Patent ID: 12259002

DETAILED DESCRIPTION

In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted.

An example thrust air bearing supports a rotating shaft, the thrust air bearing including a plurality of foil units arranged in a circle. Each foil unit includes a top foil portion, and a bump foil portion integrally provided with the top foil portion and disposed opposite the top foil portion in a circumferential direction forming the circle. The foil unit is disposed such that the top foil portion lies on top of the bump foil portion of another adjacent foil unit.

In some examples, the thrust air bearing includes a plurality of foil units, and the top foil portion and the bump foil portion of each foil unit are integrally provided. That is, by attaching one foil unit, the top foil portion and the bump foil portion can be attached without misalignment. Additionally, disposing the foil units by arranging them in predetermined positions completes the installation of all of the top foil portions and the bump foil portions. As a result, the attachment of the bump foil portions and the top foil portions is facilitated compared to a case in which the bump foils and the top foils are individually attached.

In some examples, the thrust air bearing may further include an annular base plate to which the plurality of foil units is fixed, and a foil fixing portion fixing each foil unit to the base plate. Each foil unit may include a fix receiving portion provided between the top foil portion and the bump foil portion, and attached to the base plate by the foil fixing portion.

In some examples, the foil units may be removably attached to the base plate. When there is a defect in the foil unit, the defective foil unit can be removed from the base plate and can be easily changed to a new foil unit.

In some examples, the base plate may be provided with a positioning groove in which the fix receiving portion fits, and the positioning groove may be provided so as to extend in a radial direction of the annular base plate. The fix receiving portion may include an engaging projection portion engaging with the positioning groove, and a receiving recess portion with which the foil fixing portion engages on a side opposite the engaging projection portion. The foil units may be arranged in the circumferential direction. The foil units are positioned by the fix receiving portions fitted in the positioning grooves, and the positioning grooves are provided so as to extend in the radial direction of the annular base plate. As a result, positional misalignment of the foils units in a direction intersecting the radial direction, for example, positional misalignment in the circumferential direction can be suppressed.

In some examples, the base plate may include an outer circumferential edge and an inner circumferential edge opposite the outer circumferential edge in the radial direction. The positioning groove may be tapered such that a width in a circumferential direction of the base plate increases from an inner end portion close to the inner circumferential edge to an outer end portion close to the outer circumferential edge. The engaging projection portion may be tapered to engage with the positioning groove and may be pressure bonded to the positioning groove by the foil fixing portion. The fix receiving portion includes the engaging projection portion that engages with the positioning groove which is tapered in the radial direction, and the engaging projection portion is tapered to engage with the positioning groove. Thus, when the engaging projection portion is pressure bonded to the positioning groove by the foil fixing portion, the position of the engaging projection portion is corrected by the synergistic effect of the tapered shape of the engaging projection portion and the tapered shape of the positioning groove to enable positional misalignment in the radial direction to be suppressed.

In some examples, the positioning groove may include a bottom portion, and a pair of side portions rising from the bottom portion and facing each other in the circumferential direction. The pair of side portions may include a pair of inclined surfaces inclined such that a width in the circumferential direction gradually increases away from the bottom portion. The engaging projection portion may be inclined so as to engage with the pair of inclined surfaces, and may be pressure bonded to the inclined surfaces by the foil fixing portion. The inclined surfaces of the positioning groove are respectively formed on the side portions facing each other in the circumferential direction, and the engaging projection portion is inclined so as to engage with the pair of inclined surfaces. Thus, when the engaging projection portion is pressure bonded to the positioning groove by the foil fixing portion, the position of the engaging projection portion is corrected by the synergistic effect of the inclination of the engaging projection portion and the inclination of the inclined surfaces of the positioning groove to enable positional misalignment in the circumferential direction to be suppressed.

In some examples, the positioning groove may include a bottom portion, and there may be a gap extending in the radial direction between the bottom portion and the engaging projection portion. A cooling passage through which air can pass can be formed by the gap, so that a heat removal function can be performed.

In some examples, the positioning groove may be provided with a bulged portion spaced from the engaging projection portion in the circumferential direction and forming a gap region. Forming the gap region enables the engaging projection portion to be pulled out easily when the engaging projection portion is pulled out.

In some examples, the base plate may include an outer circumferential edge and an inner circumferential edge opposite the outer circumferential edge in the radial direction. The positioning groove may include an insertion opening open at the outer circumferential edge, and the engaging projection portion may be insertable from the insertion opening. The foil unit may be disposed such that the top foil portion lies on top of the bump foil portion of another foil unit. The aspect above facilitates the assembly of the thrust air bearing since the engaging projection portion of the foil unit can be attached by inserting the engaging projection portion into the insertion opening from a lateral side which does not interfere with other foil units.

FIG.1illustrates an example of a rotating machine1, which is, for example, an electric turbocharger. The rotating machine1includes a turbine2and a compressor3, and includes an electric motor5that drives a rotating shaft6between the turbine2and the compressor3. The turbine2includes a turbine impeller22disposed inside a turbine housing21. The compressor3includes a compressor impeller32disposed inside a compressor housing31. A motor housing4to which a stator51of the electric motor5is fixed is installed between the turbine housing21and the compressor housing31.

The turbine impeller22is fixed to the rotating shaft6of the compressor impeller32. The rotation of the turbine impeller22is transmitted to the compressor impeller32via the rotating shaft6to drive the compressor impeller32cooperatively with the electric motor5. A rotor52that assists the rotation of the rotating shaft6cooperatively with the stator51is fixed to the rotating shaft6. The rotating shaft6is rotatably supported by a plurality of bearings, at least one of which is an example thrust air bearing7. The structure for supporting the rotating shaft6by the thrust air bearing7will be described.

The rotating shaft6includes a thrust collar61that is provided so as to project in a radial direction. In the present disclosure, the thrust collar61is disposed between the rotor52and the compressor impeller32. The thrust collar61is disposed so as to be sandwiched between a pair of the thrust air bearings7. Each thrust air bearing7includes a bearing surface7afacing the thrust collar61, and a back surface7bopposite the bearing surface7a(seeFIG.7A).

The thrust air bearings7are arranged side by side in a direction of an axis L (e.g., axial direction) of the rotating shaft6. A spacer81for forming a space to accommodate the thrust collar61is disposed between the pair of thrust air bearings7. The pair of thrust air bearings7is fastened together by a plurality of fastening bolts82so as to clamp the spacer81. The plurality of fastening bolts82are installed equidistant from each other in a circumferential direction CD of the thrust air bearings7. Each thrust air bearing7rotatably supports the rotating shaft6. The pair of thrust air bearings7also forms a shaft support structure70to cooperatively suppress misalignment of the thrust collar61in the direction of the axis L.

In the description below, for example, the thrust air bearing7closer to the rotor52may be referred to as a first thrust air bearing7, and the thrust air bearing7closer to the compressor impeller32may be referred to as a second thrust air bearing7. The back surface7bof the first thrust air bearing7is supported by a member forming the motor housing4, and is positioned in a predetermined position (seeFIG.7A). The back surface7bof the second thrust air bearing7is supported by a portion of a member forming a portion of the compressor housing31, and is positioned in a predetermined position. For examples in which the first thrust air bearing7and the second thrust air bearing7may be of essentially identical structure, the first thrust air bearing7will be representatively described.

As illustrated inFIGS.2,3, and6, the thrust air bearing7includes an annular base plate71that serves as a base, a plurality of foil units9attached to the base plate71, and foil fixing portions10that fix the foil units9to the base plate71. The surface on which the plurality of foil units9is installed relative to the base plate71is the bearing surface7athat faces the thrust collar61, and the side opposite is the back surface7b.

The base plate71is located around the rotating shaft6. The base plate71(seeFIG.5) is annular (donut-shaped) and includes a substantially circular center hole CH through which the rotating shaft6is inserted. A radial direction RD of the base plate71may refer to both a centrifugal direction and a direction opposite the centrifugal direction with the axis L of the rotating shaft6as the center, assuming that the rotating shaft6is inserted through the center hole CH. For example, the radial direction RD refers to a direction perpendicular to the axis L, and additionally the circumferential direction CD of the base plate71refers to a direction in which the rotating shaft6rotates. For those examples in which the base plate71has a substantially circular external shape, the circumferential direction CD of the base plate71may be described as a direction along the substantially circular external shape of the base plate71.

The base plate71includes an outer circumferential edge71a(e.g., outer circumferential surface) that forms the substantially circular external shape, and an inner circumferential edge71b(e.g., inner circumferential surface) that is opposite the outer circumferential edge71ain the radial direction RD and forms the center hole CH. The inner circumferential edge71bis located around the shaft6. A plurality of foil units9faces the base plate71in the axial direction of the shaft6. A plurality of foil units9is annularly located around the inner circumferential edge71b. The base plate71can be perceived as being divided in two regions in the radial direction RD and, for example, includes an annular outer region71xwhich includes the outer circumferential edge71a, and an annular inner region71ywhich includes the inner circumferential edge71b. A step may be formed between the outer region71xand the inner region71y. In the present disclosure, a step descending from the outer region71xto the inner region71yis formed on the bearing surface7a. A plurality of through holes71cinto which the fastening bolts82(seeFIG.1) are inserted is formed in the outer region71xof the base plate71. The foil units9are arranged along the circumferential direction CD in the inner region71yof the base plate71.

The inner region71yof the base plate71is provided with a plurality of positioning grooves72for positioning the foil units9and a plurality of through holes73. The through holes73are formed from the back surface7bof the base plate71so as to exit bottom portions72aof the positioning grooves72. A countersunk screw19(fastening portion) that fixes the foil unit9passes through each through hole73(seeFIG.3). A countersink71din which a head portion19aof the countersunk screw19fits is formed on the back surface7bside of the through hole73. The countersunk screw19is inserted from the back surface7btoward the through hole73.

The foil unit9(seeFIGS.4B and6) is flexible and leaf-shaped (plate-shaped). For example, the foil unit9has an arc-shape. The inner region71yof the base plate71is annular (donut-shaped) in a plan view. The foil unit9is shaped so as to evenly divide the inner region71yin the circumferential direction CD in a plan view. In the description below, the circumferential direction CD of the foil unit9substantially refers to the same direction as the circumferential direction CD of the base plate71, assuming that the foil unit9is installed in the base plate71. The foil unit9includes a top foil portion91on one side in the circumferential direction CD, and a bump foil portion92on a side opposite the top foil portion91. Additionally, a fix receiving portion93is provided between the top foil portion91and the bump foil portion92. The fix receiving portion93integrally connects the top foil portion91to the bump foil portion92.

The fix receiving portion93includes an engaging projection portion94(e.g., projection portion) that is bent so as to protrude from the top foil portion91and the bump foil portion92. The engaging projection portion94has dimensions and shape such that it can fit in the positioning groove72of the base plate71. The foil unit9is positioned in a predetermined position of the base plate71by fitting the engaging projection portion94in the positioning groove72. The fix receiving portion93has a receiving recess portion95(e.g., recess portion), with which the foil fixing portion10engages, on a back side of the engaging projection portion94, that is, on an opposite side of the engaging projection portion94. A connecting hole93athrough which a shaft portion19bof the countersunk screw19is inserted is formed in a bottom plate portion93bwhich is the bottom of the receiving recess portion95.

The foil fixing portion10(seeFIGS.4A and6) has dimensions and shape such that it can fit in the receiving recess portion95, and substantially engages with the receiving recess portion95. A screw hole11into which the shaft portion19bof the countersunk screw19is screwed is formed in the foil fixing portion10. The foil fixing portion10is pressure bonded to the receiving recess portion95by screwing the countersunk screw19into the foil fixing portion10to fasten the countersunk screw19, so that the fix receiving portion93is clamped between the foil fixing portion10and the positioning groove72.

As illustrated inFIG.2, the foil units9are uniformly arranged in the circumferential direction CD in the inner region71yof the base plate71, and are disposed so as to cover all or a portion of the annular inner region71yas a whole. The top foil portion91of one of the foil units9is disposed so as to lie on top of the bump foil portion92of another adjacent foil unit9. For example, six (a plurality of) foil units9are annularly arranged so as to be located around the rotating shaft6. For example, the top foil portion91of a first foil unit9A lies on top of the bump foil portion92of a second foil unit9B located adjacent to the first foil unit9A. The top foil portion91of the first foil unit9A faces the bump foil portion92of the second foil unit9B in the axial direction of the shaft6.

As illustrated inFIGS.3and6, the bump foil portion92has an undulating plate shape in a cross-sectional view, and is disposed so as to follow the surface of the inner region71yof the base plate71. The top foil portion91has a flat plate shape. The top foil portion91is disposed on the bump foil portion92in the axial direction of the rotating shaft6. The top foil portion91is inclined such that a leading end portion91bis spaced further away from the bump foil portion92than a root portion91aconnected to the fix receiving portion93. The position of the bump foil portion92in the circumferential direction CD is on a front side in a direction of rotation of the rotating shaft6on the basis of one foil unit9installed in the base plate71. Conversely, the position of the top foil portion91in the circumferential direction CD is on a rear side in the direction of rotation.

The shapes and engaging relationships of the positioning groove72of the base plate71, the fix receiving portion93of the foil unit9, and the foil fixing portion10will next be described further in detail with reference toFIGS.3to6.

The base plate71is provided with the same number of the positioning grooves72as the number of the foil units9to be installed. The positioning grooves72are provided so as to extend in the radial direction RD (centrifugal direction) of the annular base plate71. The positioning grooves72are disposed equidistant from each other in the circumferential direction CD. Each positioning groove72includes an inner end portion72cclose to the inner circumferential edge71bof the base plate71, and an outer end portion72dopposite the inner end portion72cin the radial direction RD and close to the outer circumferential edge71aof the base plate71. The inner end portion72cof the present disclosure reaches the inner circumferential edge71bof the base plate71and is open. The outer end portion72dof the present disclosure reaches the boundary between the inner region71yand the outer region71xof the base plate71. In a plan view, the positioning groove72has a width greater at the outer end portion72dthan at the inner end portion72c, and is tapered with the width in the circumferential direction CD increasing from the inner end portion72ctoward the outer end portion72d.

The positioning groove72includes the bottom portion72aand a pair of side portions72brising from the bottom portion72a. The bottom portion72acommunicates with the through hole73into which the shaft portion19bof the countersunk screw19is inserted. The pair of side portions72b(seeFIG.5) is provided so as to face each other in the circumferential direction CD of the base plate71, and extends in the radial direction RD to be connected to the inner end portion72cand the outer end portion72d.

The side portion72bof the present disclosure (seeFIG.3) includes a vertical wall surface72erising substantially vertically from the bottom portion72a, and an inclined surface72fbent from the vertical wall surface72eand rising at an angle from the vertical wall surface72e. The inclined surface72fis connected to a surface of the inner region71ysupporting the bump foil portion92. A pair of the inclined surfaces72fis disposed so as to face each other, and is inclined such that the distance therebetween gradually increases away from the bottom portion72a. For example, the pair of the inclined surfaces72fis inclined such that a width in the circumferential direction CD of the base plate71gradually increases away from the bottom portion72a.

The fix receiving portion93(e.g., connecting portion) of the foil unit9is located between the top foil portion91and the bump foil portion92. The fix receiving portion93is integrally connects the top foil portion91and the bump foil portion92. The fix receiving portion93is bent from the top foil portion91and the bump foil portion92, and formed so as to be substantially trapezoidal in a cross-sectional view. For example, the fix receiving portion93includes the bottom plate portion93band a pair of side plate portions93c. The bottom plate portion93bfaces the bottom portion72aof the positioning groove72. The pair of side plate portions93cis bent from the bottom plate portion93band is each respectively connected to the top foil portion91and the bump foil portion92. The pair of side plate portions93cis tapered in a plan view so as to engage with the positioning groove72(seeFIG.6). When the fix receiving portion93is engaged with the positioning groove72, the outer surface portion that contacts the positioning groove72is the engaging projection portion94, and the opposite inner surface portion is the receiving recess portion95.

The bottom plate portion93bhas a shape conforming to the tapered shape of the positioning groove72in a plan view, and for example, is a substantially isosceles triangle having a short side portion and two long side portions of equal length. The vertical angle portion of the bottom plate portion93bis disposed so as to follow along the inner end portion72cof the positioning groove72, and the short side portion is disposed so as to follow along the outer end portion72dof the positioning groove72. The side plate portions93care vertically arranged from the two long side portions of the bottom plate portion93b, and are inclined such that the distance therebetween gradually increases away from the bottom plate portion93b. The angle of inclination of the side plate portions93cis substantially the same as the angle of inclination of the inclined surfaces72fof the positioning groove72. As a result, the outer sides of the side plate portions93c, that is, portions of the engaging projection portion94are inclined so as to engage with the inclined surfaces72fof the positioning groove72. It should be noted that the bottom plate portion93bof the present disclosure is spaced from wall surfaces of the positioning groove72.

The foil fixing portion10engages with the receiving recess portion95of the fix receiving portion93. The foil fixing portion10has, for example, a substantially isosceles trapezoidal shape in a plan view, and includes an inner end surface portion10athat is installed so as to follow along the inner end portion72cof the positioning groove72, an outer end surface portion10bthat is installed so as to follow along the outer end portion72d, and a pair of side surface portions10cof equal length. The pair of side surface portions10cis tapered in a plan view conforming to the pair of side plate portions93cof the fix receiving portion93, and is installed so as to abut the pair of side plate portions93c.

The foil fixing portion10has, for example, a substantially isosceles trapezoidal shape in a cross-sectional view (seeFIG.3). The foil fixing portion10(seeFIG.6) includes a lower surface portion10dthat faces the bottom plate portion93bof the fix receiving portion93, an upper surface portion10eopposite the lower surface portion10d, and the pair of side surface portions10c. The pair of side surface portions10cis inclined such that a width therebetween gradually increases away from the lower surface portion10d. The angle of inclination of the side surface portions10cis substantially the same as the angle of inclination of the side plate portions93c. As a result, the side surface portions10care inclined so as to engage with the side plate portions93c.

As illustrated inFIG.3, when the engaging projection portion94is engaged with the positioning groove72, a gap S is formed between the bottom portion72aof the positioning groove72and the engaging projection portion94. That is, the positioning groove72and the engaging projection portion94are formed in dimensions so as to allow for the gap S to be formed. As a result, when the engaging projection portion94is pressed by the foil fixing portion10, small misalignments are corrected, so that the engaging projection portion94can be pressure bonded to the side portion72b, for example the inclined surface72f, of the positioning groove72.

The gap S extends in the radial direction RD from the inner circumferential edge71bto the outer circumferential edge71aof the base plate71. A cooling passage through which air can pass can be formed by the gap S, and as a result, a heat removal function can be performed.

As illustrated inFIGS.2and6, the outer end portion72dof the positioning groove72is provided with a bulged portion72g. The bulged portion72gis a groove that communicates with the positioning groove72. The bulged portion72gis provided so as to be spaced from the engaging projection portion94in the circumferential direction CD, and forms a gap region AR which does not contact the engaging projection portion94. The engaging projection portion94can be easily pulled out by inserting a tool or the like into the gap region AR when it is pulled out the engaging projection portion94. Additionally, a cooling passage through which air can pass is formed by allowing the gap region AR to communicate with the gap S formed in the bottom portion72aof the positioning groove72, so that a heat removal function can be performed. In the present disclosure, the bulged portion72gcommunicates with the gap S.

An example of a method for assembling the foil unit9to the base plate71will be described with reference toFIG.6. The foil units9are located so as to face the base plate71in the axial direction of the rotating shaft6. The foil units9are annularly arranged on the inner region71yof the base plate71so as to be located around the rotating shaft6. The foil units9are temporarily placed by inserting the fix receiving portions93into the positioning grooves72, so that the orientation and the positions in the circumferential direction CD and the radial direction RD of the foil units9can be easily adjusted.

The foil fixing portion10is then press fit into the receiving recess portion95of the foil unit9, and at the same time, the countersunk screw19is inserted from the back surface7bof the base plate71to be screwed together with the foil fixing portion10. The foil fixing portion10engages with the receiving recess portion95of the foil unit9so as to expand the receiving recess portion95due to the tightening of the countersunk screw19. As a result, the engaging projection portion94, which is the back side of the receiving recess portion95, is pressure bonded to the inclined surfaces72fof the positioning groove72and may be engaged therewith.

When the fastening of all the foil units9by the countersunk screws19and the foil fixing portions10is completed, the assembly of the foil units9to the base plate71is completed. The pair of thrust air bearings7for which the assembly of the foil units9is completed is installed in the rotating machine1so as to sandwich the thrust collar61. Here, the head portions19aof the countersunk screws19are disposed on the back surfaces7bof the pair of thrust air bearings7. The head portions19aof the countersunk screws19that are present on the back surface7bof the first thrust air bearing7are disposed so as to be held down by the motor housing4(seeFIGS.3and7A). The head portions19aof the countersunk screws19that are present on the back surface7bof the second thrust air bearing7are disposed so as to be held down by the compressor housing31. As a result, loosening of the countersunk screws19that causes misalignment of the foil units9from the base plate71can be suppressed, and the bearing function of the thrust air bearings7can be stably maintained.

The action of the thrust air bearings7rotatably supporting the rotating shaft6will next be described with reference toFIG.7. As illustrated inFIG.7A, the pair of thrust air bearings7is disposed so as to sandwich the thrust collar61fixed to the rotating shaft6, and forms the shaft support structure70. In a resting state, that is, when not rotating, the leading end portion91bof the top foil portion91of the foil unit9is in contact with the thrust collar61.

As illustrated inFIG.7B, when rotation starts along with the rotation of the rotating shaft6, air pressure is applied to the root portion91aof the top foil portion91, thereby producing a wedge effect. The leading end portion91bof the top foil portion91is held spaced from the thrust collar61due to the wedge effect. When the rotating shaft6tries to shift in the direction of the axis L (thrust direction), the thrust collar61approaches the top foil portions91on one side. As a result, the top foil portions91are buffered by the undulating bump foil portions92, so that the shifting of the rotating shaft6in the thrust direction is suppressed.

The action and effect of the thrust air bearings7above will be described. The thrust air bearing7includes the foil units9with the top foil portion91and the bump foil portion92of each foil unit9being integrally provided. That is, by attaching one foil unit9, the top foil portion91and the bump foil portion92can be attached without misalignment. The attachment of the bump foil portions92and the top foil portions91is thus facilitated compared to a case in which the bump foils and the top foils are individually attached. Additionally, disposing the foil units9by arranging them in predetermined positions completes the installation of all of the top foil portions91and the bump foil portions92.

Furthermore, the foil units9of the thrust air bearing7are removable from the base plate71. As a result, when there is a defect in the foil unit9, the defective foil unit9can be removed from the base plate71, and can be easily changed to a new foil unit9. For example, in a resting state, the top foil portions91are in contact with the bump foil portions92, and are separated when the rotating shaft6rotates. That is, the top foil portions91are repeatedly brought into contact with and separated from the bump foil portions92, so that the plating and the like on the surface may be removed. In such thrust air bearing7, the defective foil units9alone can be changed during maintenance, which is very efficient.

The positioning grooves72of the thrust air bearing7are provided extending in the radial direction RD of the annular base plate71. The fix receiving portion93includes the engaging projection portion94that engages with the positioning groove72. The foil units9are positioned by the fix receiving portions93that are fitted in the positioning grooves72, and the positioning grooves72are provided extending in the radial direction RD. As a result, positional misalignment in a direction intersecting the radial direction RD, for example, the circumferential direction CD can be suppressed.

The fix receiving portion93of the foil unit9includes the engaging projection portion94that engages with the positioning groove72tapered in the radial direction RD. The engaging projection portion94is tapered to engage with the positioning groove72. Thus, when the engaging projection portion94is pressure bonded to the positioning groove72by the foil fixing portion10, the position of the engaging projection portion94is corrected by the synergistic effect of the tapered shape of the engaging projection portion94and the tapered shape of the positioning groove72to thereby enable positional misalignment in the radial direction RD to be suppressed.

The inclined surfaces72fof the positioning groove72are respectively formed on the side portions72bfacing each other in the circumferential direction CD. The engaging projection portion94is inclined so as to engage with the pair of inclined surfaces72f. Thus, when the engaging projection portion94is pressure bonded to the positioning groove72by the foil fixing portion10, the position of the engaging projection portion94is corrected by the synergistic effect of the inclination of the engaging projection portion94and the inclination of the inclined surfaces72fof the positioning groove72to thereby enable positional misalignment in the circumferential direction CD to be suppressed.

There is the gap S, which extends in the radial direction RD, between the bottom portion72aof the positioning groove72and the engaging projection portion94. A cooling passage through which air can pass can be formed by the gap S, so that a heat removal function can be performed.

The outer end portion72dof the positioning groove72is provided with the bulged portion72gthat forms the gap region AR, so that the engaging projection portion94can be easily pulled out using the gap region AR when it is pulled out the engaging projection portion94.

Another example thrust air bearing has a base plate71A with a positioning groove72A illustrated inFIG.8. The thrust air bearing shares the same structure and elements with the thrust air bearing7described above, and shares the same action and effect produced by the same structure and elements except for the base plate71A. Thus, with reference toFIG.8, the base plate71A will be mainly described, focusing on the differences, with the same reference signs used for the same structure and elements, and detailed description thereof being omitted.

The base plate71A includes the outer circumferential edge71aand the inner circumferential edge71bopposite the outer circumferential edge71ain the radial direction RD. The outer end portion72dof the positioning groove72A reaches the outer circumferential edge71aof the base plate71A and is open to form an insertion opening72j. The engaging projection portion94of the foil unit9can be inserted from the insertion opening72j.

The engaging projection portion94of the foil unit9can be attached by inserting the engaging projection portion94into the insertion opening72jfrom a lateral side which does not interfere with other foil units9, so that the assembly of the thrust air bearing7is facilitated.

It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail. For example, although the above examples have been described as a thrust air bearing installed in an electrically-assisted turbocharger as an example of a rotating machine, some examples can be widely applied to thrust air bearings that rotatably support a rotating shaft.