The all-new Toyota Yaris - powertrains 27.07.2020: POWERTRAINS New fourth-generation Toyota hybrid electric powertrain All hybrid components are new, optimised for size, weight and efficiency New 1.5-litre Hybrid Dynamic Force Engine Greater fuel economy and emissions eff

POWERTRAINS




    New fourth-generation Toyota hybrid electric powertrain

    All hybrid components are new, optimised for size, weight and efficiency

    New 1.5-litre Hybrid Dynamic Force Engine

    Greater fuel economy and emissions efficiency, together with increased power and torque

    Significantly greater EV driving capability, at speeds up to 130 km/h




Fourth-generation hybrid electric system



The new Yaris uses the latest, fourth-generation Toyota hybrid technology and introduces new components that have been engineered to be compact, lightweight and efficient. It also equips the car with its first TNGA engine.



For the engineering team, the focus was not just on delivering a more efficient system, but also on making the car more enjoyable to drive, with tuning and calibration to suit European roads.



The data indicates the scale of the achievement. Overall efficiency has increased by 20%, which typically would be at the cost of performance. In fact, power is 16% higher at 116 DIN hp (total system output), with a 15% improvement in 0-100 km/h acceleration, to 9.7 seconds, and sharper response to the driver’s use of accelerator.



The car’s all-electric EV capabilities have been transformed: speeds of up to 130 km/h can be reached and EV driving is possible for longer periods in urban traffic. This means drivers can enjoy many of the benefits of a battery electric vehicle, but at a lower price and with no concerns about when or where the battery can be recharged.



CO2 emissions have dropped to 85 g/km and the WLTP combined cycle fuel economy figure is 3.7 l/100/km, a 20% improvement.



These values are unprecedented for a Toyota model and demonstrate the ability of hybrid electric technology to deliver even higher efficiency, without sacrificing performance.



The engineering team was committed to addressing the most common criticisms Toyota heard from Yaris Hybrid drivers. These focused on overtaking acceleration performance at highway speeds (the acceleration time from 80 to 120 km/h has been cut by two seconds to 8.1 seconds); quicker and more responsive acceleration at lower speeds, for example when negotiating a roundabout; and more linear, natural acceleration when driving on open, winding roads, to create a stronger fun-to-drive quality.



Each of the four principal components in the hybrid system contributes to the new Yaris’ enhanced drivability: the all-new Hybrid Dynamic Force Engine makes its debut in the car; the new lithium-ion battery; the all-new hybrid transaxle; and the power control unit. All have been developed using the TNGA philosophy, ensuring efficient design and ease of production at scale.

 




1.5-litre Hybrid Dynamic Force Engine



The all-new 1.5-litre Hybrid Dynamic Force engine is from the same TNGA engine family as the 2.0-litre four-cylinder unit featured in the Toyota Corolla and C-HR. It has a long stroke, 14.0:1 compression ratio and high-speed combustion with better temperature and pressure control. This contributes to the its exceptionally high thermal efficiency – 40% – ensuring that more of the energy potential of every drop of fuel is captured.



In common with all Toyota’s hybrid engines, it uses the Atkinson cycle, which keeps the intake valves open for longer, delaying the compression stroke. This improves efficiency and fuel economy, but reduces power output. Nonetheless, the new engine has a maximum output of 93 DIN hp/68 kW with a peak 120 Nm of delivered at lower revs (3,600 rpm).



The three-cylinder configuration also bring benefits in terms of noise levels. When running at 4,000 rpm, its performance is like a four-cylinder unit operating at 3,000 rpm, thus delivering more power and torque, but generating less noise.




The transmission is a e-CVT automatic – an electric continuously variable transmission – which provides linear acceleration feel and quiet operation.

 




Motor/generators



The hybrid system in the new Yaris has two motor/generators – MG1 and MG2. MG2 is linked to the front wheels and can be used as the power source to drive the vehicle. The motor rpm at which power can be directed to the wheels determines the maximum speed at which the car can be driven in EV (electric vehicle) mode, making MG2 critical to the car’s drivability on electric power.



MG1 is deployed to start the engine and to generate power to charge the battery.

 




Lithium-ion Hybrid Battery



The new Yaris adopts a lithium-ion hybrid battery, with voltage rising from 144 to 177.6 V. The number of cells has been reduced, from 120 to 48. The current flow is significantly improved: by 100% into the battery and 50% out.



With a significantly higher power density, the battery is both smaller and lighter, by 12 kg. Its compact dimensions allow it to be located beneath the rear passenger seat, together with the auxiliary battery, avoiding intrusion in the load space.



Lithium-ion battery technology is better able to supply current flow, which is key to the new Yaris having powerful EV performance in urban driving.

 




Hybrid Transaxle


The all-new hybrid transaxle is more compact and lightweight, with the two motor generators placed on multiple shafts instead of being placed one behind the other, reducing the unit’s width by around 37 mm. Motor/Generator 2 benefits from new segment-type coils on the stator, which makes the unit more compact. It can deliver 59 kW of power and 141 Nm of torque to the front wheels at a maximum 17,000 rpm.



The key benefit is a major improvement in performance, so that the engine can be turned off and the vehicle run in all-electric EV mode at speeds up to 130 km/h.



The transaxle also has a new oil pump, driven by the ring gear, which provides lubrication for both the gears and motor/generator 2.

 



Power Control Unit



The Power Control Unit has the capacity to handle 100 A of current, boosting the 177 V from the battery to 580 V and using transistor control in the inverter to change the current from direct to alternating. The transistors’ efficiency is affected by heat control inside the unit; by arranging them vertically, they can be cooled on both sides, allowing for more accurate heat control and thereby a higher frequency of current switching – up to 10,000 times a second. This makes a significant contribution to the system’s efficiency and transfer of power to the motor.



The converter in the power control unit converts the 177 V from the hybrid battery to 12V to power the car’s auxiliary components.

 




Power Split Device



The power split device is the heart of the hybrid system, governing the interaction between the components. It enables the car to operate as a parallel hybrid with the motor/generator 2 powering the car alone, or in combination with the hybrid petrol engine.

 


Additional powertrains



The new Yaris is also available with a 1.5-litre petrol engine with six-speed manual or continuously variable transmission (W-CVT) with a wide range – W – in first gear. This is essentially the same new three-cylinder unit featured in the hybrid system; compared to competitor small-capacity turbocharged engines, it offers good emissions and fuel economy performance.



In certain markets, a 1.0-litre three-cylinder petrol engine, similar to the one featured in the previous-generation Yaris, is available as an entry point to the new Yaris range.

 


- Stephan Lesuisse, photos Toyota