Audi held a TechDay in Ingolstadt focused on its efforts to electrify the driveline, and provided more details on the upcoming Q5 hybrid-electric vehicle, the A1 e-tron range extended electric vehicle and the R8 e-tron battery-electric vehicle.
In electric mobility, Audi distinguishes between two groups of vehicles: fully hybrid vehicles, driving a maximum of about 3 km (1.86 miles) under electric power; and high-energy battery vehicles for longer distances. These are the plug-in hybrids, the range extender vehicles and the strictly electrical vehicles. At TechDay, Audi spent time describing the issues and its approaches for constituent elements of different electric drive systems including electric motors and power electronics; battery pack; charging; thermal management; energy recuperation; electromechanical brakes; torque distribution; safety; lightweighting; and the use of a cell phone in the human machine interface (HMI). (To be summarized in Part 2.)
Q5 hybrid
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| Q5 hybrid and drivetrain. Click to enlarge. |
The Q5 hybrid quattro, which goes into production in 2011, is the first hybrid model from Audi with two drive systems. Its gasoline engine, a 2.0 TFSI, and its electric motor are mounted directly behind one another as a parallel hybrid system, with system output of 180 kW (245 hp) and 480 N·m (354 lb-ft) for sporty dynamics. The mean consumption in the normal cycle (NEDC) is limited to less than 7.0 liters per 100 km (33.6 US mpg), corresponding to CO2 emissions of less than 160 grams per km (257.5 g/mile).
The new top model of the Q5 series accelerates in 7.1 seconds from 0 to 100 km/h and attains a top speed of 222 km/h (138 mph). In electric mode the hybrid SUV can cover a distance of up to three kilometers (1.86 miles) at a maximum speed of 60 km/h (37 mph).
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| Q5 hybrid motor. Click to enlarge. |
The turbocharged gasoline direct injection 2.0 TFSI in the Audi Q5 hybrid quattro has a displacement of 1984 cc (121 cu in), with output of 155 kW (211 hp) and maximum torque of 350 N·m (258 lb-ft) permanently available at 1500 to 4200 rpm. The Audi valve lift system (AVS) further increases power, torque and efficiency by switching the stroke of the exhaust valves between two stages depending on the load and rpm.
The 2.0 TFSI has been overhauled in some respects for use in the Audi Q5 hybrid. The drive of the ancillary units has been dropped, and the crankshaft bearing and fine tuning of the turbocharger have been adapted to the specific demands. A secondary air system at the cylinder head makes sure that the exhaust gas treatment cuts in particularly quickly. Integrated in the engine control unit, the hybrid manager controls the efficient change and smooth transitions between the operating modes, and was fully developed by Audi alone.
A largely modified eight-speed tiptronic serves the power transmission without the aid of a torque converter. Its place is taken by the disk-shaped electric motor, combined with the multi-plate clutch operating in an oil bath that it couples and decouples the electric motor and the TFSI. The hybrid gear unit contributes significantly to the efficiency of the Audi Q5 hybrid— its eight gears are widely spaced. When the 2.0 TFSI is turned off, an electric pump maintains the oil pressure in the hydraulic system to safeguard the convenient start-stop feature.
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| Cooling systems. Click to enlarge. |
The power electronics, connected to the battery and the electric motor by high-voltage cabling, is located in the plenum chamber of the engine compartment. Cooling is provided by a separate low-temperature water-filled circuit. The component includes a DC/DC converter that couples the electric consumers in the 12 V electrical system with the high-voltage network.
A permanently excited synchronous machine serves as an electric motor, as a starter and—during deceleration—as a generator. It outputs up to 33 kW (45 hp) of power and 211 N·m (156 lb-ft). The electric motor is integrated in the cooling circuit of the engine.
| Audi Q5 Hydrogen Fuel Cell Concept |
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| Audi is also studying the potential of fuel cell drive systems for long-range electric mobility—the Audi Q5 HFC (Hybrid Fuel Cell) concept car has this technology on board. |
| The concept car relies on synergism and consequently utilizes many technical components from the future hybrid models. Two high-pressure cylinders store hydrogen under a pressure of 700 bar. The polymer electrolyte membrane (PEM) fuel cell outputs 98 kW (133 hp). |
| The lithium-ion battery serving hybridization has an energy content of 1.3 kWh. The drive is provided by two electric motors close to the wheels; the motors have a combined top output of 90 kW and a torque of up to 420 N·m (310 lb-ft). |
| The efficiency of the fuel cell drive lies above 50% in a wide operating range. |
A lithium-ion battery system, weighing 38 kg (83.78 lb), serves as the energy store for the electric motor of the Audi Q5 hybrid quattro. The compact unit with its 26 liter (6.87 US gallon) capacity is positioned in a crash-safe area under the loading floor, with hardly any detriment to the luggage compartment. The battery consists of 72 cells; at 266 volts its nominal energy is 1.3 kWh and its output 39 kW.
The lithium-ion battery is air-cooled in two ways, depending on the requirement. At low-temperature load, it draws temperate air from the vehicle interior by way of a fan. If its temperature exceeds a certain limit, a separate refrigerant circuit is activated. It is coupled to the main climate control system of the vehicle and uses a separate evaporator. This heavy-duty active cooling system distinguishes the Audi Q5 hybrid quattro from many other hybrid vehicles, Audi noted, and makes a key contribution to the high electrical availability of the hybrid system.
As a component of the modular longitudinal platform, the powertrain of the Q5 hybrid quattro can also be used in other Audi models with longitudinally mounted engines. They include the new Audi A8 as well as the A6 and the A6 Avant of the next generation.
A1 e-tron
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| A1 e-tron technical data. Click to enlarge. |
The Audi A1 e-tron is a range extended electric vehicle. The synchronous motor of the Audi A1 e-tron is mounted transversely in the front, with its low installation benefiting the center of gravity. It has a continuous power of 45 kW (61 hp), with a torque of 150 N·m (111 lb-ft) already available from a standstill. The peak performance lies at 75 kW (102 hp), the maximum torque at 240 N·m (177 lb-ft). Acceleration from 0 to 100 km/h takes 10.2 seconds.
The electric range is similar to that of the e-tron Spyder, about 50 km (31 miles). A small rotary engine in the rear serves as a range extender. In range mode the A1 can cover a further distance of 200 km (124 miles).
The torque flows to the front axle via a single-staged transmission flanged to the electric motor. The selector lever stems from the series production model, following the appropriate adaptation. The modes are D, R, N and Range—on this level the range extender is activated depending on the applied operating strategy; the electronic management system cuts in the extender with smooth transitions. The current load requirement and the energy level of the battery are the most important factors.
In the engine compartment next to the electric motor are the power electronics, which control the electric traction. The DC converter coupling the 14 V electrical system to the high-voltage system, the switching unit for protecting the high-voltage components and the charging module are also accommodated in the front end.
Shaped like a T, the battery pack of the Audi A1 e-tron is located underneath the rear part of the center tunnel and under the rear seats. The lithium-ion battery, operating at 270 volts, has a normal energy level of 12 kWh, and is water-cooled to stay within an optimal temperature range. The socket for the standard charge plug is located behind the rings in the single frame of the Audi A1 e-tron.
A fully discharged battery requires less than three hours’ charging from a 230 V grid; a 380 V high-voltage current reduces the time to less than an hour under optimal conditions. A display next to the plug-in connection shows the remaining charging time and the charge state. This value and the current range also appear in the driver's information display of the instrument cluster.
During travel the large electric motor driving the A1 e-tron can convert the deceleration energy into electric current and feed it back to the electrical system, by operating briefly as a generator. The energy return flow begins once the driver releases the accelerator.
The extent of the recuperation is controllable in five stages by rocker switches on the steering wheel. At stage 1 the deceleration is slight, and at stage 5 considerable. In urban traffic the A1 e-tron can recover through recuperation almost a third of the energy needed for driving. When the rocker switches lie at 0 and the driver releases the accelerator, the vehicle needs no energy at all—it simply glides.
A small single-disk rotary piston engine serves as the range extender on board the Audi A1 e-tron. It has a chamber capacity of 254 cc (15.5 cu in) and constantly runs at 5000 rpm in its optimal efficiency range. The rotary piston engine drives a generator that produces up to 15 kW (20 hp) electrical charging power.
The great strengths of the rotary piston engine are its vibration-free and practically noiseless operation, small dimensions and the extremely low weight. Including the generator, the entire assembly group weighs about 65 kg (143 lb). This weight already includes the special power electronics, the intake, exhaust and cooling systems as well as the acoustic encapsulation and the auxiliary frame.
According to the draft for standardization for determining the consumption of range extender vehicles, the rate of fuel consumption by the Audi A1 e-tron is 1.9 liters per 100 km (124 mpg US)—a CO2 equivalent of 45 g per km (72 g/mile). The fuel is supplied from a tank with a capacity of 12 liters (3.17 gallons US).
The ancillary units of the A1 e-tron are electrified. A high-voltage refrigerant compressor operating according to the current power requirement drives the air conditioning system, for greater efficiency compared with conventional concepts. The power steering operates electrohydraulically as in the series production model. The hydraulic brake system includes a brake servo, with the vacuum supplied by an electrically operated pump, also demand-controlled.
In 2011 Audi will be joining three project partners—the energy supplier E.ON, the Munich public utility company and Munich Technical University—in launching a fleet test with the A1 e-tron. (Earlier post.) By the middle of the year the first vehicles should be hitting the road in the Bavarian capital, while at the same time 200 new charging stations will become operational.
R8 e-tron
The Audi R8 e-tron is a high-powered sports car with a battery-electric drive. Its four motors—which can be individually actuated—provide a total power of 230 kW (313 hp). The four asynchronous motors—two each on the front and rear axles—make the Audi R8 e-tron a quattro. Power is transmitted to the wheels via the single-staged transmission and short input shafts. With up to 4,500 N·m (3,319 lb-ft) torque at the wheels available from a standstill, the R8 e-tron accelerates from 0 to 100 km/h in 4.8 seconds.
The large, fluid-cooled lithium-ion battery and the power electronics lie directly behind the passenger compartment. The result is an optimal center of gravity and a load distribution of 42:58 between the front and rear axles—just like the series production R8 with its 5.2 liter FSI.
The rechargeable lithium-ion battery installed in the Audi R8 e-tron consists of single cells with a high energy density connected in parallel and in series, and ensures a high output. The 550 kg (1,213 lb) battery stores 53 kWh of energy, with the usable share amounting to 42.4 kWh. In the final design stage of the Audi e-tron, the battery will enable a range of about 250 km (155 miles) when operated in the NEDC cycle.
For recharging the battery a household current with 230 volts suffices; the process takes six to eight hours for a fully discharged battery. A high-voltage current will reduce the charging time to about two and a half hours.
The distribution of the electric drive torque in the R8 e-tron distinctly favors the rear axle. Like the standard Audi R8, about 70% of the power acts at the rear in regular operation, with the remaining 30% going to the front wheels. Should slip occur at an axle, this balance changes in a fraction of a second.
The R8 e-tron also manages the lateral dynamics through its four motors. They allow torque vectoring, the selective acceleration of individual wheels and therefore active distribution of torque. Understeering and oversteering can be compensated by small power boosts and brake interventions. The electrically driven high-powered sports car retains neutrality even at maximum lateral acceleration.
The running gear employs double triangular control arms at the front axle and trapezium links made of forged aluminum components at the rear axle—a configuration that has proven its merit in motor sports as an optimal layout for high dynamics, maximum precision and exact intrinsic steering behavior. Notwithstanding the firmness of the springs and shock absorbers, they still afford good comfort. The rack and pinion steering with its direct gear ratio provides finely differentiated feedback. The steering is electro-mechanically assisted depending on the speed. The Audi R8 e-tron rolls on 19-inch wheels.
Audi will be bringing a limited edition of the R8 e-tron to the roads in late 2012. It will be built at quattro GmbH in Neckarsulm, which has extensive experience in the construction of exclusive sports cars.
Source: Green Car Congress
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