GENEVA: Toyota joins engine downsize bandwagon
New Toyota 1.2T arrives in Auris sold as Corolla outside Europe
Toyota has joined the engine downsize bandwagon, introducing at the Geneva show a new turbocharged 1.2-litre I4 to replace its normally aspirated 1.6 in the C segment Auris sold in other markets as the Corolla.
The new, direct injection engine is one of 14 new powerplants the automaker is launching globally between April 2014 and the end of 2015.
Last year Toyota announced its plan to introduce a series of new, highly fuel efficient engines, created using a number of combustion and loss reduction technologies that had previously been reserved for hybrid engines. The new 1.2T is the second unit from this family to come to Europe bearing the Toyota badge, following on from the three-cylinder one-litre engine that was introduced in the redesigned Aygo and updated Yaris in 2014.
Like the one-litre, the 1.2T uses advanced technologies that allow it to change from the Otto to the Atkinson cycle when running under low loads, vertical vortex high tumble air flow intake ports, an exhaust manifold integrated in the cylinder head and advanced heat management measures.
The 1.2T adds direct injection and a water-cooled turbo and heat exchanger. The VVT-i intelligent variable valve timing system used on the one-litre is upgraded to a VVT-iW (Variable Valve Timing – intelligent Wide) system, which allows more valve timing flexibility.
The combination of these technologies results in claimed outstanding performance and efficiency. With a displacement of just 1,197cc, the engine delivers 114bhp (85kW) and constant torque of 185Nm between 1,500 and 4,000rpm. It will accelerate the updated Auris hatchback launched around it from rest to 62mph (100km/h) in 10.1 seconds. Acceleration from 50 to 75mph in fifth gear takes 13.7 seconds, and top speed is set at 124mph. All of this is achieved despite a focus on fuel economy and CO2 emissions: the car achieves 60.1mpg on the combined cycle and emits 109g/km of CO2.
The key to achieving this level of fuel consumption without compromising performance is to apply higher compression, but generally, as compression increases, so does the risk of uncontrolled combustion – knocking.
The 1.2T’s high 10:1 compression ratio has been made possible thanks to a series of technologies that improve control of the combustion process. This way, the risk of knocking can be avoided.
First, the intake ports have been designed to generate a more intense flow and a vertical vortex and the piston shape has been optimised to improve cylinder turbulence. As a result, fuel and intake air mix faster and form a more homogenous mixture. This leads to a higher combustion speed, which helps prevent knocking.
Advanced heat management in itself is a great way to improve fuel economy, but it is also another way to reduce the risk of knocking. The 1.2T engine was designed in such a way that the temperature of each individual part can be optimised. For example, the bottom of the pistons is cooled by oil jets and the cooling of the cylinder head is separate from that of the engine block. This means the temperature in the combustion chamber can be reduced while keeping the block itself hot enough to reduce friction.
Direct injection makes a contribution as well, as it helps dissipate the heat in the combustion chamber, and the charge air passes through the intercooler, which uses a low-temperature cooling circuit.
Low end torque and quick response
A low inertia turbocharger, the VVT-iW valve system and the D-4T direct injection system work together to ensure excellent torque delivery, from the lowest engine speeds. Together with the limited volume intake system, this ensures immediate response when the accelerator pedal is pressed.
The injection system has been newly developed for the 1.2T engine. Compact in design, it is perfect for use in a small displacement engine. It allows multiple injections per cycle and the optimised width and reduced length of the spray pattern ensure combustion quality, regardless of engine regime and load.
From Otto to Atkinson
The VVT-i system operates on both the intake and the exhaust side, and allows torque to be maximised at all engine speeds. In addition, the VVT-iW allows for intake valve closing to be delayed, which means the engine can operate in both the Otto and Atkinson cycle.
The Atkinson cycle is used in extremely low engine load conditions when the intake valve remains open for a fraction of time, after the compression stroke has set in, allowing part of the gas charge to be pushed back into the intake. As a result, the effective compression stroke is shortened. Pumping losses are reduced, as there is less pressure on the piston, and the throttle valve can be opened wider.
Stop and start
A new start control has been developed to ensure quick and smooth engine restart. When the system shuts down the engine, it controls the stop position to leave the piston half way in the compression stroke. On restart, it applies stratified injection in the first compressed cylinder to counter vibrations. And by retarding the ignition, torque increase is kept in check, preventing the engine from revving excessively, thus ensuring a calm and confident take-off.