Exhaust gas turbocharger

Abstract

The invention relates to an exhaust gas turbocharger with a manifold-flow casing, in particular a dual-flow casing (47) and a turbine wheel (34) which is rotatably arranged within said manifold-flow casing, onto which an exhaust gas flow (14; 16) may be led via at least one of several flow channels (18, 26), and an outlet opening (78; 80) following said one flow channel (18, 26) and covering an angle of 180° max. about an axis of rotation (44) of the turbine wheel (34), so that a shaft (38) is rotating which is arranged coaxially and non-rotationally relative to the turbine wheel (34), which is supported in a shaft bearing (42).

Claims

1. An exhaust gas turbocharger with a manifold dual-flow casing (47) and a turbine wheel (34) which is rotatably arranged within said manifold dual-flow casing (47), onto which an exhaust gas flow (14; 16) is led via at least two flow channels (18, 26), and at least two outlet openings (78, 80) respectively following each of said at least two flow channels (18, 26) and each of said at least two outlet openings (78, 80) covering an angle of 180° maximum about an axis of rotation (44) of the turbine wheel (34), so that a shaft (38) having a circular cross-section is rotatably arranged coaxially and non-rotationally relative to the turbine wheel (34), the shaft (38) is supported in a shaft bearing (42), characterized in that the shaft bearing (42) has an inner circumferential surface having a non-circular shape extending in surrounding coaxial relationship with the shaft (38), the non-circular inner circumferential surface has a cross-sectional curvature which varies in a circumferential direction, the shaft bearing (42) is a multi-surface radial plain bearing with the non-circular inner circumferential surface comprising a number of discrete adjoining bearing surfaces (70, 72, 74, 76) which number is either equal to the number of the flow channels (18, 26) or an integer multiple of the number of the flow channels (18, 26), wherein the discrete adjoining bearing surfaces (70, 72, 74, 76) are oriented relative to the least two outlet openings (78, 80).

2. The exhaust gas turbocharger according to claim 1, characterized in that the discrete adjoining bearing surfaces (70, 72, 74, 76) are formed consistent with respect to the shape and a distance to a shaft bearing center axis (46).

3. The exhaust gas turbocharger according to claim 1, characterized in that the discrete adjoining bearing surfaces (70, 72, 74, 76) of the multi-surface radial plain shaft bearing (42) are further defined in their circumferential position about a shaft bearing center axis (46) relative to a bearing housing (28) which is non-rotationally connected or integral with the manifold-flow casing, wherein at least one of the discrete adjoining bearing surfaces (70, 72, 74, 76) is arranged such that a radial force, which acts on the shaft (38) due to a one-sided application of the exhaust gas flow, is supported at the least one of the discrete adjoining bearing surfaces (70, 72, 74, 76) in a direction in which the multi-surface radial plain shaft bearing (42) exhibits a maximum bearing stiffness.

4. The exhaust gas turbocharger according to claim 3, characterized in that the at least two outlet openings (78, 80) of the at least two flow channels (18, 26) each cover an angle (82) which is less than 180° and that the non-circular inner circumferential surface of the multi-surface radial plain shaft bearing (42) has four discrete adjoining bearing surfaces (70, 72, 74, 76), the cross-sectional curvature of the non-circular inner circumferential surface of the multi-surface radial plain shaft bearing (42) having a first of two largest inner diameters lying along a first plane (93) passing through the shaft bearing center axis (46) and having a second of two largest inner diameters lying along a second plane (94) passing through the shaft bearing center axis (46), the first plane (93) and the second plane (94) intersect at an interface (92) between the two outlet openings (78, 80) under an angle of intersection of about 45° with the shaft bearing center axis (46).

5. The exhaust gas turbocharger according to claim 1, characterized in that the multi-surface radial plain shaft bearing (42) comprises a bearing sleeve (53) which is non-rotationally defined relative to the bearing housing (28).

6. The exhaust gas turbocharger according to claim 1, characterized in that the multi-surface radial plain shaft bearing (42) further comprises several lubricant pockets (62, 64, 66, 68), each of the lubricant pockets (62, 64, 66, 68) formed proximate a juncture of each pair of discrete adjoining bearing surfaces (70, 72, 74, 76), each of the lubricant pockets (62, 64, 66, 68) extend in parallel relationship to the shaft bearing center axis (46) and each of the lubricant pockets (62, 64, 66, 68) leads into a respective radial recess (58; 59; 60; 61) which is in permanent alignment with a respective lubricant supply duct (54; 55; 56; 57) in the bearing housing (28) when the shaft (38) is rotating.

7. The exhaust gas turbocharger according to claim 3, characterized in that the discrete adjoining bearing surfaces (70, 72, 74, 76) of the multi-surface radial plain shaft bearing (42) are directly integrated into the bearing housing (28).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments as well as from the drawings. The above mentioned features and feature combinations in the description of the figures as well as the following features and feature combinations in the description of the figures and/or shown in the figures alone are not only applicable in the indicated combination but also in other combinations or alone, without deviating from the scope of the invention. In the drawings:

(2) FIG. 1 schematically illustrates a combustion reciprocating piston engine with an exhaust system which is followed by an exhaust gas turbocharger,

(3) FIG. 2 shows the exhaust gas turbocharger from FIG. 1 in a section along line II-II in FIG. 1, wherein a breakout extends in the area of a multi-surface radial plain bearing along line A-A in FIG. 1, and

(4) FIG. 3 shows the pressure profile at the multi-surface radial plain bearing according to FIG. 2, which is implemented as a four-surface radial plain bearing.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 schematically illustrates a combustion reciprocating piston engine 2 with an exhaust system 4 which is followed by an exhaust gas turbocharger 6 which is depicted only partially.

(6) The combustion reciprocating piston engine 2 is implemented as a four-cylinder in-line engine whose outer cylinders 8, 10 or combustion chambers, respectively, are combined in a first exhaust manifold 12, wherein the previously common first exhaust gas flow 14 is led into a first flow channel 18 of the exhaust gas turbocharger 6. However, the two inner cylinders 20, 22 or combustion chambers, respectively, are combined via a second exhaust manifold 24. The previously common second exhaust gas flow 16 is led into a second flow channel 26 of the exhaust gas turbocharger 6.

(7) Thus, during operation of the exhaust gas turbocharger 6, the exhaust gas flows 14, 16 are led onto a turbine wheel 34 via the two flow channels 18, 26. Thereby, a shaft 38 and a compressor wheel 40 are set in rotation as will be described below. Consequently, the compressor wheel 40 provides charging air for the combustion reciprocating piston engine 2 in a manner not shown in detail.

(8) The exhaust gas turbocharger 6 comprises a three-part casing with a bearing housing 28 which is arranged between a compressor casing 30 and a turbine casing 32 and is securely bolted with the latter. In the turbine casing 32 (only shown as a section) the turbine wheel 34 of a turbine 36 is rotatably arranged, which is non-rotationally connected via a shaft 38 with the compressor wheel 40 which is rotatably arranged in the compressor casing 30.

(9) The shaft 38 is supported in the bearing housing 28 by means of a shaft bearing 42. The shaft extends along an axis of rotation 44 which ideally coincides with a bearing center axis 46 of the shaft bearing 42, i. e. which is arranged coaxially to the bearing center axis 46. The shaft 38 is flushed with oil and ideally rotates contactless and wear-free in the shaft bearing 42.

(10) The turbine casing 32 is implemented as a dual-flow casing 47 which is a version of a manifold-flow casing. The dual-flow casing 47 comprises a first turbine inlet 48 and a second turbine inlet 50 each of which is associated with one of the two flow channels 18, 26, respectively, via which the exhaust gas flow 14, 16, respectively, is supplied to the turbine wheel 34, which is discharged from the dual-flow casing 47 via a turbine outlet 52 which is arranged coaxially to the turbine wheel 34 on a side facing away from the shaft 38.

(11) The shaft 38 is non-rotationally connected at one end with the turbine wheel 34 and non-rotationally connected at the other end with the compressor wheel 40. The shaft bearing 42 for supporting the shaft 38 comprises a bearing sleeve 53 and is accommodated non-rotationally and axially secured in the bearing housing 28 by means of a press fit.

(12) From FIG. 2 it may be seen that the shaft bearing 42 is a multi-surface radial plain bearing which is implemented as a four-surface bearing and comprises four lubricant pockets, a first lubricant pocket 62, a second lubricant pocket 64, a third lubricant pocket 66 and a fourth lubricant pocket 68 which extend in parallel to the bearing center axis 46. Radial recesses, a first recess 58, a second recess 59, a third recess 60 and a fourth recess 61 of the shaft bearing 42, each of which in alignment with an associated supply duct, a first supply duct 54, or a second supply duct 55, or a third supply duct 56, or a fourth supply duct 57, respectively, are led into these lubricant pockets 62, 64, 66, 68, which are arranged in the bearing housing 28. Thus, the radial recesses 58, 59, 60, 61 are in permanent alignment with the associated supply ducts 54, 55, 56, 57 even with the shaft 38 rotating so that it is ensured that the shaft 38 during operation of the exhaust gas turbocharger 6 is completely surrounded by a lubricant film which separates the shaft 38 from four bearing surfaces, a first bearing surface 70, a second bearing surface 72, a third bearing surface 74 and a fourth bearing surface 76 of the multi-surface radial plain bearing, which are correspondingly formed in respect of shape and distance to the bearing center axis 46.

(13) Because the four-surface bearing comprises the four bearing surfaces 70, 72, 74, 76, the number of the bearing surfaces 70, 72, 74, 76 of the multi-surface radial plain bearing is twice the number of the two flow channels 18, 26 which exhibit a spiral shape and lead the exhaust gas flows 14, 16 each via an outlet opening 78, 80 to the turbine 36.

(14) Outlet openings of the flow channels 18, 26, a first outlet opening 78 and a second outlet opening 80, respectively, surround the turbine wheel 34 each under an angle 82 about the axis of rotation 44, which is slightly smaller than 180°. Consequently, the two outlet openings 78, 80 are arranged offset relative to one another at an angle of 180° about the axis of rotation 44. The two outlet openings 78, 80 are separated from each other by means of tongues, a first tongue 84 and a second tongue 86, respectively, which may be implemented according to the turbine disclosed in DE 10 2013 021 567 A1. Thereby an interface 92 is formed at which the two outlet openings 78, 80 and the two flow channels 18, 26, respectively, are essentially separated from each other. Near the tongues 84, 86, merely a small amount of exhaust gas flows between the blades 90 from the one flow channel 18 or 26, respectively, to the other flow channel 26 or 18, respectively,

(15) As may be seen in particular from FIG. 3, the interface 92 intersects a first plane 93 and a second plane 94 which are formed at the largest inner diameters of the shaft bearing 42. Thus, the interface 92 intersects the planes 93, 94 in the bearing center axis 46 so that an angle of intersection of approx. 45° results.

(16) FIG. 3 shows the pressure profile at the four-surface radial plain bearing in its transverse plane. It is evident from the illustration that the pressure at the bearing surfaces does not have its maximum in the interface 92. Rather, the pressure has two maxima in a plane 98, which lie opposite the direction of rotation 100 of the shaft 38 and offset by an angle of intersection of appr. 15° relative to the bearing center axis 46. Furthermore, the pressure exhibits two additional maxima in another plane 102 which extends perpendicularly to the plane 98.

(17) In an alternative exhaust gas turbocharger (not shown in the drawings) which comprises three flow channels a six-surface radial plain bearing is used.