The compact 1.4 litre direct-injection engine develops up to 125 kW and has a maximum torque of an amazing 240 newton metres in the range from 1,750 to 4,500 rpm thanks to the combination of an exhaust turbocharger with a mechanically driven supercharger.

The 1.4 litre engine delivers a power output of 90 kW per litre, representing a peak value for a series production four-cylinder engine. Furthermore, the TSI delivers a torque corresponding to a naturally aspirated engine with a swept volume of approximately 2.3 litres. And its fuel consumption is around 20 percent lower.

THE CONCEPTUAL IDEA
A compact FSI engine with turbo and supercharging as an approach to the solution

The most effective way to reduce fuel consumption is referred to as down sizing. A reduction in cubic capacity and therefore lower friction losses result in a low specific consumption, which equates to better efficiency. However, an engine with a low cubic capacity only meets the current requirements for active road safety and pleasurable driving to a very limited extent. As a result, the objective can only be achieved by supercharging.

Classic turbo engines with a small cubic capacity using exhaust turbochargers, have only been used to a very limited extent in the past since they have low moving-off power and are therefore less acceptable.

This problem can be solved by a mechanically driven supercharger that supplies additional fresh air to the engine even at low speeds. The challenge was to combine these two systems in a rational way.

The only candidate for injection technology was the FSI technology that is now used by Volkswagen in numerous model ranges. Experience gathered during the last few years by engine developers at Volkswagen in this injection technology had revealed that FSI could be ideally complemented by the two different charging techniques, the result being a previously unheard of increase in efficiency.

This gave rise to the world’s first direct-injection engine with twin charging for use in high-volume series production – the TSI.

THE IMPLEMENTATION
Supercharger for power at low speeds, turbocharger for power at high speeds

The choice for the basic power unit was the FSI from the EA 111engine series as used in the Golf in power levels of 66 kW (1.4-litre) or 85 kW (1.6-litre). The 1.4-litre engine is a four-valve four-cylinder engine with a swept volume of 1,390 c.c., a cylinder gap of 82 millimetres and a bore/stroke ratio of 76.5 to 75.6 millimetres. The focus in developing the TSI engine was placed on designing a new, highly resilient grey cast iron cylinder crankcase in order to withstand the high pressure of up to 21.7 bar over long periods, a water pump with integrated magnetic clutch and twincharging technology.

However, the injection technology was also modified. A multiplehole high-pressure injection valve with six fuel outlet elements is used for the first time in the 1.4 litre TSI engine.

The injector, like that in the naturally aspirated FSI engines, is arranged on the intake side between the intake port and cylinder head seal level. The quantity of fuel to be injected between idling speed and the 90 kW/litre output power requires a wide variability in the fuel flow through the completion of injection under full-load conditions on the one hand and idling speed with reproducibly low injection volumes on the other hand. The maximum injection pressure was increased to 150 bar in order to achieve this wide range of throughflow. Furthermore, only FSI technology made it possible to achieve a compression ratio of 10:1 which is high for supercharged engines.

The Volkswagen engine developers selected a supercharger with a mechanical belt drive in order to increase the torque at low engine speeds. This supercharger unit is based on the Roots principle. One special feature of the supercharger is its internal step-down ratio on the input end of the synchronisation gear pair.

The exhaust turbocharger also kicks in at higher engine speeds (with wastegate control). The supercharger and exhaust turbocharger are connected in series in this case. The supercharger is operated by a magnetic clutch. A control flap ensures that the fresh air required for the operating point can get through to the exhaust turbocharger or the supercharger. The control flap is open when the exhaust turbocharger is operating alone. In this case, the air follows the normal path as in conventional turbo engines, via the front charge-air cooler and the throttle valve into the induction manifold.

One of the major challenges facing the development was to achieve the best possible interplay between the turbo and superchargers arranged in series. Only when both units – the supercharger and the exhaust turbocharger – complement one another optimally can the small power unit achieve its required, level torque characteristic over a broad engine speed range in conjunction with a previously unheard of increase in efficiency.

THE RESULT
A twin-charged FSI with two power levels

The ambitious objective of squeezing an output per litre in excess of 90 kW per litre swept volume out of a 1,400 c.c. engine could not be achieved with single-stage supercharging alone. However, an upstream supercharger enables the boost pressure buildup of the exhaust turbocharger to be significantly increased.

The maximum boost pressure of the TSI is approximately 2.5 bar at 1,500 rpm, with the exhaust turbocharger and the mechanical supercharger being operated with about the same pressure ratio (approx. 1.53). A straight exhaust turbocharged engine without supercharger assistance would only achieve a pressure ratio of about 1.3 bar here. The more rapid response of the exhaust turbocharger enables the supercharger to be depressurised earlier by continuous opening of the bypass valve. This means supercharger operation is restricted to a narrow map area with predominantly low pressure ratios and, therefore, low power consumption. Consequently, the disadvantage of the mechanical supercharger system in terms of consumption can be limited.

In practice, this means the supercharger is only required for generating the required boost pressure in the engine speed range up to 2,400 rpm. The exhaust turbocharger is designed for optimum efficiency in the upper power range and provides adequate boost pressure even in the medium speed range. In dynamic driving, this is inadequate for the specified in-gear acceleration values in the low engine speed range. In these driving situations, the supercharger is engaged to permit a spontaneous boost pressure buildup. The way in which these two systems complement each other means there is absolutely no turbo lag.

The supercharger is no longer needed above an engine speed of 3,500 rpm at most, as the exhaust turbocharger can definitely provide the necessary boost pressure even dynamically during the transition from coasting to full-load operation.

THE DRIVING EXPERIENCE
High performance and torque produce low fuel consumption and a dynamic driving experience

The supercharger, delivers a boost pressure of 1.8 bar even just above idling speed. This provides the power needed when moving off. An electromagnetic clutch integrated into the module of the coolant pump is responsible for switching the supercharger on and off. It is driven by an additional belt. A torque of 200 newton metres is available at a speed of only 1,250 rpm – and all the way through to 6,000 rpm. In dynamic supercharger mode, the automatic boost pressure control decides whether the supercharger will be switched on in accordance with the tractive power required, or if the turbocharger alone can generate the necessary boost pressure. The supercharger is switched on again if the speed drops to the lower range and then power is demanded again. The turbocharger alone delivers boost pressure above 3,500 rpm.

In practice, the 1.4 TSI drives like a big naturally aspirated engine with 2.3-litre capacity. This is because the maximum torque of 240 newton meters is available from 1,750 rpm to 4,500 rpm. The boost pressure gauge installed as standard in the cockpit of the Golf GT 1.4 TSI is the only signal of the furious activity being undertaken by the twinchargers and the complex procedure of harmonizing both systems taking place under the bonnet. The driver likes it, because when the needle is fully deflected then the acceleration really presses the occupants back into their sports seats (fitted as standard).

The smooth torque characteristic allows the driver to refrain from gear changes whilst still driving briskly. It goes without saying that the TSI is a much more freer revving engine than a diesel engine. Indeed, the 1.4 TSI has a maximum engine speed of 7,000 rpm. Thanks to this outstanding engine performance, overtaking on country roads is particularly effortless and much more rapid than is the case with a naturally aspirated engine. The value for in-gear acceleration from 80 to 120 km/h in fifth gear in 8.0 seconds can only serve as a reference here. Active safety has seldom been improved in this way without having an effect on fuel consumption.

This is because very low fuel consumption values are possible due to the generous torque and the high level of power that allow a correspondingly relaxed driving style in the Golf GT, the 1.4 TSI engine obtains a fuel consumption figure of only 7.71/100km. In the Golf GT, the 1.4 TSI gets along with only 7.7 l/100 km of fuel used. This is about 20 percent less than in a naturally aspirated engine with comparable torque and power and a cubic capacity of approximately 2.3 litres.

In combination with a DSG transmission, the power developed by the 1.4 TSI will be appreciated even more due to the gearshifts without any interruption in traction. Furthermore, the advantage in terms of fuel consumption, far from being compromised by this innovative automatic, is in fact the same.

QUALITY AND PRODUCTION
High-quality materials and assembly assure a long service life

The selection of materials that are resistant to high-temperatures does more than make it possible to keep consumption down to the best possible level at high speed. In spite of the high output per litre, the high pressure level in the engine and possible engine speeds of up to 7,000 rpm, the TSI is designed for a long service life with the same criteria that apply to all power units from Volkswagen. More than 250 prototype and pilot series engines were put through their paces in all necessary test cycles. Every single component of this new power plant has been designed for the engine service life and has come through its baptism of fire. Endurance runs corresponding to a mileage of 300,000 km (186,420 miles) have been successfully completed. The cylinder crankcase is made from grey cast iron and guarantees complete operating reliability even at the high peak pressures of up to 120 bar. The highly qualified personnel at the Chemnitz Engine Works use optimised production processes and the latest measuring technology to ensure that these high-tech power plants are assembled without defects.

THE PRICE

	Golf GT 1.4 TSI	Golf 2.0 FSI
Swept volume	1,390 cc	1,984 cc
Bore/stroke	76.5/75.6 mm	82.5/92.8 mm
Valves per cylinder	4	4
Compression	10.0 : 1	11.5 : 1
Compressor	Supercharging Turbocharger	–
Boost pressure	2.5 bar	–
Power	125 kW at 6,000 rpm	110 kW at 6,000 rpm
Torque	240 Nm at 1,750 - 4,500 rpm	200 Nm at 3,500 rpm
0 - 100 km/h	7.9 s*	8.8 s*
In-gear 80 - 120 km/h	8.0 s*	9.0 s*
5th gear
Maximum speed	220 km/h	209 km/h
Consumption	7.71/100*	8.01/100*
CO2 emissions	183 g/km*	192 g/km*

* Manual gearbox