Engines may use a turbocharger to improve engine torque and/or power output. A turbocharger may include a turbine disposed in line with the engine's exhaust stream, and coupled via a drive shaft to a compressor disposed in line with the engine's intake air passage. The exhaust-driven turbine may then supply energy, via the drive shaft, to the compressor to boost the intake air pressure. The desired amount of boost may vary over operation of the engine. One approach to controlling the boost pressure is to use a variable geometry turbine to vary the flow of exhaust gas through the turbine. The variable geometry turbine may include a variable turbine nozzle configured to control the angle at which exhaust gas strikes the turbine blades, and/or to control a cross-sectional area of channels upstream from the turbine blades through which the exhaust passes.
One type of variable geometry turbine includes a number of pivot-able nozzle vanes. Exhaust gas flowing through the turbine nozzle flows through channels formed between the nozzle vanes. Pivoting the vanes in one direction may increase the cross-sectional area of channels upstream of the turbine and may decrease the incident angle of gas flowing across the turbine blade(s). Pivoting the vanes in the other direction may decrease the cross-sectional area of channels upstream of the turbine and may increase the incident angle of gas flowing across the turbine blade.
Engine braking is a technique wherein the engine may be used to help slow a vehicle in order to, for example, reduce wear on a vehicle's brakes and/or to reduce the amount of heat that may otherwise be generated if only the vehicle brakes are used to slow, or stop the vehicle. During engine braking the exhaust gas stream is constricted thereby creating a backpressure in the exhaust passage. The piston(s) in the engine are thereby forced to work against the backpressure to expel the combusted gas from the cylinder(s). In a turbocharged engine with a variable geometry the nozzle vanes can be used to constrict the flow. However when the flow is restricted the gas that is allowed to pass is directed toward the turbine with greatly increased speed. This may cause shock waves. This may generate strong interaction and excitation on turbine blades downstream. This shock wave induced excitation, which may also be referred to as force response excitation, or fluid structure interaction, may be a source of high cycle fatigue concern of the turbine blades and a limiting factor of further increasing the exhaust braking power of turbocharged diesel engines.
The basic design of variable geometry turbines has been modified to yield various advantageous results. For example, U.S. Patent Publication 20130042608 attempts to provide a way to independently vary the cross-sectional area of the channels between nozzle vanes and the angle of incidence of gas flowing across the turbine blade. The disclosure provides an annular turbine nozzle having a central axis and a number of nozzle vanes. Each nozzle vanes include a stationary vane and a sliding vane. The sliding vane is positioned to slide in a direction substantially tangent to an inner circumference of the turbine nozzle. The vane modification accordingly attempts to substantially maintain a desired angle of incidence and a preferred cross-sectional area of the channels over a range of engine operating conditions.
The inventors herein have identified a number of shortcomings with this approach. For example, the disclosure fails to address the potential shock issues when the cross-sectional area of the channels is made small to constrict flow in an engine braking condition and the flow is consequently relatively very fast.
Embodiments in accordance with the present disclosure may provide a variable geometry turbine that may include a turbine wheel and a plurality of adjustable vanes radially positioned around the turbine wheel. The turbine may also include a flow disrupting feature on one or more outside surfaces of one or more of the plurality of adjustable vanes. In some example embodiments the flow disrupting feature may be a plurality of flow disrupting features that may each be adjacent to a respective trailing edge of the plurality of adjustable vanes. In this way the intensity of a possible shock wave may be reduced on the turbine blades. Also in this way possible excitation on the turbine blades may be reduced.
With various embodiments the adjustable vanes may be adjustable in a pivoting fashion, and/or they may be adjustable in another fashion. For example, each may include two or more portions that may move relative to one another. In some embodiments one or more nozzle vanes may each include a stationary portion and a sliding portion. In such embodiments one of the portions, for example a portion that may extend forward in a leading edge direction, may include one or more flow disrupting features in accordance with the present disclosure.
In some example embodiments the flow disrupting feature may be grooves or dimples. In some cases the grooves or dimples may be of different scales on an otherwise smooth nozzle vane surface. The nozzle vane surface may face the turbine blades. In this way the flow disrupting feature(s) may effectively disperse a sharp and strong shock wave into much weakened shock waves that may be spread over a finite area.
Some example embodiments may provide a nozzle vane for a variable geometry turbine for a turbocharger. The nozzle vane may include a leading edge and a trailing edge. The nozzle vane may also include an outside surface for directing a flow of exhaust gases toward a turbine of the turbocharger from the leading edge toward the trailing edge, and one or more flow disrupting features on the outside surface to disrupt the flow adjacent to the trailing edge.
Various other example embodiments may provide a method, including during engine braking, expanding exhaust gas through a variable geometry nozzle of a turbocharger; and disrupting flow via flow disrupting grooves on a surface of nozzle vanes upstream from exhaust vanes of the turbocharger.
Various embodiments may provide a solution that may be applied to a wide variety of variable geometry turbines with swing nozzle vanes. In this way it may be avoided that the turbine blades be made more thick and therefore thick enough to have the structure natural frequency to operational frequency ratio above, for example 7.0, as may heretofore have been proposed in order to withstand a strong shock wave induced excitation or force response excitation on the turbine blades.
Some embodiments may provide a change in the orientation of grooves on the nozzle surface which may manipulate the angle of interaction or excitation in the space domain of the shock wave on the turbine blade, and may thus regulate and weaken the excitation in the time domain on the specific location of the turbine blade. With the weakened shock wave excitation in accordance with the present disclosure, the turbine blade design may be optimized for better aerodynamic performance, in terms of efficiency and flow capacity, with structural natural frequency to operational frequency ratio as low as 5. This may reduce the inertia and weight, of the nozzle without high cycle fatigue concerns due to shock wave induced excitation on the blades.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.