[e:HEV featuring a 1.5-liter Atkinson Cycle DOHC Engine]
Significantly downsized e:HEV suitable for compact models
Among engines developed exclusively for e:HEV, the most compact engine is the 1.5-liter Atkinson cycle DOHC i-VTEC engine. The highly efficient layout was pursued through various measures such as adopting a new design for the intake manifold and installing an air cleaner on the upper part of the intake manifold. The motors were also downsized, reducing the size of the e:HEV including auxiliary equipment by more than 20% in both width and length compared to the previous version of the 2-motor hybrid system. These downsizing measures made it possible to install the e:HEV to compact vehicles which have limited space in the engine room.
As for the engine, by combining Honda’s strengths, namely the VTEC*1 and electric VTC*2, and also by thoroughly increasing combustion speed and reducing friction, maximum thermal efficiency of over 40% was achieved, to realize excellent fuel economy.
In addition, quietness was further enhanced by adding an insulator to the chain case, which reduces noise emitted by the engine at its source. Furthermore, by optimizing the control of the electric VTC, vibration during engine startup was reduced. The engine restarts smoothly after the idle stop.
Powertrain featuring a 1.5-liter Atkinson Cycle DOHC i-VTEC Engine
For the generator motor and traction motor which are combined with the 1.5-literAtkinson cycle DOHC i-VTEC engine, the magnetism of the rotor was increased and the manufacturing method of the stator was changed from the previous concentrated winding method to the segment winding method. This increases the volumetric efficiency by tightly bundling multiple rectangular cross-sectional wires. Moreover, by improving voltage resistance while reducing the thickness of the coating of the rectangular wire, the new motor realizes larger torque output while also achieving a reduction of the width by more than 12% compared to the motor used for the previous version of the two-motor hybrid systems. Realizing greater torque than that of a typical*3 2.4-liter naturally aspirated engine, e:HEV models offer customers a powerful and smooth ride.
Motor Stator Manufactured with Segment Winding Method
*1 Variable valve timing & lift mechanism
*2 Continuous variable valve timing control mechanism
*3 Comparison with a Honda 2.4-liter inline-4 naturally aspirated engine
[e:HEV featuring a 2.0-liter Atkinson Cycle DOHC Engine]
e:HEV that realizes excellent driving performance, fuel economy and quietness at a high level
The 2.0-liter Atkinson cycle DOHC i-VTEC engine was adopted for the e:HEV in the pursuit of powerful driving and a high level of quietness, which give the driver more leeway in their driving. With high-precision valve control technologies of Honda VTEC*1 and electric VTC*2, this engine delivers excellent driving performance, fuel economy and quietness at a high level.
Compared to the previous version of the 2.0-liter engine used for the e:HEV, a higher thermal efficiency was achieved by increasing the compression ratio, reducing intake air loss and thoroughly reducing friction. Moreover, an exhilarating engine feel was pursued, interlinking vehicle speed and engine revolutions.
The engine's compression ratio was increased from 13.0 to 13.5 by downsizing the combustion chamber and improving the surface design of the piston crown (piston head). As a part of such improvement, combustion efficiency was successfully enhanced by adopting a sodium-filled exhaust valve as a knocking countermeasure.
In addition, a high-flow tumble port was adopted to facilitate homogenization of the air-fuel mixture, which increased the amount of EGR (exhaust gas recirculation) and successfully reduced pumping losses. In addition, friction reduction technologies were extensively applied to some parts such as the camshaft, crankshaft, piston, cylinder, and chain guide.
2.0-liter Atkinson Cycle DOHC i-VTEC Engine
A high-output, high-torque traction motor was combined with this engine unit to realize powerful yet smooth acceleration over a wide speed range, from low to high speeds. In addition, the width of the generator gear connected to the generator motor was optimized to reduce meshing noise, resulting in a quieter drive.
Traction motor, Generator motor
*1 Variable valve timing & lift mechanism
*2 Continuously variable valve timing control mechanism
[e:HEV featuring a 2.0-liter Direct-Injected Atkinson Cycle DOHC Engine]
e:HEV that pursues high environmental performance and sporty driving
A 2.0-liter direct-injected Atkinson cycle DOHC engine was adopted for the e:HEV to pursue a more exhilarating and higher quality driving experience without compromising excellent environmental performance.
In addition to leveraging the Atkinson cycle with excellent thermal efficiency, the injection system was changed from the regular port injection system to direct injection system that injects fuel directly into the cylinder.
By burning fuel completely, this 2.0-liter direct-injected Atkinson cycle DOHC engine has achieved an improvement in every aspect, including driving performance, fuel economy, exhaust emissions and quietness compared to the 2.0-liter engine previously used for the e:HEV.
The system injects fuel at a pressure as high as 35 MPa in up to four separate injections to atomize the fuel while preventing it from adhering to the cylinder sidewalls, which suppresses emissions (harmful substances in combustion gases) over a wide range of engine speed (rpm), from low to high. Moreover, this engine features a high-tumble intake port that takes in intake air at high speed to generate a strong tumble flow inside the cylinder, as well as the tumble retaining piston whose head is shaped like a shallow bowl to retain and accelerate the tumble flow generated by the intake port, realizing the maximum thermal efficiency*1 of approximately 41%, the world's top-level efficiency. Furthermore, the adoption of the direct injection system has increased stoichiometric torque by 30%, making it possible to generate the required torque without increasing the fuel ratio. This has expanded the range where Engine Drive Mode can be used and enhanced quietness during high-speed cruising.
For the triton motor, a high-output, high-torque motor was adopted to generate large torque comparable to that of a typical*2 3.0-liter-class V6 engine. Moreover, the quietness was further improved by adopting a damper with a newly designed structure on the flywheel that reduces fluctuations in torque transmitted from the engine. This e:HEV realizes both heart-pounding, powerful acceleration and high-quality driving.
Furthermore, this e:HEV features direct acceleration that offers direct and powerful acceleration feel that tightly links to the driver’s accelerator inputs. It also features linear shift control that provides an exhilarating driving experience with a rhythmical engine sound.
*1 Honda measurement
*2 Comparison with the maximum torque of previous Honda models equipped with 3.0-liter V6 engine. Honda internal survey.
[e:HEV featuring a 2.0-liter Direct-Injected Atkinson Cycle DOHC Engine and Two Motors in Parallel Axis Arrangement]
e:HEV that realizes both the fun of driving and sophisticated quality at a high level
The e:HEV that pursues even greater driving pleasure and quality without compromising excellent environmental performance features a 2.0-liter direct injection Atkinson cycle DOHC engine and the most powerful motors in the e:HEV series. The high-torque and high-rpm motors were placed with a parallel arrangement, a change from the previous coaxial arrangement, resulting in a significant increase in allowable torque and maximum speed in motor drive compared to the previous coaxial arrangement.
If the motor torque was increased with the previous motor arrangement, the motor size as well as the package would have been too large for the vehicle. To address this issue, the generator motor and traction motor positions were changed. By adopting parallel shafts, the motor torque was increased without changing the package.
The permanent magnet for the rotor was newly developed. While ensuring heat resistance by miniaturizing the magnet element, the adjustments were made to the material composition to increase the magnetic force, resulting in the highest torque among the e:HEV series.
In addition, for the internal shape of the rotor, the multi-ring structure that combines multiple rhombic shapes in a mesh-like pattern was adopted to achieve high performance in both dispersion of centrifugal force and the immobilization of the rotor more efficiently than the previous double-ring structure. Furthermore, the magnet was downsized to reduce the centrifugal force itself and achieve higher rotation speed.
In addition, the previous structure, in which the gear for motor drive and the gear for engine drive shared a single gear (double engagement), has been changed to a new structure in which separate gears are installed for motor drive and engine drive. The new structure enabled optimal ratio settings for each gear, and the ratio of the gear directly connected to the engine was optimized so that the maximum speed in motor drive is increased while the engine speed in engine drive mode was set low so that it would be suitable for high-speed cruising. This helped the e:HEV to achieve both excellent driving power and quietness.
Unlike typical series hybrid and series-parallel hybrid systems, the Honda two-motor hybrid system has the advantage of having an engine drive mode where the vehicle is driven directly by the engine. Previously, there was a single gear available for engine drive, making engine drive available almost exclusively for high-speed cruising. However, for the parallel axis two-motor hybrid system, a gear that enables engine drive at a lower gear ratio*1 was added, which significantly increased the towing capacity compared to the previous system. Moreover, the addition of the gear made engine drive during city driving possible, and improved fuel economy during gradual acceleration.
*1 Not available for some of e:HEV models
