Balancing shaft and method for producing same

Abstract

The invention relates to a balancing shaft and to a method for producing same. The balancing shaft comprises: - an unbalanced shaft (1) comprising an end-side drive journal (2), end-face centering bores (16, 17) and a bearing journal (3, 4), the periphery of which is merely partially cylindrical, - and a bearing ring (12) which encloses the bearing journal, and an inner radius RL of which rests against the cylindrical partial periphery (8) of the bearing journal, the inner radius RL of the bearing ring being greater than the minimum-circumscribed-circle radius rz of the bearing journal. The minimum circumscribed circle (C) of the bearing journal is concentric with the centering bores, the drive journal being eccentric with respect to the centering bores by the difference between radii RL - rz, and being concentric with the bearing ring.

Description

[0001] Balance shaft and method for its manufacture

[0002] The invention relates to a balance shaft and a method for its production. The balance shaft comprises:

[0003] - an unbalanced shaft with an end drive pin, front-side centering holes and a bearing pin whose circumference is only partially cylindrical,

[0004] - and a bearing ring surrounding the bearing journal, which bears against the cylindrical partial circumference of the bearing journal with an inner radius R, wherein the inner radius R of the bearing ring is larger than the enveloping circle radius rz of the bearing journal.

[0005] Balance shafts are used to balance inertial forces and / or moments in reciprocating piston internal combustion engines. For example, the mass balance of a four-cylinder in-line engine is achieved by two balance shafts that rotate in opposite directions at twice the crankshaft speed.

[0006] A balance shaft of this type with an unbalanced shaft and a bearing ring mounted on it is known from DE 10 2019 101 320 A1. Another balance shaft of the type mentioned above is currently in series production in BMW reciprocating piston internal combustion engines. The different radii of the inner ring and the bearing journal are implemented in these series parts.

[0007] From DE 198 07 180 A1 a balance shaft with an end drive pin is known which is eccentric to the axis of rotation of the balance shaft.

[0008] The present invention is based on the object of considerably simplifying the manufacture of a balance shaft of the type mentioned above.

[0009] The solution to this problem is provided by the features of claim 1. Accordingly, the enveloping circle of the bearing journal should be concentric with the centering holes, with the drive journal being eccentric to the centering holes by the radius difference R - rz and concentric with the bearing ring. As explained below, this geometric design significantly simplifies the machining of the unbalanced shaft into the finished part. In current series production, the drive journal of the finished unbalanced shaft is concentric with its centering holes.Since the operational axis of rotation of the balance shaft is concentric with the drive journal and the bearing ring, and – to avoid deformation of the bearing ring due to component tolerances – the inner radius R of the bearing ring adjacent to the bearing journal is larger than the enveloping circle radius rz of the bearing journal, the radius difference R - rz must be compensated by eccentric machining of the bearing journal relative to the centering holes. This eccentricity cannot, of course, be created by a simple turning process between centers in the centering holes. Instead, a complex milling process or a complex eccentric turning process is required, with correspondingly high investment and / or manufacturing costs.The present invention eliminates this disadvantage by aligning the drive pin with the centering holes, allowing machining of the bearing seat through the comparatively simple and cost-effective turning of the unbalanced shaft between centers in the centering holes. The eccentricity of the drive pin with respect to the centering holes can also be achieved relatively easily by turning or milling the drive pin using a bell-shaped tool.

[0010] Further features of the invention will become apparent from the following description and the drawing, which shows an exemplary embodiment of a balance shaft according to the invention for second-order mass balancing of an inline four-cylinder internal combustion engine. The eccentricities shown therein are greatly exaggerated for the purpose of illustrating the invention. They show:

[0011] Figure 1 shows the balance shaft in perspective;

[0012] Figure 2 shows the balance shaft in longitudinal section.

[0013] The balance shaft comprises an unbalanced shaft 1, machined from a cast or forged blank, with an end drive journal 2, 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) that axially supports the balance shaft in the internal combustion engine, and a gear (also not shown) that drives the balance shaft. The bearing journals 3, 4 have only a partially cylindrical circumference, with the cylindrical partial circumference 8 in each case oriented in the direction of the shaft unbalance u (see arrow in Figure 2), which is generated by the centers of gravity of both the unbalanced sections 5, 6, 7 and the bearing journals 3, 4, which are eccentric to the operational axis of rotation 9 of the balance shaft.

[0014] The radial bearing of the unbalanced shaft 1 in the internal combustion engine is provided by needle bearings 10, whose inner raceways 11 are each formed by a bearing ring 12 surrounding the bearing journal 3, 4. Each bearing ring 12, together with a bearing journal back 13 radially opposite the cylindrical partial circumference 8, defines a free space in which a sheet metal spring 14 is tensioned against the bearing journal back 13 on the one hand and the bearing ring 12 on the other, and tensions the bearing ring 12 radially against the cylindrical partial circumference 8. The axial fastening of the bearing rings 12 on the unbalanced shaft 1 is also provided by the sheet metal springs 14, which are each axially connected in a form-fitting manner to the bearing journal back 13 on the one hand and the bearing ring 12 on the other.

[0015] The bearing rings 12 each bear against the cylindrical partial circumference 8 of the bearing journals 3, 4 with an inner radius R. Deformation of the precisely cylindrical inner raceway 11 of each bearing ring 12 is prevented due to unavoidable component tolerances by the inner radius R of the bearing ring 12 being larger than the enveloping circle radius rz of the respective bearing journal 3, 4.

[0016] Figure 2 illustrates the geometric relationships on the dimensioned bearing journal 4, where the enveloping circle C lying on the cylindrical partial circumference 8 is also shown rotated by 90°. The enveloping circle C is concentric with a machining axis 15, which in turn is concentric with centering holes 16 and 17 machined into the end faces of the unbalanced shaft 1. The machining of each cylindrical partial circumference 8 is carried out by a simple turning process, namely by mounting the unbalanced shaft 1 on centers in the centering holes 16, 17, so that the origin of the enveloping circle radius rz lies on the machining axis 15.

[0017] The operational rotational axis 9 of the balance shaft is concentric with the bearing rings 12 and the drive pin 2 and eccentric to the machining axis 15 by the radius difference R - rz. The final machining of the drive pin 2 is performed using a bell-shaped tool, which moves eccentrically to the centering holes 16, 17 by the radius difference R - rz.

[0018] The eccentricities shown in the figures are in the millimeter range for the purpose of illustrating the invention and are therefore greatly exaggerated. In reality, the radius difference R - rz is, for example, only 35 micrometers.

Claims

Patent claims balance shaft, comprising: - an unbalanced shaft (1) with an end drive pin (2), front-side centering holes (16, 17) and a bearing pin (3, 4) whose circumference is only partially cylindrical, - and a bearing ring (12) which surrounds the bearing journal (3, 4) and which bears with an inner radius R against the cylindrical partial circumference (8) of the bearing journal (3, 4), the inner radius R of the bearing ring (12) being greater than the enveloping circle radius rz of the bearing journal (3, 4), characterized in that the enveloping circle (C) of the bearing journal (3, 4) is concentric with the centering bores (16, 17), the drive journal (2) being eccentric to the centering bores (16, 17) by the radius difference R - rz and concentric with the bearing ring (12). Balance shaft according to claim 1, characterized in that the bearing ring (12) together with a bearing journal back (13) radially opposite the cylindrical partial circumference (8) delimits a free space, wherein the balance shaft comprises a sheet metal spring (14) which is tensioned in the free space against the bearing journal back (13) on the one hand and the bearing ring (12) on the other hand and tensions the bearing ring (12) radially against the cylindrical partial circumference (8).Method for producing a balance shaft according to one of the preceding claims, characterized in that the drive pin (2) is machined by means of a bell tool.

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