19 June 2012 / Vehicles
Toyota's Prius v has a Hybrid Synergy Drive series-parallel hybrid drivetrain designed to provide the best balance of driveability, economy and low emissions.
Much of the hybrid system is borrowed from the Prius hatch, however this new seven seat model uses a lithium-ion high voltage battery for the first time in a Toyota in New Zealand. This compact battery is located in the centre console, helping to create additional space for the rear seats.
The Prius v 1.8 litre Atkinson cycle engine delivers 73kW of power at 5,200rpm and 142Nm of torque at 4,000rpm. The vehicle's 650 Volt electric drive motor has 60kW of power and 207Nm of torque.
Combined power is a maximum 100kW while fuel consumption is only 4.1 litres/100km on the ECE101/01 combined cycle. Just 99 grams of CO2 are emitted per kilometre travelled.
The 2ZR-FXE petrol engine was purpose designed for use in hybrid vehicles. It uses the Atkinson cycle to improve fuel economy and emissions. This makes full use of combustion energy by effectively making the expansion stroke longer than the compression stroke, harnessing more of the energy which would otherwise be lost out of the exhaust.
Prius v has a state-of-the-art electrical system which stores energy until it is required to power the vehicle. The system consists of two electric motor generators, an inverter, voltage converter and 201.6 Volt lithium-ion battery.
This new battery has a unique, vertically double-stacked structure, allowing it to fit inside the centre console. The new location saves space for seating in the rear of the vehicle and centralises weight distribution. There's an overall weight saving of 7 kg compared to the Prius hatch's nickel-metal hydride battery.
Electrical energy is gathered during regenerative braking and from excess petrol engine energy. This energy is converted from AC to DC for storage in the hybrid battery. When required for electric-only driving (EV mode) or to help with acceleration, the stored energy is converted back to AC to help drive the electric motor.
The heart of the Prius v electrical system is the Power Control Unit (PCU). This unit is located under the bonnet and is responsible for the conversion of energy from DC to AC. The PCU also converts power from the high-voltage hybrid battery to 12V to power ancillary devices such as the power steering and headlights. This does away with the need for a conventional 12V alternator driven from the petrol engine.
Prius v's hybrid system also contains a combination of two planetary gears which act as an electronically controlled infinitely variable transmission (E-CVT) for seamless changes to the transmission ratio, resulting in optimum performance, driveability and economy. Using these planetary gears provides a significant weight saving as a separate automatic transmission or belt-and-pulley style CVT is not required.
Unique software has been developed to control the E-CVT, smoothly adjusting the revolutions of the petrol engine, generator and drive motor when the vehicle is accelerating, and allowing the petrol engine to be switched off when the vehicle is stationary or decelerating. The new software also allows for three on-demand driving modes: EV (electric vehicle), ECO and POWER.
At start-up and at speeds up to 50km/h, Prius v can automatically operate in EV mode, driving on electric power only. This allows for very quiet driving with zero emissions, perfect for short-distance urban driving up to approximately 2 km, depending on the level of hybrid battery charge. All reversing is done using electric power only.
'Eco' mode prioritises fuel economy by slightly reducing throttle response and limiting power consumption from the air conditioning system. 'Power' mode boosts system performance.
Toyota's new Prius v has a unique system that uses the vehicle's electric motor torque to improve ride comfort. The system, known as body control with torque demand, is designed to counteract the 'floating' feeling occupants can experience when the vehicle is travelling on smooth motorways or undulating roads.
The system uses wheel-speed sensors to measure road input, then feeds this information to the hybrid system controller which instructs the motor to apply torque. This electric motor torque helps to counteract the direction in which the vehicle is naturally 'pitching' or 'bouncing'.