Balance shaft and manufacturing method thereof

Abstract

The invention provides a balance shaft and a manufacturing method thereof. The invention relates to a balancing shaft (1), comprising an end-side drive journal (2), an end-side centring bore (16, 17) and a bearing journal (3, 4), the circumference of which is only partially cylindrical, and a bearing ring (12), which surrounds the bearing journal and rests on the cylindrical partial circumference (8) of the bearing journal with an inner radius RL, wherein the inner radius RL of the bearing ring is greater than the envelope circle radius rZ of the support journal. An envelope circle (C) of the bearing journal is concentric with the centering bore, wherein the drive journal is eccentric with a radius difference RL-rZ from the centering bore and concentric with the bearing ring.

Description

Technical Field

[0001] The present invention relates to a balancing shaft and a manufacturing method thereof. The balancing shaft comprises:

[0002] an unbalanced shaft having an end-side drive journal, an end-side centering bore and a bearing journal, the circumference of which is only partially cylindrical,

[0003] - and a bearing ring surrounding the bearing journal, said bearing ring having an inner radius R L The bearing ring is in contact with the cylindrical part of the circumference of the bearing journal, wherein the inner radius R L Greater than the radius r of the enveloping circle of the bearing journal Z .

[0004] The balancing shaft is used to balance the inertia forces and / or moments of inertia in a reciprocating piston internal combustion engine. For example, the mass balancing of a four-cylinder in-line engine is performed by two balancing shafts, which rotate in opposite directions at double the crankshaft speed. Background Art

[0005] Such a balancing shaft is known from DE 10 2019 101 320 A1, which has an unbalanced shaft and a bearing ring mounted thereon. Another balancing shaft of the type mentioned at the beginning is currently used in series in reciprocating piston internal combustion engines of BMW. Different radius dimensions of the inner ring and the bearing journal are realized at the series component.

[0006] DE 198 07 180 A1 discloses a balancing shaft which has an end-side drive journal which is eccentric with respect to the axis of rotation of the balancing shaft. Summary of the invention

[0007] The invention is based on the object of significantly simplifying the production of a balancing shaft of the type mentioned in the introduction.

[0008] The object is achieved by the features of claim 1. Therefore, the envelope circle of the bearing journal should be concentric with the centering bore, wherein the drive journal is spaced apart from the centering bore by a radius difference R L -r Z Eccentric and concentric with the bearing ring. As explained below, the geometric design significantly simplifies the machining of the unbalanced shaft into a finished component. In actual mass production, the drive journal of the finished unbalanced shaft is concentric with its centering hole. Since the axis of rotation of the balancing shaft is concentric with the drive journal and with the bearing ring, and in order to avoid deformation of the bearing ring caused by component tolerances, the inner radius R of the bearing ring that abuts against the support journal is L Greater than the radius r of the enveloping circle of the bearing journal Z , so the radius difference R L -rZ This must be compensated for by eccentric machining of the bearing journal relative to the centering bore. Of course, the eccentricity cannot be produced by a simple turning process between the tips in the centering bore. For machining, a complex milling process or a complex eccentric turning process with relatively high investment and / or manufacturing costs is required. The present invention eliminates this disadvantage by the eccentricity of the drive journal relative to the centering bore, so that the machining of the bearing seat is achieved by a relatively simple and cost-effective turning process of the unbalanced shaft between the tips of the centering bore. The eccentricity of the drive journal relative to the centering bore can also be achieved relatively simply by turning or milling the drive journal with the aid of a bell-shaped tool. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Further features of the invention are apparent from the following description and the accompanying drawings of an exemplary embodiment of a balancing shaft according to the invention for second-order mass balancing of a straight-four-cylinder internal combustion engine. For the purpose of illustrating the invention, the eccentricities shown there have greatly exaggerated dimensions. The accompanying drawings show:

[0010] Figure 1 A perspective view showing a balance shaft;

[0011] Figure 2 A longitudinal section through a balancing shaft is shown. DETAILED DESCRIPTION

[0012] The balancing shaft comprises an unbalanced shaft 1 which is machined from a cast or forged blank and has a drive journal 2 at the end, two bearing journals 3 and 4 and unbalanced sections 5, 6 and 7. The drive journal 2 accommodates a deep groove ball bearing (not shown) which axially supports the balancing shaft in the internal combustion engine and a gear (also not shown) which drives the balancing shaft. The bearing journals 3, 4 have only partially cylindrical circumferences, wherein the cylindrical partial circumferences 8 are respectively oriented in the direction of the shaft imbalance u (see Figure 2 ), which is oriented as shown by the arrows in FIG. 1 , and which is produced by a mass center of gravity of the unbalanced sections 5 , 6 , 7 and of the bearing journals 3 , 4 which is eccentric relative to the axis of rotation 9 of operation of the balancing shaft.

[0013] The unbalanced shaft 1 is radially supported in the internal combustion engine by means of needle bearings 10, the inner raceway 11 of which is formed by a bearing ring 12 surrounding the bearing journals 3, 4. Each bearing ring 12, together with a bearing journal back 13 radially opposite the cylindrical partial circumference 8, delimits a free space in which a leaf spring 14 is tensioned against the bearing journal back 13 on the one hand and against the bearing ring 12 on the other hand, and tensions the bearing ring 12 radially against the cylindrical partial circumference 8. The axial fastening of the bearing ring 12 on the unbalanced shaft 1 is also carried out by means of leaf springs 14, which are each axially connected in a form-fitting manner to the bearing journal back 13 on the one hand and to the bearing ring 12 on the other hand.

[0014] The bearing ring 12 has an inner radius R L The bearing ring 12 is in contact with the cylindrical part circumference 8 of the bearing journal 3, 4. Taking into account the unavoidable component tolerances, the inner radius R L Greater than the radius r of the envelope circle of the corresponding bearing journal 3, 4 Z To prevent deformation of the precisely cylindrical inner raceway 11 of each bearing ring 12 .

[0015] Figure 2 The diagram shows the geometrical relationship at the bearing journal 4 to scale, where the enveloping circle C is also drawn in a manner twisted by 90° at the cylindrical partial circumference 8. The enveloping circle C is concentric with the machining axis 15, which in turn is concentric with the centering holes 16 and 17 machined in the end face of the unbalanced shaft 1. The machining of each cylindrical partial circumference 8 is carried out by a simple turning process, i.e., with the unbalanced shaft 1 accommodated at the tip in the centering holes 16, 17, so that the enveloping circle radius r Z The origin is located on the machining axis 15.

[0016] The axis of rotation 9 of the balancing shaft is concentric with the bearing ring 12 and the drive journal 2 and is spaced apart from the machining axis 15 by a radius difference R L -r Z The drive journal 2 is finished by cutting with the aid of a bell-shaped tool, which is cut with a radius difference R L -r Z Displaced eccentrically relative to the centering holes 16 , 17 .

[0017] For the purpose of illustrating the invention, the eccentricities shown in the drawings are in the millimeter range and the dimensions are greatly exaggerated. L -r Z For example, only 35 microns.

Claims

1. A balancing shaft, comprising: an unbalanced shaft (1) having an end-side drive journal (2), end-side centering holes (16, 17) and bearing journals (3, 4), the circumference of which is only partially cylindrical, - a bearing ring (12) surrounding the bearing journal (3, 4), the bearing ring having an inner radius R L The bearing ring (12) bears against a cylindrical partial circumference (8) of the bearing journal (3, 4), wherein the inner radius R L Greater than the radius r of the envelope circle of the bearing journal (3, 4) Z , The invention is characterized in that the envelope circle (C) of the bearing journal (3, 4) is concentric with the centering hole (16, 17), wherein the drive journal (2) is spaced apart from the centering hole (16, 17) by a radius difference R L -r Z Eccentric and concentric with the bearing ring (12).

2. The balancing shaft according to claim 1, characterized in that: The bearing ring (12) delimits a free space together with a bearing journal back (13) which is arranged coaxially opposite the cylindrical partial circumference (8), wherein the balancing shaft comprises a leaf spring (14) which, in the free space, bears against the bearing journal back (13) on the one hand and against the bearing ring (12) on the other hand and tensions the bearing ring (12) radially against the cylindrical partial circumference (8).

3. A method for producing a balancing shaft according to any one of the preceding claims, characterized in that The drive journal (2) is machined by cutting using a bell-shaped tool.

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