25-Years of VW Diesels...
Featured in the VW Vortex... Compiled by Jamie VonDrusca

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Volkswagen's 25th Anniversary of Diesel Technology - In celebration of the 25th anniversary of TDI technology, Volkswagen announces several key technologies.

        The following is an extensive news release from VWAG celebrating the 25th anniversary of the TDI diesel engine. A good portion of the information presented applies to the European market only, but some of the new products and technologies highlighted will find their way into North American Volkswagen and Audi products.

        Twenty-five years ago, Volkswagen achieved a breakthrough in passenger-car diesel engines. It is celebrating this anniversary with three technical highlights:

1)  the world's first 10-cylinder TDI diesel engine, with a displacement of five liters and a power output of 230 kW (313 bhp) - currently the most powerful passenger-car diesel in the world

2)  a new generation of transmissions capable of handling the enormous increase in power and torque from the new diesel engines, with provision for all-wheel drive

3)  the many-faceted VW exhaust emission control strategy, which will comply with forthcoming pollution limits by means of internal engine design measures and after-treatment of the exhaust gas.


Looking back

       In the spring of 1976, when series production of VW's first diesel passenger-car engine began - the legendary 1.5-liter, 50-bhp naturally aspirated unit for use in the Golf - this was the start of the diesel's triumphal progress, initially in VW Group products but later throughout the automobile world. Whereas many people were reluctant to accept this trend towards a type of engine that in the past had always been a rather rough runner, and doubted its suitability, the compression-ignition engine has long since ceased to be an unusual phenomenon on the passenger-car market and has become a genuine trendsetter with a higher efficiency level than any rival form of power unit. Above all, its response at low engine speeds and the immense reserves of pulling power it can make available instantly are convincing reasons why the modern passenger-car diesel engine has become such a convincing source of driving pleasure.

        Today, the passenger-car diesel has already passed the 10-, 20- and 30-percent market share marks in Germany and is likely to break the 40-percent barrier any time now. Before long it could even account for half of the power units in cars sold on the German market. Progress in its development, for example the introduction of direct injection, turbocharging and exhaust gas recirculation, is also proving of benefit to the spark-ignition engine.

        Stimulated by the oil crisis in the early 1970s and encouraged by the first statutory exhaust emission limits, with which the diesel in those days was actually able to comply more readily than the spark-ignition engine, a development process began that had the initial task of making good the performance handicap of a relatively small engine and reducing the diesel's higher noise emissions. Although the 1.5-liter diesel provided the kind of performance expected of it right from the start and was capable of accelerating the Golf from a standstill to 100 km/h (62 mph) in only 18 seconds and maintaining a continuous top speed of 140 km/h (87 mph), it was evident that higher power would be needed in the next development stage. This speeded up the transition to forced aspiration by turbocharger in the early 1980s; by 1982 the "Turbodiesel" (TD) had appeared and developed 70 bhp from a displacement of 1.6 liters.

150-hp four cylinder 1.9-liter TDI...        At the beginning of the 1990s, Volkswagen together with its Audi brand took a further most decisive step forward by introducing direct injection. The first four-cylinder diesel engine with this form of fuel injection appeared in 1991, and was known as the TDI, the initials standing for turbocharged direct injection. Once again, the major problem to be overcome initially concerned the engine's noise emissions, but despite this it was clear that direct injection was the only practicable way to access all the performance reserves inherent in the diesel combustion principle. Compared with comparable indirect injection engines, the TDI had a fuel-saving potential of up to 15 percent, and as the noise problem was brought under control the TDI engines were able to achieve their rightful lead over their competitors.

        A further development stage led to the adoption of the variable-geometry turbocharger, which further improved the flexibility of the four-cylinder TDI engine and enabled the power output of what was by now a 1.9-liter unit to be boosted from 90 to 110 bhp. This development progress was marked by coloring the "I" red in the TDI logo.

        Volkswagen once again scaled new heights in diesel engine development by adopting high-pressure fuel injection. Knowing that combustion quality depends directly on the absolute pressure at which fuel can be injected into the cylinders, VW decided to adopt the pump-injector principle, which from the very start was able to guarantee the necessary high injection pressures. At the same time, a defined volume of fuel was injected as a pilot stroke before the main injection stroke - the ideal method of achieving a smooth combustion process in a high-performance diesel engine. The two red letters "DI" in the logo are a sign that the pump-injector principle is being used.

        As a sign of true leading-edge technology, there are also production models with all three letters of the TDI badge in red. With high-performance charge-air intercooling and optimized fuel injection, the most powerful version of the 1.9-liter four-cylinder engine has since the beginning of this year been rated at 150 bhp, the highest power output currently available. The current generation of two-valve, four-cylinder engines is produced in three power outputs, namely 100, 130 and 150 bhp, and is clear evidence of the potential possessed by Volkswagen's TDI engines using the pump injector principle.


Formula One in diesel engine technology: leading-edge features of the new V-10 TDI

313-hp 553-ft/lbs V-10 TDI        Volkswagen is celebrating twenty-five years of diesel engine development for its passenger-car range with a new top-level engine for the luxury car and SUV vehicle categories - a ten-cylinder TDI unit with twin ('biturbo') turbochargers and pump-injector fuel injection for the ultimate in tractive force and pulling power. With an output of 230 kW (313 bhp) and a maximum torque of 750 newton-metres (553 lb/ft of torque), this five-liter passenger-car diesel engine has a hitherto unattained performance level.

        It clearly imposes severe loads on the transmission and driveline components, making a version of the various all-wheel-drive systems developed to production maturity within the Volkswagen Group the only practicable means of transferring this power and torque reliably to the road.

        It's no coincidence that this new top-level diesel from Volkswagen has ten cylinders and thus an important design element in common with modern Formula One engines. VW's development teams could be said to be emulating their motor sport colleagues by exploring such new paths. Although they were able to make full use of the vast experience already gained from the construction of the existing 3-, 4-, 5- and 6-cylinder TDI engines, the sheer size and power of the new unit made an unconventional design approach and totally new manufacturing methods necessary.

Weight-saving, compact construction

        Whereas the most widely used of the current TDI engines, the 1.9-liter four-cylinder unit, has a crankcase and cylinder block made from high-quality grey cast iron, the new top-level engine makes use of the weight-saving concept developed for the 1.2-liter, three-cylinder that powers the Lupo "three-liter" model. It was of course important for weight saving not to be obtained at the expense of noise. The 10-cylinder engine therefore has a particularly rigid aluminum crankcase with an innovative grey cast iron bearing tunnel into which combustion forces are introduced directly by way of the cylinder head studs.

       This change to an aluminum cylinder block enables another important new technology to be adopted - plasma coating of the cylinder walls. This process, developed by Volkswagen and used here for the first time on a production diesel engine, creates a surface layer in the cylinders with a thickness of a few tenths of a millimeter and makes the cylinder walls permanently resistant to deformation and wear.

        Arranging the cylinders in a V pattern in two rows of five has the advantage that the main auxiliaries such as the water pump and the water-cooled alternator can be located within the V and driven by shaft without lateral forces developing.

        In order to accommodate the intake pipes within the V as well, the cylinder heads were converted to the cross-flow principle as also used successfully on the four-cylinder TDI engines with pump injector fuel supply and two valves per cylinder. The two exhaust manifolds are on the outer faces of the two cylinder banks of this V10 engine.

Eliminating vibration and torque reactions

        Among the new engine's most important criteria are not only peak power and torque figures and the supreme performance they permit, but also exceptional freedom from vibration. The choice of a 90-degree included angle between the cylinder banks permits the free inertial forces to be fully balanced out. In addition, the crankshaft throws are offset in such a way that second-order free moments of inertia are negligibly small.

        In order to suppress the remaining first-order free inertial moments as completely as possible, the engine has, in addition to the usual counterweights on the crankshaft webs, a balance shaft that rotates at the same speed as the crankshaft but in the opposite direction. In addition, vibration under load is smoothed out by the uniform ignition spacing of 72 degrees between the cylinders; this is achieved by offsetting the crankpins by 18 degrees. By these methods, engine oscillation caused by the moving masses can be limited to only a few thousandths of a millimeter, and the V10 TDI engine is capable of standing up to any comparison with a 12-cylinder engine. The torsional vibration damper on the crankshaft is of viscous pattern and occupies a space only 24 millimeters deep.

        The method used to drive the camshafts also helps to make this engine exceptionally compact. Instead of a timing chain or toothed belt, a helical-cut spur gear train is provided at the flywheel end of the engine. This is also capable of transmitting the high peak loads that occur in the timing gear because the pump-injector units also have to be actuated. The timing case in which the gearwheels is a high-strength casting bolted directly to the engine's bearing tunnel as a means of attenuating the transmission of noise to the engine block. A plate-type joint in the timing gear compensates for the difference in thermal expansion compared with the aluminum engine block. From the timing gear, intermediate shafts and gears drive the auxiliaries such as the air conditioning compressor, power steering pump, water pump and 190 Amp/h alternator.

        Since this engine is destined for use not only in the new high-performance saloon model but also as a powerful, economical unit for the SUV model currently under development, which is required to have good off-road capabilities, its lubricating system must be capable of coping with even extreme operating situations. With its duplex oil delivery pump and two scavenging pumps, its operating reliability has been confirmed in numerous tests performed at extreme operating angles. A sensor is provided to warn the driver when the oil level falls too low, and the engine oil change intervals can be prolonged to as much as 50,000 kilometres (31,000 miles).

Combustion gas flow and engine management

        The new V10 TDI engine owes its lead in the mixture formation, combustion and power-output areas to leading-edge fuel injection technology, forced aspiration, exhaust gas recirculation and advanced engine management. This includes use of the latest pump injector system for the fuel supply with five-hole injector nozzles delivering the fuel to the combustion chambers at pressures up to 2050 bar.

        Twin turbochargers supply the combustion air, one for each cylinder bank (the "biturbo" principle). The variable turbine blades are not actuated pneumatically as in previous versions of the turbocharger, but electrically, which provides more accurate control of blade movement. In addition to the charge-air intercooler there are coolers integrated into the exhaust gas recirculation lines to increase efficiency. The engine can be regarded as two five-cylinder units coupled together mechanically but with separate air intake and exhaust systems; these two units are jointly controlled by interconnected electronic diesel-engine management systems of the latest type, supplied by the Bosch company.

        The Volkswagen V10 TDI engine exhaust emissions are below the latest limits and it can, if more stringent demands arise, be equipped with exhaust after-treatment systems such as the CRT particle filter with continuous regeneration which Volkswagen has developed.

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