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Turbo
Oct 5, 2005 16:04:27 GMT 7
Post by Soulfly on Oct 5, 2005 16:04:27 GMT 7
What is a Turbo? A turbo is essentially an air pump. It is powered by waste energy in the form of high temperature gas exiting from the engine exhaust, and produces compressed air for the engine intake. Compressing the intake air has several benefits: It increases the amount of air (therefore Oxygen) that is combusted in the engine. This equates to an increase in effective engine capacity without incurring the thermal losses of a larger engine. The higher Oxygen density produces cleaner burning engines. Reduces fuel consumption in diesel engines. Allows vehicles to use smaller and lighter engines for the equivalent power output. Compressing the intake air is known as 'boosting'. Boost is measured in either pounds per square inch (psi) or as a proportion of normal atmospheric pressure (Bar). A turbo producing 1 Bar (14.7psi) of boost will be forcing twice the amount of air into the engine that it would receive without the turbo. This means that the effective capacity of the engine is increased by 100% for every 1 Bar of boost produced. Turbocharging has made a resurgence in recent years, both for performance applications such as rallying, and for increasing the drivability of family vehicles through use of low pressure high response turbos. This has lead to many technical developments including low-loss ball bearing cores, variable nozzle turbines and more efficient designs of compressor and turbine wheels. Cutaway Diagram of a Turbocharger www.turbo.co.nz/alltech/referencelibrary/images/T04Cutaway.jpg [/img] Diagram Key Number Description 1 Compressor Housing 2 Compressor Wheel Lock Nut 3 Compressor Wheel 4 Piston Ring / Seal Ring 5 Oil Slinger 6 Thrust Bearing 7 Floating Journal Bearing 8 Oil Feed 9 Shaft 10 Floating Journal Bearing 11 Turbine Wheel 12 Thrust Collar 13 Retaining Rings 14 Core (Centre Housing Rotating Assembly) 15 Retaining Rings 16 Piston Ring / Seal Ring 17 Exhaust Housing
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Turbo
Oct 5, 2005 16:05:46 GMT 7
Post by Soulfly on Oct 5, 2005 16:05:46 GMT 7
I tried to insert the pic but failed.
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Turbo
Oct 5, 2005 16:09:50 GMT 7
Post by Soulfly on Oct 5, 2005 16:09:50 GMT 7
How the turbo Anti-Lag System works
Bang-bang (also known as ALS which stands for Anti-Lag System) is an engine management technique that allows to minimize the turbo lag time.
As you might be aware of, turbochargers display what is known as lag time which is the time needed for the turbine to reach its full throttle from an intermediate rotational speed state. The duration of a turbocharger's lag depends on many factors among which its inertia, airflow efficiency, back pressure, etc. The problem is partly dealt with by fitting a turbo dump valve, which acts each time the driver lifts his foot from the throttle. The dump valve will evacuate the pressurized air coming out of the turbocharger while the inlet manifold is closed thus allowing the turbine not to stall and avoiding possible damage to its bearings. In race cars it is very common to fit oversized turbochargers in order to be able to produce enough boost pressure and assure a sufficient engine output. Big turbochargers display significant amounts of lag due to their increased rotational inertia. In such cases the dump valve is insufficient to allow the turbocharger not to loose too much speed when the driver lifts off. Additionally rally cars hold a turbo restrictor, which is regulated by the FIA. One of the restrictor' effects is to increase lag time. This is why in racing cars, and more specifically in rally cars, where torque and engine availability are critical factors, most applications use anti-lag systems.
During lag time the engine is much less responsive and its output well below nominal. To counter the effect of the turbocharger's lag time drivers used to anticipate the engine's reactions by accelerating well before they would have done in a non-turbo car. Others have used a technique, introduced by the German driver Walter Röhrl, known as "left foot braking" where the driver uses his left foot to brake the car while his right foot accelerates to keep the turbocharger in optimal load. Left foot braking is very hard on the brakes which are put into extreme stress but is very efficient in keeping the turbo spinning. ALS was a simple idea but one that was relatively difficult to implement. Only when electronic engine management systems were advanced enough to allow taking into consideration many more parameters than in the past it became possible to use them efficiently in handling ALS. To the best of my knowledge Toyota Team Europe were the first to use it in racing (Toyota's implementation is known as Toyota Combustion Control System while Mitsubishi call the system Post Combustion Control System).
How ALS works
When the driver lifts his foot from the gas pedal the ignition timing is altered with sometimes 40° or more of delay (retard) and the intake air and fuel supply mixture is made richer. The inlet butterfly is kept slightly open or an air injector is used to maintain air supply to the engine. This results in air/fuel mixture that keeps getting in the combustion chambers when the driver no longer accelerates. The ignition being delayed, the air/fuel mixture reaches the exhaust tubes mostly unburned. When the spark plug fires, the exhaust valve is starting to open due to the ignition delay mentioned above. Additionally, the exhaust temperature being extremely high, the unburned fuel explodes at the contact of the exhaust tubes. Luckily the turbo sits right there and the explosion keeps it turning (otherwise it would slow down since its intake, the exhaust gases, is cut-off). The effect is vastly lower response times with some downsides:
A quick rise of the turbocharger's temperature (which jumps from ~800°C to the 1100°C+ region) whenever the system is activated
A huge stress on the exhaust manifold and pipes (mounted on a street car a bang-bang system would destroy the exhaust system within 50-100 km)
The turbo produces significant boost even at engine idle speeds
The explosions which occur in the exhaust tubes generate important flames which can, sometimes, be seen at the end of the exhaust tube
Reduced engine brake
The ALS effect is mostly dependent on the air allowed into the engine, the more air supplied the more the ALS effect will be noticeable. Consequently ALS systems can be more or less aggressive. A mild ALS will maintain a 0 to 0.3 bar pressure in the inlet manifold when activated whereas, when inactive, the pressure in the inlet manifold with the throttle closed would be in the region of -1 bar (absolute vacuum). Racing ALS versions can maintain a pressure of up to 1.5 bar in the inlet manifold with the throttle closed. While the systems mounted in Toyota and Mitsubishi racing cars are relatively smooth and noiseless those fitted in Ford and Subaru cars are much more noisy and aggressive. The bang-bang system owns its name to the loud explosion noises one hears whenever the driver lifts off. Most racing implementations have user selectable anti-lag settings depending on the terrain, usually three settings can be selected by the driver going from mild to very aggressive.
Note that some regional or national European events prohibit the use of ALS systems while more and more WRC events regulate the noise levels allowed by competition cars effectively disabling ALS.
Starting in 2002 new anti-lag techniques, such as Exhaust Gas Recirculation (EGR), are slowly overtaking the method described above as they are kinder on the engine's mechanical parts.
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Turbo
Oct 6, 2005 16:26:55 GMT 7
Post by maximusmcmlxxv on Oct 6, 2005 16:26:55 GMT 7
COMMON CAUSES OF TURBO FAILURE
1. Hot shut down. That is, turning engine off prematurely without allowing sufficient time for the turbo to cool.
2. Infrequent oil, oil filter, and air filter changes.
3. Foreign matter and / or obstructions in turbo charger air or oil system.
4. Improper engine maintenance. Operating engine when out of tune or in need of adjustment or maintenance.
5. Related engine part or engine failure. For example, a cracked head, broken or worn piston rings, blown head gasket, clogged radiator, and impact damage due to accident.
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Turbo
Feb 10, 2006 21:31:18 GMT 7
Post by Gee Dean on Feb 10, 2006 21:31:18 GMT 7
Turbos have three major subassemblies: an exhaust turbine housing, a bearing housing, and a compressor housing. The exhaust and bearing housings each have a wheel with integral blades, and are connected together by a shaft mounted on bearings. Some turbos--like this Turbonetics Super Thumper that can support over 2,400 hp--offer a ceramic ball bearing option. A: Turbine wheel, B: Bearing and seal, C: Turbo shaft, D: Exhaust turbine housing, E: Backplate, F: Compressor wheel, G: Compressor housing, H: Bearing housing, I: Inducer bore, J: Exducer bore For any turbo series, the higher the A/R ratio, the better the top-end performance. The lower the A/R ratio, the better the low-speed response. Inlet Ducting Power level defines the inlet duct sizing. Generally the compressor inlet should be about 1 inch larger in outer diameter than the outlet. You can't go too far wrong if the inlet ducting is the same size as the compressor inducer orifice size. the intake manifold Turbochargers Mount the turbo(s) as close to the engine's exhaust ports as possible. Twin AiResearch TO4E turbos were selected for this application. On a 350 Chevy V-8, the twins spool fast and make for a cleaner installation. See last month's issue for detailed turbo sizing and selection guidelines. Wastegate Short of buying stock in a piston company, the primary means of preventing engine-destroying over-boost is an adjustable wastegate. Located in the exhaust collector downstream of any individual primary tubes, a wastegate keeps boost at a preset level by routing excess exhaust gas around the turbine and out the tailpipe. Exhaust Outlet and Wastegate Discharge Pipe Smaller exhaust outlets help a turbo spool up faster on a street car; larger outlets help flow on the top-end. In any event, the turbine outlet pipe should be no smaller than the exducer size. Discharge pipe size is determined by the combination's power level. On a high-power street car with full exhaust, the discharge tube diameter should at least equal the valve orifice size. Blow-Off Valve In a blow-through system sudden throttle closure when the engine is under boost can cause the turbo to surge or choke. On a road-race, rally, or street car, this can slow response time if you need to quickly get back on the throttle. A blow-off or bypass valve quickly relieves pressure when you back off the throttle. It may be mounted on the compressor outlet duct (after the ducts merge on a twin-turbo setup), between the intercooler and throttle-body, or even directly on the intercooler. The large poppet valve, dual valveguides, and centersection on Innovative Turbo's Pro gates are made from billet stainless steel for durability and corrosion-resistance. A reinforced Fluorocarbon full-rolling diaphragm replaces the typical flat diaphragm for improved valve actuation and precise control. Note the large bowl area around the valve In place of the usual poppet valve, Turbonetic's NewGen wastegate has a 2-inch-od Inconel swing valve that pivots in a cast stainless base. Such a design is said to open quicker and has less flow restriction than a traditional poppet configuration. This swing-valve 'gate can support 1,000-plus horsepower. Premium piston materials and "secret" high-tech coatings help race turbo motors survive. An HTC turbo slug-fest, from left: Mahle LS1, Ultralloy 351F, CP Pistons turbo small-block Chevy, Hemi fueler "green."
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