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Toyota Prius 4_1

Inside the Toyota Prius4….

By Andrew Marsh, 02.11.15
Posted in: In-depth | New Model Information | Public

The latest generation of Prius was revealed in Las Vegas during September 2015, and will start deliveries in Japan by December 2015 – in Europe we will wait until February 2016. The principles are the same as Prius3:

  • 1.8l Atkinson cycle petrol engine driving the front wheels with a one electric motor and one generator / motor in a split drive transaxle.
  • Optimised aerodynamic body, with a Cd reduced to 0.24.
  • The traction battery is either Nickle-metal hydride (Ni MH) or lithium-ion (Li-Ion) for plug-in hybrid extended range capability.
  • Steel body structure.

However every single aspect is new.

From the bi-LED headlights, to the standard fitment CMOS camera / front RADAR autonomous braking system, the Prius4 is a step change from Prius3 technology. Oddly the blind spot detection system uses short range ultra-sonic sensors rather than RADAR, but the automated parking system does now do everything – just as introduced by VWG some years ago. Prius4 is the first time that Toyota have used a full colour head up display. Note how the front and rear light clusters extend well into the bumper skins. © Toyota Europe GmbH

Prius4 will be the first vehicle to use the Toyota New Global Architecture (TNGA) platform, which will appear under future generations of many vehicles including the replacement Prius derivatives, replacement Auris as well as the replacement Avensis.  The layout of the engine bay is more or less fixed, as is the suspension / steering / brakes/ / fuel system / exhaust system / seats / HVAC module.

The new global platform places the rear seat on a frame above the rear floor pan. The high voltage battery pack which used to sit behind the rear seat back rests can now be placed underneath the rear seat, inside the vehicle – and directly above the fuel tank. The battery pack remains air cooled and….. the Ni MH as well as the Li Ion units occupy exactly the same space. Meanwhile the 12V battery moves from the boot into the engine bay. © Toyota Europe GmbH

The big feature is the new multi-link rear suspension. The boot space is increased to 512 litres thanks to moving the high voltage battery forwards, and even with a space saver wheel it has a capacity of 457 litres. But what’s this? ………© Toyota Europe GmbH

….… Prius4 has a rear electric drive motor! Thanks to the new rear suspension package and moving the traction battery forwards the boot space even with the additional air cooled inverter is the same as the front wheel drive model with a space saver spare wheel. The system is deployed to assist with acceleration, to start the vehicle and to aid traction in slippery conditions. The system remains ‘off’ during steady cruise or braking. © Toyota Europe GmbH

The high voltage batteries have been improved. The Ni MH unit weighs 1kg less at 40.3kg, is smaller and accepts charge up to 28 % faster. The newly developed Li Ion unit weights just 34.5kg, and has the isolation ‘service plug’ in the same location as the Ni MH unit. Both units operate at between 202V and 207V. © Toyota Europe GmbH

The new global platform for Prius4 uses 19% by body shell weight of ultra high strength steel alloy compared to 3% for Prius3. 1500 MPa yield strength steel alloy is used for the A pillar lower reinforcement, the front section of the sill reinforcement and selected zones of the front chassis leg. 980 MPa yield strength steel alloy s used for the cant rail reinforcement, the B pillar reinforcement, the B pillar roof bow, the front floor reinforcement, the door anti-intrusion beams, the front lower bumper beam crush elements and the rear bumper beam. Aluminium alloy is used for the front bumper beam (but not the crush cans), the bonnet and tailgate. © Toyota Europe GmbH

The structure laid bare…. The portal frame at the rear ties in the rear suspension body cross member, the C pillar reinforcement and the tailgate aperture – just as we saw in 2008 with BMW X6. So the bolt-on stiffener panels are now banished. The side frame shows the integration of the A, B and C pillar reinforcements with the cant rail and sill, whilst the lower image shows the linking of the tunnel to the C pillar portal frame. © Toyota Europe GmbH

The body structure in manufacturing uses conventional spot welding and laser screw welding (LSW) which allows more joints to be added between resistance spot welds. This contributes to a 30% increase in torsional stiffness as well as a 70% reduction in welding equipment during manufacture. The process is also tolerant to the gap between panels during the laser welding process. The repair process should be interesting……..© Toyota Europe GmbH

The underside is fully enclosed, adaptive cooling pack air inlet shutters used, and the aerodynamic attachment over the upper surfaces is improved. Careful aero management extends to the A pillar external trim (‘1’), the position of the front wing to optimise airflow over the front wheels (‘2’), and the rear wing / rear diffuser to reduce turbulence. © Toyota Europe GmbH

The engine is all new, achieving 40% conversion of fuel burn to mechanical output – a new bench mark for any passenger car engine. This involved automated shutters for the cooling pack, heat recovery via an exhaust system heat exchanger to boost warm up efficiency and addition of electric heating not only for the seats but the steering wheel as well, to reduce HVAC demands. The official EU fuel consumption figures are not released yet, but using a Japanese drive cycle Prius4 can travel with the petrol engine operating for 40km (24.8 miles) on just 1 litre of fuel.

What we see is classic Toyota – careful improvement by evolution, but using brand new components and sub-assemblies. Indeed much of the architecture is flavoured by the conventional petrol and diesel  powered future vehicles that will use this platform as much as the hydrogen fuel cell powered MIrai. Now that really is a global architecture.



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