|The emissions control system on the Tier 2 Bin 5 TDI. Click to enlarge.|
Audi used its TechDay event in Germany to outline its strategy for achieving a 20% reduction in fuel consumption and CO2 emissions from its models by 2012.
At the heart of the strategy are the next-generation, Tier 2 Bin 5 compliant diesels (earlier post) and a set of technologies from what Audi calls its Modular Efficiency program. Hybrid systems round off Audi’s efficiency strategy.
According to a 2006 study by the European environmental organization Transport and Environment, Audi’s new car fleet averaged 177 g/km CO2 in 2005, down from 190 g/km in 1997. A 20% reduction by 2012 would put Audi at approximately 140 g/km—more than the expected European legislative target of 130 g/km for vehicle technology.
We shall continue to bolster the position of the TDI as a highly efficient power system. And with our TFSI engines, optimized vehicle architecture and hybrid modules, we shall offer solutions for all standards and all applications, solutions that combine a high degree of driveability with exemplary low fuel consumptions.—Rupert Stadler, Chairman of the Board of Management of AUDI AG
TDI diesels. The first of the new 2008 diesel engines will be three-liter V-6 units for the Audi A4 and Audi Q7. These engines will develop 176 kW (240 hp) and deliver peak torque of 500 Nm (369 lb-ft) in the Audi A4 and 550 Nm (406 Nm) in the Audi Q7.
Audi says that additional models will quickly follow. By 2010, Audi plans to offer the new technologies in other vehicles segments and power classes.
A new piezo common rail injection system supports injection pressures of 2,000 bar (200 MPa or 29,000 psi). New combustion chamber sensors will enable more precise regulation of the combustion processes. A combination of efficient exhaust gas recirculation and optimized turbocharging will deliver a sharp reduction in engine-out emissions.
The exhaust gases first pass through an oxidation catalytic converter located close to the engine, then to a diesel particulate filter. (See drawing above.) Both the oxidation catalytic converter and the particulate filter are part of the standard exhaust gas aftertreatment system on current Audi TDI vehicles.
For further NOx reduction, Audi is adding a urea SCR system, which will reduce NOx emissions by up to 90%. The SCR system comprises the catalytic converter, the metering module, an AdBlue tank and heated lines, as well as multiple sensors.
The sensors measure NOx concentration before the diesel particulate filter and after the DeNOx converter to compute the necessary injection volume of AdBlue. In addition, pressure and temperature sensors monitor the operation of the exhaust gas aftertreatment system.
The AdBlue volume of about 22.5 liters is divided between two reservoirs. The active tank holds 7 litres and is located directly under the fuel filler neck, while the passive tank holds 15.5 liters and is in the underfloor area.
A 5-bar pump transfers the AdBlue solution from the active tank to the metering module on the exhaust system. The passive tank holds additional volume. A transfer pump tops up the active tank as necessary. Both the fuel tank and the AdBlue tanks are filled at the fuel filler flap. Vehicles with ultra low emission system can thus also be recognized by the additional filler neck under the fuel filler flap.
AdBlue freezes at a temperature of -11°C. This means that the AdBlue tank system needs to be partially heated for operation in extremely cold conditions. The active tank, the metering pipe and the metering pump are then automatically heated.
Audi will market these new models in the USA and in Europe from the second half of 2008.
Modular Efficiency Program. To further reduce the fuel consumption of its TDI and turbocharged direct-injection TFSI gasoline engines, Audi is working on the Modular Efficiency Program, whose various modules will be used on future models.
A core element of the program is the start/stop system and regenerative braking. The energy management system uses the coasting and braking phases to generate and store electrical energy which is then used to relieve the load on the alternator and the vehicle electrical system at standstill and when accelerating.
The Audi system uses supercapacitors for energy storage. In coasting and braking phases, the secondary voltage from the DC/DC converter is raised to into the range from 16 to 40 volts and the supercaps are charged. Its voltage rises with increasing charge up to 40 V. The maximum electric charging power is 1,000 W. A full charge takes about 13 seconds.
When the coasting/braking phase is over, the supercap is discharged in a controlled manner, making use of up to 300W. It supplies electrical energy to the vehicle electrical system and so relieves the load on the alternator, or the vehicle battery when the engine is not running.
Audi is currently testing two vehicles that are equipped with both a start/stop system and technology for energy recuperation in conjunction with TDI and TFSI engines. Together, the two systems reduce fuel consumption in the Audi A5 2.0 TFSI and A6 2.7 TDI by about 0.4 liters per 100 km.
Other elements of the Modular Efficiency program are ancillaries with optimized power requirements, a newly designed air-conditioning system and a gearbox preheating system to increase the efficiency of the transmission.
|Audi’s e-models deliver a further 8-10% reduction in fuel consumption. Click to enlarge.|
e-models. Audi’s e-models (earlier post) will support further reduction in fuel consumption with optimized rolling resistance, better aerodynamics figures, specially configured gearboxes and transmission ratios, and reduced friction.
The current Audi A3 1.9 TDI e offers average fuel consumption of 4.5 l/100km (52.3 mpg US) (combined cycle) and CO2 emissions of 119 grams per kilometer. In the future, Audi will expand the range of such especially efficient models, offering e-models as TDI, FSI and TFSI in the high-volume model series. From 2009, the technologies that so effectively reduce fuel consumption will be gradually introduced on all Audi models.
|The Q7 hybrid performance and fuel consumption. Click to enlarge.|
Hybrids. Audi says that hybrid systems may “still be interesting” for specific requirements in certain markets. Audi is developing hybrid systems for several model series and will put these into series production wherever substantial benefits for the customer can be seen. The gasoline-electric hybrid systems must, according to Audi, rival the efficiency of the latest TDI technology.
Audi has been working on a Q7 hybrid (earlier post), first shown in 2005.
Audi’s hybrid drive in the Q7 uses a 3.6 liter FSI V6 with an output of 206 kW (280 bhp) and a peak torque of 375 Nm (277 lb-ft). A 34 kW electric motor located between the V6 and the torque converter of the six-speed tiptronic gearbox adds up to 285 Nm (210 lb-ft) of additional torque. The motor has a diameter of 330 millimeters and a length of 55 mm.
A separating clutch links the three-phase synchronous motor with the engine. This makes it possible to drive the car with either of the power plants or with both together.
Power is stored in a 1.7 kWh, 288V NiMH battery pack, made from 240 cells. A fan ventilates it with cooled air from the vehicle interior to make sure that it remains in the optimal temperature range. The battery weighs 69 kg and the hybrid module with the electric motor 40 kg.
A number of modifications in the periphery were necessary for the 3.6 FSI to be used on the Audi Q7 hybrid. The A/C compressor, the oil pumps for the power steering and automatic gearbox and the vacuum pump for the brake booster are all electrically driven. The new electrohydraulic power steering has the advantage that it needs almost 90% less fuel than a conventional system. The vehicle electrical system receives its 3 kW of power from the drive battery via a voltage transformer.
The hybrid system supports three basic driving modes are possible. The FSI and the electric motor can each work on their own as the drive unit, or the vehicle can combine the power of the two for acceleration. In this mode, the gasoline engine is responsible for basic operation, whereby it also needs to supply energy to the battery.
The electric motor can be used alone for speeds up to 50 km/h (31 mph)—i.e. in city traffic. The capacity of the battery allows the vehicle to be driven up to two kilometers (1.2 miles) on purely electrical power. When the capacity limit of the battery has been reached, the combustion engine is activated to recharge the battery.
The output of 206 kW / 280 bhp and the torque of 375 Nm that the 3.6-liter FSI engine develops are enough to accelerate the standard Audi Q7 from 0 to 100 km/h in 9.3 seconds. If the driver wants to accelerate even faster, the electronics also activate the electric motor.
Audi estimates that the hybrid Q7 offers combined NEDC fuel consumption of 9.9 l/100km (23.8 mpg US), a 22% reduction from the standard 12.7 l/100km. Estimated CO2 emissions from the hybrid are 231 g/km, compared to 304 g/km in the conventional Q7.
|The future of fuels from Audi’s perspective. Click to enlarge.|
Biofuels. Although Audi began supporting biodiesel in 1996 with approval for 100% rapeseed methyl ester (B100) in its entire TDI fleet, it withdrew that approval in 2003, and now only supports blends of up to 5% biodiesel due to a variety of concerns with engines and exhaust systems.
Rather than expecting improvements in esterized vegetable oils, Audi is instead looking to hydrogenated vegetable oils (HVO) produced in refinery processes and to second-generation biomass-to-diesel (BTL) synthetic fuels.
The synthetic biofuel (such as SunFuel) improves the combustion process inside the engine, according to Audi, and reduces well (field)-to-wheel lifecycle CO2 emissions.
Audi calculates that an A3 1.9 TDI driven on SunFuel emits less than 20 grams of CO2 per kilometer, even taking the entire process chain into account. Audi provides extensive support for this integrated approach for better fuels, and says that clear political signals are needed if they are to become widespread.
Audi also touched on the potential of other Fischer-Tropsch fuels derived from natural gas or coal, noting, however, that “large volumes of CO2 are released in the CTL process.”
E85 concept. Audi is developing an E85 concept based on the 2.0 TFSI engine. Configured for operation using ethanol, it develops 320 Nm (236 lb-ft) of torque at 1,500 rpm, with rated output of 132 kW/177 hp.
Audi does not use bioethanol’s higher octane rating to increase torque and output, but rather to optimize the engine’s efficiency. The advantage of this strategy, according to Audi, is that the increase in fuel consumption that results from the lower energy content of ethanol can be reduced by up to 50% under certain conditions, cutting the losses in range.
Only relatively minor modifications are needed on the vehicle itself. New materials are needed in the complete fuel system, including the tank, primer pump, fuel lines and activated charcoal filter system, which are not affected by the highly corrosive components of the fuel. Seals, gaskets and O-rings could otherwise be prone to swelling.
Similarly, all materials that come into contact with ethanol in the periphery of the engine&madsh;in particular in the injection system—have been modified so that the metallic surfaces are also resistant to the fuel. Because ethanol only has a low lubricating effect, the valves and their rings have been replaced with hardened versions and the delivery rate of the high-pressure fuel pump has been adjusted.
|The 2.0 TFSI CNG engine. Click to enlarge.|
CNG. Audi has also developed a natural gas vehicle concept based on the TFSI engine. The Audi A5 2.0 T-CNG uses four pressure tanks on board with a total volume of 130 liters (21 kg of CNG), supporting an all-CNG range of 420 km (261 miles).
The gasoline tank has been reduced in size to 14 liters—still enough for a range of 180 km (112 miles).
The Audi A5 2.0 T-CNG is powered by a direct injection engine with the latest TFSI technology. Based on the current EA888 series, its capacity has been increased from 1.8 to 2.0 liters. The bivalent four-cylinder engine has the same output in both fuel modes – gasoline and natural gas: 120 kW/161 hp.
The use of CNG cuts CO2 emissions by around 20% compared to the conventional TFSI engine.
To support CNG operation, Audi extended the engine management system with additional functions for controlling the CNG injectors and for the changeover and safety functions. The intake manifolds were modified accordingly, and to ensure the engine retains its long service life, especially high-quality valve rings were used. The coating of the catalytic converter was also modified to take the different exhaust composition into account.
Audi also decided to make systematic use of the very high knock resistance of CNG fuel to improve the efficiency of the engine. Here, the 2.0 T-CNG was able to benefit from a typical FSI characteristic: the high compression ratio.
While intake manifold injection CNG engines can only achieve a compression ratio of about 9.1:1 in gasoline mode, if it is turbocharged. the Audi engine is able to run with a compression ratio of 12:1. This means that greater efficiency is also possible in gasoline mode.
The driver’s role. The driver has a major responsibility for a driving style that contributes to reduced fuel consumption, according to Audi.
Individual driving style can reduce fuel consumption, and with it emissions, by up to 30 percent without compromising on speed and dynamism.
To support improved driving behavior, Audi is developing additional assistance and information systems. A first example is the gear shift indicator found as standard on the e-models and on the new Audi A5. This indicates the best gear for the current driving situation.
For the future, Audi is working on a navigation system that takes consumption-relevant data into account and which gives route recommendations accordingly. The necessary information about road conditions or traffic lights will be available with the next generation of digital road maps. Similarly, an on-board electronic driver trainer is being developed. This system is able to analyse the current driving style and give tips accordingly.
With a new Cross Coupé quattro study shown at TechDay, Audi presented another concept. The driver can select a particularly fuel economical mode at the touch of a button for certain situations. In “efficiency” mode, the engine and gearbox maps are switched to a low-consumption map, the power draw to the major consumers and comfort modules is limited, and cruise control gives priority to fuel consumption as it regulates the vehicle speed. This mode is consciously selected by the driver and is only associated with slight losses in performance and comfort. Yet it saves about 20% fuel compared to “sport” mode.