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Refreshed 2014 Toyota Yaris features revamped 1.0L engine switchable between Atkinson and Otto cycles

Refreshed 2014 Toyota Yaris features revamped 1.0L engine switchable between Atkinson and Otto cycles

Toyota’s refreshed 2014 Yaris for Europe offers a choice of four powertrains, including a thoroughly reworked 3-cylinder 1.0 gasoline unit that is the first member of a new family of 14 highly efficient engines to be launched by 2015.

With a thermal efficiency of 37%, the engine delivers a combined-cycle fuel consumption of 4.1 l/100 (57.4 mpg US), and CO2 emissions reduced to 95 g/km in conjunction with a stop/start system. (Mass-produced gasoline engines on average have a thermal efficiency of between 30 and 35%, Toyota said.)

The hybrid powertrain has also been revamped, with its CO2 emissions reduced still further to 75 g/km and corresponding combined-cycle consumption lowered to 3.3 l/100 (71.3 mpg US). A 4-cylinder, 1.33-liter gasoline engine and 1.4-liter diesel complete the range.

The hybrid Yaris, which already accounts for a third of this model’s sales, was adapted to comply with the Euro 6 Standard and has benefited from adjustments that lowered its CO2 emissions.

The Yaris Hybrid is powered by a 4-cylinder Atkinson-cycle 1497cc engine; 50mm shorter than the 1.8 liter Prius engine and also 17 kg (37.5 lbs) lighter. It includes a cooled exhaust gas recirculation (EGR) system, an electric water pump, a low-friction distribution chain, an intake manifold made of a composite material and a compact exhaust manifold.

In the Atkinson cycle, compression and expansion are asymmetrical. The inlet valves close later than in a traditional Otto cycle, delaying the compression. This creates a higher expansion ratio for less compression, reducing pumping losses and converting combustion energy to engine power more effectively. In addition, the exhaust temperature is lower than that of conventional engines. The cooled EGR system reintroduces cooled exhaust gas into the combustion chamber, also limiting pumping losses and further reducing engine operating temperatures.

As for the 3-cylinder 1.0 gasoline engine, it has undergone a major revamp with a view to improving its performance, reducing its emissions and its noise and vibration levels. The CO2 emissions of the Euro 6-compliant 1.0-liter engine have been reduced from 110 to 99 g/km and 95 g/km in conjunction with the Stop & Start system.

To achieve this, engineers have sought above all to optimize the power-to-weight ratio of the engine. For example, the combination of the cylinder head and the exhaust manifold has reduced weight and improved compactness.

In order to reduce consumption yet still maintain performance, the compression ratio has been increased from 10.5 to 11.5, while a further development of Toyota’s variable valve technology allows the engine to switch between Atkinson and Otto cycles. (The application of the Atkinson cycle in non-hybrid engines is an approach Toyota is pursuing broadly.

The engine now adopts the Atkinson cycle at low load for a better fuel efficiency in urban driving and cruising at low revs while being able to return to the Otto cycle at high load and high speed.

The intake ports and pistons have been redesigned to increase the tumble effect (vertical swirl in the combustion chamber) to promote combustion speed. Scavenging and combustion chamber cooling has been increased to delay knocking and a large volume of cooled exhaust gas recirculation is used to reduce pumping losses.

Lastly, friction levels have been reduced through the adoption of diamond like carbon (DLC) for the valve actuators, changes to the surface treatment of the pistons and the timing chain drive mechanism, and better engine cooling management, most notably due to the shape of the oil sump which ensures that the engine reaches optimum operational temperature more quickly.

Connected to a 5-speed manual gearbox, the 3-cylinder engine is not only very inexpensive to run but also allows the Yaris 1.0 to offer to the driver a very good torque feeling especially adapted to city driving.

The 1.33L gasoline and 1.4L diesel engines have benefited from secondary modifications aimed at reducing noise and vibration: firstly, by providing better insulation for the exhaust system and secondly by fitting a redesigned torque rod for the diesel version.

These two engines are connected to 6-speed manual gearboxes, achieving a compromise between performance and fuel consumption. They both enable the Yaris to reach a top speed of 175 km/h (109 mph with fuel consumption in the combined cycle of 4.8 l/100 (49 mpg US) for the 1.33L gasoline unit and 3.8 l/100 (62 mpg US) for the 1.4 D-4D.

The 1.33 gasoline engine is also available with a continuously variable Multidrive S transmission. More compact and lighter than a conventional automatic transmission, Multidrive combines an easy, comfortable and smooth driving style with optimum engine torque control for considerable fuel savings in city traffic. Multidrive S also offers a manual mode with 7 fixed gear ratios that can be selected through the steering wheel paddles or through the shift lever.

Improved ride comfort and handling. The new Yaris has been designed with a more rigid upper and lower body structure, offering a more direct and linear response to steering inputs, allowing a more comfortable ride whilst maintaining balanced body control.

Frontal rigidity has been increased through the adoption of a new windshield bonding material and a thicker dashboard bulkhead structure. Both the instrument panel beam and its connections to the dashboard and central tunnel have been stiffened in order to improve steering response.

Central and rear body rigidity have been increased through the use of 36 additional welding spots, redesigned tunnel bracing to add rigidity to the vehicle floor, a redesigned wheelhouse area, and a reinforced rear bumper attachment to reduce body roll deformation.

The rear suspension has been redesigned to incorporate a new, stiffer torsion beam combined with softer coil springs and a new long polyurethane bound stopper. This improves ride comfort whilst maintaining good body roll control, and also enhances the front/rear grip balance of the vehicle, to reduce understeer tendencies.

The front suspension also features softer coil springs for greater ride comfort. Simultaneously, the introduction of rebound springs within the shock absorbers increases front anti-roll stiffness, improving handling and reducing body roll during cornering.

In addition, new front and rear shock absorber valve technology reduces the transmission of vibrations from the road surface and further improves the new Yaris’ ride quality without compromising its handling agility.

Finally, new control logic to the electric power steering system takes advantage of these bodyshell stiffness and suspension enhancements to offer customers significantly improved steering feel, responsiveness and accuracy for a more engaging driving experience.

Reduced NVH. Complementing the reduction in unwanted vibration through increased body stiffness and suspension re-tuning, the new 2014 Yaris also benefits from a marked reduction in interior noise levels.

Based on customer feedback, Toyota engineers identified three noise-reduction priorities. First, the reduction of high frequency noise from the engine and the road surface. Second, the reduction of low frequency noise from the engine. And, third, the reduction of wind noise during high speed driving.

To minimize the penetration of high frequency noise through the dashboard bulkhead and vehicle floor, the dashboard silencer has been completely re-engineered, the instrument panel and console box sound absorption material have been upgraded, and a noise-optimized carpet was introduced.

The dashboard silencer surface area has been maximized by reducing the size of all feed-through apertures, and its thickness increased and material composition optimized for better sound insulation. A similar principle has been applied to the instrument panel and console box cavities, which now incorporate double the quantity of sound-absorbing material.

These measures improve cabin sound performance both during acceleration and whilst driving at a constant speed.

Low frequency engine booming has been minimized by the adoption of a newly-designed engine torque rod (for 1.4 diesel models), and the redesign and relocation of the exhaust system hangers.

The intrusion of wind noise at high speed has been reduced by the adoption of a new, spoiler-shaped cowl louvre which reduces turbulence air at the base of the windscreen, a new door weather strip design which improves sealing, most notably around the door mirror area, and double the quantity of sound absorption material in the door cavity.

A European project. Toyota has been altering its strategy to give more responsibilities and freedom had to be given to its 17 Research and Development Centers around the globe. This change in attitude to the Group’s worldwide strategy led to the creation of specialist hubs in each region of the world.

Toyota Motor Europe has been given a leading role in defining future A- and B- and C-segment cars. Toyota Motor Europe has also become Toyota’s skill center in the three areas that identify the specific nature of the European market: the importance of the diesel engine; the customer expectations for perceived quality; and their demands for vehicle dynamics.

This specialization is achieved through the increased collaboration with European suppliers, the work carried out with leading European universities on advanced research and through the local alliances, such as the agreement signed with BMW for diesel engines.

All of these new responsibilities fall specifically to the Product Planning Department, the Research and Development Center at Zaventem (near Brussels) and the European Design Development Center (EDD) based in the south of France, all three of which already have to their credit the restyled versions of the Avensis in 2012, the Verso in 2013, the Verso 1.6 D-4D at the beginning of 2014 and now the new Yaris.