Patent Application
20150226110
The present disclosure relates to a reduced wear waste-gate valve assembly for a turbocharger.
Internal combustion engines (ICE) are often called upon to generate considerable levels of power for prolonged periods of time on a dependable basis. Many such ICE assemblies employ a supercharging device, such as an exhaust gas turbine driven turbocharger, to compress the airflow before it enters the intake manifold of the engine in order to increase power and efficiency.
Specifically, a turbocharger is a centrifugal gas compressor that forces more air and, thus, more oxygen into the combustion chambers of the ICE than is otherwise achievable with ambient atmospheric pressure. The additional mass of oxygen-containing air that is forced into the ICE improves the engine's volumetric efficiency, allowing it to burn more fuel in a given cycle, and thereby produce more power. Frequently, such turbochargers are driven by the engine's exhaust gases.
A typical exhaust gas driven turbocharger includes a central shaft that is supported by one or more bearings and that transmits rotational motion between a turbine wheel and an air compressor wheel. Both the turbine and compressor wheels are fixed to the shaft, which in combination with various bearing components constitute the turbocharger's rotating assembly. Turbochargers frequently employ waste-gate valves to limit operational speeds of the rotating assembly in order to maintain turbocharger boost within prescribed limits and prevent rotating assembly over speed.
One embodiment of the disclosure is directed to a turbocharger for pressurizing an airflow for delivery to an internal combustion engine having a cylinder that is configured to receive an air-fuel mixture for combustion therein. The engine also includes a reciprocating piston disposed inside the cylinder and configured to exhaust post-combustion gases therefrom. The turbocharger includes a turbine housing and a compressor cover, a rotating assembly having a turbine wheel disposed inside the turbine housing, and a compressor wheel disposed inside the compressor cover. The compressor wheel is configured to be rotated about an axis by the post-combustion gases.
The turbocharger also includes a waste-gate assembly configured to selectively redirect at least a portion of the post-combustion gases away from the turbine wheel and thereby limit rotational speed of the rotating assembly and pressure of the airflow received from the ambient. The waste-gate assembly includes a valve, a rotatable shaft connected to the valve, and a bushing fixed relative to the turbine housing and disposed concentrically around the shaft such that the shaft rotates inside the bushing to thereby selectively open and close the valve. The shaft is defined by an outer surface in contact with the bushing. The outer surface includes a coating composed of a ceramic-based material.
The bushing may be defined by an inner surface that is in contact with the shaft. The inner surface may be at least partially coated with the ceramic-based material. The coating may be applied via a physical deposition or a thermal spray process.
The bushing may be defined by an inner surface in contact with the shaft. The inner surface may include an insert or multiple inserts configured at least partially from the ceramic-based material. Each insert maybe configured as a continuous sleeve or as a discrete section.
The waste-gate assembly may also include an arm fixed to the shaft. The waste-gate assembly may additionally include an actuator having a rod operatively connected to the arm via a rod end and configured to displace or rotate the arm to thereby selectively open and close the valve. The rod end may include an insert configured from the ceramic-based material. Additionally, the rod end may define an aperture and the arm may include a pin that is engaged with the aperture. Accordingly, the pin's engagement with the aperture provides and secures an interface between the rod end and the pin. The insert may be disposed at the interface.
The inorganic crystalline or ceramic-based material may have a matric composite structure that includes both ceramic and non-ceramic materials. For example, the ceramic-based material may be one of a silicon carbide, silicon nitride, chromium carbide, zirconia, carbon-carbon composite, and metal-ceramic composite.
The ceramic-based material may also have a substantially homogenous crystalline structure.
Another embodiment of the present disclosure is directed to an internal combustion engine having the turbocharger as described above.
The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of the embodiment(s) and best mode(s) for carrying out the described invention when taken in connection with the accompanying drawings and appended claims.
Referring to the drawings wherein like reference numbers correspond to like or similar components throughout the several figures,
Combustion chambers 20 are formed within the cylinders 14 between the bottom surface of the cylinder head 16 and the tops of the pistons 18. As known by those skilled in the art, each of the combustion chambers 20 receives fuel and air from the cylinder head 16 that form a fuel-air mixture for subsequent combustion inside the subject combustion chamber. The cylinder head 16 is also configured to exhaust post-combustion gases from the combustion chambers 20. The engine 10 also includes a crankshaft 22 configured to rotate within the cylinder block 12. The crankshaft 22 is rotated by the pistons 18 as a result of an appropriately proportioned fuel-air mixture being burned in the combustion chambers 20. After the air-fuel mixture is burned inside a specific combustion chamber 20, the reciprocating motion of a particular piston 18 serves to exhaust post-combustion gases 24 from the respective cylinder 14.
The engine 10 additionally includes an induction system 30 configured to channel an airflow 32 from the ambient to the cylinders 14. The induction system 30 includes an intake air duct 34, a turbocharger 36, and an intake manifold (not shown). Although not shown, the induction system 30 may additionally include an air filter upstream of the turbocharger 36 for removing foreign particles and other airborne debris from the airflow 32. The intake air duct 34 is configured to channel the airflow 32 from the ambient to the turbocharger 36, while the turbocharger is configured to pressurize the received airflow, and discharge the pressurized airflow to the intake manifold. The intake manifold in turn distributes the previously pressurized airflow 32 to the cylinders 14 for mixing with an appropriate amount of fuel and subsequent combustion of the resultant fuel-air mixture.
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The compressor wheel 52 is configured to pressurize the airflow 32 being received from the ambient for eventual delivery to the cylinders 14. The compressor wheel 52 is disposed inside a compressor cover 54 that includes a compressor volute or scroll 56. The compressor scroll 56 receives the airflow 32 and directs the airflow to the compressor wheel 52. The compressor scroll 56 is configured to achieve specific performance characteristics, such as peak airflow and efficiency of the turbocharger 36. Accordingly, rotation is imparted to the shaft 38 by the post-combustion exhaust gases 24 energizing the turbine wheel 46, and is in turn communicated to the compressor wheel 52 owing to the compressor wheel being fixed on the shaft.
The rotating assembly 37 is supported for rotation about the axis 43 via journal bearings 58. During operation of the turbocharger 36, the rotating assembly 37 may frequently operate at speeds over 100,000 revolutions per minute (RPM) while generating boost pressure for the engine 10. As understood by those skilled in the art, the variable flow and force of the post-combustion exhaust gases 24 influences the amount of boost pressure that may be generated by the compressor wheel 52 throughout the operating range of the engine 10.
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The coating 68 may have a specific thickness, such as in the range of 0.3-30 μm, which may be controlled even more precisely in the range of 2-5 μm, and be composed from a material having a ceramic base. Accordingly, the coating 68 may have a substantially homogenous crystalline structure, i.e., other than having a small portion of common impurities, and be primarily composed of a base ceramic material. Alternatively, the coating 68 may have a matrix composite structure purposefully incorporating both ceramic-ceramic or ceramic and non-ceramic materials. Such a matrix structure of the coating 68 may, for example, be a silicon carbide, silicon nitride, chromium carbide, zirconia, carbon-carbon, or metal-ceramic composite.
The inner surface 66-1 of the bushing 66 may similarly include the ceramic-based coating 68 to further reduce abrasion between the shaft 64 and the bushing 66. Similar to that on the outer surface 64-1 of the shaft 64, the coating 68 on the inner surface 66-1 may have a thickness in the range of 0.3-30 μm and be controlled more precisely in the range of 2-5 μm. Additionally, the coating 68 may cover the inner surface 66-1 either entirely or partially according to the above discussion with respect to locations of highest specific loading. The coating 68 may be applied via a process of physical vapor deposition (PVD) or chemical vapor deposition (CVD). PVD is a type of coating method used to deposit thin films by the condensation of a vaporized form of the desired film material onto the surface of a workpiece, in the present case the coating 68 on the outer surface 64-1 and/or the inner surface 66-1. PVD involves purely physical processes such as high-temperature vacuum evaporation with subsequent condensation, or plasma sputter bombardment rather than involving a chemical reaction at the surface to be coated as in chemical vapor deposition. CVD is a type of coating method used to deposit thin films by condensation of a vaporized form of the desired film material onto the surface of a workpiece, such as the coating 68 on the outer surface 64-1 and/or the inner surface 66-1.
The coating 68 may also be applied via a process of thermal spray. Thermal spraying techniques are coating processes in which heated or melted material is sprayed onto a surface of a workpiece. During the process, the feedstock, i.e., coating precursor, is heated by electrical means, such as plasma or arc, or chemical means, such as a combustion flame. The material for thermal spraying of the coating 68 is fed in powder form, heated to a molten or semi-molten state and accelerated toward the outer surface 64-1 or the inner surface 66-1 in the form of micrometer-size particles. Combustion or electrical arc discharge is usually used as the source of energy for thermal spraying. Resulting coatings are made by the accumulation of numerous sprayed particles. The thermally spray coated surfaces may need to be ground and polished to maintain a smooth surface finish with surface rougness (Ra) of less than 1 micron. By contrast, the PVD or CVD coated surfaces may not need to be polished to maintain the required Ra of less than 1 micron, at least in part due to appreciably smaller coating thickness as compared to thermally sprayed on coatings.
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The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment can be combined with one or a plurality of other desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.
