Compressor shroud unit, compressor arrangement, turbocharger, internal combustion engine, and vehicle

Abstract

A compressor shroud unit (u1 - u4) for a compressor arrangement (32, 32', 32'') of a turbocharger (30) is disclosed. The compressor shroud unit (u1 - u4) comprises a shroud surface (s1 - s4) configured to form a delimiting surface of a diffuser section (D1, D2, D3) of the compressor arrangement (32, 32', 32''). The compressor shroud unit (u1 - u4) comprises a number of protrusions and / or recesses (3) distributed across the shroud surface (s1 - s4). The present disclosure further relates to a compressor arrangement (32, 32', 32'') for a turbocharger (30), a turbocharger (30), an internal combustion engine (40), and a vehicle (2) comprising an internal combustion engine (40).

Description

[0001] Compressor Shroud Unit, Compressor Arrangement, Turbocharger, Internal Combustion Engine, and Vehicle

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a compressor shroud unit for a compressor arrangement of a turbocharger. The present disclosure further relates to a compressor arrangement for a turbocharger, a turbocharger for an internal combustion engine, an internal combustion engine, and a vehicle comprising an internal combustion engine.

[0004] BACKGROUND

[0005] Internal combustion engines are used in some vehicles to provide motive power to the vehicle. Internal combustion engines, such as four-stroke internal combustion engines, typically comprise a number of cylinders and a piston arranged in each cylinder. The piston normally comprises one or more piston rings configured to seal a space between a mantle surface of the piston and a cylinder wall of a cylinder in which the piston is arranged.

[0006] The pistons are connected to a crankshaft of the engine and are arranged to reciprocate within the cylinders upon rotation of the crankshaft. The crankshaft is arranged in a crankcase of the engine. The engine usually further comprises one or more inlet valves and outlet valves per cylinder as well as one or more fuel supply arrangements for supplying fuel to the cylinders. The one or more inlet valves and outlet valves are controlled by a respective valve control arrangement usually comprising one or more camshafts rotatably connected to a crankshaft of the engine, via a belt, chain, gears, or similar. A four-stroke internal combustion engine completes four separate strokes while turning a crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction.

[0007] Air inlet charging systems, such as turbocharger systems, are used on internal combustion engines to increase the performance and / or the fuel efficiency of the engine. A turbocharger system comprises a turbine unit and a compressor arrangement comprising a compressor wheel, wherein the turbine unit is driven by exhaust gas of the engine to power the compressor wheel of the compressor arrangement. The compressor wheel forces air to an air inlet assembly of the engine which allows more fuel to be added and hence higher power output of the engine. A turbocharger is an efficient means of supercharging an engine since it utilizes energy of the exhaust gasses of the engine to compress the inlet air of the engine.

[0008] During operation of an internal combustion engine, some gas will leak through the space between the mantle surfaces of the pistons and the cylinder walls of the cylinders into the crankcase of the internal combustion engine. Such leakage of gas is especially prone to appear in expansion strokes of the pistons but can also appear during other strokes, such as compression strokes of the pistons. Such gas is commonly referred to as blow-by gas. The blow-by gas normally comprises a mixture of air, burned and unburned gases, particles, oil droplets, and combustion residues. Gas can also leak into the crankcase of an internal combustion engine from other sources, for example from an air inlet charging system, such as a turbocharger system, valve systems, air compressor systems, and the like.

[0009] In order to avoid too high pressures in a crankcase volume of the crankcase, internal combustion engines are provided with a crankcase ventilation outlet for venting gas from the crankcase volume. Traditionally, the gas from the crankcase volume of the crankcase has been vented to the surroundings. However, environmental concerns, as well as some legislations, require a closed crankcase ventilation system which means that the gas is led to the air inlet assembly of the internal combustion engine. In this manner, the gas is returned to combustion chambers such that any particles, oil droplets, and residues in the gas can be combusted and such that the emissions formed thereof can be handled in an exhaust aftertreatment system of the internal combustion engine.

[0010] In engines equipped with a turbocharger, the gas from the crankcase is typically directed to an air inlet duct situated upstream of the compressor arrangement. This is because the pressure is usually higher downstream of the compressor arrangement, which could result in a reverse flow of gas from the internal combustion engine’s air inlet system back to the crankcase volume via the crankcase ventilation outlet.

[0011] Many internal combustion engines with a closed crankcase ventilation system comprise some type of gas cleaning assembly for cleaning the gas before the gas is led to an air inlet duct of the engine. Such types of gas cleaning assemblies can comprise one or more filter units, oil separation arrangements, and the like.

[0012] However, also small remaining amounts of oil droplets conducted to a compressor arrangement may be deposited onto surfaces of the compressor arrangement on which the oil droplets are converted into soot particles. After some operational time of the internal combustion engine, accumulated soot particles may clog a diffuser section of the compressor arrangement which reduces the operational efficiency of the compressor arrangement. A reduced operational efficiency of a compressor arrangement normally reduces the operational efficiency of an internal combustion engine comprising the compressor arrangement. In other words, a reduced efficiency of a compressor arrangement of an internal combustion engine normally increases the fuel consumption of the engine.

[0013] Internal combustion engines are vital components of vehicles which are burdensome and costly to service, maintain, and repair. Therefore, it is an advantage if components and subsystems of the internal combustion engine can operate for extended periods before requiring servicing, maintenance, and repair.

[0014] SUMMARY

[0015] It is an object of the present invention to overcome, or at least alleviate, at least some of the above-mentioned problems and drawbacks.

[0016] According to a first aspect of the invention, the object is achieved by a compressor shroud unit for a compressor arrangement of a turbocharger. The compressor shroud unit comprises a shroud surface configured to form a delimiting surface of a diffuser section of the compressor arrangement, wherein the compressor shroud unit comprises a number of protrusions and / or recesses distributed across the shroud surface.

[0017] Since the compressor shroud unit comprises the number of protrusions and / or recesses distributed across the shroud surface, a turbulent flow can be ensured in a boundary layer close to the shroud surface. In this manner, occurrences of particle deposition on the shroud surface can be reduced, such as of oil droplets from a crankcase ventilation system of an internal combustion engine comprising the compressor arrangement. This reduces the likelihood of clogging in the diffuser section of the compressor arrangement.

[0018] As a further result, a compressor shroud unit is provided having conditions for maintaining a high operational efficiency of a compressor arrangement comprising the compressor shroud unit. Moreover, a compressor shroud unit is provided having conditions for reducing the need for performing service, maintenance, and repair of a compressor arrangement comprising the compressor shroud unit.

[0019] Accordingly, a compressor shroud unit is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved. Optionally, the number of protrusions and / or recesses comprises a number of dimples.

[0020] Thereby, a turbulent flow can be ensured in the boundary layer close to the shroud surface in a simple and efficient manner.

[0021] Optionally, the number of protrusions and / or recesses comprises a number of grooves and / or ridges. Thereby, a turbulent flow can be ensured in the boundary layer close to the shroud surface in a simple and efficient manner.

[0022] Optionally, the number of protrusions and / or recesses comprises a number of grooves configured to form a stepped delimiting surface of the diffuser section of the compressor arrangement. Thereby, a turbulent flow can be ensured in the boundary layer close to the shroud surface in a simple and efficient manner.

[0023] Optionally, an average height / depth of the number of protrusions and / or recesses is less than 1 mm, or is less than 0.5 mm. Thereby, conditions are provided for ensuring a turbulent flow in the boundary layer close to the shroud surface without significantly impairing the operational efficiency of a compressor arrangement comprising the compressor shroud unit.

[0024] According to a second aspect of the invention, the object is achieved by a compressor arrangement for a turbocharger, wherein the compressor arrangement comprises a compressor shroud unit according to some embodiments of the present disclosure.

[0025] Since the compressor arrangement comprises a compressor shroud unit according to some embodiments, a compressor arrangement is provided in which a turbulent flow can be ensured in a boundary layer close to the shroud surface of the compressor arrangement. In this manner, occurrences of particle deposition on the shroud surface can be reduced, such as of oil droplets from a crankcase ventilation system of an internal combustion engine comprising the compressor arrangement. This reduces the likelihood of clogging in the diffuser section of the compressor arrangement.

[0026] As a further result, a compressor arrangement is provided having conditions for maintaining a high operational efficiency also after extended periods of operation. Moreover, a compressor arrangement is provided having conditions for reducing the need for performing service, maintenance, and repair of the compressor arrangement. Accordingly, a compressor arrangement is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above- mentioned object is achieved.

[0027] Optionally, the compressor arrangement comprises a compressor wheel and a hub unit, and wherein the hub unit comprises a hub surface forming a delimiting surface of the diffuser section of the compressor arrangement.

[0028] Optionally, the compressor wheel is configured to rotate around a rotation axis during operation of the compressor arrangement, and wherein the angle between the rotation axis and a main extension direction of the diffuser section, at a location radially outside the compressor wheel, is within the range of 60 - 120 degrees, or is within the rage of 72 - 108 degrees. Thereby, an advantageous flow characteristic through the compressor arrangement can be ensured while providing conditions for reducing occurrences of particle deposition on the shroud surface or the compressor arrangement.

[0029] Optionally, the hub unit comprises a number of protrusions and / or recesses distributed across the hub surface. Thereby, a turbulent flow can be ensured in a boundary layer close to the hub surface. In this manner, occurrences of particle deposition on the hub surface can be reduced, such as of oil droplets from a crankcase ventilation system of an internal combustion engine comprising the compressor arrangement. This also reduces the likelihood of clogging in the diffuser section of the compressor arrangement.

[0030] As a further result, a compressor shroud unit is provided having improved conditions for maintaining a high operational efficiency also after extended periods of operation. Moreover, a compressor arrangement is provided having improved conditions for reducing the need for performing service, maintenance, and repair of the compressor arrangement.

[0031] Optionally, the hub surface is a stepped surface. Thereby, a turbulent flow can be ensured in the boundary layer close to the hub surface in a simple and efficient manner.

[0032] According to a third aspect of the invention, the object is achieved by a turbocharger for an internal combustion engine, wherein the turbocharger comprises a compressor arrangement according to some embodiments of the present disclosure.

[0033] Since the turbocharger comprises a compressor arrangement according to some embodiments, a turbocharger is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

[0034] According to a fourth aspect of the invention, the object is achieved by an internal combustion engine comprising a turbocharger according to some embodiments of the present disclosure. Since the internal combustion engine comprises a turbocharger according to some embodiments, an internal combustion engine is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

[0035] Optionally, the internal combustion engine comprises an air inlet assembly configured to conduct air to the compressor arrangement and a crankcase ventilation outlet connected to the air inlet assembly. Thereby, an internal combustion engine is provided in which deposition of particles originating from the crankcase ventilation outlet on the shroud surface of the compressor arrangement can be avoided.

[0036] According to a fifth aspect of the invention, the object is achieved by a vehicle comprising an internal combustion engine according to some embodiments of the present disclosure. Since the vehicle comprises an internal combustion engine according to some embodiments of the present disclosure, a vehicle is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

[0037] Optionally, the vehicle is a heavy road vehicle, such as a truck or a bus. Thereby, a heavy road vehicle is provided having at least some of the above-mentioned advantages.

[0038] Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Various aspects of the invention, including its particular features and advantages, will be readily understood from the example embodiments discussed in the following detailed description and the accompanying drawings, in which:

[0041] Fig. 1 schematically illustrates a vehicle according to some embodiments of the present disclosure, Fig. 2 schematically illustrates an internal combustion engine of the vehicle illustrated in Fig. 1,

[0042] Fig. 3 schematically illustrates a cross section of a compressor arrangement of a turbocharger of the internal combustion engine illustrated in Fig. 2,

[0043] Fig. 4 schematically illustrates a compressor shroud unit of the compressor arrangement according to the embodiments illustrated in Fig. 3 as seen in a direction coinciding with a rotation axis of a compressor wheel of the compressor arrangement,

[0044] Fig. 5 schematically illustrates a compressor shroud unit according to some further embodiments, and

[0045] Fig. 6 schematically illustrates a cross section of a compressor arrangement according to some further embodiments.

[0046] DETAILED DESCRIPTION

[0047] Aspects of the present invention will now be described more fully. Like reference signs refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and / or clarity.

[0048] Fig. 1 schematically illustrates a vehicle 2 according to some embodiments of the present disclosure. According to the illustrated embodiments, the vehicle 2 is a truck, i.e. type of heavy road vehicle. However, according to further embodiments, the vehicle 2, as referred to herein, may be another type of manned or unmanned vehicle for land or water based propulsion such as a lorry, a bus, a construction vehicle, a tractor, a car, a ship, a boat, or the like.

[0049] The vehicle 2 comprises an internal combustion engine 40. According to the illustrated embodiments, the internal combustion engine 40 is configured to provide motive power to the vehicle 2 via wheels 41 of the vehicle 2.

[0050] Fig. 2 schematically illustrates the internal combustion engine 40 of the vehicle 2 illustrated in Fig. 1. According to the illustrated embodiments, the internal combustion engine 40 is a diesel engine, i.e. a type of compression ignition engine. The internal combustion engine 40 may thus be configured to operate on diesel or a diesel-like fuel, such as biodiesel, biomass to liquid (BTL), or gas to liquid (GTL) diesel. Diesel-like fuels, such as biodiesel, can be obtained from renewable sources such as vegetable oil which mainly comprises fatty acid methyl esters (FAME). Diesel-like fuels can be produced from many types of oils, such as rapeseed oil (rapeseed methyl ester, RME) and soybean oil (soy methyl ester, SME). According to further embodiments, the internal combustion engine 40, as referred to herein, may an Otto engine with a spark-ignition device, wherein the Otto engine may be configured to run on petrol, alcohol, fuel gas, or combinations thereof. Fuel gas and alcohol, such as ethanol, can be derived from renewable biomass. According to embodiments herein, the internal combustion engine 40 is a four-stroke internal combustion engine 40.

[0051] For reasons of brevity and clarity, the internal combustion engine 40 is in some places herein referred to as the combustion engine 40, or simply the engine 40. According to some embodiments, the combustion engine 40, as referred to herein, may be configured to power another type of unit than a vehicle, such as for example an electric generator.

[0052] The combustion engine 40 comprises a turbocharger 30. As is further explained herein, the turbocharger 30 comprises a turbine unit configured to be driven by exhaust gas from an exhaust outlet 46 of the internal combustion engine 40. The turbocharger 30 further comprises compressor arrangement 32 with a compressor wheel connected to the turbine unit of the turbocharger 30.

[0053] According to the illustrated embodiments, the combustion engine 40 comprises an air filter unit 43 and a charge air cooler 44. The compressor arrangement 32 of the turbocharger 30 is configured to force air from the air filter unit 43 to the air inlet 42 of the engine 40. The charge air cooler 44 is arranged between the compressor arrangement 32 of the turbocharger 30 and the air inlet 42 of the combustion engine 40. The charge air cooler 44 is configured to cool the compressed air before the air is conducted to the air inlet 42. In this manner, the power output and fuel efficiency of the combustion engine 40 can be improved.

[0054] The internal combustion engine 40 comprises an air inlet assembly 48 forming a flow path for air between the air filter unit 43 and a compressor inlet of the compressor arrangement 32. In other words, the air inlet assembly 48 is configured to conduct air from the air filter unit 43 to the compressor arrangement 32.

[0055] The internal combustion engine 40 further comprises a crankcase ventilation outlet 49. The crankcase ventilation outlet 49 is connected to a crankcase volume of the combustion engine 40 and to the air inlet assembly 48 of the combustion engine 40. In this manner, crankcase gasses, for example originating from blow-by gasses, can be vented to the air inlet assembly 48 at a position upstream of the compressor arrangement 32 of the turbocharger 30. Fig. 3 schematically illustrates a cross section of the compressor arrangement 32 of the turbocharger 30 of the internal combustion engine 40 illustrated in Fig. 2. The compressor arrangement 32 comprises a compressor wheel 23 configured to rotate around a rotation axis Ra during operation of the compressor arrangement 32. In Fig. 3, the cross section is made in a plane comprising the rotation axis Ra of the compressor wheel 23. The compressor wheel 23 may also be referred to as an impeller. Below, simultaneous reference is made to Fig. 1 - Fig. 3, if not indicated otherwise.

[0056] The compressor arrangement 32 further comprises a shaft 24. The shaft 24 is connected to the compressor wheel 23 and to the turbine unit of the turbocharger 30 explained with reference to Fig. 2 above. The compressor arrangement 32 comprises a compressor inlet 51 and a compressor outlet, wherein the compressor wheel 23 is configured to compress, i.e. , pump, air from the compressor inlet 51 to the compressor outlet 52 upon rotation around the rotation axis Ra thereof.

[0057] The compressor arrangement 32 further comprises a compressor shroud unit u1 and a hub unit 25. The compressor shroud unit u1 comprises a shroud surface s1 forming a delimiting surface of a diffuser section D1 of the compressor arrangement 32. Likewise, the hub unit 25 comprises a hub surface 25’ forming a delimiting surface of the diffuser section D1 of the compressor arrangement 32.

[0058] The diffuser section D1 of the compressor arrangement 32 is arranged to decelerate the air exiting the compressor wheel 23, converting the kinetic energy of the air into pressure. This process is vital for enhancing the static pressure of the air before it enters the air inlet 42 of the internal combustion engine 40, directly influencing the performance and efficiency of the turbocharger 30. The efficiency of the diffuser section D1 of the compressor arrangement 32 impacts the overall operation. The diffuser section D1 of the compressor arrangement 32 can contribute to smooth airflow transitions, reduce turbulence, and provide a broader operating range for the turbocharger 30. Moreover, the diffuser section D1 of the compressor arrangement 32 plays a significant role in the longevity and reliability of the turbocharger 30, with its condition closely tied to the need for maintenance of the turbocharger 30 and potential efficiency losses.

[0059] Fig. 4 schematically illustrates the compressor shroud unit u1 of the compressor arrangement 32 according to the embodiments illustrated in Fig. 3 as seen in a direction coinciding with the rotation axis Ra of the compressor wheel 23 of the compressor arrangement 32. Below, simultaneous reference is made to Fig. 1 - Fig. 4, if not indicated otherwise.

[0060] The compressor shroud unit u1 comprises a surface s’ facing the compressor wheel 23 when the compressor arrangement 32 is assembled as is illustrated in Fig. 3. Moreover, as mentioned above, the shroud surface s1 is configured to form a delimiting surface of the diffuser section D1 of the compressor arrangement 32 when the compressor arrangement 32 is assembled as is illustrated in Fig. 3. In Fig. 4, the boundary between the surface s’ facing the compressor wheel 2 and the shroud surface s1 is indicated with a dotted line.

[0061] According to embodiments herein, the compressor shroud unit u1 comprises a number of protrusions and / or recesses 3 distributed across the shroud surface s1. According to the embodiments illustrated in Fig. 4, the number of protrusions and / or recesses 3 comprises a number of dimples 4, i.e. , a number of small indentations or depressions, distributed across the shroud surface s1. The number of dimples may have a circular or oval shape. The compressor shroud unit u1 may comprise a large number of dimples, such as a number exceeding 20, or exceeding 50.

[0062] Fig. 5 schematically illustrates a compressor shroud unit u2 according to some further embodiments. The compressor arrangement 32 according to the embodiments illustrated in Fig. 2 may comprise a compressor shroud unit u2 according to the embodiments illustrated in Fig. 5.

[0063] According to the embodiments illustrated in Fig. 5, the number of protrusions and / or recesses 3 of the compressor shroud unit u2 comprises a number of grooves 5 and ridges 6, i.e., a number of cuts or depressions and a number of raised strips or lines, distributed across the shroud surface s2 of the compressor shroud unit u2.

[0064] According to the embodiments illustrated in Fig. 5, the compressor shroud unit u2 comprises four grooves 5 and four ridges 6 arranged in an alternating manner on the shroud surface s2 of the compressor shroud unit u2. Moreover, according to the embodiments illustrated in Fig. 5, the grooves 5 and ridges 6 are arranged such that they form a spiral shape on the shroud surface s2 of the compressor shroud unit u2.

[0065] However, according to further embodiments, the grooves 5 and ridges 6 may be arranged in another manner than depicted in Fig. 5. Moreover, the compressor shroud unit u2 may comprise another number of grooves 5 than four and / or another number of ridges 6 than four. Moreover, the compressor shroud unit u2 may comprise only grooves 5 or only ridges 6.

[0066] Furthermore, according to some embodiments, the compressor shroud unit u2 may comprise a combination of dimples 4 according to the embodiments illustrated in Fig. 4 and grooves 5 and / or ridges 6 according to the embodiments illustrated in Fig. 5.

[0067] Fig. 6 schematically illustrates a cross section of a compressor arrangement 32’ according to some further embodiments. As indicated in Fig. 2, the turbocharger 30 of the internal combustion engine 40 may comprise a compressor arrangement 32’ according to the embodiments illustrated in Fig. 6.

[0068] The compressor arrangement 32’ according to the embodiments illustrated in Fig. 6 comprises the same features, functions, and advantages as the compressor arrangement 32 explained with reference to Fig. 3, with some differences pointed out below. The shared features, functions, and advantages are not further explained herein for reasons of brevity and clarity.

[0069] According to the embodiments illustrated in Fig. 6, the compressor shroud unit u3 of the compressor arrangement 32’ comprises a number of protrusions and / or recesses 3 comprising a number of grooves 5’ forming a stepped delimiting surface of the diffuser section D2 of the compressor arrangement 32’. The wording stepped delimiting surface means that the surface is characterized by a series of raised or recessed levels, creating a succession of edges and sections resembling steps.

[0070] The compressor shroud unit u3 according to the embodiments illustrated in Fig. 6 may comprise at least one of a number of dimples 4 according to the embodiments illustrated in Fig. 4 and a number of grooves 5 and ridges 6 according to the embodiments illustrated in Fig. 5.

[0071] The following is explained with simultaneous reference to Fig. 1 - Fig. 6. Since the compressor shroud unit u1 - u3 comprises a number of protrusions and / or recesses 3 distributed across the shroud surface s1 - s3, a turbulent airflow can be ensured in a boundary layer close to the shroud surface s1 - s3. In this manner, occurrences of particle deposition on the shroud surface s1 - s3 can be reduced, such as of oil droplets originating from the crankcase ventilation outlet 49 of an internal combustion engine 40 comprising the compressor arrangement 32, 32’. Such oil droplets can be converted into soot particles, which, over time can accumulate to form layers of soot clogging the diffuser section D1, D2 of the compressor arrangement 32, 32’. Thus, by creating a turbulent airflow in the boundary layer close to the shroud surface s1 - s3, the likelihood of clogging in the diffuser section D1, D2 of the compressor arrangement 32, 32’ can be reduced.

[0072] As a further result, a compressor shroud unit u1 - u3 is provided having conditions for maintaining a high operational efficiency of the compressor arrangement 32, 32’ as well as having conditions for reducing the need for performing service, maintenance, and repair of the compressor arrangement 32, 32’.

[0073] According to the embodiments illustrated in Fig. 6, the angle a1 between the rotation axis Ra and a main extension direction md of the diffuser section D2, at a location radially outside the compressor wheel 23, is approximately 90 degrees. In other words, according to the embodiments illustrated in Fig. 6, the main extension direction md of the diffuser section D2, at the location radially outside the compressor wheel 23, substantially coincides with a rotation plane of the compressor wheel 23. As understood from the above, the rotation plane of the compressor wheel 23 is perpendicular to the rotation axis Ra of the compressor wheel 23.

[0074] Fig. 7 schematically illustrates a cross section of a compressor arrangement 32” according to some further embodiments. As indicated in Fig. 2, the turbocharger 30 of the internal combustion engine 40 may comprise a compressor arrangement 32” according to the embodiments illustrated in Fig. 7.

[0075] The compressor arrangement 32” according to the embodiments illustrated in Fig. 7 comprises the same features, functions, and advantages as the compressor arrangement 32’ explained with reference to Fig. 6, with some differences pointed out below. The shared features, functions, and advantages are not further explained herein for reasons of brevity and clarity.

[0076] According to the embodiments illustrated in Fig. 7, and the angle a2 between the rotation axis Ra of the compressor wheel 23 and a main extension direction md of the diffuser section D3, at a location radially outside the compressor wheel 23, is approximately 79 degrees. As understood from the above, the feature that the angle a2 between the rotation axis Ra and the main extension direction md of the diffuser section D3 is approximately 79 degrees means that the angle between the rotation plane of the compressor wheel 23 and the main extension direction md of the diffuser section D3 is approximately 11 degrees. However, according to further embodiments, the angle a2 between the rotation axis Ra of the compressor wheel 23 and the main extension direction md of the diffuser section D3, at the location radially outside the compressor wheel 23, may be within the range of 60 - 120 degrees, or may be within the rage of 72 - 108 degrees. In other words, according to such embodiments, the angle between the rotation plane of the compressor wheel 23 and the main extension direction md of the diffuser section D3 may be within the range of ± 30 degrees, or may be within the rage of ± 18 degrees.

[0077] Also in the embodiments illustrated in Fig. 7, the compressor shroud unit u4 of the compressor arrangement 32” comprises a number of protrusions and / or recesses 3 comprising a number of grooves 5’ forming a stepped delimiting surface of the diffuser section D3 of the compressor arrangement 32”. As an alternative, or in addition, the compressor shroud unit u4 according to the embodiments illustrated in Fig. 7 may comprise at least one of a number of dimples 4 according to the embodiments illustrated in Fig. 4 and a number of grooves 5 and ridges 6 according to the embodiments illustrated in Fig. 5.

[0078] According to some embodiments, an average height / depth of the number of protrusions and / or recesses 3 is less than 1 mm, or is less than 0.5 mm. That is, in more detail, the average height / depth of the number of dimples explained with reference to Fig. 4 may be less than 1 mm, or less than 0.5 mm, the average height / depth of the number of grooves 5 and ridges 6 explained with reference to Fig. 5 may be less than 1 mm, or less than 0.5 mm, and the average height / depth of the number grooves 5’ explained with reference to Fig. 6 and 7 may be less than 1 mm, or less than 0.5 mm. In this manner, conditions are provided for ensuring a turbulent flow in the boundary layer close to the shroud surface s1 , s2, s3 without significantly impairing the operational efficiency of a compressor arrangement 32, 32’, 32” comprising the compressor shroud unit u1 - u4.

[0079] The following is explained with simultaneous reference to reference to Fig. 1 - Fig. 7. The main extension direction md of the diffuser section D1, D2, D3, as referred to herein, is set by the extension directions of the compressor shroud unit u1 - u4 and of the hub unit 25, 26, 27. According to the embodiments illustrated in Fig. 3, Fig. 6, and Fig. 7, the diffuser section D1, D2, D3 of the compressor arrangement 32, 32’, 32” has a substantially constant width along an intended airflow direction therethrough. In other words, according to these embodiments, the compressor shroud unit u1 - u4 is substantially parallel to the hub unit 25, 26, 27 at the diffuser section D1 , D2, D3 of the compressor arrangement 32, 32’, 32”. However, according to some further embodiments, the compressor shroud unit u1 - u4 and the hub unit 25, 26, 27 may be arranged in a non-parallel manner to obtain a converging or diverging airflow passage through the diffuser section D1 , D2, D3. A converging airflow passage means that the width of the diffuser section D1, D2, D3 decreases along the intended airflow direction therethrough. Conversely, a diverging airflow passage means that the width of the diffuser section D1, D2, D3 increases along the intended airflow direction therethrough.

[0080] According to the embodiments illustrated in Fig. 3, the hub surface 25’ is a smooth and flat surface. However, according to further embodiments, the hub surface 25’ of the compressor arrangement 32 according to the embodiments illustrated in Fig. 3 may comprises a number of protrusions and / or recesses distributed across the hub surface 25’. Such number of protrusions and / or recesses may comprise at least one of a number of dimples 4, as explained with reference to Fig. 4, and a number of grooves 5 and ridges 6, as explained with reference to Fig. 5.

[0081] According to the embodiments illustrated in Fig. 6 and Fig. 7, hub surface 26’, 27’ of the respective compressor arrangement 32’, 32” is a stepped surface, i.e. , a surface characterized by a series of raised or recessed levels, creating a succession of edges and sections resembling steps. As an alternative, or in addition, the hub unit 26, 27 of the compressor arrangement 32’, 32” according to the embodiments illustrated in Fig. 6 and Fig. 7 may comprise at least one of a number of dimples 4, as explained with reference to Fig. 4, and a number of grooves 5 and ridges 6, as explained with reference to Fig. 5, distributed across the hub surface 26’, 27’. According to some embodiments, and average height / depth of the number of protrusions and / or recesses distributed across the hub surface 25’, 26’, 27’ may be less than 1 mm, or may be less than 0.5 mm.

[0082] By providing the hub surface 25’, 26’, 27’ with a number of protrusions and / or recesses, a turbulent flow can be ensured in a boundary layer close to the hub surface 25’, 26’, 27’. In this manner, occurrences of particle deposition on the hub surface 25’, 26’, 27’ can be reduced, such as of oil droplets originating from the crankcase ventilation outlet 49 of the internal combustion engine 40 comprising the compressor arrangement 32, 32’. Thus, by creating a turbulent airflow in the boundary layer close to the hub surface 25’, 26’, 27’, the likelihood of clogging in the diffuser section D1 , D2 of the compressor arrangement 32, 32’ can be further reduced. Moreover, a high operational efficiency of the compressor arrangement 32, 32’, 32” can be further maintained and the need for performing service, maintenance, and repair of the compressor arrangement 32, 32’, 32” can be further reduced. It is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended independent claims. A person skilled in the art will realize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the present invention, as defined by the appended independent claims.

[0083] As used herein, the term "comprising" or "comprises" is open-ended, and includes one or more stated features, elements, steps, components, or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions, or groups thereof.

Claims

CLAIMS1. A compressor shroud unit (u1 - u4) for a compressor arrangement (32, 32’, 32”) of a turbocharger (30), wherein the compressor shroud unit (u1 - u4) comprises a shroud surface (s1 - s4) configured to form a delimiting surface of a diffuser section (D1 , D2, D3) of the compressor arrangement (32, 32’, 32”), and wherein the compressor shroud unit (u1 - u4) comprises a number of protrusions and / or recesses (3) distributed across the shroud surface (s1 - s4).

2. The compressor shroud unit (u1) according to claim 1 , wherein the number of protrusions and / or recesses (3) comprises a number of dimples (4).

3. The compressor shroud unit (u2) according to claim 1 or 2, wherein the number of protrusions and / or recesses (3) comprises a number of grooves (5, 5’) and / or ridges (6).

4. The compressor shroud unit (u3, u4) according to any one of the preceding claims, wherein the number of protrusions and / or recesses (3) comprises a number of grooves (5’) configured to form a stepped delimiting surface of the diffuser section (D2, D3) of the compressor arrangement (32’, 32”).

5. The compressor shroud unit (u1 - u4) according to any one of the preceding claims, wherein an average height / depth of the number of protrusions and / or recesses (3) is less than 1 mm, or is less than 0.5 mm.

6. A compressor arrangement (32, 32’, 32”) for a turbocharger (30), wherein the compressor arrangement (32, 32’, 32”) comprises a compressor shroud unit (u1 - u4) according to any one of the preceding claims.

7. The compressor arrangement (32, 32’, 32”) according to claim 6, wherein the compressor arrangement (32, 32’, 32”) comprises a compressor wheel (23) and a hub unit (25, 26, 27), and wherein the hub unit (25, 26, 27) comprises a hub surface (25’, 26’, 27’) forming a delimiting surface of the diffuser section (D1 , D2, D3) of the compressor arrangement (32, 32’, 32”).

8. The compressor arrangement (32, 32’, 32”) according to claim 7, wherein the compressor wheel (23) is configured to rotate around a rotation axis (Ra) during operation of the compressor arrangement (32, 32’, 32”), and wherein the angle (a1 , a2) between the rotation axis (Ra) and a main extension direction (md) of the diffuser section(D1 , D2, D3), at a location radially outside the compressor wheel (23), is within the range of 60 - 120 degrees, or is within the rage of 72 - 108 degrees.

9. The compressor arrangement (32, 32’, 32”) according to claim 7 or 8, wherein the hub unit (25, 26, 27) comprises a number of protrusions and / or recesses distributed across the hub surface (25’, 26’, 27’).

10. The compressor arrangement (32’, 32”) according to any one of the claims 7 - 9, wherein the hub surface (26’, 27’) is a stepped surface.

11. A turbocharger (30) for an internal combustion engine (40), wherein the turbocharger (30) comprises a compressor arrangement (32, 32’, 32”) according to any one of the claims 6 - 10.

12. An internal combustion engine (40) comprising a turbocharger (30) according to claim 11.

13. The internal combustion engine (40) according to claim 12, wherein the internal combustion engine (40) comprises an air inlet assembly (48) configured to conduct air to the compressor arrangement (32, 32’, 32”) and a crankcase ventilation outlet (49) connected to the air inlet assembly (48).

14. A vehicle (2) comprising an internal combustion engine (40) according to claim 13.

15. The vehicle (2) according to claim 14, wherein the vehicle (2) is a heavy road vehicle, such as a truck or a bus.

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