i.e. at the end of the chamfer 14, the shaft diameter is Df 1 , where Dv < Df 1 < Dmn applies.

[0031] In the area of the double-flat guide 11, there is a groove 15 into which a retaining ring 16 is inserted in the fully assembled camshaft adjuster 10. This retaining ring prevents the coupling element 12 from being pulled off the shaft 2. A chamfer bordering the double-flat guide 11 is designated 17. The diameter of the shaft 2, designated Ds, in the area of the groove 15 is smaller than the shaft diameter Dmn, but larger than the minimum diameter Dv of the shaft 2 in the area of the four-point bearing 3.

[0032] The embodiment shown in Fig. 2 differs from the embodiment shown in Fig. 1 in that the four-point contact bearing 3 comprises two rows of rolling elements 23, 24. In the case outlined in Fig. 2, the rolling elements 4 of each row of rolling elements 23, 24 are guided in a separate cage 6. A common outer ring 7 is assigned to both rows of rolling elements 23, 24. Regarding the design of the contour 11 of the compensating coupling 13, there are no differences between the embodiment shown in Fig. 2 and the embodiment shown in Fig. 1.

[0033] The embodiment according to Fig. 6 also does not differ from the embodiments according to Figs. 1 and 2 with regard to the contour 11 of the compensating coupling 13. However, there are differences with regard to the design of the outer ring 7. In the case of Fig. 6, this is formed by two mutually mirror-symmetrical outer ring parts 26, 27. The Gothic profile 28 is thus provided by the entirety of the outer ring parts 26, 27. With regard to the four-point contact between the rolling element 4 and the bearings 2, 7, i.e. the shaft 2 and the single-part or multi-part outer ring 7, all four-point bearings 3 of the arrangements according to Figs. 1 to 6 have the same structure.

[0034] As shown in Figures 3 and 4, the camshaft adjuster 10 comprises the four-point bearing 3 according to Fig. 1 . The four-point bearing 3 according to Fig. 2 or the four-point bearing 3 according to Fig. 6 could also be installed at the corresponding location with the same function. Adjacent to the four-point bearing 3, also within the electric motor 18, is an output element 19 which is rigidly connected to the shaft 2 and drives the shaft 2. The output element 19 is formed by the rotor of the electric motor 18 or is fixedly connected to the rotor. Axially between the output element 19 and the coupling element 12 is a seal 20 held in the housing of the electric motor 18. The seal 20 comprises a metallic core 21 and a sealing lip 22 which bears against the shaft 2. The four-point bearing 3 is the only rolling bearing of the shaft bearing 1 that supports the shaft 2 .

[0035] List of reference symbols

[0036] 1 shaft bearing

[0037] 2nd wave

[0038] 3 four-point bearings

[0039] 4 rolling elements, ball

[0040] 5 groove with gothic profile

[0041] 6 cage

[0042] 7 Outer ring

[0043] 8 Groove in the outer ring

[0044] 9 disc

[0045] 10 camshaft adjusters

[0046] 11 Double-flat guide

[0047] 12 Coupling element

[0048] 13 Compensating coupling, Oldham coupling

[0049] 14 Chamfer of the shaft on the end face adjacent to the four-point bearing

[0050] 15 Groove in the area of the double-flat guide

[0051] 16 Retaining ring

[0052] 17 Chamfer, adjacent to the double-flat guide

[0053] 18 electric motor

[0054] 19 Output element

[0055] 20 Seal

[0056] 21 core

[0057] 22 Sealing lip

[0058] 23 rolling element row

[0059] 24 rolling element rows

[0060] 25 Gothic profile, formed by the inner ring, ie the shaft

[0061] 26 Outer ring part

[0062] 27 Outer ring part

[0063] 28 Gothic profile, formed by the outer ring

[0064] Dmn Shaft diameter Df1 Diameter of the end face of shaft 2, adjacent to the chamfer 14

[0065] Ds Diameter of the groove 15 provided for receiving the retaining ring 16

[0066] Dv minimum diameter in the area of groove 5 in shaft 2

[0067] MA central axis

Claims

Patent claims 1. Shaft bearing (1), comprising a four-point bearing (3) and a shaft (2), wherein rolling elements (4) of the four-point bearing (3) roll in a groove (5) of the shaft (2) describing a Gothic profile (25), and a contour (11) of a compensating coupling (13) is formed by the shaft (2).

2. Shaft bearing (1) according to claim 1, characterized in that the contour of the compensating coupling (13) is in the form of a double-flat guide (11) formed by the shaft (2).

3. Shaft bearing (1) according to claim 2, characterized in that the maximum diameter (Dmn) of the shaft (2) in the region of the double-flat guide (11) corresponds to the diameter (Dmn) of the shaft (2) in the four-point bearing (3) immediately adjacent shaft sections.

4. Shaft bearing (1) according to claim 3, characterized in that said shaft sections are arranged between two discs (9) connected to an outer ring (7) of the four-point bearing (3).

5. Shaft bearing (1) according to one of claims 1 to 4, characterized in that the shaft (2) is connected in a section between the four-point bearing (3) and the contour (11) of the compensating coupling (13) to an output element (19) which is to be attributed to an electric motor (18).

6. Shaft bearing (1) according to claim 5, characterized by a contacting seal (20) located between the output element (19) and the contour (11) of the compensating coupling (13).

7. Shaft bearing (1) according to one of claims 1 to 6, characterized in that a groove (15) is formed in the region of the contour (11) of the compensating coupling (13), into which a retaining ring (16) is inserted.

8. Shaft bearing (1) according to one of claims 1 to 7, characterized in that the four-point bearing (3) is designed as a single-row rolling bearing.

9. Shaft bearing (1) according to one of claims 1 to 7, characterized in that the four-point bearing (3) is designed as a double-row rolling bearing.

10. Electromechanical camshaft adjuster (10), comprising an electric motor (18) which comprises an output shaft (2) which is assigned to a shaft bearing (1) designed according to claim 1.

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