All-wheel drive systems were originally found only in off-road vehicles as they were useful in providing better traction in rough and slippery conditions, especially mud and snow. In the 1980s, most Japanese carmakers began offering variants of many passenger car models with a simple all-wheel drive system. This was not apparent to the rest of the world as such variants were sold only in Japan and mainly in areas like Hokkaido where snow and ice were prevalent.

This continues today but with the advent of cars with hybrid powertrains, the conventional all-wheel drive system that has been used all along is not so suitable. With hybrid cars, minimising power losses from wind resistance and rolling resistance as well as mechanically are vital to maximise performance. Even tyres used have to be low-resistance tyres and more effort is put into reducing drag.

For this reason, the Toyota Prius, the first mass-produced hybrid car in the world, has not had all-wheel drive in the 20+ years the model has been sold. Now, for its fourth generation since 1997, the Prius gets all-wheel drive for the first time and the system has been engineered specifically for model. The all-wheel drive system is known as Intelligent All-Wheel Drive (AWD-i), All-Wheel Drive-electric (AWD-e) or E-Four, depending on the market. In Japan, this new variant costs about 5% to 7% more than other variants with front-wheel drive only.

The system provides grip and stability in very slippery conditions. It is active from the time the car moves off, automatically engaging to minimise wheel slippage and comes in action at higher speeds when loss of traction is detected. Torque in then to the rear wheels when sensors detect a loss of grip. The system does not operate in normal driving conditions, or under braking.

Unlike mechanical AWD systems, there is no driveshaft between the front and rear axles and no centre differential, saving weight. Instead, there is an additional independent, magnet-less 5.3 kW/570 Nm (with a 10.4 reduction ratio) electric motor – a Toyota first – and inverter, located on the rear axle and powered by the hybrid battery.

The latest Prius has the second generation of Toyota’s Safety Sense suite with enhanced performance of systems to detect and warn the driver of accident risks and to initiate braking and steering adjustments to help prevent a collision, keep the car to its correct path and a safe distance from vehicles ahead, or reduce the consequences if an impact is inevitable. The enhancements can deliver real-world reductions in common road traffic accidents.

Toyota is committed to ‘democratising’ these important new technologies, ensuring they are made widely available so that as many drivers as possible can benefit from the protection and support they provide. This strategy is central to Toyota’s ultimate goal of a safe mobility society with zero road accident fatalities and injuries.

2019 Toyota Prius is the fourth generation of the world’s first mass-produced hybrid car.

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[Chips Yap]

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