Audi highlights its range of electrification efforts; Q7 diesel PHEV, A7 fuel cell PHEV, BEV, 48V and more; 750 Wh/l by 2025
Audi presented a range of its ongoing work on electromobility and efficiency—from fuels and systems to full vehicles—under the “Future Performance Days 2015” banner.
On the full vehicle side, Audi put forward the Audi Q7 e-tron 3.0 TDI quattro plug-in hybrid (earlier post); the Audi A7 h-tron quattro fuel cell vehicle (earlier post); the Audi e-tron quattro concept battery-electric SUV (earlier post); the Audi TT clubsport turbo concept (earlier post); the Audi RS 5 TDI competition concept (earlier post); and the Audi R18 e-tron quattro (earlier post). On the systems and fuels side, Audi discussed battery technology; wireless charging; 48 V electrification (earlier post); Audi fuel cell technology; and Audi e-fuels (earlier post).
Audi is systematically driving forward the electrification of its cars with both high-voltage, electric drive e-tron models as well as lower voltage mild hybrids. The new mild hybrids are set to make inroads into the model range on a broad front—in ten years’ time, Audi aims to offer all new models with this technology, with the exception of the e-tron lineup. The current 12-volt electrical system and, above all, the new 48-volt system offer many ways of making driving even sportier, more comfortable and more efficient.
Audi Q7 e-tron 3.0 TDI quattro plug-in hybrid. The Q7 e-tron quattro features a six-cylinder TDI engine and quattro drive that deliver 275 kW (373 hp) of system power and 700 N·m (516.3 lb-ft) of system torque. It accelerates from 0 to 100 km/h (62.1 mph) in 6.0 seconds and consumes not more than a best-in-segment 1.7 liters of fuel per 100 kilometers (138.4 US mpg) in the New European Driving Cycle (NEDC), corresponding to 46 grams CO2 per km (74.0 g/mi).
|3.0 litre V6 TDI engine. Click to enlarge.|
The 3.0 TDI, a highly efficient, latest-generation V6 diesel engine, delivers 190 kW (258 hp) of power and 600 N·m (442.5 lb-ft) of torque. The electric motor produces 94 kW of power and 350 N·m (258.1 lb-ft) of torque. Together with a decoupler, it is integrated into the eight-speed tiptronic.
During fast cornering, the quattro permanent all-wheel drive works closely with the wheel-selective torque control, an intelligent software feature. This brakes the inside wheels ever so slightly, thus further enhancing the car’s agility and stability.
|In ten years’ time, Audi aims to offer all new models with mild hybrid technology, with the exception of the e-tron lineup.|
The lithium-ion battery comprises 168 prismatic cells and is liquid-cooled. With a capacity of 17.3 kWh, it allows a 56 kilometer (34.8 mi) range in electric mode in the NEDC—like the fuel consumption, another record in the segment. The total range with the TDI engine is 1,400 kilometers (869.9 mi).
Making their world premiere in a diesel engine are active engine mounts in the Audi Q7 e-tron 3.0 TDI quattro. Utilizing electromagnetic oscillation coil actuators to induce phase-offset counter oscillations, they largely eliminate vibrations. The engine mounts are always active when the combustion engine is running.
New multi-phase charging technology allows charging with 7.2 kW of power. A full charge on an industrial outlet thus takes less than two-and-half hours. Audi also offers a package of special e-tron services, from switching to green electricity (Audi Energy) to the “Audi Charge&Fuel Card”. With the e-tron services in the Audi connect portfolio, drivers can use their smartphones to control such functions as charging and heating or cooling.
The driver can choose between four modes. “EV” mode prioritizes electric driving, while in “hybrid” mode the decision regarding the drive type is left largely to the hybrid management system. It charges the battery in “battery charge” mode; in “battery hold” it saves the available electric energy for a later time.
Depending on the driving situation, the SUV can boost, coast and recuperate. During everyday driving, most braking operations use the electric motor, which then works as a generator. The Audi Q7 e-tron quattro normally starts off purely on electric power. When switching into hybrid mode and for boosting, the driver has to depress the active accelerator (another Audi innovation) beyond a certain point of resistance. The position of this pressure point varies depending on the charge state.
One important efficiency component is the specially developed thermal management system with a heat pump. This makes it possible for the waste heat from the electrical drive components to be made available to the interior of the Q7 e-tron quattro. It heats and cools the interior quickly and effectively. At the same time, the fact that it uses so little energy significantly increases the electric range compared with a conventional electric heating system. Audi is the first manufacturer worldwide to use this technology in a production plug-in hybrid.
|Thermal management systems in the Q7 e-tron quattro. Click to enlarge.|
|Heat pump: heating. Click to enlarge.||Heat pump: cooling. Click to enlarge.|
In the Audi Q7 e-tron quattro, the standard MMI navigation plus works closely with the hybrid management system. This makes it possible to use navigation data and real-time traffic information to compute an ideal driving strategy at the start of the trip.
Underway, the predictive efficiency assistant provides precise near-field information to help the driver save fuel. Using navigation and camera data as well as the information from the radar sensors of the optional adaptive cruise control (ACC), it generates a detailed image of the route up to three kilometers (1.9 mi) ahead. On approaching speed limit signs, town signs, bends, traffic circles and intersections, the system visually signals the driver well in advance to release the accelerator pedal. At the same time, the active accelerator pulses once against the sole of his or her foot.
Besides the predictive efficiency assistant, other driver assistance systems include the collision avoidance assist; turn assist; cross traffic assist rear; and trailer maneuver assist. The adaptive cruise control including traffic jam assist takes over the braking, acceleration and steering from the driver on well-paved roads at speeds of up to 65 km/h (40.4 mph) as long as traffic is slow-moving.
Hill descent control and an off-road mode for the electronic stabilization control ESC are standard. A tilt angle display is standard with the optional air springs.
Audi expanded the infotainment to include essential e-tron displays. For example, fuel economy statistics and a graphic display of the electric range is shown on the navigation map. The driver can program times for charging as well as preheating or cooling and adapt them to his or her requirements, such as departure time, so as to save resources and costs.
This is made possible by the second-generation modular infotainment platform, which uses the high computing power of the Tegra 30 chip from Audi’s partner NVIDIA. Operation is by voice, with the multifunction steering wheel or with the brand new MMI all-in-touch, the touchpad with haptic feedback.
Audi connect, which is also standard, connects the Q7 e-tron quattro to the internet via the fast LTE standard. With the Audi MMI connect app, the smartphone can be used to remotely control charging and interior heating or cooling, call up the battery status and display data about past trips.
The Q7 PHEV will arrive in dealerships in Germany in 2016, and will likely come to the US, although perhaps with a gasoline-engine variant.
Audi e-tron quattro concept SUV. Covered in greater detail in an earlier post, the battery-electric e-tron quattro concept provides a very close foreshadowing of the production model to follow in 2018.
Aerodynamically-optimized design with a drag coefficient of 0.25, the electric e-tron quattro drivetrain delivers up to 370 kW of power output. The Audi e-tron quattro concept uses three electric motors:one electric motor drives the front axle, the two others act on the rear axle. During boosting, the driver can draw temporarily on 370 kW and more than 800 N·m (590.0 lb-ft) of torque. The concept study offers sports car-like performance.
Audi e-tron quattro concept sprints from a standstill to 100 km/h (62.1 mph) in 4.6 seconds and quickly reaches the electronically governed top speed of 210 km/h (130.5 mph).
Audi battery technology; modularity is key. Audi’s expertise spans cell development, the arranging of the cells into modules, the operating strategies during driving operation, and use of the battery after the end of its service life in the car. Its emphasis is on lithium-ion battery systems, which are put together using a flexible, modular concept.
|High voltage battery for the Q7 e-tron quattro. Click to enlarge.|
At the competence center for high-voltage battery technology at Gaimersheim, just outside the main plant in Ingolstadt, Audi specialists are developing the traction batteries for future electric mobility. Whether for a plug-in hybrid car (PHEV, plug-in-electric vehicle) or a purely electric car, the battery structure follows a uniform modular concept. This gives Audi the flexibility to respond swiftly to future requirements in the marketplace. The modular strategy also means the batteries can be used across all models and brands throughout the entire Volkswagen Group.
The battery module uses a sturdy cuboid aluminum housing slightly smaller than a shoe box. The module weighs around 13 kilograms (28.7 lb) and within the battery system is mounted on a cooling plate through which cooling fluid circulates. It can accommodate three types of cell: round cells such as those used in the R8 e-tron 2.0; prismatic cells—each of them about half the size of a paperback book—or long, flat pouch cells.
The prismatic cells have separate aluminum housings, so they are more robust than pouch cells. Their outer skin is made from aluminum-coated polymer and this in turn brings weight advantages. In terms of the performance of the battery system, the individual strengths and weaknesses of both concepts cancel each other out. The two suppliers (LG and Samsung SDI, earlier post) with which Audi works have each specialized in a particular design.
The strength that prismatic and pouch cells have in common is the dense packaging. They both use 75% of the available volume, a much higher figure than round cells (50 percent), which also require more complex contacting.
Round cells are generally only suitable for all-electric vehicles, according to Audi. While they store a high amount of energy compared to the other designs, their power output is comparatively low.
Pouch cells and prismatic cells are more versatile. With minor changes to their exterior dimensions, they can be configured specifically for maximum power output, maximum energy or a combination of both, making them ideal for a plug-in hybrid vehicle.
The key criterion is the coating thickness of the electrodes—the thinner these are, the greater the contact surface between electrolyte and active material; the resulting high charge transfer assures a corresponding performance density. Conversely, high coating thicknesses for the electrodes produce a high energy density.
Over the past three years Audi has succeeded in increasing the current capacity of prismatic cells by 50%—from 25 Ah per cell to 37 Ah. Energy density has increased by a similar degree. Pouch cells now achieve up to 550 watt hours per liter of volume, and Audi expects them to reach about 750 Wh/l by 2025. An important incidental effect is that battery costs have fallen by around half in the past five years. That is making electric mobility affordable for more and more customers.
Together with Volkswagen Group Research, Audi is also getting involved in long-term projects that are investigating innovative cell chemistry. At the special high-voltage competence center near Ingolstadt, the focus is on the development of complete systems: packaging, cooling, validation and, in partnership with body development, integration into the automobile. It is above all working on the battery system’s rigidity and its behavior in a crash situation—Audi is testing loads at up to 150 times the force of gravity.
Second life. Audi designs its batteries for service lives of more than 150,000 kilometers (93,205.7 miles) and at least eight years in operation. Even then, these batteries still possess a large portion of their nominal capacity—too high for them to be recycled. Under a venture with the motto “From Road to Grid”, Audi is therefore currently working on a concept to convert old batteries into stationary energy stores.
A first test setup located near Ingolstadt recently started supplying the grid.
A container for four traction batteries of various sizes works in tandem with a photovoltaic system that is capable of supplying up to 20 kW of power on sunny days. A second container houses the connection and control technology: Its power electronics convert the direct current from the batteries into alternating current at a standard voltage of 400 V. When the batteries have been run down to ten percent of their capacity, they are sent for recycling.
Audi’s innovative storage platforms are suitable as a power source for quick-charging stations with an output of more than 250 kW. Alternatively they can serve as buffers for renewables such as wind and solar power—whether as part of the grid or as home installations. Audi has already drawn up plans for larger systems with a capacity of around 500 kWh.
Fast charging and Audi wireless charging. Progress in charging technology is crucial to the success of electromobility. Whether charging with direct or alternating current, the new solutions from Audi for all-electric cars and plug-in hybrids will be extremely convenient for customers. There will also be wireless options. Market launch is scheduled to begin in 2017.
Direct current charging with 150 kW of power is the next step. With this technology, a sporty SUV such as the Audi e-tron quattro concept would be able to charge its large 95 kWh battery to 80% capacity in less than half an hour, enough for a cruising range of around 400 kilometers (248.5 mi). A full charge—enough for more than 500 kilometers (310.7 mi)—would take around 50 minutes.
Audi and other German manufacturers use the Combined Charging System (CCS). It enables electric cars to be charged with direct current (DC) and alternating current (AC) using the standard Combo 2 connector. The official charging solution of the European Union, which is based on the CCS standard, has already been ratified.
To further promote these standards worldwide, Audi co-founded the Charging Interface Initiative (CharIN) with BMW, Daimler, Opel, Porsche and Volkswagen, connector manufacturers Mennekes and PhoenixContact, and the TÜV SÜD inspection authority in May 2015.
In China and Japan, where other standards already exist (GB/T and CHAdeMO, respectively), country-specific requirements will be accommodated. Installation of CCS charging stations has already begun in Europe and the United States. The majority of stations currently available on the market support DC charging with 50 kW.
Current efforts are geared toward ensuring the establishment and operation of a fast-charging infrastructure with at least 150 kW by the market launch of the first all-electric sport SUV from Audi. The Audi e-tron quattro concept introduced at the IAA in Frankfurt was equipped with the CCS charging interface. The new standard allows for charging with up to 350 kW.
Audi considers it very important to offer the customers of its all-electric models a very convenient and capable charging system. This also requires cooling of the charging connector while connected to the charging station. This is the only way to continuously transfer the full power without thermally overloading the pins.
AWC (Audi wireless charging) is an inductive AC charging technology Audi is developing as an alternative that also makes home charging extremely convenient. The company hopes to launch AWC in 2017.
With AWC, the energy is transferred via a floor charging plate connected to the electric grid. The plate has an integrated primary coil and an inverter (AC/AC converter). Connected to a 16 ampere, single-phase outlet, the first-generation system offers a charging power of 3.6 kW, with higher powers of up to 11 kW possible in the next version.
When the driver approaches to within a few meters of the charging plate with the Audi e-tron, the plate establishes radio contact with the car. The driver then sees the precise position of the floor plate on the display. Charging can begin immediately after proper positioning or according to a timer. With the piloted parking systems Audi is currently developing for production use, the car handles positioning itself. The driver can get out of the car and then initiate the parking procedure remotely via her smartphone.
Prior to charging, an integrated electric motor in the floor plate raises the primary coil. This minimizes the distance between it and the secondary coil, which is integrated into the front section of the Audi e-tron floor pan, regardless of the specific vehicle.
The floor plate’s alternating electromagnetic field induces an alternating current in the car’s secondary coil across the air gap. An AC/DC converter inverts the current, which is then fed into the high-voltage electrical system. There it charges the battery and powers additional consumers such as the heating or air conditioning as needed. The driver can interrupt the charging process at any time, and charging stops automatically when the battery is full.
Because the alternating field is only generated when a car is over the plate and the coil is active, there is no risk to people or animals. The small air gap prevents the magnetic field from interfering with electronic devices. The first generation of the AWC technology is ideal for use in home garages or office building parking garages. A later version can be integrated in a modified form into the public infrastructure, such as into the asphalt of roads and parking lots.
The Audi A7 Sportback h-tron quattro. Introduced last year at the LA Auto Show, the technology study Audi A7 h-tron quattro fuel cell vehicle sprints from 0 to 100 km/h (62.1 mph) in 7.9 seconds and reaches a top speed of 200 km/h (124.3 mph). It can cover more than 500 kilometers (310.7 mi) on a single tank, with nothing more than a few drops of water leaving the tailpipe.
The A7 Sportback h-tron quattro uses a 170 kW electric drive system with a fuel cell as the energy source. Each of the two electric motors drive the wheels of one axle. Like the engine of a conventional A7 Sportback, the fuel cell of the Audi technical concept car is mounted in the front.
The stack comprises more than 300 individual cells; the core of each of these individual cells is a polymer membrane, with a platinum-based catalyst on both sides of the membrane. Hydrogen is supplied to the anode, where it is broken down into protons and electrons. The protons migrate through the membrane to the cathode, where they react with oxygen present in air to form water vapor. Meanwhile, outside the stack the electrons supply the electrical power—depending on load point, the individual cell voltage is roughly 0.6 to 0.8 volts.
The fuel cell operates in the high-voltage range. The most important auxiliaries include a coolant pump and the recirculation fan—a turbo compressor that forces air into the cells, returning unconsumed hydrogen back to the anode and thus increasing efficiency. These components have a high-voltage electric drive and are powered by the fuel cell.
Because the exhaust system transports only water, it can be made of lightweight polymer.
There is a separate cooling circuit for cooling the fuel cell. The unit, which operates at a temperature of approximately 80 degrees Celsius, places higher demands on the vehicle cooling than an equivalent combustion engine, but achieves superior efficiency of as high as 60%—nearly double that of a typical combustion engine.
Cold starting is possible at temperatures down to -28 degrees Celsius. A heat exchanger and a thermoelectric, self-regulating auxiliary heating element maintain pleasant temperatures in the cabin.
A special feature of the A7 Sportback h-tron quattro is its plug-in hybrid concept; the technology demonstrator is equipped with an 8.8 kWh lithium-ion battery taken from the Audi A3 Sportback e-tron. It is located beneath the luggage compartment and has a separate cooling circuit for thermal management.
The high-performance battery makes the ideal partner to the fuel cell. It can store energy recovered from brake applications and supply considerable power for full- load boosting. On battery power, the Audi A7 Sportback h-tron quattro covers as much as 50 kilometers (31.1 mi). Depending on voltage and amperage, a full charge takes between two and four hours.
The battery operates at a different voltage level than the fuel cell. For that reason, there is a DC converter (DC/DC) between the two components. This tri-port converter is located behind the stack. The power electronics in the front and rear of the vehicle convert the direct current from the fuel cell and battery into alternating current for the two electric motors.
The Audi A7 Sportback h-tron quattro is the first fuel cell car with quattro drive—more specifically with an e-quattro drive—that has no mechanical connecting parts. The front electric motor drives the front wheels; the unit in the back the rear wheels. Torque at both axles can be electronically controlled in the event of slip and steplessly varied. The e-quattro concept requires precise coordination of the electric motors—the technology demonstrator offers the sporty, stable and high- traction drive of a production car with mechanical quattro drive.
The electric motors, which together with the voltage converters are cooled by a low-temperature circuit, are permanently excited synchronous machines. Each of them has an output of 85 kW, or 114 kW if the voltage is temporarily raised. Maximum torque for each is 270 N·m (199.1 lb-ft). The electric motors’ housings incorporate planetary gear trains with a single transmission ratio of 7.6:1.
A mechanical parking lock and a differential function round off the system. Driving in the Audi A7 Sportback h-tron quattro offers the full performance of electric drive in conjunction with the advantages of the new e-quattro.
The silent thrust is available in full from the start. At full load, the fuel cell reaches maximum output within one second, more dynamically than a combustion engine because the entire drivetrain includes just a few mechanical parts.
When the driver presses the EV button, the technology demonstrator drives solely on battery power. Switching from automatic transmission mode D to S increases the level of energy recovery when braking, so that the battery is charged up effectively during sporty driving. Braking is also generally all-electric. The four disk brakes only become involved if more forceful or emergency braking is required.
The four hydrogen tanks of the Audi A7 Sportback h-tron quattro are located beneath the base of the trunk, in front of the rear axle, in the center tunnel. An outer skin made from carbon fiber reinforced polymer (CFRP) encases the inner aluminum shell.
The tanks can store around five kilograms (11.0 lb) of hydrogen at a pressure of 700 bar—enough to drive over 500 kilometers (310.7 mi). According to the NEDC, fuel consumption is roughly one kilogram (2.2 lb) of hydrogen per 100 kilometers (62.1 mi) – an amount with an energy content equivalent to 3.7 liters (1.0 US gal) of gasoline.
The tank flap is in the right side section of the five-door coupe, concealing a filler connector for the hydrogen. Fully refueling with H2 takes around three minutes, roughly the same as with a conventional automobile. The tanks communicate with the refueling system via an infrared interface, indicating the pressure and temperature levels in each tank for optimal refueling.
Fuel cell technology. As part of its efforts to further develop fuel cell technology, Audi acquired a package of important patents from the Canadian company Ballard Power Systems Inc. in early 2015 that will form the basis for the development of the next generation of fuel cells. (Earlier post.) All brands in the Volkswagen Group will benefit from this know-how, and the Group will continue to collaborate with Ballard.
Audi is also working with Volkswagen and other partners on the future of the fuel cell as part of the HyMotion 5 project. The focus here is on new materials for the bipolar plates separating the individual cells in the stack. These will make the fuel cell significantly lighter, smaller, more robust and more powerful. Additional strengths are easy cold starting, long service life, spontaneous response and low hydrogen consumption. The price should also drop because the proportion of costly components such as platinum in the fuel cell will decrease.
Audi has been working on fuel cell concepts for more than ten years. The first technology demonstrator was the compact A2H2 in 2004, which was already equipped with a polymer electrolyte membrane fuel cell (PEM). It had a 110 kW electric motor, and a nickel-metal hydride battery served as a buffer. The Audi Q5 HFC (Hybrid Fuel Cell) followed in 2009. Its PEM fuel cell had an output of 90 kW and was supported by a compact lithium-ion battery.
Audi A4 Avant g-tron. Scheduled to launch in late 2016, the A4 Avant g-tron is yet another offer from Audi for the sustainable mobility of the future. It follows the A3 Sportback g-tron as the brand’s second model to use natural gas or climate-friendly Audi e-gas.
The engine is based on the new 2.0 TFSI featuring an advanced, highly efficient combustion process developed by Audi. The turbocharged power plant produces 125 kW (170 hp). Maximum torque of 270 N·m (199.1 lb-ft) is available at approx. 1,650 rpm. The pistons and valves have been specially modified for gas operation and allow for an optimal compression ratio.
An electronic controller reduces the high pressure of the gas flowing from the tank from as much as 200 bar to a working pressure of 5 to 10 bar in the engine. This pressure control function is performed dynamically and precisely in response to the power requested by the driver. The correct pressure is always present in the gas line and at the injector valves—low pressure for efficient driving in the lower speed range, and higher pressure for more power and torque.
In the NEDC, the Audi A4 Avant g-tron consumes less than four kilograms CNG (compressed natural gas) per 100 kilometers (8.8 lb), corresponding to customer fuel costs of roughly €4 (as of October 2015). CO2 emissions are less than 100 grams per km (160.9 g/mile). The tank capacity of 19 kilograms (41.9 lb) of gas allows for a range of more than 500 kilometers (310.7 mi).
When the amount of gas remaining drops below approx. 0.6 kilograms (1.3 lb)—analogous to a residual pressure of 10 bar—the control unit switches to gasoline operation. The bi-fuel A4 Avant g-tron can cover an additional 450 kilometers (279.6 mi) in this mode. The potential overall range is comparable to that of a car with a TDI engine.
The filler necks for gas and gasoline are located under a common tank flap. After refueling, and whenever it is very cold, the engine is started with gasoline initially, then switched over to natural gas operation as quickly as possible. Two displays in the instrument cluster keep the driver up-to-date on the fill levels of the tanks.
Audi installs the four cylindrical CNG tanks as a compact module in the rear end of the Avant. They are optimized for the available space, and each is specifically sized. Sheet steel shells with tensioning straps hold the cylinders and protect them against damage, such as curbs. The complete CNG tank module, which also includes the 25 liter (6.6 US gal) gasoline tank, is fitted to the body during production of the A4 Avant. The spare wheel well in the body is eliminated.
The battery also moves from the luggage compartment to the engine compartment. The loading floor is even with the loading lip, thus offering a full-fledged luggage compartment.
The CNG tanks with an operating pressure of 200 bar at 15 degrees Celsius follow the Audi lightweight construction philosophy. Due to their innovative layout, they weigh 56% less than comparable steel cylinders. Their inner layer is a gas-tight matrix of polyamide. The second layer, a composite winding of carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP), provides for maximum strength. The third layer is pure GFRP and serves primarily as a visual inspection aid, turning milky white where damaged.
Before being installed in a car, each tank is tested at 300 bar during production. The actual bursting pressure is much higher still and far exceeds the legal requirements.
With Audi e-gas, the A4 Avant g-tron is CO2-neutral in operation. e-gas is a synthetic methane produced from water and CO2 with the help of green electricity in multiple power-to-gas plants. Audi operates the world’s first industrial-scale power-to-gas plant in Werlte, but now also procures e-gas from other facilities.With power-to-gas technology, the brand with the four rings is making it possible to store excess renewable energy. The company and its partners are intensively driving the development of various synthetic fuels known as Audi e-fuels, including by means of new biological production processes.
Audi e-fuels. Audi’s e-fuels initiative, covered in greater detail in an earlier post, is intended to produce fuels that do not depend on petroleum, and that bind as much CO2 during their production as they emit during combustion. Current e-fuels are Audi e-gas, Audi e-diesel, Audi e-gasoline and Audi e-ethanol. With Audi e-gas, Audi already offers A3 g-tron customers climate-neutral mobility.
In 2013, the Audi e-gas plant in Werlte (Emsland) came on stream. With help from wind power, the Audi e-gas, a synthetic methane, is produced from water and carbon dioxide. The process is performed in two major process steps: electrolysis and methanation. In the first step, the plant uses renewably generated electricity to split water into hydrogen and oxygen. Over the medium term, the hydrogen can also be used to power fuel-cell vehicles such as the Audi A7 Sportback h-tron quattro.
The absence of any universal hydrogen infrastructure at present means the focus at the moment is on the second process step: the hydrogen is then reacted with CO2, which comes from a nearby waste biogas plant, to produce synthetic methane, or Audi e-gas. Chemically, it is nearly identical to fossil-based natural gas, so it can be distributed throughout Germany over the natural gas grid to CNG filling stations and be used in Audi g-tron models.
Every year the Audi e-gas plant produces up to 1,000 tons of e-gas, binding up to 2,800 tons of CO2 in the process. This quantity enables 1,500 Audi g-tron models to drive 15,000 kilometers (9,320.6 mi) each a year with no carbon footprint.
Audi is convinced of the potential of the power-to-gas principle and is cooperating with other partners from the energy sector to cover the increasing demand for fuel. One of these cooperation partners is the Thüga group, a network of municipal power utilities. It also runs a power-to-gas plant in Frankfurt am Main, which is testing, among other things, the addition of hydrogen to the natural gas grid.
Another Audi partner is Viessmann GmbH, a heating specialist from Allendorf in the state of Hesse, which is operating the first power-to-gas plant involving biological methanation in Germany. Another example is the cleantech company Electrochea in Copenhagen, which aims to bring biological methanation into the megawatt class. The conversion of hydrogen into methane takes place in both instances not as in Werlte by means of a thermochemical, catalytic process, but in a biological process: special microorganisms are fed by the hydrogen and CO2, producing the Audi e-gas in the process.
A production plant for Audi e-diesel started pilot operation in Dresden-Reick at the end of 2014 in partnership with sunfire. The plant works in accordance with the power-to-liquid principle (PtL) and utilizes green electricity as the primary energy. The raw materials are water and carbon dioxide, which a biogas plant provides. Part of the CO2 will be extracted in future from the ambient air by means of direct-air-capturing—a technology of Audi’s Zurich-based partner Climeworks.
The efficiency of the overall process at around 70% is very high compared with other processes for manufacturing synthetic liquid fuels. In the first step, water heated up to form steam is broken down into hydrogen and oxygen by means of high-temperature electrolysis. In two further steps, the hydrogen reacts with the CO2 in synthesis reactors—again under pressure and at high temperature. The result is known as blue crude, which—similar to crude oil—can be refined to create the end product Audi e-diesel. The synthetic fuel is free from sulfur and aromatics; its high cetane number makes it readily ignitable.
Audi is currently developing Audi e-gasoline, another CO2-neutral future fuel based on renewable raw materials. Global Bioenergies S.A. operates a pilot plant near Reims (France) to produce isobutene. The Fraunhofer Center for Chemical-Biotechnological Processes (CPB) in Leuna (Saxony-Anhalt) converts the gaseous isobutene using hydrogen into liquid iso-octane, a high quality designer fuel. It contains no sulfur or benzene, and, as such, it burns very cleanly.
Global Bioenergies has built a demonstration plant in Leuna that will begin producing larger quantities of iso-octane in 2016. Over the medium term, the project partners aim to modify the process so that it requires no biomass, instead requiring just water, hydrogen from renewable sources, CO2 and sunlight.
Another project is underway in Hobbs (New Mexico, USA). Here Audi and Joule have been running a research plant for producing high-purity e-ethanol and e-diesel since 2012. Special microorganisms use sunlight, carbon dioxide, and salt or brackish water to produce liquid fuels. The end product of this bio-technologically optimized photosynthesis process comes in the form of alkanes—components of diesel fuel—and ethanol. Even today the specific yields per area of the demonstration plant are eight times higher than with the production of bioethanol from corn, which is widespread in the United States, and still three times higher than with sugar-beet based bioethanol, which is mainly produced in Brazil. Further increases are expected.
12V and 48V electrification technologies. A very efficient mild hybrid can already be implemented with the existing 12-volt electrical system. Its key components are a lithium-ion battery with 11 Ah capacity and a belt starter generator, which at the same time is used as a starter motor.
The belt starter generator paves the way for new functions. The start-stop phase can already begin at around 15 km/h (9.3 mph) residual speed. If the driver takes his or her foot off the accelerator at high speed, the car coasts for a short time with the engine switched off. With a maximum 5 kW the recuperation output is considerable—in addition, the generator can assist the combustion engine with up to 1 kW. As a result, the TDI or TFSI can be operated closer to its ideal load point. The belt starter generator based on 12 volts has the potential overall to reduce the fuel consumption by up to 0.4 liters per 100 kilometers.
The new 48-volt subsidiary electrical system, which is about to enter volume production at Audi, features a Li-ion battery providing 10 Ah electrical capacity; the belt starter generator, however, produces 12 kW, translating into fuel savings of up to 0.7 liters per 100 kilometers.
With 48 volts, the same mild-hybrid functions can be implemented as with 12 volts, but to a greater extent—the coasting phase with the combustion engine switched off, for instance, can last up to 30 seconds.
Apart from hybridization, the 48-volt electrical system, which Audi is pioneering within the Volkswagen Group, offers many other advantages. Its higher voltage allows for much smaller cable-cross sections, which also reduces the weight of the cable harness along with power dissipation. Above all, though, it can provide four times as much power as the 12-volt electrical system and, as such, opens up the prospect of innovative, compelling technologies for the driveline and suspension.
One of these new solutions is the electrically driven compressor; Audi has already showcased this solution in various technology studies. The electrically driven compressor sits in a bypass in the intake tract behind the intercooler and is activated via a flap. It is switched in series behind the turbocharger and always assists the turbocharger if the exhaust provides insufficient energy for instant torque buildup.
Instead of the turbine wheel, the electrically driven compressor incorporates a small electric motor, which accelerates the compressor wheel to very high speeds in around 250 milliseconds with approximately 7 kW of power. The motor always develops its power without any perceptible delay whether while moving off or accelerating at low speeds. The electrically driven compressor eliminates the need for constant downshifting, keeping engine speeds low. Sporty drivers will appreciate the passing power and immediate delivery of power when exiting a curve.
The electrically driven compressor is suited for many Audi model lines, for diesel and gasoline engines alike. It will soon be part of volume production in the TDI sector. Here and also with the TFSI engines, Audi will focus the usage of the electrically driven compressor on the six- and eight-cylinder engines.
The higher voltage facilitates compelling suspension technologies as well. Audi will shortly be launching the first of these as part of volume production—the electromechanical active roll stabilization (EAWS). Here a compact electric motor with a three-stage planetary gearbox separates the two halves of the stabilizer from each other.
With a comfort-oriented driving style, the two halves are decoupled from each other, resulting in excellent ride comfort. In response to sportier gear changes, the tubes are interconnected and twisted against each other. With each electric motor developing 1.5 kW of peak output, they produce anything up to 1,200 N·m (885.1 lb-ft) of torque.The effect is taut, sporty handling: the car rolls less into the bends, the tendency to understeer reduced, lateral acceleration increased. The front and rear stabilizer can be adjusted independently of each other. As such, the control unit can make the handling even sportier on request.
Another of the system’s strengths is recuperation. If the wheels on one axle are deflected to greatly differing extents on bumps in the road, they excite the stabilizer—its motor now operates as a generator and converts each impulse into electrical energy. Thanks to this effect, the electromechanical active roll stabilization only has to develop minimal power overall. With moderate gear changes on a very bumpy road, the power requirements can even be virtually zero.
Compared with conventional hydraulically switched stabilizers, the 48-volt-based system from Audi offers major advantages. It can develop more power, it works faster and more efficiently, and it is activated even at low speeds. The absence of oil also means the electromechanical active roll stabilization is maintenance-free and environmentally friendly.
A second 48-volt project, which Audi uses to recover energy in the suspension, is still at the prototype stage. It is known under the working title eROT—an electromechanical rotary damper replaces today’s hydraulic damper.
In terms of the basic principle, eROT is not unlike the electromechanical active roll stabilization: a strong lever arm absorbs the forces that are induced on the wheel carrier with a sporty driving style and on a bumpy road. Via a series of gears, it transmits this force to an electric motor, which converts it into electricity.
The recuperation output is 150 watts on average on German roads—from 3 watts on a freshly tarmacked freeway to 613 watts on a poorly maintained country road. This corresponds to a CO2 saving of three grams per kilometer (4.8 g/mi) under customer driving conditions.
The eROT system responds quickly and with minimal inertia. It is used to recover energy and acts as an actively controllable shock absorber. In doing so, it eliminates the mutual independence of the rebound and compression stage, which limits the effectiveness of modern hydraulic dampers. Thanks to eROT, Audi is able to tailor the compression stage to comfortable-soft characteristics without having to make compromises with the desired rebound damping setting. The system’s horizontal position constitutes another advantage—the elimination of the upright dampers frees up additional installation space.
In 2016, the 48-volt subsidiary electrical system will be launched in a new model, which will also feature the electrically driven compressor and the electromechanical active roll stabilization on-board. The increased voltage promotes above all dynamism and driving pleasure. The generator still works on the basis of 12 volts, a DC/DC converter interconnects the 12-volt electrical system and the 48-volt subsidiary electrical system.
The next expansion stage is planned for 2017 when the mild hybrid will be rolled out on the basis of 48 volts. The 12-volt system is now linked via a powerful DC/DC converter to the 48-volt system, which is then promoted to become the main electrical system and is powered by a 48-volt belt starter generator. The requisite lithium-ion battery is roughly as big as a large lead battery. Air cooling is sufficient for thermal management. The mild hybrid based on 12 volts is set to follow at around the same time.
Over the medium term, Audi intends to convert auxiliaries such as pumps and superchargers for the engine, transmission and air conditioning system to 48 volts. Today they are driven hydraulically or by the combustion engine—however, if they are operated electrically, they can be controlled even more effectively according to demand; they would also be lighter and more compact. The same applies to large static convenience consumers such as window heating or sound systems. Small consumers such as control units or lights will, however, remain in the 12-volt system well into the future.
Audi TT clubsport turbo. The technical concept car, which debuted at the Wörthersee Tour 2015, combines a powerful TFSI engine with an electric biturbo for the first time. The Audi TT clubsport turbo was inspired by the successful Audi 90 IMSA GTO race car of the late 1980s and is powered by an enhanced-output 2.5 TFSI engine. From 2,480 cc of displacement, the five-cylinder engine produces 441 kW (600 hp) of power and 650 nm (479.4 lb-ft) of torque, with more than 600 N·m (442.5 lb-ft) available from 3,000 to 7,000 rpm.
This means that the sonorous TFSI produces 176 kW (240 hp) and 260 Nm (191.8 lb-ft) per liter of displacement. Its exhaust system is designed for minimal back-pressure; a side pipe to the ambient air is located immediately after the racing-type muffler.
The Audi TT clubsport turbo show car has an unladen weight of just 1,396 kg (3,077.7 lb). It needs just 3.6 seconds for the standard sprint from 0 to 100 km/h (62.1 mph), and its top speed is 310 km/h (192.6 mph). The TT clubsport turbo flaunts its strength over the first few meters of a sprint. Its electrically driven compressor lets it cover up to six meters (19.7 ft) more within the first 2.5 seconds than a comparable car without this new technology.
In the lower engine speed range, the electrically driven compressor increases torque by up to 130 N·m (95.9 lb-ft). It revs up to maximum rpm rapidly and without any perceptible delay, and it continues to boost charge pressure when too little drive energy is left in the exhaust gas for the conventional turbocharger. This allows the conventional turbocharger to be designed more for high charge pressures and thus high engine output. The 2.5 TFSI develops its immense power with no perceptible lag, so it is available at a tap of the accelerator in any situation.
A dedicated 48-volt electrical sub-system supplies electrical energy to the electrically driven compressor. A compact lithium-ion battery in the luggage compartment stores the energy generated by recuperation when coasting. A DC/DC converter provides the connection to the 12-volt electrical system.
Power transmission is via a manual six-speed gearbox and quattro permanent all-wheel drive, whose multiplate clutch is mounted on the rear axle for better weight distribution. A coilover suspension system enables highly precise adjustment of the body’s ride height and the compression and rebound of the shock absorbers as needed. An electric lifting function protects the equipment from damage by street curbs. Electronic Stabilization Control (ESC) and wheel-selective torque control round out the dynamic qualities of the suspension.
The Audi RS 5 TDI competition concept. The Audi RS 5 TDI competition concept (earlier post) uses a technology similar to that in the Audi TT clubsport concept. An electrically driven compressor provides for powerful, spontaneous thrust even at low engine speeds. It works together with a 3.0 liter, biturbo V6 TDI producing 320 kW (435 hp) and 800 N·m (590.0 lb-ft) of torque.
The RS 5 TDI competition concept is based on a technical concept car that Audi presented in summer 2014 on the 25th anniversary of the TDI engine. Following extensive further development, the sport TDI with 320 kW (435 hp) and 800 N·m (590.0 lb-ft) of torque sprints from zero to 100 km/h (62.1 mph) in 4.0 seconds and to 200 km/h (124.3 mph) in less than 16 seconds.
A key innovation is that in addition to two exhaust-gas turbochargers, an electrically driven compressor is also used. A small electric motor with 7 kW of power drives a turbine to a speed of up to 72,000 revolutions per minute within 250 milliseconds for extremely fast buildup of charge pressure. Typical exhaust-gas turbochargers take two to three times as long to reach a comparable turbine speed. Thanks to its electrically driven compressor technology, high charge pressure is available quickly in the RS 5 TDI competition concept in any driving situation. This is essential for excellent sporty engine response.
The compressor is powered via a 48 volt electrical sub-system. It enables the rapid transmission of larger amounts of electrical energy and is thus ideally suited for supplying power to the compressor.
The Audi R18 e-tron quattro. The hybrid drive of the three-times 24 Hours of Le Mans winner is designed for motorsport conditions, the most grueling test environment for production development.
Motorsport is an integral part of the Audi DNA—for 35 years the brand with the four rings has been testing new technologies while competing on the track. The 24 Hours of Le Mans and the FIA World Endurance Championship WEC are decisive test environments. It is here that the sport’s regulators specifically promote technical innovations.
That also applies to the TDI engine, still the most efficient and most environmentally friendly powerplant in Audi’s view. For this reason Audi’s involvement in prototype motor racing with TDI engines stretches back to the 2006 season. The pace of volume-production development has been accelerated on the back of the insights gained on the track. The engines also fulfill the EU’s most stringent emissions requirements. With the Le Mans prototypes, Audi has managed in ten years to reduce the fuel consumption by 40% while maintaining similar power output figures.
Audi is convinced of the additional potential inherent in the TDI engine. In line with this philosophy, the amount of energy available in the Audi R18 e-tron quattro will once again be reduced between 2015 and 2016. The WEC regulations have also been structured in such a way that hybrid systems play an ever-increasing role. Here too, racing helps accelerate the development of future volume-production technology.
The Audi R18 e-tron quattro concept separates the drives on each axle—the combustion engine permanently drives the rear wheels, while the electric motor temporarily powers the front wheels. The V6 TDI develops more than 410 kW (around 558 hp) from four liters of displacement, with torque of over 850 N·m (626.9 lb-ft).
Compared to its predecessor, many components of the current Audi R18 e-tron quattro have been substantially fine-tuned, including the hybrid system. At the 24 Hours of Le Mans it managed to recover four instead of two megajoules per lap, i.e. twice the amount of energy. The energy recovered during braking is fed for a short period into a flywheel accumulator, which can store up to 700 kilojoules. The accumulator, which is located on the left next to the driver in the cockpit, combines high energy density with high charging output.
When accelerating out of the bend, the energy reaches a water-cooled electric motor with integrated power electronics. It drives the front wheels with more than 200 kW (272 hp)—for a few seconds the Audi racing car is turned into the e-quattro. The driver can adjust all the important parameters of the hybrid system via buttons on the steering wheel. A great many factors are at work here, such as the current race tactics and strategy, the condition of the brakes and tires, or the quality of road grip.