Turbocharger

The Turbo-charged engines took over the F1 field and ended the Ford Cosworth DFV era in the mid 1980s. The W8 uses two four-cylinder VR engines mated together, and the W16 uses two eight-cylinder VR banks. The project's high cost was compensated for by its performance, and led to other engine manufacturers following suit. W8 and W16 designs were developed in a similar fashion. Renault was the first manufacturer to apply turbo technology in the F1 field, in 1977. For example, two VR6 engines mated together at 72 degrees result in a W12 configuration, which is significantly shorter than a V12 engine but only marginally wider. In Formula 1, in the so called "Turbo Era" of 1977 and onwards, engines with a capacity of 1500 cc could achieve anywhere from 1000 to 1500 hp (746 to 1119 kW) (Renault, Honda, BMW). Volkswagen has also developed a series of engines which use narrow angle designs mated together at 72 degrees.

Pontiac also introduced a turbo in 1980 and Volvo Cars followed in 1981. The Porsche Cayenne, which shares its chassis with the VW Touareg, also uses the 3.2 L VR6 as its base engine. Buick was the first GM division to bring back the turbo, in 1977, followed by the famed Mercedes-Benz 300D and Saab 99 in 1978. The VR6 is also used in other Volkswagen Group products, namely:. BMW led the resurgence of the automobile turbo with the 1973 2002 Turbo, with Porsche following with the 911 Turbo, introduced at the 1974 Paris Motor Show. The VR6 was used by Volkswagen in:. Turbos were also leading at Le Mans in 1976. The 3.2 and 3.6 litre VR6s will also be used to power a new MKV platform R32 (for Europe) and a new R36 model (North America).

The Offy turbo peaked at over 1,000 hp in 1973, while Porsche dominated the Can-Am series with a 1100 hp 917/30. The introduction of the Passat VR6 also marked the first time a VR6 powered vehicle was made available in North American before Europe. Offenhauser's turbocharged engines returned to Indianapolis in 1966, with victories coming in 1968. Both the 3.2 and 3.6 feature FSI direct injection. Both of these engines were abandoned within a few years, and GM's next turbo engine came more than two decades later. For North American, the Passat receives a new 3.6 L VR6 with a narrower 10.6 degree cylinder angle, producing 280 PS (276 hp/206 kW). Its Turbo Jetfire was a 215 in³ (3.5 L) V8, while the Corvair engine was a 140 in³ (2.3 L) flat-6. In 2005, the European market version of Volkswagen's fifth generation Passat went on sale with a revised version of the 3.2 L VR6 as its top-spec motor.

The Oldsmobile is often recognized as the first, since it came out a few months earlier than the Corvair. The 3.2 is now used as a range-topper in Audi A3 or as an entry level version in the VW Touareg and Porsche Cayenne, although the version used in the Cayenne features modifications to the heads as well as the intake and timing systems. The A-body Oldsmobile Cutlass and Chevrolet Corvair were both fitted with turbochargers in 1962. This variant produced 250 PS (247 hp/184 kW) and 320 Nm (236 ft•lbf) of torque in TT trim and 241 PS(238 hp/177 kW) in R32 trim. The first production turbocharged automobile engines came from General Motors. In 2003, a high performance 3.2 L version of the engine was introduced to power VW's limited-production Golf R32 and a new range-topping variant of the Audi TT. The turbocharger hit the automobile world in 1952 when Fred Agabashian qualified for pole position at the Indianapolis 500 and led for 100 miles before tire shards disabled the blower. The multivalve V6 was only introduced in North America in 2002 (where it retained the VR6 name).

Turbo-Diesel trucks were produced in Europe and America (notably by Cummins) after 1949. The corresponding multivalve V5 was only released in 2001, with a 20 PS power increase, to 170 PS (168 hp/125 kW). It is important to note that turbosupercharged aircraft engines actually utilized a gear-driven centrifugal type supercharger in series with a turbocharger. The VR6 name was dropped as a commercial designation, and the 4WD system (4Motion) was now standard on the V6 in Europe. Aircraft such as the Lockheed P-38 Lightning, Boeing B-17 Flying Fortress and B-29 Superfortress all used exhaust driven "turbo-superchargers" to increase high altitude engine power. The new version was not available in the Passat (as it was incompatible with the then-current generation's longitudinal layout), but was introduced as the range topper in the Golf and Bora. The primary purpose behind most aircraft-based applications was to increase the altitude at which the airplane can fly, by compensating for the lower atmospheric pressure present at high altitude. This engine produced 204 PS (201 hp/150 kW) and 265 Nm (195 lb.ft) of torque.

Turbochargers were first used in production aircraft engines in the 1930s prior to World War II. For 1999, VW added further modifications to the design, with the introduction of the 24-valve 2.8 L VR6. The engine was tested at Pike's Peak in Colorado at 14,000 feet to demonstrate that it could eliminate the power losses usually experienced in internal combustion engines as a result of altitude. It was introduced in the Passat in 1997, and later in the Golf and Bora in 1999. One of the first applications of a turbocharger to a non-Diesel engine came when General Electric engineer, Sanford Moss attached a turbo to a V12 Liberty aircraft engine. This version, which had a 2.3 L capacity, was capable of 150 PS (148 hp/110 kW) and had a maximum torque of 209 Nm (154 lb.ft). Diesel ships and locomotives with turbochargers began appearing in the 1920s. In 1997, VW removed a cylinder from the VR6, creating the VR5, the first block to use an uneven number of cylinders in a V design.

His patent for the internal combustion turbocharger was applied for in 1905. The corresponding Vento/Jetta VR6 versions appeared in the same years. The turbocharger was invented by Swiss engineer, Alfred Buchi, who had been working on steam turbines. North America only received this engine in 1995, at the same time the European model started to use the 2.9 L in the VR6 Syncro model. On September 21, 2005, Foresight Vehicle announced the first known implementation of such unit for automobiles, under the name TIGERS (Turbo-generator Integrated Gas Energy Recovery System).[2]. In 1992, with the introduction of the Golf's third generation, a six-cylinder engine was available for the first time in a lower-midsize segment hatchback in Europe. Turbo-Alternator[1] is a form of turbocharger that generates electricity instead of boosting engine's air flow. This version also had a free flowing 6 cm (2.5 in) catalytic converter, enlarged inlet manifold and larger throttle body.

Special attention to engine cooling and component strength is required because of the increased combustion heat and power. The Passat, Passat Variant wagon and US-spec Corrado used the original 2.8 L design, while the Euro-spec Corrado and the 4WD Passat Syncro received a 2.9 L version with 190 PS (187 hp/140 kW). Most applications produced by the major manufacturers (Beech, Cessna, Piper and others) increase the maximum engine intake air pressure by as much as 35%. The VR6 engine was introduced in Europe in 1991 in the Passat and Corrado, and in North America the following year. For this reason, such aircraft are sometimes refered to as being turbo-normalised. These engines produced 174 PS (172 hp/128 kW) and 240 Nm (177 ft·lbf) of torque. In aftermarket applications, aircraft turbochargers sometimes do not overboost the engine, but rather compress ambient air to sea-level pressure. The original VR6 engine displaced 2.8 L and featured a 12 valve design.

As the aircraft climbs, the wastegate is gradually closed, maintaining the manifold pressure at or above sea-level. There are several different variants of the VR6 engine. In the interests of engine longevity, the wastegate is usually kept open, or nearly so, at sea-level to keep from overboosting the engine. This is most similar to a DOHC Inline-6 engine. The wastegate is controlled manually, or by a pneumatic/hydraulic control system, or, as is becoming more and more common, by a flight computer. However, later (24 valve) VR6 engines use one camshaft for all intake valves and one camshaft for all exhaust valves. Most modern turbocharged aircraft use an adjustable wastegate. This is most similar to the operation of a SOHC V6 engine.

Small car turbos are increasingly being used as the basis for small jet engines used for flying model aircraft—though the conversion is a highly specialised job—one not without its dangers. In early (12 valve) VR6 engines, one camshaft is used per bank of cylinders. Contemporary examples of turbocharged performance cars include the Dodge SRT-4, Volkswagen GTI, Subaru Impreza WRX, Mazda RX-7, Mitsubishi Lancer Evolution, and the Porsche 911 Turbo. This simplifies engine construction and reduces costs. The Porsche 944 utilized a turbo unit in the 944 Turbo (Porsche internal model number 951), to great advantage, bringing its 0-100 km/h (0-60 mph) times very close to its contemporary non-turbo "big brother", the Porsche 928. The narrow angle between cylinder banks also allows just two camshafts to drive all of the valves, and a single cylinder head to be used. Saab has been the leading car maker using turbochargers in production cars, starting with the 1978 Saab 99. As a result, it is nearly as smooth as an Inline-6.

Small cars in particular benefit from this technology, as there is often little room to fit a larger-output (and physically larger) engine. In addition, the VR6 is able to use the firing interval of an Inline-6 engine.
Today, turbocharging is most commonly used on two types of engines: Gasoline engines in high-performance automobiles and diesel engines in work trucks. A wider V6 engine of conventional design would have required lengthening existing vehicles to provide enough crumple zone between the front of the vehicle and the engine, and between the engine and the passenger cell. Diesels are particularly suitable for turbocharging for several reasons:. By using the narrow 15° VR6 engine, it was possible to install a six-cylinder engine in existing Volkswagen models. In fact, for current automotive applications, non-turbocharged diesel engines are becoming increasingly rare. The VR6 was specifically designed for transverse installation in front wheel drive vehicles.

Turbocharging is very common on diesel engines in conventional automobiles, in trucks, for marine and heavy machinery applications. The combination of the two can be roughly translated as "in-line Vee.". Many diesel engines do not have any wastegate because the amount of exhaust energy is controlled directly by the amount of fuel injected into the engine, and slight variations in boost pressure do not make a difference for the engine. The name, VR6 comes from a combination of Vee and the German word Reihenmotor (straight engine). This is limited to keep the turbo inside its design operating range by controlling the wastegate which shunts the exhaust gases away from the exhaust side turbine. It is similar to the V engine, but with the cylinders offset from each other and tilted by 15° instead of the usual 60°. Boost refers to the increased manifold pressure that is generated by the intake side turbine. VR6 is an engine configuration developed by the Volkswagen Group.

On modern diesel engines, this problem is virtually eliminated by utilising a variable geometry turbocharger. . Race cars often utilise anti-lag to completely eliminate lag at the cost of reduced turbocharger life. SEAT Leon Cupra. Putting your foot down at 1200 engine rpm and having no boost until 2000 engine rpm is an example of boost threshold and not lag. Audi TT. Newer turbocharger and engine developments have caused boost thresholds to steadily decline to where day-to-day use feels perfectly natural. Audi A3 Mk.II.

The boost threshold of a turbo system describes the minimum turbo rpm at which the turbo is physically able to supply the requested boost level. VW Sharan/SEAT Alhambra/Ford Galaxy. Lag is not to be confused with the boost threshold, however many publications still make this basic mistake. VW Transporter T4 and T5. An example of this is the current BMW E60 5-Series 535d. VW Touareg. Sequential turbochargers are usually much more complicated than single or twin-turbocharger systems because they require what amount to three sets of pipes-intake and wastegate pipes for the two turbochargers as well as valves to control the direction of the exhaust gases. VW Phaeton.

Such combinations are referred to as "sequential turbos". VW Corrado. Being individually smaller they do not suffer from excessive lag and having the second turbo operating at a higher rpm range allows it to get to full rotational speed before it is required. VW Bora/VW Jetta Mk.IV. Below this rpm, both exhaust and air inlet of the secondary turbo are closed . VW Vento/VW Jetta Mk.III. Early designs would have one turbocharger active up to a certain rpm, after which both turbochargers are active. VW Passat (B3, B4, and B6 chassis).

A typical arrangement for this is to have one turbo active across the entire rev range of the engine and one coming on-line at higher rpm. Golf R32 MK.IV and Mk.V. Some car makers combat lag by using two small turbos (like Toyota, Subaru, Maserati, Mazda, and Audi). VW Golf Mk.III and Mk.IV. Such an arrangement of turbos is typically referred to as a "twin turbo" setup. The two smaller turbos produce the same (or more) aggregate amount of boost as a larger single turbo, but since they are smaller they reach their optimal rpm, and thus optimal boost delivery, faster.

Other setups, most notably in V-type engines, utilize two identically-sized but smaller turbos, each fed by a separate set of exhaust streams from the engine. Turbine clipping is measured and specified in degrees. The amount a turbine wheel is and can be clipped is highly application-specific. This imparts less impedance onto the flow of exhaust gasses at low rpm, allowing the vehicle to retain more of its low-end torque, but also pushes the effective boost rpm to a slightly higher level.

By clipping a minute portion off the tip of each blade of the turbine wheel, less restriction is imposed upon the escaping exhaust gases. Another common method of equalizing turbo lag, is to have the turbine wheel "clipped", or to reduce the surface area of the turbine wheel's rotating blades. Lag is also reduced by using a precision bearing rather than a fluid bearing, this reduces friction rather than rotational inertia but contributes to faster acceleration of the turbo's rotating assembly. Increasing the upper-deck air pressure and improving the wastegate response help but there are cost increases and reliability disadvantages that car manufacturers are not happy about.

Another way to reduce lag is to change the aspect ratio of the turbine by reducing the diameter and increasing the gas-flow path-length. Unfortunately, their relative fragility limits the maximum boost they can supply. Ceramic turbines are a big help in this direction. Lag can be reduced by lowering the rotational inertia of the turbine, for example by using lighter parts to allow the spool-up to happen more quickly.

Conversely on light loads or at low rpm a turbocharger supplies less boost and the engine is more efficient than a supercharged engine. (Centrifugal superchargers do not build boost at low RPM's like a positive displacement supercharger will). The directly-driven compressor in a positive-displacement supercharger does not suffer this problem. 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.

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. Diesel engines are usually much kinder to turbos because their exhaust gas temperature is much lower than that of gasoline engines and because most operators allow the engine to idle and do not switch it off immediately after heavy use. In custom applications utilising tubular headers rather than cast iron manifolds, the need for a cooldown period is reduced because the lighter headers store much less heat than heavy cast iron manifolds. It is still a good idea to not shut the engine off while the turbo and manifold are still glowing.

The water boils in the cartridge when the engine is shut off and forms a natural recirculation to drain away the heat. Turbos with watercooled bearing cartridges have a protective barrier against coking. A turbo timer is a device designed to keep an automotive engine running for a pre-specified period of time, in order to execute this cool-down period automatically. Even small particles of burnt oil will accumulate and lead to choking the oil supply and failure.

Not doing this will also result in the critical oil supply to the turbocharger being severed when the engine stops while the turbine housing and exhaust manifold are still very hot, leading to coking (burning) of the lubricating oil trapped in the unit when the heat soaks into the bearings and later, failure of the supply of oil when the engine is next started causing rapid bearing wear and failure. This lets the turbo rotating assembly cool from the lower exhaust gas temperatures. Saab, in its owner manuals, recommends a period of just 30 seconds. After high speed operation of the engine it is important to let the engine run at idle speed for one to three minutes before turning off the engine.

The use of synthetic oils is recommended in turbo engines. Replacing a turbo that lets go and sheds its blades will be expensive. As long as the oil supply is clean and the exhaust gas does not become overheated (lean mixtures or retarded spark timing on a gasoline engine) a turbocharger can be very reliable but care of the unit is important. Turbocharger manufacturer Aerocharger uses the term 'Variable Area Turbine Nozzle' (VATN) to describe this type of turbine nozzle.

This type of turbine is called a Variable Nozzle Turbine (VNT). It utilised a turbo from Garrett, called the VNT-25 because it uses the same compressor and shaft as the more common Garrett T-25. The first car manufacturer to use these turbos was the limited-production 1989 Shelby CSX-VNT. The vanes are controlled by a membrane identical to the one on a wastegate but the level of control required is a bit different.

In many setups these turbos don't even need a wastegate. These turbochargers have minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. Some turbochargers utilise a set of vanes in the exhaust housing to maintain a constant gas velocity across the turbine, the same kind of control as used on power plant turbines. Another method of raising the boost pressure is through the use of check and bleed valves to keep the pressure at the membrane lower than the pressure within the system.

This solenoid can be controlled by Automatic Performance Control, the engine's electronic control unit or an after market boost control computer. The wastegate is opened and closed by the compressed air from turbo (the upper-deck pressure) and can be raised by using a solenoid to regulate the pressure fed to the wastegate membrane. This regulates the rotational speed of the turbine and the output of the compressor. To manage the upper-deck air pressure the turbocharger's exhaust gas flow is regulated with a wastegate that bypasses excess exhaust gas entering the turbocharger's turbine.

Turbochargers with foil bearings are in development which eliminates the need for bearing cooling or oil delivery systems. Some car makers use water cooled turbochargers for added bearing life. Lower friction means the turbo shaft can be made of lighter materials, reducing so-called turbo lag or boost lag. Some turbochargers use incredibly precise ball bearings that offer less friction than a fluid bearing but these are also suspended in fluid-dampened cavities.

The oil is usually taken from the engine-oil circuit and usually needs to be cooled by an oil cooler before it circulates through the engine. These feature a flowing layer of oil that suspends and cools the moving parts. Such high rotation speeds would cause problems for standard ball bearings leading to failure so most turbo-chargers use fluid bearings. A turbo spins very fast; most peak between 80,000 and 150,000 rpm (using low inertia turbos, 190,000 rpm) depending on size, weight of the rotating parts, boost pressure developed and compressor design.

Compressed air from a turbo may be (and most commonly is, on petrol engines) cooled before it is fed into the cylinders, using an intercooler or a charge air cooler (a heat-exchange device). It is not uncommon for a turbocharger to be pushing out air that is 90 °C (200°F). When a gas is compressed, its temperature rises. The pumping-effect heating can be alleviated by aftercooling (sometimes called intercooling).

The higher temperature is a volumetric efficiency downgrade for both types of engine. This increase in charge temperature is a limiting factor for petrol engines that can only tolerate a limited increase in charge temperature before detonation occurs. A main disadvantage of high boost pressures for internal combustion engines is that compressing the inlet air increases its temperature. This last factor makes turbocharging aircraft engines considerably advantageous—and was the original reason for development of the device.

However, for operation at altitude, the power recovery of a turbocharger makes a big difference to total power output of both engine types. This disadvantage does not apply to specifically designed turbocharged diesel engines. A disadvantage in gasoline engines is that the compression ratio should be lowered (so as not to exceed maximum compression pressure and to prevent engine knocking) which reduces engine efficiency when operating at low power. This engine rpm is referred to as the boost threshold.

Because it is a centrifugal pump, a typical turbocharger, depending on design, will only start to deliver boost from a certain rpm where the engine starts producing enough exhaust gas to spin the turbocharger fast enough to make pressure. For automobile use, typical boost pressure is in the general area of 80 kPa (11.6 lbf/in²), but it can be much more. However, there are some parasitic losses due to heat and exhaust backpressure from the turbine, so turbochargers are generally only about 80% efficient, at peak efficiency, because it takes some work for the engine to push those gases through the turbocharger turbine (which is acting as a restriction in the exhaust) and the now-compressed intake air has been heated, reducing its density. For example, at 100% efficiency a turbocharger providing 101 kPa (14.7 lbf/in²) of boost would effectively double the amount of air entering the engine because the total pressure is twice atmospheric pressure.

The energy from the extra fuel leads to more overall engine power. The increase in pressure is called "boost" and is measured in pascals, bars or lbf/in². The additional fuel is provided by the proper tuning of the fuel injectors or carburetor. This greatly improves the volumetric efficiency of the engine, and thereby creates more power.

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). But because of "turbo lag" (see below), engines with mechanical superchargers are typically more responsive. Because the turbine of a turbocharger is in-itself a heat engine, a turbocharger equipped engine will normally compress the intake air more efficiently than a mechanical supercharger. The term supercharger is very often used when referring to a mechanically driven turbocharger, which is most often driven from the engine's crankshaft by means of a belt (otherwise, and in many aircraft engines, by a geartrain), whereas a turbocharger is exhaust-driven, the name turbocharger being a contraction of the earlier "turbosupercharger".

The compressor and turbine spin on the same shaft, similar to a turbojet aircraft engine. A turbocharger also has a turbine that powers the compressor using wasted energy from the exhaust gases. 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 is an exhaust gas driven supercharger.

. 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 compressor used in internal-combustion engines to increase the power output of the engine by increasing the mass of oxygen entering the engine. For other meanings of turbo, see turbo (disambiguation).

This article describes the internal combustion engine component often known as a turbo. Automobile magazine (February 2006).. Happy 100th Birthday to the Turbocharger. Don Sherman.