The present invention relates to a turbomachine and in particular to a turbomachine having a bearing assembly comprising a baffle. The turbomachine may be a turbocharger or power turbine. The invention further relates to a baffle element for use in the turbomachine.

Background of the invention

Turbomachines are machines that transfer energy between a rotor and a fluid. For example, a turbomachine may transfer energy from a fluid to a rotor or may transfer energy from a rotor to a fluid. Two examples of turbomachines are a power turbine, which uses the rotational energy of a rotor driven by a fluid to do useful work, for example, generating electrical power; and a compressor which uses the rotational energy of the rotor to compress a fluid.

Turbochargers are well known turbomachines for supplying air to an inlet of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing connected downstream of an engine outlet manifold. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a compressor housing. The compressor wheel delivers compressed air to an engine inlet manifold.

The turbocharger shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a central bearing housing connected between the turbine and compressor wheel housings.

Figure 1 shows a schematic cross-section through a known turbocharger. The turbocharger comprises a turbine 1 joined to a compressor 2 via a central bearing housing 3. The turbine 1 comprises a turbine wheel 4 for rotation within a turbine housing 5. Similarly, the compressor 2 comprises a compressor wheel 6 which can rotate within a compressor housing 7. The compressor housing 7 defines a compressor chamber within which the compressor wheel 6 can rotate. The turbine wheel 4 and compressor wheel 6 are mounted on opposite ends of a common turbocharger shaft 8 which extends through the central bearing housing 3.

The turbine housing 5 has at least one exhaust gas inlet volute 9 (in Fig. 1 two volutes are shown) located annularly around the turbine wheel 4, and an axial exhaust gas outlet 10. The compressor housing 7 has an axial air intake passage 11 and a volute 12 arranged annularly around the compressor chamber. The volute 12 is in gas flow communication with a compressor outlet 13.

The bearing housing 3 defines a chamber. The turbocharger shaft 8 is rotatably supported within the chamber by a bearing assembly which comprises two journal bearings 14 and 15 housed towards the turbine end and compressor end respectively of the bearing housing 3. The bearing assembly further includes a thrust bearing 16 which interacts with an oil seal assembly including an oil slinger 17. Oil is supplied to the bearing assembly from the oil system of the internal combustion engine via oil inlet 18 and is fed to the bearings 14, 15, 16 by oil passageways 19. The oil fed to the bearings 14, 15, 16 may be used to both lubricate the bearings and to remove heat from the bearings. As the shaft 8 rotates, the slinger 17 rotates with it, and directs oil outwards (that is, in a direction which has a radially-outward component), towards a drain 20.

In use, the turbine wheel 4 is rotated by the passage of exhaust gas from the exhaust gas inlet 9 to the exhaust gas outlet 10. Exhaust gas is provided to exhaust gas inlet 9 from an exhaust manifold (also referred to as an outlet manifold) of the engine (not shown) to which the turbocharger is attached. The turbine wheel 4 in turn rotates the compressor wheel 6 which thereby draws intake air through the compressor inlet 11 and delivers boost air to an inlet manifold of the engine via the volute 12 and then the outlet 13.

The compressor wheel 6 creates a low pressure region at its radially inward portion, and this has an undesirable tendency to draw oil from the bearing housing 3. Leakage of oil into the compressor is a key cause of failure. To impede the movement of oil in the axial direction towards the compressor 3, a baffle (or“oil baffle”) 21 is provided in the chamber of the bearing housing, at a position at which it receives oil thrown by the slinger 17. The baffle 21 has a frusto-conical formation which is co-axial with the rotation axis. The baffle 21 includes a substantially frusto-conical“front” surface facing generally towards the turbine 1 , and, as shown in Fig. 1 , further includes a frusto-conical rear surface facing towards the compressor 2. Although the slinger 17 directs some oil directly to the drain 20, the slinger 17 directs other oil against the front surface of the baffle, and the front surface of the baffle 21 guides this oil to the drain 20.

Summary of the invention

The invention aims to provide a new and useful baffle element for a turbomachine, a bearing assembly comprising the baffle element, and a turbomachine such as a turbocharger including the bearing assembly. The inventors have discovered that in a known turbocharger such as the one described above, there is a tendency for a body of oil, rotating in the same sense as the shaft, to form and persist on the front surface of the baffle (that is, the one facing in the axial direction towards the turbine). This body of oil blocks the desired flow of oil back to the drain, and may cause oil leakage through a central aperture of the baffle towards the compressor.

In general terms, the present invention proposes that the baffle element is formed with at least one guidance surface which, in a circumferential direction about the rotation axis, converges towards the rotation axis. Oil moving on the baffle element in the circumferential direction encounters the guidance surface(s), and the guidance surface(s) guide the oil towards the rotation axis. There the oil again encounters the slinger, which directs it back outwards, and some of the oil is directed towards the drain. Thus, the guidance surfaces reduce the build-up of oil on the baffle element, and so reduce the risk of oil leaking into the compressor.

One specific expression of the invention is a baffle element for use in a baffle assembly of a turbo-machine, the baffle element including:

a central opening which in use is positioned on a rotational axis of the turbo-machine; a skirt portion encircling the central opening, and

one or more guidance surfaces formed on the skirt portion, each guidance surface having a corresponding normal direction out from the skirt portion of the baffle element which has a radially-inward component (in other words, the guidance surface(s) face towards the central opening), and each guidance surface converging towards the central opening in a first circumferential direction (e.g. it“spirals” towards the central opening).

Thus, if oil moves on the baffle element in the first circumferential direction, and encounters the guidance surface(s), the guidance surface(s) urge the oil in a radially inward direction.

In an embodiment of the invention, the skirt portion of the baffle element includes a front surface which, when the baffle element is in use with the central opening encircling the axis of the turbo-machine, faces towards the turbine wheel. The skirt portion of the baffle element further includes a rear surface, opposite to the front surface, which, when the baffle element is in use, faces away from the turbine. The front surface is preferably rotationally symmetric about a central position of the central opening, and its normal direction out from the skirt portion of the baffle element has a radially-inward component. In an embodiment, the front surface of the skirt portion may be frusto-conical. Similarly the rear surface is preferably rotationally symmetric about the central position of the central opening, and its normal direction out from the skirt portion of the baffle element has a radially-outward component.

A radially-innermost portion of the baffle element may be a first annular portion encircling the axis. On at least one axial side, the first annular portion may be substantially planar with a normal direction parallel to the axis.

A radially-outermost portion of the baffle element may be a second annular portion encircling the axis, and including a second substantially planar surface with a normal direction parallel to the axis.

The intersection between one of the guidance surface(s) and any axial plane is preferably concave. That is, at positions on the guidance surface successively further in the first circumferential direction, the normal direction to the guidance surface out from the skirt portion of the baffle element has a successively greater component in a second circumferential direction, opposite to the first circumferential direction.

The guidance(s) surfaces may be formed at a radially-intermediate position on the skirt portion of the baffle element, such as substantially half way between the radially-innermost and -outermost surfaces.

For example, consider a circular line on the skirt portion of the baffle element which is centred on the axis and which is intermediate between the radially-innermost portion of the baffle element and the radially-outermost portion. Denoting the radial distance from the inner circumference of the baffle element to the circle by y, and defining the value B as the ratio of the radial distance y to the radius r of the central opening of the baffle element, the circle preferably intersects the guidance surfaces for at least one value of B which is greater than zero and less than 0.3, and preferably less than 0.2.

Each guidance surface may be located on a corresponding one of the front or rear surfaces of the skirt portion, i.e. protruding from and interrupting the front or rear surface. Thus, in one embodiment, at least one guidance surface is on the front surface of the skirt portion. In another embodiment, at least one guidance surface is on the rear surface of the skirt portion. In a third embodiment, at least one guidance surface is on the front surface of the skirt portion, and at least one guidance surface is on the rear surface of the skirt portion. One or more of the guidance surface(s) may be formed on one or more respective ramps upstanding from the front and/or rear surface of the skirt portion, the ramp(s) being elongate in a direction which is generally parallel to the first circumferential direction. The ramp(s) may extend from the front/rear surface of the skirt portion by an increasing distance at correspondingly increasing distances in the first circumferential direction. Thus, any oil which moves over the axially-facing surface (referred to here as the“taper surface”) of the ramp(s) in the first circumferential direction is directed axially towards the turbine. In other words, whereas the guidance surface(s) give rotating oil a radially-inward push, the taper surface(s) of the ramp(s) give the rotating oil an axial push.

In an embodiment, the normal direction to the guidance surface out from the skirt portion of the baffle element may have an axial component. If the guidance surface is located on the front surface of the skirt portion, this component may be in the“front” axial direction, i.e. the axial direction which, in use, is towards the turbine.

In an embodiment, the ramps include an opening, such as at an end of the ramp which is furthermost in the first circumferential direction. The openings permit any oil on a surface of the baffle opposite the front surface to pass through towards the front surface of the baffle, especially if the oil is moving about the axis in the first circumferential direction.

In the case that one or more (or all) of the guidance surfaces are formed on the rear surface of the skirt, the ramps would have the function of redirecting oil moving on the rear surface of the skirt. That is, they would have the effect of “scraping” oil from the rear surface of the skirt. Optionally in this case also apertures may be provided to allow oil to move from the rear surface of the baffle to the front.

Preferably, on at least one of the front and rear surfaces of the skirt element, there are plurality of said guidance surfaces (e.g. at least three or at least four), angularly spaced apart about the central opening, such as by equal angles. For example, a plurality of first guidance surfaces may be provided on the front surface of the skirt element, and a plurality of second guidance surfaces may be provided on the rear surface of the skirt element.

In further aspects, the invention provides a bearing assembly and a turbo-machine including a baffle element according to the first aspect of the invention. The baffle element may have any one or more of the features of the baffle element described above. Specifically, a second expression of the invention is a bearing assembly for a turbo-machine, the bearing assembly having:

a housing;

a plurality of bearing elements mounted on the housing, the bearing elements being adapted for supporting a shaft having a longitudinal axis, and permitting the shaft to rotate about the axis;

an oil delivery mechanism for supplying oil to the bearing elements;

a baffle element mounted on the housing, the baffle having:

(i) a central opening, centred on the axis;

(ii) a skirt portion encircling the central opening, and

(iii) at least one guidance surface formed on the skirt portion, the at least one guidance surface having a normal direction out from the skirt portion of the baffle element which has a radially-inward component, and the at least one guidance surface converging towards the central opening in a first circumferential direction,

whereby, if oil moves on the baffle element in the first circumferential direction and encounters the guidance surface, the guidance surface urges the oil in a radially inward direction.

A third specific expression of the invention is a turbo-machine, the turbo-machine having: a housing;

a shaft having a longitudinal axis;

a plurality of bearing elements mounted on the housing, the bearing elements supporting the shaft, and permitting the shaft to rotate about the axis;

an oil delivery mechanism for supplying oil to the bearing elements;

a slinger element fast with the shaft, for directing oil away from the axis;

a baffle element mounted on the housing, the baffle having:

(i) a central opening centred on the axis;

(ii) a skirt portion encircling the central opening, and

(iii) at least one guidance surface formed on the skirt portion, the at least one guidance surface having a normal direction out from the skirt portion of the baffle element which has a radially-inward component, and the at least one guidance surface converging towards the central opening in a first circumferential direction,

whereby, if oil moves on the baffle element in the first circumferential direction and encounters the guidance surface, the guidance surface urges the oil in a radially inward direction. In this document a surface of a first object is said to“face towards” a second object if the normal direction out of the surface has a positive component in the separation direction from a centre of the first object to a centre of the second object, and“face away” from the second object is the normal direction out of the surface has a negative component in the separation direction. The term“face” does not imply that the normal to the surface is parallel to the separation direction.

Brief description of the drawings

A non-limiting embodiment of the invention will now be described, for the sake of example only, with reference to the following figures, in which:

Fig. 1 is a cross-sectional drawing of a known turbocharger;

Fig. 2 is a front perspective view of one form of baffle element which can be used in the turbocharger of Fig. 1 ;

Fig. 3 is composed of Fig. 3(a) which is a first front perspective view of a baffle element which is a first embodiment of the invention, and Figs. 3(b) and 3(c) which are enlarged portions of Fig. 3(a);

Fig. 4 is a differently-annotated form of Fig. 3(a);

Fig. 5 is a second front perspective view of the baffle element of Fig. 3;

Fig. 6 is a third front perspective view of the baffle element of Fig. 3;

Fig. 7 is a rear perspective view of the baffle element of Fig. 3;

Fig. 8 is a further front perspective view of the baffle element of Fig. 3;

Fig. 9 is a further rear perspective view of the baffle element of Fig. 3;

Fig. 10 is a first front perspective view of the baffle element which is a second embodiment of the invention;

Fig. 11 is a second front perspective view of the baffle element of Fig. 10; and Fig. 12 is a rear perspective view of the baffle element of Fig. 10.

Detailed description of the embodiments

Fig. 2 shows one possible form 30 which the baffle element 21 of the turbocharger 1 of Fig. 1 may take. That is, it may be positioned within a chamber within a bearing housing, at a position at which it receives oil thrown by a slinger, as shown in Fig. 1. The“front” of the baffle element is shown, that is the surface of the baffle element 30 which is visible when looking in the axial direction from the right of Fig. 1 to the left. In other words, this is the surface which faces towards the turbine wheel 4, and faces away from the compressor 2. The baffle element 30 includes a radially-inner annular portion 31 which is substantially planar. The radially-inner annular portion 31 defines a central circular aperture 35. When the baffle element 30 is in use in a turbocharger, the centre of the circular aperture 35 lies on the rotational axis of the turbine 1 and compressor 2, and the plane of the annular portion 31 is perpendicular to the rotational axis of the turbine 1 and compressor 2.

Around the radially-inner annular portion 31 is a skirt portion 32 which is circularly symmetric about the rotational axis. The skirt portion is“laminar” (i.e. sheet-like) but not flat. The“front” surface 34 of the skirt portion 32 faces towards the turbine, and gradually diverges from the rotational axis in the axial direction. That is, the front surface 34 extends both radially and axially, with its radially outer portion further towards the turbine wheel 4 than the radially inner portion of the front surface 34. The intersection between the front surface 34 and any axial plane is a circular line, centred on the rotational axis. Any line on the surface 34 perpendicular to the circumferential direction is inclined both to the radial and the axial directions. Optionally, the surface 34 may be frusto-conical, i.e. any line on the surface 34 perpendicular to the circumferential direction is straight, but alternatively any line on the surface 34 perpendicular to the circumferential direction may be curved.

Around the skirt portion 32 is an annular radially-outer portion 33, which is generally laminar and planar, with its plane perpendicular to the axial direction. The radially-outer portion 33 is formed with apertures 36, 37 for mounting the baffle element 30 to the bearing housing 3, using elements (not shown) which pass through the apertures 36, 37 into corresponding cavities (not shown) in the bearing housing 3. The elements substantially fill the apertures 36, 37 so that oil cannot pass through them from one side of the baffle element 30 to the other.

Four grooves 38 are formed in the radially-outer portion 33 for engaging portions of the bearing housing 3. The grooves 38 are elongate in the circumferential direction, and are used for clamping the thrust bearing in place and stopping the thrust bearing working loose.

A gutter portion 39 of the baffle element is provided, on a side of the skirt portion 32 which in use is below the axis, for directing oil which is collected on the front surface 34 of the skirt portion 32 into the drain 20. The baffle element 30 may be produced by stamping a flat metal plate. The arrow 55 shows a possible rotation direction of the turbine wheel 4 and compressor wheel 6, but in fact the baffle element is mirror symmetric in a plane including the axis and the dashed line 56, and for this reason the baffle element 30 would be equally effective if the rotation direction were opposite. In use, for example within a turbocharger as shown in Fig. 1 , some of the oil directed outwardly by the slinger 17 goes straight to the drain 20. Other oil however, falls onto the front surface 34 of the skirt portion 32. This oil has angular momentum in the direction 55. The present inventors have discovered that a stable body of oil can form on a radially-inward portion of the front surface 34, rotating in the rotation direction 55. As this body of oil becomes thicker, the baffle element 30 becomes less effective at preventing oil from moving axially towards the compressor 2, and oil begins to leak into the compressor chamber, for example through the circular aperture 35.

Referring now to Fig. 3(a) a baffle element 130 which is an embodiment of the invention is shown in front perspective view. Figures 4, 5 and 6 are other perspective views of the front of the baffle element 130, while Fig. 7 is a rear perspective view of the baffle element 130. Like the baffle element 30, the baffle element 130 can be used as the baffle 21 of the turbocharger 1 (i.e. it may be positioned within a chamber within a bearing housing, at a position at which it receives oil thrown by a slinger, as shown in Fig. 1), and it may also be used as a baffle element in other turbo-machines. Also like the baffle element 30, the baffle element 130 may be produced by stamping a flat metal plate.

The baffle element 130 includes many portions which are equivalent to respective portions of the baffle element 30, and which are denoted by respective reference numerals 100 higher. For example, the baffle element 130 includes a planar radially-inward portion 131 , a laminar skirt portion 132 having a front surface 134, and a generally-planar radial ly-outer portion 133.

Like the baffle element 30, when the baffle element 130 is in use the front surface 134 of the skirt portion 132 faces towards the turbine wheel 4, and gradually diverges from the axis in the axial direction towards the turbine wheel 4. That is, the front surface 134 extends both radially and axially, with its radially outer portion further towards the turbine wheel 4 than the radially inner portion of the front surface 134. Any line on the front surface 134 perpendicular to the circumferential direction is inclined both to the radial and the axial directions. Optionally, the surface 134 may be frusto-conical, i.e. any line on the front surface 134 perpendicular to the circumferential direction is straight, but alternatively any line on the front surface 134 perpendicular to the circumferential direction may be curved. A rear surface 146 of the skirt portion 132 is shown in Fig. 7. The front face 134 of the skirt portion 132 has a general form similar to the front surface 34 of the skirt portion 32. However, in contrast to the baffle element 30 of Fig. 2, the baffle element 130 includes six ramps 140a, 140b, 140c, 140d, 140e, 140f upstanding from the front surface 34. The ramps 140a, 140b, 140c, 140d, 140e, 140f are identical in shape to each other, and are angularly spaced about the axis with a pairwise angular spacing of about 25%. Figs. 3(b) and 3(c) are enlarged views of two portions of Fig. 3(a), showing the ramps 140a and 140c in more detail.

Each ramp 140a, 140b, 140c, 140d, 140e, 140f has three major surfaces. Firstly, there is an approximately axially-facing surface 141a, 141c, referred to as a“taper surface”. Secondly, there is a radially-inwardly facing guidance surface 142a, 142b, 142c, 142d, 142e, 142f. Finally, there is a circumferentially-facing end surface 143c The ramps 140a, 140b, 140c, 140d, 140e, 140f are curved (rounded) at the corner which is furthermost from the front face 134 of the skirt portion 132, where the three major surfaces meet. In other words, due to the rounding, the corner of each ramp 140a, 140b, 140c, 140d, 140e, 140f is a rounded surface (shown as region 144c in Fig.3(c)), rather than a point at which the three major surfaces meet.

Because of the ramps 140a, 140b, 140c, 140d, 140e, 140f, the baffle element 130 has no plane of mirror symmetry, and is only for use in a turbocharger (or other turbo-machine) in which the rotation direction is a first circumferential direction marked 155 in Fig. 3(a).

Each of the guidance surfaces 142a, 142b, 142c, 142d, 142e, 142f gradually converges towards the rotational axis in the first circumferential direction. That is, the guidance surface 142a, 142b, 142c, 142d, 142e, 142f is successively closer to the axis in successive positions in the first circumferential direction.

Fig. 3(b) denotes by ni and n ₂ the normal directions to two points on the guidance surface 142a. Note that these normal directions ni and n ₂ are defined in the direction out from the skirt portion 32 of the baffle element 30 (i.e. not the opposite direction, into the guidance surface). Both ni and P2 have a component in the axial direction, towards the turbine 4. Furthermore, both ni and n ₂ have a component in a second circumferential direction which is opposite to the first circumferential direction. n ₂ is the normal to the guidance surface 142a at a point further in the first circumferential direction 155 than the point where ni is the normal to the guidance surface 142a, and n ₂ has a greater component in the second circumferential direction than ni. Note that the ramps 140a, 140b, 140c, 140d, 140e, 140f are at a radially intermediate position on the front surface 134, between the radially inner portion 131 and the radially outer portion 133. Referring to Fig. 4, for any axial position on the front surface 134, there is a corresponding circle 150. The circle 150 touches the front surface 134 in some angular ranges about the axis. It also intersects with the ramps 140a, 140b, 140c, 140d, 140e, 140f. Denoting the radial distance from the inner circumference of the baffle element to the circle 150 by y, and defining the value B as the ratio of the radial distance y to the radius r of the aperture 135, the circle 150 preferably intersects the guidance surfaces 142a, 142b, 142c, 142d, 142e, 142f for at least one value of B which is greater than zero and less than 0.3, and preferably less than 0.2.

In use, for example within a turbocharger as shown in Fig. 1 , some of the oil thrown outwardly by the slinger 17 goes directly to the drain 20. Other oil however, falls onto the front surface 134 of the skirt portion 132. This oil has angular momentum in the first circumferential direction 155. As the oil moves circumferentially, it encounters one of the guidance surfaces 142a, 142b, 142c, 142d, 142e, 142f. Due to the fact that, in the first circumferential direction 155, the guidance surfaces 142a, 142b, 142c, 142d, 142e, 142f converge towards the axis, the oil is guided radially inwards, towards the radially-inward portion 131. There the oil is transferred back to the slinger 17, which again directs it radially outward. The oil then has another chance of reaching the drain 20.

Figs. 8 and 9 are respectively views of the front and rear surfaces of the baffle element 130 of Fig. 3, in the form of line drawings.

Turning now to Figs. 10-12, a baffle element 230 which is a second embodiment of the invention is shown. Like the baffle element 30, the baffle element 230 can be used as the baffle 21 of the turbocharger of Fig. 1 , and it may also be used as a baffle element in other turbo-machines. Also like the baffle element 30, the baffle element 230 may be produced by stamping a flat metal plate. Elements of the baffle element 230 which are identical to corresponding elements of the baffle element 130 are given reference numerals 100 higher. The only difference between the baffle element 230 and the baffle element 130 is that the six end surfaces 143c of the ramps 140a, 140b, 140c, 140d, 140e, 140f are replaced in the baffle element 230 by six apertures 245a, 245b, 245c, 245d, 245e, 245f. The apertures 245a, 245b, 245c, 245d, 245e, 245f tend to guide oil moving on the rear surface 246 in the circumferential direction 255 to move from the rear surface 246 to the front surface 234 of the skirt portion 232. The mechanical action is rather similar to the way in which when cheese is moved on the front surface of a cheese-grater against a cutting surface of the cheese-grater, the cheese passes through an aperture defined by the cheese-grater, to a rear surface of the cheese-grater. Since the apertures 245a, 245b, 245c, 245d, 245e, 245f tend to guide oil from the rear surface 246 to the front surface 234 of the baffle element 230, the oil is less likely to leak to the compressor 2.

Although only two embodiments of the baffle element have been described, many variations are possible within the scope of the invention as will be clear to a skilled reader.

For example, in the embodiments described, the guidance surfaces are formed on ramps upstanding from the front surface of the skirt element. Each ramp corresponds to a depression on the rear surface of the baffle. However, in variations of the embodiment one or more of the guidance surfaces may formed on the rear surface of the skirt element, such as on ramps upstanding from the rear surface of the skirt element which correspond to depressions on the front surface of the baffle.