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The turbocharger is a rotating machine comprising a turbine and a compressor mounted on a common shaft. Its task is to recharge the internal combustion engine.
Turbocharging was patented in 1905. By a Swiss doctor’s Alfred Buchi. After 33 years described the system has been implemented for trucks. The cars of its widespread use began in 1973.
The turbocharger consists of:
compressor wheel rotor,
the sliding bearing,
the compressor body,
the middle turbo housing,
To drive the turbo exhaust gas energy is being used. They contain 30% of the energy generated by the combustion of fuel mixture. Turbo is driven by the above mentioned gases (shaft speed is from 100 to 200 thousand. Rev / min and sometimes more) drives the compressor rotor. It is rigidly mounted on the same shaft as the shaft of the turbocharger. Shaft connection (connection to the turbine wheel and compressor rotor) is one of the main elements of the turbocharger. The rotors are installed in the hulls, and the whole assembly is hold in the middle hull by means of thrust and sliding. Various oil supplied by oil, whose task is to keep the oil film to journal rotating components. The rotors are protected against the ingress of oil through the oil seal rings.
The rotor provides the additional air compressor intake manifold into the combustion chamber. Supply more air to the combustion chamber allows to burn more fuel and therefore the drive unit is able to increase power (efficiency). This is not the only advantage of the turbocharger but essential. The advantages can also include reducing emissions and, in the case of vehicle tuning, no need to change the volume of a cylinder power unit (remember when installing a turbocharger system to provide adequate cooling it).
In modern cars, in which attention is drawn largely on issues of ecology, the engines are significantly labored. Their volume displacements are becoming smaller and obtained power ratings comparable to the previously used engines of larger volume displacement. As can be seen the use of turbochargers in modern power units is on the agenda. Compared to previous years, the emphasis has changed to their burden. Currently, the turbocharger is one of the most important elements of a modern engine. Therefore, it must be made of good material, as long as possible to be able to be operated.
Material called “Niresist” is used for turbine casings. It contains: 11-16% Ni, 2.5% Si, up to 2% Mn, 4% Cr and 8% Cu. This material has a high heat resistance, resistance to abrasion and corrosion. To build the hulls of compressors used aluminum alloys. For turbine rotors material is used with the name “Inconel” (an alloy of nickel, chromium, cobalt, iron and nickel content of 46-65%), “MarM247 ‘(19% Cr, 9% Fe, 5% Nb, 3% Mo, 0 9% Ti, 0.6% Al, and 0.05% C), or titanium. All of these materials used for turbine rotors are characterized by high heat resistance, and hence high resistance to high operating temperatures and corrosion resistance. Chromium-nickel-tungsten (containing 0.25% C, 0.4% Mn, 1.5% Cr, 4.2% Ni and 1% W), in other words, structural steels for quenching and tempering are applied to the construction of Turbocharger . Bearings, which must be characterized by resistance to high operating temperatures and abrasion resistance usually are made of bronze alloys B102.
Turbocharger working conditions
The working conditions of modern turbochargers are quite heavy. High speeds, reach up over 200 thousand. rev / min. Exhaust gas temperature using a turbocharger are higher than in the case of the discharge smoke from naturally aspirated engines. For engines with ignition gas temperature approx. 700 degrees Celsius, and in the case of a spark-ignition engine is up to approx. 1000 degrees Celsius. As a result, the exhaust gas temperature and pressure pulsations to the present exhaust is necessary to use quenched and materials on such elements as impellers, turbine casings, compressors, shafts and plain bearings.
Long-term operation of the turbocharger is directly related to the care of the vehicle. By taking care of the vehicle is meant frequent oil changes (preferably once a year) with the oil filter and air filter. This results in avoiding getting particles of different materials to the impeller of the compressor, which is very precise and sensitive to such contaminants part.
The most frequent damage to the turbocharger includes:
impurities in the intake air (dust, dirt, sand, and the like.)
impurities in the exhaust gas (extraneous matter coming from the fuel tank, valves, etc. or debris.)
the oil level is too low,
carbon residue resulting from the exhaust gas temperature is too high.
Control of the turbocharger
For proper operation of the turbocharger is needed to adapt and continuously adjusting the amount of air supplied to the engine. Therefore, modern turbocharger systems are equipped with additional regulatory elements. One solution is to use retrofitting turbocharger wastegate valve (ie. The exhaust vent valve). It is located in front of the inbound exhaust gas to the turbine (typically integral with the body of the turbine). In the case of an open exhaust valve goes directly into the exhaust system of the vehicle (bypassing the turbine). The opening of the valve is adjustable, which directly affects the load on the turbine. This is commonly referred to as variable boost pressure. The simplest control valve is described mechanical control. In the closed position, the spring pushes the valve so that the fumes were placed in the turbine. When the cylinder pressure begins to increase open side channel, transmitting gases to the exhaust system of the vehicle, while bypassing the turbine. Well-chosen clamping force of the spring and the force generated by the actuator provides the boost pressure adjustment automatically.
More advanced solutions with wastegate are controlled via a vacuum actuator. In this embodiment the spring is used, however, the task is opposite to that in the above described case. Instead of maintaining the valve closed, in this embodiment the spring is designed to maintain the valve in the open position and for closing the said actuator is responsible. This type of solution requires the application of vacuum through the vacuum pump, but to operate the turbocharger. This solution allows you to control boost pressure regardless of the pressure in the intake. The advantages of this solution is mainly better control over the work of the drive unit which slightly reduces the turbocharger response time (ie. Turbo lag). Despite the popularity of the wastegate solutions in spark-ignition engines and cheaper construction compression-ignition engines, it is replaced by a variable geometry turbocharger exhaust vanes.
Variable geometry exhaust vanes
As used turbocharger equipped with a steering wheel with variable geometry exhaust. Probably ask what are the handlebars. Now the turbocharger vanes are vanes attached to a common ring located on the circumference of the turbine. To control the pitch (the position of the rotor blades with respect to) is a pneumatic cylinder. The ability to change the angle of the steering wheel causes the air flow, possibly without turbulence, flows into the turbine. At low speeds, steering wheels are inclined at a large angle, so that the charge was as much as possible without having a negative impact on the turbocharger. Also, if you need to reduce the degree of recharging described solution works. In this case, the blades are set in such a way that the flow was turbulent. This results in a reduction of the charge pressure. The advantages of this solution is the higher efficiency than in the case of the wastegate valve, the lower temperature and the exhaust gas pressure (without loss of power), less reaction time of the turbocharger.
After an introduction to car turbochargers with variable geometry vanes were used only in diesel engines. This was due to a slightly lower temperature of the exhaust gases. The spark-ignition engines exhaust temperature exceeds 900 ° C, which results in the need to use more expensive materials of construction. The first car that uses described the type of turbocharger was 911, which was specially designed by BorgWarner turbocharger. Representatives of the company, however, did not betray what material can withstand the prevailing high exhaust gas temperature, was used in the construction of the described item.
The diesel engine is not a significant excess air ratio lambda, as well as the air flow throttled by a throttle valve, in spite of its occurrence. It is rather significant in power units spark ignition engines. It is in this kind of power an important issue, because of the work of the turbocharger, is to keep the excess air ratio lambda in the vicinity of unity. Why? Because the light load power unit or such. Foot off the accelerator pedal (off the throttle), the air flow is not continuous. This results in difficult working conditions of the compressor, wherein the impeller rotates at a relatively high speed. This occurs by the piling up of boost pressure before the throttle. For preventing such a phenomenon is used blow-off valve or otherwise called dump valve. The task of the blow-off valve is to reduce the (dropping) the pressure in the section of the intake throttle-rotor. The performance cars blow-off valve releases compressed air to the atmosphere. Accompanied by a characteristic whistling turbo-charged engines. Control valve with a blow-off can be done in two ways (as in the case of the wastegate). Through the boost pressure or by means of a vacuum cylinder.
The way forward is to control turbochargers by electric actuators, and not, as has been described above air. The main advantage is speeding up the response of the drive unit in the turbine to sudden acceleration pedal.
This is done in such a way that when you press the accelerator pedal, the electric actuator is started, which aims to achieve sufficiently high speed compressor. After obtaining the proper speed turbo is switched on (one compressor and turbine shaft, using the clutch). Another advantage of this solution is to prevent the driver to excessive speed of the turbine. Described modern solution, of course, is equipped with sensors and controllers, so that the work of the turbocharger was the most efficient.
Turbochargers it does not look like the present and future of the automotive industry today, at least in the conventional power units drive. The future of the automotive industry is not yet determined. Work is underway on different energy sources and alternative fuels. However, these are the future plans. So far, let’s enjoy what we have that is turbocharged petrol and diesel units.
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