Overview: Toyota Auris HSD

We are used to the Toyota Prius. It has a clear identity. It’s a stand-alone hybrid model, a niche product, and it has little in common with any other Toyota. You either want one or you don’t.

But Toyota has a vision for its hybrid drivetrains that goes beyond niche marketing and that takes the technology right into the mainstream. We all know that this is going to happen sooner or later, but Toyota has a timetable. By the early 2020s, the Company expects to be selling a hybrid version of every one of its models.

The new Auris HSD is the first step on the road to mainstream hybrids, not just for Toyota, but also for car buyers. For the first time, when the hybrid Auris goes on sale in July, a customer will be able to consider a hybrid powertrain along with the various other engine and trim options. It will be just one of the many decisions the buyer will make in choosing a ‘normal’ family car. The historical significance of this is great.

The Auris HSD will be available in two versions, differentiated by their CO2 outputs: 89g/km and 92g/km. The new hybrid adopts the revised exterior styling introduced across the Auris 2010 model range, including a completely redesigned front-end. It also incorporates a number of features specific to the HSD model, which help improve the car’s aerodynamic efficiency. Ride height has been reduced by 5mm, and unique alloy wheels and a large rear spoiler are fitted. Together, these changes improve the car’s Cd from 0.290 to 0.283. Additionally, low rolling-resistance tyres are fitted.

Solar cells on the roof of the Auris operate the ventilation system.

Although the Auris HSD is a new model, its powertrain is a direct transplant from the Prius. It’s a series-parallel hybrid with a 1798cc petrol engine and an electric motor. The car operates using either drive unit or both together.

The petrol engine develops 97PS at 5200rpm and 142Nm at 4000rpm. The electric motor — synchronous, with a permanent magnet — contributes 81PS and a maximum of 207Nm between zero and 13,000rpm. Total system output is 134PS — the numbers don’t add up because the petrol engine and the electric motor are never both working flat-out at the same time.

A power split device with a planetary gear system combines and distributes power from the engine and the electric motor according to driving conditions. During overrun and braking, torque from the wheels is directed to the generator, which is the electric motor working backwards.

The electric motor and power split device are housed in a single transmission casing that is the size of a conventional gearbox. Power is transmitted to the wheels through an electrically controlled continuously variable transmission.

In normal driving, the electric motor works in tandem with the petrol engine to boost acceleration. Operating with the electric motor alone, the car’s range is 1.3 miles at a maximum speed of 31mph.

The Auris HSD has four driving modes. Three of them can be selected by the driver. ‘EV’ mode is selected for running on electric power alone, ‘ECO’ allows the car’s control system to mix and match power sources according to the driving conditions. ‘Power’ mode alters the system’s priorities in favour of road performance.

As usual with alternative powertrains, the driver has the dubious benefit of an energy flow display on the dashboard. Perhaps more usefully, a simple power consumption gauge shows how much power is being used or generated at any given time.

The possibility that the quietness of the drivetrain might show up noise from other sources has led Toyota to pay attention to NVH. Notably, a multi-layer acoustic windscreen is fitted.

The Auris’s ventilation system is run from solar power, with photovoltaic cells covering the entire roof, while additional solar panels on the top of the dashboard are used to feed charging sockets for electronic gadgets. Toyota intends to extend the use of solar power to charge the vehicle’s main battery pack.

Toyota’s Hybrid Synergy Drive powertrain.
Text and design copyright Under the Skin 2010. We recommend Firefox.