shaft bearing and electromechanical camshaft adjuster

Abstract

Shaft bearing (1), comprising a shaft (2), wherein a contour (11) of a compensating coupling (13) is formed by the shaft (2), characterized in that rolling elements (4) of a four-point bearing (3) roll in a groove (5) of the shaft (2) describing a Gothic profile (25) and 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 attributable to an electric motor (18).

Description

[0001] The invention relates to a shaft bearing in which rolling elements, in particular balls, roll directly on a shaft. The invention further relates to an electromechanical camshaft adjuster with a shaft bearing designed as a rolling bearing, in particular a ball bearing.

[0002] From DE 69 25 932 U, a radial ball bearing is known which is intended for supporting the shaft of a water pump. The radial ball bearing comprises two separate rows of balls, wherein the rolling elements, i.e., balls, roll directly on the shaft in inner raceways. Each row of rolling elements of the radial ball bearing according to DE 69 25 932 U is assigned a separate outer ring. The two outer rings are connected to each other by a thin-walled sleeve, the ends of which are radially crimped inwards.

[0003] Another water pump bearing for motor vehicles is disclosed in DE 68 00 972 U. This bearing also features a double-row rolling bearing, with the rolling elements rolling directly on a shaft. In contrast to the device according to DE 69 25 932 U, in the case of DE 68 00 972 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 68 00 972 U also has annular grooves into which sealing washers are inserted.

[0004] DE 76 14 054 U relates to an electric external rotor motor in which a bell-shaped external rotor, extending over an inner stator, is mounted with a rotor shaft via roller bearings in a bore of the inner stator. The external rotor motor includes a double-row radial ball bearing with a common outer ring. The associated inner raceways are machined directly into the rotor shaft.

[0005] A spindle element for a ball screw drive described in DE 10 2014 224 957 B3 comprises a spindle which is supported by a rolling bearing, namely a ball bearing, wherein the inner ring of the rolling bearing is integrally formed 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 suitable for producing the wave-like recess in which the balls roll.

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

[0007] DE 10 2019 110 863 A1 discloses an Oldham coupling for a compensating coupling of an electromechanical camshaft adjuster. A motor shaft with a double flat at the shaft end forms part of the Oldham coupling.

[0008] JP 2003-343575A shows a water pump with a pump shaft supported by a four-point bearing. Other shaft bearing arrangements are known from US 5,683,183A and DE 7614054U.

[0009] The invention is based on the objective of providing a shaft bearing that is further developed compared to the prior art and is characterized by a particularly favorable relationship between space utilization and mechanical load-bearing capacity, while at the same time offering rational manufacturing possibilities.

[0010] This problem is solved 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 9.

[0011] The shaft bearing arrangement according to the application comprises a four-point bearing and a shaft, wherein rolling elements of the four-point bearing roll in a groove of the shaft describing a Gothic profile. At the same time, the shaft – spaced apart from the four-point bearing – forms the contour of a compensating coupling.

[0012] The invention is based on the consideration that the transmission of torque between a shaft and a compensating coupling can cause tilting moments to act on the shaft. Therefore, it is advisable to mount the shaft in such a way that it can absorb tilting loads. Generally, tilting loads acting on a shaft can be absorbed more effectively the further the areas where moments, which tend to cause the shaft to tilt about a tilting axis orthogonal to its longitudinal axis, are supported are located 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 capable of absorbing tilting loads.

[0013] The solution proposed in the application deliberately departs from this approach by suggesting that the shaft itself be used as the inner ring of a rolling bearing, specifically a four-point contact bearing. In this design, the lever arm on which the rolling elements act in the form of a tilting load is smaller than the radius of the shaft because the rolling elements roll in a groove machined into the shaft. For a given tilting moment, this rolling bearing is thus subjected to higher loads than a bearing whose rolling elements describe a larger pitch circle. The pitch circle, according to the common definition, is the circle that passes through the centers of all the rolling elements.

[0014] It has been shown that potentially adverse effects resulting from the small diameter and thus the short lever arms with regard to possible tilting loads, due to the four-point bearing arrangement 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 embodiments in which there is no further bearing between the four-point bearing and the contour of the compensating coupling, viewed in the axial direction of the shaft.

[0015] The contour of the compensating coupling provided by the shaft can, in particular, be a double-flat guide. Overall, the compensating coupling is designed, for example, as an Oldham coupling. For design possibilities of an Oldham coupling, reference is made to DE 10 2007 049 072 A1.

[0016] Regarding the characteristics 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 used as rolling elements. In each case, the rolling elements, viewed in cross-section, make contact with the respective bearing ring at two points, both on the outer and inner ring sides, whereby at least one of the bearing rings may be split. A four-point contact bearing differs significantly from a deep groove ball bearing with respect to the bearing ring-rolling element contacts. The total of four contact points between the bearing rings and each rolling element, provided it absorbs forces, is achieved by means of so-called Gothic profiles on the bearing rings.

[0017] In a design advantageous from a manufacturing perspective, the shaft can have a uniform diameter, except in 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 immediately adjacent to the four-point bearing. These latter shaft sections are, for example, arranged between two disks connected to an outer ring of the four-point bearing, which can, in particular, function as non-contact seals.

[0018] In addition to or as an alternative to non-contact seals, a contact seal may be present. For example, a contact seal is arranged between an output element and the contour of the compensating coupling. The term "output element" here 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. In the case of a shaft driven by a geared motor, that is, a combination of an electric motor and a gearbox, the output element is an output-side element of the gearbox.

[0019] In each of these cases, the shaft is 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.

[0020] Optionally, a groove is formed in the contour of the compensating coupling, into which a retaining ring is inserted. The retaining ring prevents the coupling element, guided on the aforementioned contour, from being pulled off the shaft.

[0021] Deviating from a generally uniform shaft diameter, diameter variations are possible to achieve advantages in terms of assembly. For example, the section of the shaft in which the contacting seal, i.e., a shaft seal ring, is to be installed 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 ring over the coupling section during assembly from the end face of the shaft opposite the four-point bearing without force or contact.

[0022] The four-point contact bearing can be designed as a single-row or multi-row, in particular double-row, bearing. In the case of a multi-row design of the four-point contact bearing, the rolling elements of the different rows of rolling elements are not necessarily of 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 deals with various bearing designs, including angular contact ball bearings and four-point contact bearings.

[0023] The electromechanical camshaft adjuster according to claim 9 comprises an electric motor which includes a shaft that is attributable to a shaft bearing designed according to claim 1. The shaft of the electric motor can be coupled via a compensating clutch, for example an Oldham clutch, to an input shaft of a three-shaft transmission, for example in the form of a wave gear, wherein the output shaft of the three-shaft transmission is rotationally fixed to the camshaft to be adjusted.

[0024] Several embodiments of the invention are explained in more detail below with reference to a drawing. This drawing shows: Fig. 1 a first embodiment of a shaft bearing with a four-point bearing and a contour of a compensating coupling, Fig. 2 opposite Fig. 1 modified embodiment of a shaft bearing comprising a double-row four-point bearing, Fig. 3 in a partially cutaway view an electromechanical camshaft adjuster including the shaft bearing according to Fig. 1, Fig. 4 a detail A from Fig. 3, Fig. 5 a wave of the arrangement according to Fig. 3 and a retaining ring in front view, Fig. 6 an alternative design of a four-point bearing for an electromechanical camshaft adjuster.

[0025] Unless otherwise stated, the following explanations apply to all embodiments. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0026] An electromechanical camshaft adjuster, designated 10, which is designed in a known manner for adjusting the valve 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 supported by the four-point bearing 3 interacts with the camshaft of the internal combustion engine to be adjusted via a transmission (not shown), namely a 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 wave gear. The compensating clutch 13 comprises a clutch element 12, which is displaceable in a limited radial direction relative to the shaft 2 by means of a double-flat guide 11 provided by the shaft 2. Generally, the double-flat guide 11 is referred to as the contour of the compensating clutch 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.

[0027] The four-point bearing 3, designed to support 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 acts as an inner ring, in the central plane of the bearing 3 defined by the centers of all the balls 4, but rather at two points symmetrically located next to the central plane. The Gothic profile 28 of an outer ring 7 of the four-point bearing 3 is designed analogously. In this case, a groove in which the balls 4 roll is designated 8.

[0028] In contrast to unloaded shaft bearings, which have a separate inner ring mounted on the shaft, the use of the shaft 2 as the inner ring of a rolling bearing 3, here a four-point bearing 3, is characterized in this case 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.

[0029] In the exemplary embodiments according to the Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. Two disks 9 are inserted into the outer ring 7 at the end face of the shaft 5. The disks 9 do not contact the shaft 2, whose central 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 located in the groove 5. At the end of the shaft 2 where the four-point bearing 3 is located, the shaft 2 terminates in 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 Df1, where Dv < Df1 < Dmn.

[0030] 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, preventing the clutch element 12 from being pulled off the shaft 2. A chamfer adjacent to the double-flat guide 11 is designated 17. The diameter of the shaft 2 in the area of ​​the groove 15, designated Ds, 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.

[0031] The exemplary embodiment according to Fig. 2 differs from the embodiment shown in the following. Fig. 1 by the fact that the four-point bearing 3 comprises two rows of rolling elements 23, 24. In the in Fig. In the case sketched in Figure 2, the rolling elements 4 of each row of rolling elements 23, 24 are guided in a separate cage 6. Both rows of rolling elements 23, 24 share a common outer ring 7. Regarding the design of the contour 11 of the compensating coupling 13, there are no differences between the embodiment shown in Figure 2 and the embodiment shown in Figure 2. Fig. 2 and according to the exemplary embodiment Fig. 1.

[0032] The exemplary embodiment according to Fig. 6 does not differ, with regard to the contour 11 of the compensating coupling 13, from the embodiments according to the Fig. 1 and Fig. 2. However, differences exist regarding the design of the outer ring. 7. In the case of Fig. 6 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 bearing rings 2, 7, that is, the shaft 2 and the one- or multi-part outer ring 7, all four-point bearings 3 of the arrangements according to the Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 to Fig. 6 are structured the same way.

[0033] As in the Fig. 3 and Fig. As shown in Figure 4, the camshaft adjuster 10 includes the four-point bearing 3 according to Fig. 1. The four-point bearing 3 could also be used at the corresponding location with the same function. Fig. 2 or the four-point bearing 3 after Fig.6. 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 rigidly connected to the rotor. A seal 20, held in the housing of the electric motor 18, is located axially between the output element 19 and the coupling element 12. The seal 20 comprises a metallic core 21 and a sealing lip 22, which rests against the shaft 2. The four-point bearing 3 is the only rolling bearing of the shaft bearing 1 that supports the shaft 2. Reference symbol list 1 Shaft bearing 2nd wave 3 Four-point bearings 4 rolling elements, ball 5 grooves with Gothic profile 6 cage 7 Outer ring 8 grooves in the outer ring 9 disc 10 camshaft adjusters 11 Double-flat guide 12 Coupling element 13 Compensating clutch, Oldham clutch 14. Chamfer of the shaft at its end face adjacent to the four-point bearing 15 grooves in the area of ​​the double-flat guide 16 retaining ring 17th chamfer, adjacent to the double flat guide 18 Electric motor 19 Output element 20 Seal 21 core 22 Sealing lip 23 rolling element row 24 rolling element row 25 Gothic profile, formed by the inner ring, i.e. the shaft 26 Outer ring part 27 Outer ring part 28 Gothic profile, formed by the outer ring Dmn shaft diameter Df1 Diameter of the end face of shaft 2, adjacent to chamfer 14 The diameter of the groove 15 provided for receiving the retaining ring 16 Dv minimum diameter in the area of ​​groove 5 in shaft 2 MA Central Axis

Claims

[1] Shaft bearing (1) comprising a shaft (2) wherein the shaft (2) forms a contour (11) of a compensating coupling (13), characterized by , that rolling elements (4) of a four-point bearing (3) roll in a groove (5) of the shaft (2) describing a Gothic profile (25) and 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 attributable to an electric motor (18). [2] Shaft bearing (1) according to claim 1, characterized by , 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 by , that the maximum diameter (Dmn) of the shaft (2) in the area 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 by , that the aforementioned shaft sections are arranged between two disks (9) connected to an outer ring (7) of the four-point bearing (3). [5] Shaft bearing (1) according to any one of claims 1 to 4, characterized by a contacting seal (20) located between the output element (19) and the contour (11) of the compensating clutch (13). [6] Shaft bearing (1) according to any one of claims 1 to 5, characterized by , that in the area of ​​the contour (11) of the compensating coupling (13) a groove (15) is formed into which a retaining ring (16) is inserted. [7] Shaft bearing (1) according to any one of claims 1 to 6, characterized by , that the four-point bearing (3) is designed as a single-row rolling bearing. [8] Shaft bearing (1) according to any one of claims 1 to 6, characterized by , that the four-point bearing (3) is designed as a double-row rolling bearing. [9] Electromechanical camshaft adjuster (10) comprising an electric motor (18) which includes an output shaft (2) which is to be attributed to a shaft bearing (1) designed according to claim 1.

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