Multi-stage turbocharging system utilizing VTG turbine stage(s)

Abstract

Multi-stage turbocharging, and more particularly, an advanced multi-stage turbocharging system using the variable turbine power of one or more variable turbine geometry (VTG) turbochargers to adjust compressor boost and exhaust back pressure to engine operating demands. The invention further relates to a turbocharged internal combustion engine, in particular a turbocharged internal combustion engine with at least one high-pressure turbine stage and one downstream low-pressure turbine stage, wherein the high-pressure turbine may be a single-flow or double-flow type, wherein the high pressure or low pressure compressor may be variable geometry, wherein the high pressure or low pressure compressor may be variably bypassed, and wherein the high pressure or low pressure turbine may be provided with an active control variable bypass or wastegate.

Description

REFERENCE TO RELATED APPLICATION [0001] This application is a non-provisional of provisional application No. 60 / 613,615 filed Sep. 27, 2004.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The invention relates to advanced multi-stage turbochargers using at least one variable turbine geometry (VTG) turbocharger stage to enable higher pressure ratios, better torque at low engine speed, increased power / altitude capability at high speeds, a wider operating range without running into choke or surge, improved flexibility, and improved transient capability. [0004] The invention further relates to a turbocharged internal combustion engine with at least one high-pressure turbine stage and one downstream low-pressure turbine stage, wherein the high-pressure turbine may be a single-flow or double-flow type, wherein the high pressure or low pressure turbine or compressor may be bypassed, wherein the high pressure or low pressure turbine or compressor may be variable geometry...

AI Technical Summary

Benefits of technology

[0027] Following extensive theoretical discussions, followed by laboratory prototyping and road testing of various turbocharger systems, the present inventors discovered that, among the hundreds of possible modifications and combinations that may be made to multi-stage turbocharger systems, a few certain specific modifications or adjustments resulted in improved fuel economy and reduced emissions while at the same time improving engine responsiveness.

Problems solved by technology

However, when operated over a broad range of engine speed and load, the compressor and turbine components are forced to function off their design points and consequently suffer losses in efficiency that adversely affects engine performance.

Conversely, if the turbocharger is matched to an engine's low speed range, the turbocharger will have a tendency to “overspeed” when the engine is operated at maximum speed and load.

The waste gate, however, allows the escape of exhaust gas energy which could be better utilized by the turbocharger turbine, and results in a substantial loss in system efficiency.

However, the increase in boost at low engine speeds produced by the diverted flapper valve might be great enough to cause the turbocharger compressor to operate in its surge or unstable area.

This in turn causes a movement of the compressor efficiency islands and choke area to lower flow and can result in lowering the compressor efficiency when the engine is operating at high speed and load.

Variable diffuser vanes is one type of variable geometry compressor that could be employed, but the movable vanes cause significant mechanical complication internally in the construction of the turbocharger and must be precisely positioned by a rather elaborate control system.

The developers of new turbocharging systems are therefore faced with a dilemma: achieving a further rise in the rated power of an engine would require the use of a relatively large turbocharger.

While being simple, this two-stage turbocharger system does not produce the combination of performance and emissions characteristics required of modern propulsion systems.

Consequently, there may be a loss of traveling comfort, i.e. unsteady acceleration and braking power response.

There is thus need for an uncomplicated system able to improve low engine RPM boost / torque, particularly in medium size trucks.

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