2016 TOYOTA PRIUS
PIONEERing genius Returns
There are not many vehicles that can claim being “game-changers” like the Toyota Prius can. The Prius was the first hybrid to be mass-produced when it was launched in Japan in 1997, making hybrid technology readily available to the car market. However, it was only with the launch of the second-generation Prius in 2005 that South Africa first tasted hybrid technology.
In keeping with the Prius name – which means “front runner” in Latin – the new-generation marvel continues to build on its green car credentials and now comes with even more technical breakthroughs to reaffirm its status as the world’s best-loved hybrid. In fact, Toyota had sold more than 3.5 million Prius hybrids before the launch of the fourth-generation model. In the past three generations each Prius had a defined role to play.
For example, the first-generation Prius created the hybrid vehicle market, the second generation raised the model’s popularity with a more advanced image, and the third generation secured mass-market success, helping Toyota progressively roll out hybrid power to its mainstream model ranges.
Glenn Crompton, Vice President of Marketing for Toyota Motors South Africa, says: “The fourth-generation Prius builds on the strengths and achievements of its predecessors and establishes new benchmarks in fuel economy, emissions and efficiency. It will add further impetus to the growing appeal of hybrids in the global market, achieving its strongest environmental performance yet, while delivering much improved styling and surprising driving dynamics from a green car.”
The new Prius is founded on the latest evolution of hybrid technology, delivering the afore-mentioned efficiency and environmental performance. This is in line with Toyota Environmental Challenge 2050 (www.toyota-global.com/sustainability/environment/), the organisation’s bold initiative to lower carbon emissions and go beyond zero environmental impact as well as achieve a net positive impact in society. The ultimate goal is to make positive contribution to a low-carbon society that is recycling-based, environmentally friendly and in harmony with nature.
However, beyond these green credentials the new Toyota Prius also embraces stronger emotional and performance qualities that give it wider and greater appeal to customers who appreciate eye-catching, original styling, high levels of sensory quality, practicality and a driving experience that is genuinely fun and rewarding. The realisation of these is based on three pillars:
- Toyota New Global Architecture (TNGA)
- Authentic Design and styling
- New generation full hybrid system
The new Prius is the first model to use a chassis based on Toyota New Global Architecture (TNGA). It will also underpin other future models and will be joined by further platforms suitable for different vehicle applications, from compact sports cars to SUVs.
The TNGA platform plays a defining role in the Prius’s essential fun-to-drive quality, giving the car a lower centre of gravity compared to the current model, and securing a more engaging driving position and more precise and responsive handling, with less body roll. This means better handling can be achieved directly from the quality of the chassis and body without having to use firmer suspension settings, or compromising ride and comfort.
It makes a big contribution to the improved driving dynamics – beyond what might be expected of an eco-car. This quality is further supported by a body that is 60% more rigid than before thanks to extensive use of high-strength steels and additional reinforcement to the centre pillars’ lower structure and the panel connection. The result is superior, direct and responsive handling.
These superb driving qualities are also enhanced by Prius’s new double wishbone rear suspension, which produces one-third the level of shock when driving on uneven roads compared to the outgoing model. To achieve better handling with more direct response, the front MacPherson strut suspension has been revised with an increase in the incline angle of the shock absorbers and the use of slant bearings.
The chassis is fully able to harness the more responsive character of the new full hybrid system. As a result greater stability is maintained, body roll is much reduced in high-speed lane changes and performance is smoother on rough surfaces. On winding roads, the new Prius holds easily to the driver’s intended line – like a train on tracks – and there is outstanding straight-line stability when driving at speed.
More on the TNGA Platform
The benefits of the TNGA platform extend to new, defined lay-out rules for the position of different state-of-the-art components which simplifies vehicle design in key areas without detracting from the styling qualities that will give each vehicle its individual character and appeal.
For example, the driving components – items such as the pedals, steering column and driver’s seat – will conform to one of five different lay-outs according to vehicle type and platform. Previously much time was spent on millimetre-adjustment to define the most suitable design and arrangement of these components to achieve the optimum driving position in every new model.
The TNGA solution provides an ergonomically ideal combination to suit the vehicle, in line with the floor height provided by the platform. Each lay-out can be further refined with detailed adjustment to the pedal and pedal operation angles as well as the position and angle of the steering column.
TNGA also brings a new approach to the design of the engine compartment, with a focus on placing components lower down in a more rationally organised “clean and tidy” space. In the new Prius this allows for better packaging, a lower vehicle centre of gravity and a more attractive, lower bonnet, which in turn improves safety by giving the driver a clearer forward view.
STYLING AND DESIGN
The new Prius is not simply “another green car,” its design and high quality throughout give it greater emotional appeal and a powerful, desirable presence, underpinned by the fundamental strengths of the new TNGA platform. As Toyota’s most advanced hybrid, it is appropriate that it is an image leader and the intention has been to produce a design that makes an immediate impact.
The car’s new, low-slung stance – made possible by the TNGA platform – suggests an excellent driving performance, supported by a distinctive new body silhouette that is both athletic and aerodynamically efficient. The result is a “human-tech” design with strong emotional quality, fully exploiting the opportunity presented by the car’s lower centre of gravity.
Prius Chief Designer Shunsaku Kodama, who at 43 was Toyota’s youngest chief designer when appointed in 2011, led a team whose youthfulness generated a natural enthusiasm to challenge the status quo, even for a vehicle as revered as Prius. He says their focus was to “inject ego” into the car by crafting a more powerful, engaging and sporty image that would increase pride of ownership beyond Prius’s traditional ethical profile.
The design theme for the new Prius is captured in the contrast created between the rich curves and hard surfaces of the bodywork. The result is a new form that stands out with its smooth yet sharp use of lines.
The frontal design is true to Prius’s heritage in making the Toyota emblem a strong focal point, but it also makes an impactful visual statement about its more advanced design and performance with a much lower bonnet height. Notably the front emblem sits at the same height above the road as it does on the Toyota 86 coupe. New headlights have permitted slimmer, more striking headlamp units to be designed and these combine with an intricate but unfussy treatment of the fog lights and air intakes to give the car a distinctive and intelligent appearance.
The lower part of the front bumper and the shape of the lower grille and wheel arches have been designed to direct airflow around and under the vehicle. An electric shutter behind the large lower grille forms a novel feature in the car’s airflow management. Derived from motor sport technology, it opens and closes in line with the airflow cooling requirements of the engine; by remaining shut during cold starts, it helps save fuel by helping the engine reach its operating temperature more quickly.
In profile, Prius displays a silhouette that is lower and more athletic. The TNGA platform has allowed for significant reduction in height in key areas to create a lower, more dynamic appearance. The overall height has been reduced by 15mm compared to the current Prius, to 1,490mm. The peak of the roof has been moved forward by 170mm, and the belt line has been dropped and angled forward and lower, emphasising the car’s stronger dynamic qualities. The rocker panel displays a light-catching surface that starts from the lowest part of the front bumper, runs beneath the front door, then races upwards, accentuating the car’s low-slung stance.
The new model retains the 2, 700mm wheelbase of the current Prius, but is 60mm longer overall at 4,540mm. It is also 15mm wider at 1,760mm.
The new Prius has a unique aerodynamic treatment to the rear section of the roof, which supports the clean flow of air over and away from the vehicle. The length and angle of the rear spoiler have been precisely calculated and the bodywork tapers towards the rear corners, helping smooth airflow and reduce drag. The low roof and rear pillars are distinctively integrated using blacked-out panels that are shaped to draw air around the side windows to the rear of the car.
Other aerodynamic aids include graduated vertical channels each side of the windscreen that direct airflow and rain water up and over the roof without generating wind noise. Aero stabilising fins are featured on the front quarter light trim and rear combination lamp housings, which control air turbulence along the side of the car. The new TNGA platform is also designed for the smoothest possible airflow beneath the car.
In combination, the car’s low wind resistance features secure a world-class 0.24 coefficient of drag.
The rear end design flows strongly from the rear spoiler down through the bumper, with the wheel placement further emphasising the car’s firmly planted stance. The slim, striking combination lamps have been moved to the outer edge of the car, following a sharp angle that is accentuated by the distinctive, unbroken line of the red LED tail lights.
Toyota has produced a vibrant colour palette for the new Prius with seven exterior finishes available – including Passion Red, Attitude Black, Glacier White, Pearl White Metallic, Graphite Grey Metallic, Satin Silver Metallic and Dark Blue Metallic.
“Peace of mind” Interior
“Peace of mind” is the theme for the cabin, which is designed to be a welcoming, quiet and comfortable space, embracing the car’s “human tech” design concept by being futuristic and stylish, yet rational and ingenious.
The design has been developed to make an emotional connection with the occupants through an improved quality feel and the use of simple, multi-functional displays that present information at a glance. The peace of mind factor is supported by better visibility front and rear, contributing to both safer driving and a lighter, more pleasant cabin atmosphere.
The cabin has a strong design that is advanced, functional and makes a big visual impact. It inherits the intuitive concept of previous Prius generations by consolidating operational functions closest to the driver and placing the information functions further away. The functionality of this approach can be seen in the layered construction of the dashboard with distinct control and display zones.
The dashboard wraps gently around the driver and flows almost seamlessly into the door panels. The number of different parts that make up the instrument panel has been reduced, for example the piano black section is now a single unit. This creates a strong visual contrast with the areas of the dashboard and door panels, finished in a high-quality white material that is scratch-resistant.
The dominant centre cluster has a silver-finish frame and a “floating” design, created using a sculpted and near-invisible rear mounting. The seven-inch touchscreen panel is designed like a tablet and allows intuitive operation of the audio, including “flick” actions to scroll through the displays. The standard six-speaker audio package gives rich and clear sound quality.
The instrument cluster features dual 4.2-inch full colour TFT (thin film transistor) LCD screens with easy to read displays. The screen nearest to the driver presents vehicle speed and ancillary information such as fuel level, odometer, trip meter, driving range, average fuel consumption, outside temperature and drive mode. The background colour changes according to the drive mode selected: blue for ECO, grey for Normal and red for Power. The second screen provides information about the hybrid system and eco-driving tips and performance, together with multimedia and climate control system details and driver assistance alerts.
The meticulous attention to detail can be seen in elements such as the Prius logo that decorates the air vents, while the high ergonomic quality extends to intuitive positioning and range of adjustment of the seats. The high sensory quality of the interior is further emphasised by a pleasingly tactile leather steering wheel trim. Overall the cabin environment is light and spacious.
Quietness has always been a distinguishing characteristic of Toyota’s hybrid vehicles and the new Prius provides a cabin environment that exudes a genuine sense of luxury with exceptionally low noise and vibration levels.
There is plenty of standard safety kit too, including rear-view camera with dynamic guidelines and no fewer than seven airbags (curtain, front, side and a driver knee airbag). Convenience features include customisable dual Multi-Information Display screens and seat heaters for driver and front passenger. The new Prius also boasts a Toyota-first full-colour Heads Up Display (HUD) projected directly to the windscreen.
Improved Driving Position
A reduction in the steering column angle from 24 to 21 degrees, a lowering of the driver’s hip point by 59mm and a new seat design all help create a more natural and engaging driving position. The range of tilt adjustment has been increased, to accommodate a wider range of driver heights.
The front seats have been completely redesigned to offer more comfort while at the same time saving weight and space. They offer a snugger fit, with better body holding that helps reduce fatigue on long journeys. The seat heating area has been increased, adding to the improved comfort level. The rear seats have also been revised for greater comfort and benefit from an improved armrest and cup holder.
Convenient Storage Provision
The efficient use of space inside the new Prius ensures ample provision of storage space. Thanks to the more compact hybrid system and HV battery and the new double wishbone rear suspension, there is no intrusion in the boot space. The cargo floor is set 110mm lower, expanding capacity to 502 litres when a spare wheel is carried.
In the cabin the storage points have been made larger or have been reprofiled to improve their usability. They include front and rear door pockets, an overhead console, glove box and a console box with a removable inner tray. The console box’s soft-close lid doubles as an armrest and it opens sideways so it is easy for the driver to access. Two cup holders are provided in front of the console box.
NEW HYBRID SYSTEM
The New Prius introduces the next generation of Toyota’s signature hybrid powertrain, the first in a new family of powertrains that builds on the two pillars that have made Toyota hybrids popular with drivers across the globe: on the one hand their fuel efficiency, and on the other the relaxed and carefree drive that they provide.
Toyota has focused its efforts on making this next generation of hybrids even easier and more intuitive to drive. The system has been set up so that it gives a natural, immediate, but smooth response to any accelerator pedal input.
Refined and confident, it delivers the right level of performance.
Of course, fuel economy has been improved as well. The new hybrid system comes in a more compact package that is lighter in weight and lower in cost. It reflects significant advances in battery, electric motor and petrol engine technologies.
The new hybrid battery offers higher energy density. At the same time as maintaining power output, its size has been reduced by 10%. Furthermore, it can now absorb 28% more energy in the same amount of time, which means that it is faster charging. The electric motors are smaller in size, yet also provide a better power-to-weight ratio, and the thermal efficiency of the petrol engine – at 38.5% already very high on the current Prius – is increased to 40% – a world’s best for a petrol unit.
Improved Petrol Engine
As in the current model, Prius’s hybrid system features a 1.8-litre VVT-i Atkinson cycle petrol engine. However, the unit has been completely re-engineered to deliver significantly better fuel economy. The gas flow, combustion, cooling and knock control have all been improved and much more effective use is made of exhaust gas recirculation.
Toyota has developed a heat recovery system that uses spent exhaust gas to speed up the warming of engine coolant. This means fuel can be saved because the hybrid system is able to stop the engine earlier and more often when it isn’t needed to power the vehicle. The engine is also helped to reach its optimum operating temperature more quickly thanks to a new dual-passage cooling system that can reduce the volume of coolant flowing into the engine, when required. This helps improve efficiency during cold weather.
Further work has been done to reduce energy losses, particularly those caused by friction. Measures include the use of thin-section, resin-coated connecting rod bearings and a low-friction camshaft chain. Friction created by the piston skirts, rotating parts and oil pump has been reduced and a new electric water pump has also helped cut the level of losses.
Conical “beehive”-type springs have been adopted to reduce the valvetrain load. And, to ensure comprehensive improvement, the entire engine underwent computer-aided engineering analysis to achieve the best rigidity and to reduce noise and vibration.
The intake and exhaust systems were also revised, resulting in an engine that enjoys better breathing, air filtration, packaging efficiency, reliability and quietness. The air filter has been made smaller and reduced in height, which helped the designers bring down the line of the bonnet. The new intake system has a resonator that creates less noise at noticeable frequencies and the intake duct is made of a porous material that suppresses resonance.
A fresh air inlet duct has been added to make sure ample air volume is obtained at motorway speeds and a clever air/fluid separating structure has been added to keep water from mixing with the intake air. Should the fresh air duct fill with water, a secondary inlet serves as the air intake.
A thinner silencer secures optimum performance and noise reduction, while also improving the underbody aerodynamics and avoiding any intrusion on the space available in the boot.
The engine block has V-shaped drilled paths that reduce losses in water jacket pressure. There is also a new water jacket spacer which helps control cylinder wall temperatures in the combustion chamber, reducing friction and preventing engine knock, which in turn supports optimum ignition timing.
Engine cooling has been improved with a new cooling module structure and attachment, and a redesign that accommodates a lower bonnet line and helps reduce the car’s centre of gravity. There is a new grille shutter behind the radiator which automatically closes when full airflow isn’t required, improving aerodynamic performance and saving fuel.
While engine cooling helps improve anti-knock performance, it can lead to an increase in cooling heat loss. To help counter this, Toyota engineers have developed a new water jacket spacer to control temperature on the surface of the cylinder. This keeps engine oil warmer with lower viscosity and reduces the temperature fluctuation. This helps reduce friction and allows more engine torque to be generated. At the top end of the temperature scale it reduces temperatures in the combustion chamber.
The engine’s maximum output of 72kW is delivered at 5,200rpm, with peak torque of 142Nm at 3,600rpm.
World-best Thermal Efficiency
Thermal efficiency is a measurement of how well an engine converts the energy available in its fuel into usable energy to power the vehicle.
As a result of the large-volume exhaust gas recirculation system, improvements in combustion efficiency and innovative ways of managing heat and reducing friction, the new Prius’s engine has a maximum 40% thermal efficiency, the highest level in the world for a mass-produced petrol engine. This surpasses the 37% of the first Prius’s 1.5-litre unit and the 38.5% level of the 1.8-litre engine in the third generation model.
Improved Exhaust Gas Recirculation
The exhaust gas recirculation system in the new Prius has an EGR cooler which lowers the temperature of the gas being circulated, thereby reducing the temperature of the intake mixture and suppressing engine knock. This allows ignition timing to be advanced, which contributes to better thermal efficiency. Cooling loss has been reduced by eight per cent as a consequence.
Multi-shaft Transaxle – a Hybrid First
The new Prius has a redesigned transaxle that offers more efficient performance and packaging and reduced weight. Its smaller dimensions, notably a 60mm decrease in length, have allowed the auxiliary battery to be relocated to the engine compartment.
The transaxle houses four components: two electric motor-generators (MG1 and MG2); a single planetary gear; and a reduction gear to the final drive. MG1 serves primarily as a generator, converting any surplus power from the petrol engine into electricity, which can be stored in the HV battery. It also serves as the engine’s starter motor. MG2 is the electric drive motor, which also acts as a generator when the car is in regenerative braking mode. It drives the car from start-up, at low speed and in EV (electric vehicle) mode and is the sole propulsion method when the vehicle is in reverse.
Improved Hybrid Software
Updates to the hybrid system software allow the new Prius to draw more on its electric drivetrain, allowing it to accelerate in a low engine rev range. It has also permitted the speed range of the electric motor (the range in which the electric motor can be used exclusively) to be increased by 60%, compared to the current model. This means there is less dependency on the petrol engine at higher speeds, improving fuel economy.
Smaller, Better Electric Motors
The two motor-generators are all-new and are smaller and lighter than before to suit the new multi-shaft transaxle design, with no negative effect on fuel economy.
Higher motor speed and new forced water-convection cooling in place of air cooling improve the efficiency of the electric-drive motor (MG2), which delivers 53kW of power and 163Nm of torque.
Fully Redesigned Power Control Unit
The power control unit (PCU) has been totally redesigned, resulting in a 33% reduction in size, a six per cent weight saving and a 20 per cent reduction in electrical losses.
The PCU is the multi-purpose electrical heart of the vehicle, housing the inverter/voltage booster, a DC/DC converter for auxiliary power and the electronic control for the motor-generators.
In place of a belt-driven alternator, the new Prius uses a DC/DC converter to recharge the 12-volt battery, using energy from the HV battery.
Nickel-metal Hydride HV battery
The nickel-metal hydride (NiMH) battery is more compact, so can be located entirely beneath the rear seats, avoiding any intrusion in the load space. Its cooling is more efficient and it has a greater energy regeneration range. The new cooling system features an air filter in the intake bezel, which is located in the trim beneath the right rear seat.
The fuel economy achieved by the new Prius marks the largest improvement between generations of the hybrid model, achieved thanks to improvements in the hybrid system and efficiency improvements throughout the car. This accomplishment reflects Toyota’s philosophy of refining existing technology – the concept of having something good, then making it better.
Every aspect of the hybrid system has been made more efficient and these improvements deliver about half the gain that’s been realised in fuel efficiency. The petrol engine uses less fuel; the electric motor-generators are smaller, lighter and more efficient; mechanical losses in the transaxle have been cut by 20%; the power control unit is more efficient; and the nickel-metal hydride HV battery is lighter and more efficient. Further gains have been made by reducing the energy load of the air conditioning system, improving the rolling resistance performance of the tyres and creating a more aerodynamically efficient vehicle design.
The new Prius’s lower centre of gravity and increased body rigidity help deliver a safe and secure drive. Passengers enjoy a smooth, comfortable ride, with minimal roll.
The TNGA concept has produced an increase of more than 60% in body rigidity, compared to the previous model, by using a ring-shaped, cyclical frame, laser screw welding (with a greater number of weld points) and structural adhesives. Together these contribute to achieving a more stable ride.
New Prius also uses a higher proportion of high-tensile strength steel in its construction, making good use of high-strength, lightweight hot-stamp materials to achieve improved rigidity. The content of this quality of steel in the vehicle has increased from three to 19%. Furthermore, Toyota’s advanced Global Outstanding Assessment (GOA) methodology for designing safer cars brings the benefits of light weight, stability and excellent collision safety performance.
The driving experience has been improved with better acceleration feel, achieved through an upgrade of the hybrid system control unit. Optimal use of the battery and electric motor have minimised the “rubber band” feeling when accelerating – the sense of a delay in acceleration when you press the throttle.
Improved Real-world Performance
The new Prius accelerates from 0-100km/h in 10.6 seconds. Highway overtaking acceleration from 80 to 120km/h can be accomplished in just 8.3 seconds and the top speed is 180km/h.
The new hybrid system’s output – petrol engine and electric motor combined – is 90kW, and the drivetrain now delivers its power in a more user-friendly manner. The new Hybrid System allows the system to draw more on its electric power, which means that acceleration feels more natural with the engine revs building up gradually as the car picks up speed.
Selectable Drive Modes
The new Prius maintains the smooth, quiet and refined drive that has characterised previous generations of the model, its shift-by-wire transmission making it as easy to drive as an automatic. The driver can choose from three selectable driving modes – Normal, ECO and Power – to suit driving conditions and personal preference.
The driver can also switch to EV mode, for short distances in pure EV driving, such as entering a parking space or garage.
Normal mode provides a suitable balance between fuel economy and throttle responsiveness. Switching to ECO mode optimises the powertrain and vehicle systems to prioritise fuel saving, adjusting throttle response and air conditioning performance. Power mode gives emphasis to acceleration feel.
The new Prius benefits from a drive assist system to provide a more responsive driving experience. The adaptive system continuously monitors the vehicle’s G-forces to understand driver behaviour and habits, a function activated when the driver selects Power mode. The hybrid system responds to the driver’s desire for more sporty performance, adjusting engine braking performance and throttle response.
Improved Front Suspension
New Prius’s high-rigidity body provides the ideal platform for a sophisticated development of its MacPherson strut front suspension, which has been revised with a focus on improved steering, handling response, stability and ride comfort. With a new rear suspension and improvements to the brakes and steering, Prius benefits from new underpinnings throughout.
The front suspension hardware, geometry and calibration have all been revised and the system has been equipped with new shock absorbers with a 37% reduction in strut friction, and a new piston valve that can generate damping force at very low damper speeds. This delivers better body control and optimum damping characteristics at high damper speeds, reducing impact harshness when travelling on rough and uneven surfaces.
Impact harshness has also been addressed with recalibration of the coil spring rates and spring pre-loading. The front anti-roll bar is mounted on a ball joint to help keep uncontrolled body roll to a minimum and the sliding parts in its bushings have been given a fluorine-resin coating to minimise friction.
New Double-wishbone Rear Suspension
The double wishbone rear suspension is all-new, designed to give Prius higher levels of handling stability and ride comfort, including a more than 50% improvement in impact shock damping. The layout offers numerous advantages compared to the current torsion beam system, including greater flexibility when it comes to fine-tuning its calibration.
The design builds on the foundation of the car’s increased body rigidity and strengthened suspension mounting points. Key design features in its hardware and geometry include wide-mounted, forward-angled shock absorbers and compact coil springs. These give reduced friction for improved ride quality and their size and positioning free up more space, allowing for a lower floor in the boot. Special aero under covers have been designed to smooth air flow around the new suspension system, part of a comprehensive underfloor aerodynamic package.
The forward angle of the new shock absorbers and careful tuning of the tyre movement curve combine to reduce longitudinal, low-frequency vibrations and suppress road shock. The rigidity and geometry of the suspension arms have been optimised to control toe change during suspension travel to give supple yet responsive handling and confidence-building stability.
Special attention was paid to reducing impact harshness through geometry and individual tuning of the bushings, with rubber bushings replacing ball joints in some key areas to allow for further fine tuning and reduction of high-frequency vibrations. The new double wishbone system features several bushings per side, compared to just one on the current torsion beam design; each can be tuned for different stiffness characteristics in two planes.
For example, the new trailing arm bushing is larger and calibrated to reduce lateral-force steer while controlling longitudinal force compliance. Soft trailing arm bushings and a low static friction property in all the bushings reduce road shock.
The trailing arm mount is positioned relatively high to optimise suspension travel, with the shock absorber strut and trailing bush mounting angles set to reduce harshness, road shock and stuttering. The anti-roll bar mounting system and calibration have been defined to secure high levels of roll rigidity for a comfortable, ‘flat’ ride. The previous torsion beam suspension did not feature a separate anti-roll bar.
New Electric Power Steering
Prius was at the heart of Toyota’s breakthroughs in development of its electric power steering (EPS) and many other models have since adopted the technology to benefit from its practicality and fuel-saving qualities.
The steering has been redesigned and recalibrated, enhancing each phase of its operation. Feel, effectiveness and feedback have all been improved and a new, quicker steering gear ratio gives a sportier quality.
The changes to the steering hardware and control software combine with the benefits of the car’s new platform, lower centre of gravity and revised front suspension to improve controllability and the turning radius (from 5.2 to 5.1m). Engineers have produced new steering rack ratio of 13.4:1. The system has gained a new, high-rigidity intermediate shaft that contributes to better steering effectiveness and greater feedback from the road surface, and it features a new, brushless electric motor that provides extra assistance when needed.
The steering’s centring feel has been improved by using an elastic support structure for the worm gear mechanism and a new EPS control logic. The EPS logic has reduced the “no assistance” area when the steering is at or near centre, to give extra controllability in straight-line driving. A further new feature is EPS damping control, which gives the system the same feel in both the steering and return phases.
The new Prius provides a more progressive build-up of assistance as steering is applied and greater controllability on steering return. The new control logic also generates a lighter feel at low speeds and a precise feel and quick response at higher speeds.
Electric power assistance is always available, even when the petrol hybrid engine is shut down to save fuel.
New Wheels and Tyres
Toyota has developed lightweight alloy wheels which complement the performance of the new Prius’s suspension and improve handling stability by being more rigid. This higher rigidity also has an impact on the level of tyre resonance that’s generated, thus reducing road noise.
The 15-inch wheel is 30% more rigid and 12.7mm wider at 165.1mm, enabling better grip to be gained from the new low rolling resistance tyres. Keen to make savings wherever possible, Toyota has also shaved 1kg off the weight of the temporary spare wheel.
The new Prius feature a Tyre Pressure Warning System. A sensor on each wheel triggers a warning light on the instrument panel, if tyre pressure drops to a level that could compromise performance and safety. The system has a locating function that shows which wheel/tyre is affected.
Electronic Brake Control with Better Feel and Security
The new Prius has a state-of-the-art electronically controlled braking system (ECB) that precisely balances the requirements of both regenerative and friction braking. The system also cooperates with the vehicle’s active safety technologies, including the ABS and vehicle stability control (VSC).
The regenerative braking function uses the electric drive motor as a generator, converting kinetic energy created when the vehicle slows down into electricity which can be stored in HV battery.
The friction-braking system uses lightweight, floating aluminium front callipers with lightweight resin pistons and ventilated 255 x 25mm discs. The rear solid discs measure 259 x 9mm and are also fitted with aluminium callipers.
A new active hydraulic brake booster and new pedal ratio help deliver quiet performance, controllability and improved braking feel. For ease of driving there has been a reduction in the degree of play in the pedal and an extension to the side of the brake pedal to make for smoother movement when switching from the accelerator.