Turbocharger System Case Study

1.1 Problem Summary and Introduction:

In accordance with the invention, a turbocharger system comprises a turbocharger having a turbine wheel and a compressor wheel mounted on a common shaft and respectively received within turbine and compressor housings. The turbine and compressor housings are mounted on a center housing including bearings for rotatably supporting the shaft, and lubricant circulation passages for supplying a lubricant such as oil to the bearings. In operation, exhaust gases from a combustion engine rotatably drive the turbine wheel which correspondingly drives the compressor wheel to supply high density charge air to the engine. Conveniently, the engine includes a separate hydraulic system such as a lubrication system

The engine also drives a relatively high pressure fluid pump for providing a source of relatively high pressure hydraulic fluid. The high pressure fluid is coupled through a control valve for selective coupling to a nozzle in the center housing of the turbocharger. When supplied with high pressure fluid, the nozzle directs the high pressure fluid into driving communication with a nonventilated hydraulic turbine mounted on the turbocharger shaft and disposed within a turbine flow chamber in the center housing. The high pressure fluid thus rotatably drives the nonventilated hydraulic turbine and thereby supplementally drives the turbocharger. Importantly, the passage of fluid through the turbine chamber is controlled so that the nonventilated hydraulic turbine runs fully submerged to prevent frothing or foaming of the fluid. Fluid exiting the turbine chamber is return to the engine hydraulic system. In one embodiment of the system of this invention, the control valve couples the high pressure system fluid back to the engine hydraulic system whenever supplemental driving of the turbocharger is not required. In this manner, the high pressure fluid pump is substantially unloaded. In another embodiment of the invention, the high pressure fluid is coupled to drive hydraulically a fan or the like for forcing cooling air across

Turbochargers for vehicle internal combustion engines normally include a compressor impeller that compresses the gas flow delivered to the intake manifold of the engine. In carbureted gasoline engines the gas flow is an air fuel mixture, while in diesel and stratified charge engines the gas flow is only air or other oxidant gas. The compressor is driven by a turbine which, in turn, is driven by exhaust flow from the engine exhaust manifold. In such vehicle engines maximum torque is required for acceleration at lower engine speeds. Accordingly, the turbine is sized to produce high compressor speeds at these low engine speeds. At higher engine speeds where exhaust gas flow is greater, the turbine and compressor can be over-driven, particularly in cruising or part throttle conditions. This over drive reduces engine efficiency by supplying excess airflow in the case of a diesel engine, and by opposing the actions of the throttle in a gasoline engine which is attempting to restrict gas flow to the engine. In both cases excessive exhaust manifold pressure is also created. Conventionally, a waste gate valve may be included to divert exhaust flow from passing through the turbine to reduce compressor speed. Operation of the valve is regulated to maintain relatively high intake manifold pressure for full throttle conditions to develop maximum torque. While effective to prevent