New Vehicle TOy OTA PrI us ToyoTa Prius Eco-Mobility’s PostEr car In the mid-90s, talks and concerns about environmental pollution from automobiles were still in its infancy. But one carmaker was clearly preparing for the future. In 1997, the Prius – the world’s first mass-produced hybrid vehicle – went on sale in Japan. And for about 15 years since then, Toyota Motor Corporation (TMC) has been leading the drive towards sustainable mobility. Introduced globally in 2001, the Prius today is sold in over 70 countries, with sales of over 3.3 million full-hybrid vehicles. The company claims this accounts for over 80 % of all global hybrid sales, resulting in reduction of some 21 mn tonnes of CO 2. The third-generation Prius alone has sold more than 1 mn units worldwide. 54 www.autotechreview.com Toyota’s eco-friendly vehicle got the name, Prius, because it was launched before environmental awareness became a mainstream social issue. Meaning ‘before’ in Latin, the first glimpse of the hybrid concept was revealed at the 1995 Tokyo Motor Show, with the market launch of the first Prius (model NHW10) following two years later in December 1997. Six year thereafter, in 2003, Toyota launched the second generation Prius, codenamed XW20, with significant amount of changes in the overall vehicle mechanics and interior space. Led by chief engineer Shigeyuki Hori, develop- ment of the second generation Prius The Toyota Prius is a full hybrid – propelled resulted in 530 patents for the vehicle. by both a battery-powered electric The overall length of the vehicle was motor and a petrol-driven IC engine. extended by 150 mm from its previous avatar. The aerodynamically-designed Kamm tail body ensured better length and wind resistance, resulting in a drag coeffi- efficiency. This results in a high level of driven with the electric motor, while elec- cient (Cd) of 0.26. on-road performance, while minimising tric pumps warm the engine with previ- XW20 was discontinued in 2009 to fuel consumption and pollution from ously saved hot engine coolant before the make way for the third generation Prius, exhaust gases. The battery gets charged, internal combustion engine is started. The the XW30. By this time, Toyota was facing when the car is driven using the petrol EV (electric vehicle) mode is engaged tough competition from other products in engine. Alternatively, when brakes are under most low-load driving conditions, the market, primarily, the Honda Insight. applied, energy that most cars waste as and allows driving at low noise and no Market pressures led the largest carmaker heat lost during braking is converted to fuel consumption. Once the battery is in Asia to cut prices of the Prius in its electricity for the car to use later. exhausted, the car automatically reverts to home market. Toyota claimed its new aer- The HSD system ensures that each the normal mode. The Prius EMS (engine odynamic body design resulted in an power unit supplies significant amounts management system) also recognises improved Cd of 0.25. In mid-2011, Toyota of power, using the least amount of fuel. when the car is stationary and switches made changes to the exterior looks of the On ignition, the vehicle is ready to be off to conserve power, automatically Prius, including updated headlamps, switching back on again, when needed. revised tail lamps, plus a distinctive front fascia and bumper. engine We drive the new Toyota Prius to bring The 2012 Toyota Prius is powered by a to you a detailed technology review of the 1.8 l 2ZR-FXE high-expansion-ratio engine best selling hybrid in the world, explain- that makes use of the Atkinson cycle. The ing in detail the changes made to its pow- engine uses a double overhead camshaft ertrain, safety and comfort features as (DOHC) 16-valve cylinder head with a well as a comprehensive look at Toyota’s 4-cylinder die-cast block. Toyota’s VVT-i Hybrid Synergy Drive. (variable valve timing – intelligent) tech- nology optimises both intake and exhaust valve timing. Hybrid Synergy d rive® This engine is part of the ZR engine family, introduced by Toyota in 2007. The Hybrid Synergy Drive (HSD) used in It has the same bore and stroke as the the Prius is a full hybrid system, which is earlier 2ZR-FE, but the compression ratio often referred to as a combined hybrid is increased to 13.0:1 from the 2ZR-FE’s because the vehicle is propelled by both a 10.0:1. The inlet valve closing is also battery-powered electric motor and a pet- retarded in the new engine, which results rol-driven internal combustion engine. in a greater effective expansion of the Based on the need, the HSD helps the engine than compression. The output for car to switch between petrol and electric The 1.8 l 2Zr-FXE high-expansion-ratio engine the 2ZR-FXE is rated at 98 hp at 5,200 power or combine the two for maximum makes use of the Atkinson cycle. rpm, while the peak torque has been autotechreview March 2012 Volume 1 | Issue 3 55 New Vehicle TOy OTA PrI us measured at 142 Nm @ 4,000 rpm. Together with the electric motor, the hybrid system net output increases to 134 hp. The previous generations of the Prius hybrid used the 1.5 l 1NZ-FXE engine. Since the initial start is handled by the battery-powered electric motors, the movement is noiseless. Even when the petrol engine comes alive, the Prius doesn’t fail you in terms of noise. Thanks to the electronically-controlled CVT, there is no drastic climb in revs, yet there is enough power for quick overtakes on the highways. Handling and ride quality is easy as well. Compared to the previous generation engine used in the Prius, the 2ZR-FXE Toyota Prius Battery Pack showing airflow. delivers improved levels of fuel efficiency. The use of the electric water pump is a case in point. The water pump is now Hybrid battery Pack Power Split device driven by electricity from the battery. The Ni-MH (nickel metal hydride) battery The power splitting device is used to dis- Engineers at Toyota have eliminated the used in the Prius is compact and light- tribute power produced by the petrol drive belt, which decreases mechanical weight, enabling a high input/output to engine to the drivetrain and the generator. loss and the flow of the coolant can be weight ratio. While the maximum systems A planetary gear consisting of a ring gear, controlled even more precisely according voltage is 650 V, the nominal voltage of pinion gears, a sun gear and a planetary to the vehicle's conditions. In fact, this is the battery pack is calculated at 201.6 V carrier is used to divide the power effi- the first production engine that requires that includes 168 cells of 1.2 V each. ciently. Essentially, it is a clever gearbox no accessory belts, an efficient way of Toyota’s hybrid system maintains the bat- that binds the gasoline engine, generator improving fuel economy. tery charge at a constant level at all times and electric motor together. In addition, the exhaust heat recircula- by monitoring and computing the cumu- tion system utilises exhaust heat, which lative amount of discharge under acceler- generator used to go waste, for the heater and to ation, and recharging by regenerative Compared to its earlier variants, the cur- warm up the engine, allowing quicker braking or with surplus power under nor- rent Prius has a more compact and light- heating and engine warm-ups. Two addi- mal running conditions. The capacity of weight generator, achieved through cen- tional mechanisms that make the engine the battery pack in the current Prius is tralised winding of the coils. It’s a syn- more efficient include the roller rocker measured at 6.5 Ah, with a battery peak chronous AC generator capable of high arm and the cool-EGR (exhaust gas recir- horsepower rating of 36 hp. speed axial rotation, realising substantial culation) system. Motor Toyota's hybrid technology uses a smaller, yet more efficient permanent magnet syn- chronous motor with a maximum DC voltage of 650 V. Peak power output of the electric motor is measured at 80 hp, while the torque is a healthy 207 Nm. One might wonder why the 98 hp engine com- bined with an 80 hp motor results in a total output of 134 hp and not more. The reason is that 80 hp is the maximum the motor can develop, but since it draws power from a 36 hp rated battery pack, the final output would be the same and hence a total output of 134 hp. Addition- ally, there’s a second motor significantly smaller in size, which is used to start the IC engine and maintain revs during operation. The second and third-generation Power split Device in the Toyota Prius. 56 www.autotechreview.com electrical power, while the car is running in the mid-speed range. Power Control Unit The power control unit in the Prius con- sists of an inverter, a voltage-boosting converter and an AC/DC converter to run the car on electric motors. The inverter converts DC supplied by the battery to AC to turn the electric motors and to use in the generator. Conversely, it converts AC generated by the electric motors and the generator into DC to recharge the battery. The car features direct cooling of switch- ing device, enabling improved cooling efficiency, inverter downsizing and weight reduction. The new Toyota Prius uses a third-generation inverter, shown here with the second-generation model.