The turbocharger was invented by Swiss engineer, Alfred Buchi, who had been working on steam turbines. His patent for the internal combustion turbocharger was applied for in 1905.
A turbocharger is an exhaust gas driven compressor used in internal-combustion engines to increase the power output of the engine by increasing the mass of oxygen entering the engine. A key advantage of turbochargers is that they offer a considerable increase in engine power with only a slight increase in weight.
A turbocharger is an exhaust gas driven supercharger. All superchargers have a gas compressor in the intake tract of the engine which compresses the intake air above atmospheric pressure, greatly increasing the volumetric efficiency beyond that of naturally-aspirated engines. A turbocharger also has a turbine that powers the compressor using wasted energy from the exhaust gases. The compressor and turbine spin on the same shaft, similar to a turbojet aircraft engine.
The compressor increases the pressure of the air entering the engine, so a greater mass of oxygen enters the combustion chamber in the same time interval (an increase in fuel is required to keep the mixture the same air to fuel ratio). This greatly improves the volumetric efficiency of the engine, and thereby creates more power. The additional fuel is provided by the proper tuning of the fuel injectors or carburetor.
Turbochargers spin between 80,000 and 150,000 rpm depending on size, weight of the rotating parts, boost pressure developed and compressor design. Such high rotation speeds would cause problems for standard ball bearings leading to failure so most turbo-chargers use fluid bearings. These feature a flowing layer of oil that suspends and cools the moving parts.
To manager air pressure, the turbocharger exhaust gas flow is regulated with a wastegate that bypasses excess exhaust gas entering the turbocharger's turbine. This regulates the rotational speed of the turbine and the output of the compressor. The wastegate is opened and closed by the compressed air from turbo and can be raised by using a solenoid to regulate the pressure fed to the wastegate membrane. This solenoid can be controlled by Automatic Performance Control, the engine's electronic control unit or an after market boost control computer.
A lag is sometimes felt by the driver of a turbocharged vehicle as a delay between pushing on the accelerator pedal and feeling the turbo kick-in. This is symptomatic of the time taken for the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its rotational inertia and reach the speed necessary to supply boost pressure. The directly-driven compressor in a positive-displacement supercharger does not suffer this problem. Conversely on light loads or at low rpm a turbocharger supplies less boost and the engine is more efficient than a supercharged engine.
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