How improved is the new Prius?
Milestone to " 40km/L "
|Toyota's new Prius|
This report focuses on technical details of Toyota's new Prius. In a press conference at the Tokyo Motor Show 2015, Toyota President Akio Toyoda, standing in front of the new Prius and accompanying an MLB hero, Ichiro, started his speech by asking the audience, "What wows you?" He talked about the company's history and vision, the importance of facing new challenges, and the desire to keep delivering exciting products to the world. Before the Tokyo Motor Show, the Toyota Prius was first exhibited at a motor show in Las Vegas (Nevada, U.S.) and then at the Frankfurt Motor Show, which was held earlier this year. The vehicle was presented at the Tokyo Motor Show without disclosing technical details. Nevertheless, visitors to the Toyota booth could feel Toyota's eagerness to launch the much-awaited new hybrid car.
Evolution of Toyota's new Prius
The new Prius is the first global vehicle to use the Toyota New Global Architecture (TNGA), an innovative approach for developing powertrain components and vehicle platforms. Toyota and its global suppliers are aiming to improve fuel economy to 40 km/liter (JC08 test cycle). In addition, Toyota is improving ride comfort, driving performance, and noise and vibration suppression of the fourth-generation Prius. The much-awaited Prius is slated for launch in Japan in early December.
According to Toyota's press releases, the Toyota Hybrid System II (THS-II) will be used in the new Prius to improve fuel economy. The system is used in the existing model, but improvements to the system elements and various performances will be made for the new model.
Changes made to the THS-II in the new Prius
|Item||Previous Prius||New Prius||Changes|
|Engine type||2ZR-FXE||<Changes to the engine> 1) Intake port: Tumble (vertical swirl) ratio changed from 0.8 to 2.8 2) Large amount of cooled EGR EGR distribution passage in intake manifold changed to tournament type 3) Spacer added to cylinder block water jacket|
|Bore x stroke (mm)||80.5X88.3|
|Maximum thermal efficiency (%)||38.5||40|
|Motor output (kW)||60||53||Compact and lightweight with higher power density (loss reduced by 20%)|
|Hybrid transaxle||For THS-II||Planetarium gear replaced with parallel axis gear (loss reduced by 20%) Compact size (by 47 mm long)|
|PCU||Compact and lightweight Volume ratio △33%|
|Drive battery||NiMH, Li||Higher performance and compact size Volume ratio △9.9% (Ni) and △23 % (Li)|
|Vehicle weight without occupants (kg)||1310||1310 targeted||L grade|
|JC08 cycle fuel economy (km/liter)||32.6||40 targeted||L grade|
(Created by MarkLines based on Toyota press release)
(1) Changes to the engine and intake port
|(Source: Toyota press release)||Changing the shape of the intake port and making the air flow into the combustion chamber as linear as possible have led to two desired results: (1) The vertical air flow along the direction of the reciprocating piston motion and the tumble ratio (ratio of vertical swirl generation) increased. (2) As a result, the air flow in the canceling direction of the tumble decreased, enabling tumble ratio to increase from 0.8 to 2.8. According to Toyota, the increased vertical swirl has enabled the rate of exhaust gas recirculation (EGR) to increase.|
(2) Changes to the engine; large amount of cooled EGR
|(Source: Toyota press release)||The EGR gas flow was changed to a tournament style in which gas flows separately from the first cylinder flow passage of the intake manifold to the fourth cylinder flow passage. This increases the cross-section of the passage while avoiding air flow interferences between cylinders. According to Toyota, this enables a larger amount of EGR gas to flow.|
(3) Changes to the engine; addition of engine block water jacket spacers
|(Source: Toyota press release)||During combustion, temperature normally rises at the top of the cylinder near the combustion chamber and is over-cooled at the bottom. By adding a water jacket that is spaced via Expad rubbers, the temperature at the top of the cylinder can be lowered to prevent knocking. At the same time, the temperature at the bottom can be increased to reduce the temperature difference between the top and bottom. This brings the thermal expansion to an even level to reduce friction.|
(4) Two-line cooling system to improve heater performance
|(Source: Toyota press release)||When starting a cold engine in the winter, the switching valve (illustrated in the diagram) is used to preferentially direct the warm coolant from the engine to the heater passage of the air conditioner to warm the cabin compartment. When the cabin temperature rises, the switching valve directs the coolant to the radiator passage to lower the coolant temperature.|
Prius components supplied by Toyota suppliers
Aisin Group (Aisin Seiki, Aisin AW, Aisin AI, and Advics Co., Ltd.)
|Electronically-controlled brake system Aluminum floating caliper pad, rotor Radiator components, grille shutter Engine components Transaxle components, etc.|
|(Electric all-wheel drive unit for Prius)||Electric all-wheel drive unit: Differential gears supplied by Aisin AI Induction motors supplied by Aisin AW Entire unit assembled by Aisin Seiki|
|Motor stator for hybrid use Power control unit (PCU) Car air-conditioning system Image sensors Millimeter-wave radar ITS Connect onboard unit|
Toyota Industries Corporation
|Electric compressor for car air-conditioning systems DC-DC converters Rear-axle drive inverter AC inverter Details pertaining to components by Toyota suppliers are available in a separate report.|
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