Car Design News: New Toyota Aurion: In Depth (AU)

Aurion achieves power and economy double

Toyota Australia's new Aurion V6 will have the most power and best fuel economy of the naturally aspirated Aussie big-six family cars. It is the most powerful vehicle ever sold by Toyota in Australia - and has more power than its naturally aspirated six-cylinder competitors in the large-car class.

Aurion's advanced 3.5-litre V6 engine delivers 200kW of power using regular unleaded petrol (ULP). Premium unleaded petrol (PULP) will produce even more power, lifting maximum output to 204kW. Aurion is also the most fuel-efficient six-cylinder car in the large-car segment, consuming just 9.9 litres/100km, based on the official combined cycle (ADR 81/01).

Toyota Australia's senior executive director sales and marketing David Buttner said Aurion defied conventional wisdom that achieving these levels of power and economy from the same engine was a paradox. "This is the automotive equivalent of breaking the three-minute mile," Mr Buttner said. "Aurion is the first Australian-built production car to achieve this power and economy double - a rare feat previously only possible with a small number of imported vehicles, such as those with hybrid drivetrains. Aurion is the performance leader among non-turbo Aussie six-cylinder family cars, delivering the power demanded by Australia's large-car buyers. At the same time, it achieves fuel efficiency that is not matched by the six-cylinder competitors in its class*."
*VFACTS Large class

Aurion V6 VVT-i engine built for performance and efficiency

Aurion's new 3.5-litre Quad Cam V6 is the most advanced engine in Toyota's Australian model line-up. It is Toyota's first dual variable valve timing with intelligence (VVT-i) engine in Australia, providing improved performance and fuel efficiency with lower emissions, and an intelligent electronic throttle (ETCS-i).

The Toyota dual VVT-i system provides optimum inlet and exhaust valve timing across the range of engine operating conditions. The dual VVT-i system in the 2GR-FE engine can independently vary inlet timing across a range of 40 degrees (relative to crankshaft angle) and independently vary exhaust timing over a range of 35 degrees. The dual VVT-i system boosts torque in the low-to-medium and high engine speed ranges.

It optimises the valve overlap period, according to engine and driving conditions, to make full use of exhaust gas recirculation. This achieves a more complete burn, and improved inlet suction resulting from exhaust gasses escaping at high speed to increase cylinder filling at high rpm. The system can vary the amount of valve overlap from one degree to 76 degrees relative to crankshaft angle. The inlet camshafts have 258 degrees of duration and the exhaust camshafts have duration of 244 degrees.

There are four main operating scenarios:
Low engine temperature, engine start, idling or light load: inlet camshaft on full retard, exhaust camshaft on full advance. This eliminates valve overlap, thereby reducing volume of exhaust gas blowback into the cylinder and inlet ports, providing stable combustion and improved fuel economy.
Medium load range: inlet timing is advanced and exhaust timing is retarded for increased overlap. This creates two parallel effects - increased internal exhaust gas recirculation to reduce oxides of nitrogen and hydrocarbon, reduced pumping losses and hence improved fuel economy.
High load range, low-to-medium engine speed: inlet timing is advanced to close the intake valve earlier, thereby reducing the volume of intake air blowback into the inlet ports and improving volumetric efficiency.
High load range, high engine speed: inlet timing retarded, exhaust timing advanced. Retarding the inlet timing (according to the inertial force of the inlet air) improves volumetric efficiency and hence power.

The engine ECU controls camshaft advance and retard via an oil control valve mounted on the cylinder head and vane-type actuators on the ends of the four camshafts. In addition, the engine has roller rockers, an electronic Acoustic Control Induction System (ACIS), Direct Ignition System (DIS) and a lightweight cast-aluminium cylinder block.

Toyota designed the 60-degree V6 for a combination of high performance, fuel efficiency, package efficiency and reliability, coupled with minimal weight, noise, vibration and harshness (NVH) and low emissions. The engine has an oversquare bore-and-stroke relationship of 94.0mm by 83.0mm for a swept capacity of 3456 cubic centimetres. Compression ratio is 10.8:1 for optimum power and economy across the engine revolution range.

The new 24-valve 2GR-FE engine has Siamese inlet ports to reduce the overall surface area of the port walls - reducing wall wetting and hydrocarbon emissions. The combustion pentroof chamber design is based on a narrow included valve angle to create a compact combustion chamber shape. It offers a low surface-to-volume ratio, thereby reducing cooling losses and increasing fuel efficiency.

The cylinder head and piston crown design have taper squish areas around the circumference of the combustion chamber and piston crown to improve both intake efficiency and anti-knocking performance. Toyota engineers have adopted roller rockers (with maintenance-free valve clearance adjusters) to reduce friction and hence optimise fuel economy.

In addition to the roller rockers, the 2GR-FE engine has cam profiles with a rounded concave portion on the ramp to increase valve lift as the valve begins to open and finishes closing, thereby increasing engine output. The Toyota 2GR-FE engine has electronic control for the ACIS - based on information on engine revolutions and throttle position.

The ACIS varies the effective length of the inlet runners to make maximum use of the inlet pulsation effect for increased breathing efficiency. It creates a long manifold effect to boost torque in the medium engine speed range and a short manifold effect to boost power at high rpm.

The stainless-steel exhaust manifold has a built-in three-way catalyst to boost catalyst temperature and reduce hydrocarbon emissions from cold start. This design accelerates the warm-up of the catalyst immediately after start-up, thus reducing exhaust emissions. Dual main mufflers are fitted to reduce exhaust back-pressure and hence boost performance.

Toyota has maximised reliability and serviceability by adopting chain camshaft drive, maintenance-free valve clearance adjusters, a replaceable element oil filter, direct ignition, electronic engine control and an air/fuel ratio sensor. Aurion's 2GR-FE engine has a service weight of 163kg.

Six speed transmission had artificial intelligence

Aurion's new six-speed electronically controlled automatic transmission has artificial intelligence and a sequential-style manual gear select shift. The Toyota U660E transmission was designed to complement Aurion's Quad Cam dual VVT-i V6 engine. The combination of Aurion's V6 engine, electronic throttle, six-speed transmission and advanced ECT software is designed to optimise driveability, acceleration feel, shift quality and fuel economy. The U660E's electronic control software has new fuel-saving features, including increased range of low-speed torque-converter lock-up control and flexible lock-up control.

The Toyota artificial intelligence (AI) shift control is a transmission algorithm designed to manage the shift regime according to road conditions and driver intention. It uses data on throttle opening angle, vehicle speed and engine speed, brake signal and accelerator pedal operation.

The transmission ECU uses this information to provide three functions: basic shift control pattern, road condition support control and driver intention support control. The AI shift can adjust the shift pattern to suit different drivers and provide engine braking for hill descents. It also reduces 'gear hunting' when going uphill.

The uphill/downhill shift control judges if the vehicle is climbing or descending, based on inputs such as throttle opening and vehicle speed. It prohibits unnecessary up-shifting if the vehicle is ascending steeply and automatically downshifts when the vehicle is descending steeply, to take advantage of engine braking.

Road condition support control (i.e. intelligent transmission software) gives Aurion smooth shifting performance in automatic mode, particularly on hilly roads. Driver intention support control judges the driver's intention based on accelerator usage and vehicle condition, to provide gear shift patterns that suit individual driving styles.
Aurion's sequential style shift has an S-mode gate shift lever. A gear position indicator is included in the instrument cluster.

Toyota's development targets for the U660E transmission were improved dynamic performance, optimum fuel economy, light weight and optimum package efficiency, smoother gear shifting, increased responsiveness and low noise. The design includes two planetary gear sets, to create a six-speed transmission with a shorter shaft length and smaller exterior dimensions than a typical five-speed ECT. It has ratios of: first, 3.300; second, 1.900; third, 1.420; fourth, 1.000; fifth, 0.713; sixth, 0.608 and reverse, 4.148. It is matched to a 3.685:1 final drive ratio.

The U660E transmission has an ultra-flat torque converter to reduce transmission length and weight. The new design reduces the torque converter length by around 12mm, compared with the torque converter for a typical five-speed ECT. The torque converter has a low-speed lock-up damper to ensure smooth low-speed lock-up.

Euro IV more than twice as tough

Toyota's new Aurion meets Euro IV emissions standards, well in advance of their mandated introduction in Australia. The Euro IV limits are less than half the Euro III standards currently required under Australian Design Rule 79/01. ADR 79/01 applies to petrol, diesel and LPG-powered passenger vehicles with a gross vehicle mass under 3.5 tonnes launched from 2005 and for all new vehicles from 2006, and mandates that they meet Euro III emissions standards.

The change from Euro III to Euro IV means carbon monoxide (CO) emissions must be more than halved, from 2.3g/km to 1.0g/km. Hydrocarbon (HC) emissions are halved under Euro IV, from 0.2g/km to 0.1g/km and allowable oxide of nitrogen emissions (NOx) are reduced from 0.15g/km under Euro III to 0.08g/km under Euro IV. In addition to reduced emission levels, Euro IV has a stricter testing regime, under which vehicles must pass the emissions benchmark at sub-zero cold start.

Aurion wins weight efficiency stakes

Toyota's new Aurion has a weight advantage over its three locally manufactured large six-cylinder rivals. Aurion delivers this advantage while providing high levels of passive safety, body strength and rigidity, and equipment levels, and low interior noise. A comparison of vehicle weights for the Aurion AT-X and its three entry-level competitors clearly shows Toyota's advantage, with the AT-X weighing in at 1590kg. Its three comparative entry-level competitors weighed in between 1625 and 1694kg.