Electric and hybrid vehicles are the poster boys of automotive technology, yet continue to be an albatross around the neck when it comes to sales, barring exceptions such as the Toyota Prius. Key hindrances in adoption of the technology, especially hybrid, have been higher cost of purchase and the lack of a significant increase in fuel-efficiency in real world conditions, in many cases. Honda’s new SPORT HYBRID system though could spark off a change. We explain how.
Honda launched the 2014 Accord Hybrid range sometime back and laid claim to the ‘most fuel-efficient’ tag in its segment. Honda claims a fuel-efficiency of 30 km/l for the Accord Hybrid and a whopping 70.4 km/l for the Accord Plug-in Hybrid model. A similar feat was achieved when the Fit Hybrid was launched in Japan with a claimed fuel-efficiency of 36.4 km/l.
The SPORT HYBRID system is made up of three systems – each designed to suit a specific application or class of vehicles. Part of the Earth Dreams technology portfolio, one of these systems is the Intelligent Multi-Mode Drive (i-MMD), which is used in the regular and plug-in variants of the Accord Hybrid range.
A key change in the powertrain package is the new 2 l four-cylinder Atkinson-cycle engine, which in most cases acts as a generator. This generator in turn charges the lithium-ion battery to power the electric motor connected to the wheels. During medium to high speed cruising, i-MMD can operate solely on the power of the gasoline engine.
The biggest change and also a break-off from traditional hybrid architectures is the new two-motor hybrid configuration. This set-up allows a continuous cycling between three different modes – EV drive, hybrid drive and engine drive, based on various parameters. Honda claims this improves fuel-efficiency significantly, as only the right amount of power from the right source is utilised at any given point of time.
The hybrid version and the plug-in version differ only by the size of the on-board battery and the inclusion of an on-board charging system and chord in the case of the plug-in variant. The li-ion battery pack in the regular variant is rated at 1.3 kWh and is charged through the petrol engine and regenerative braking. This unit is good enough to supplement the engine, when required under acceleration or other situations.
The plug-in version features a much larger 6.7 kWh battery pack and can be charged through a 120 V outlet in less than three hours. Using a 240 V outlet would reduce the charging time to under an hour. Owners can also remotely monitor the charging state of their car using the free HondaLink EV application for smart phones. With a full-charge, Honda claims a range of 21.58 km in the EV drive mode. This mode is on while starting from a stop, light cruising & acceleration and during braking. The petrol engine stays off in the EV mode and is also disconnected from the drivetrain, further reducing friction and increasing efficiency.
The electric motor and petrol engine work together in this mode during acceleration or high-speed operation. The front wheels are solely powered by the electric propulsion motor. The engine, despite being disconnected from the wheels, provides energy to the electric generator motor, which in turn powers the battery pack. This method allows for provision of added electrical power to the propulsion motor or to charge the battery. A key advantage of using the electric motor to power the wheels is that acceleration is more responsive since maximum torque is available right from the start.
ENGINE DRIVE MODE
In this mode, the Atkinson cycle engine comes directly into play in relation to powering the front wheels. Propulsion is provided through an electronic CVT unit with lock-up clutch. Although it’s termed as a transmission, the unit essentially connects the generator motor and the electric drive motor. This results in direct utilisation of the engine power by the front wheels.
2 l ATKINSON-CYCLE ENGINE
The 2 l Atkinson-cycle engine develops 141 hp and is claimed to be one of the most thermal-efficient units in the world. Based on internal testing, Honda claims the engine to be the most energy efficient mass-produced petrol engine in the world with a rating of 214 g/kWh of 87 octane petrol. The Atkinson Cycle approach results in enhanced fuel-efficiency and lower emissions despite a trade-off in power. This power deficit though is compensated by the electric motor explained above. Coupled with the motor, the powertrain system develops a total output of 196 hp.
The engine itself is part of the Earth Dreams technology portfolio and features cast-in iron cylinder liners to improve durability. In line with the aim of improving efficiency and driving pleasure, each journal on the forged steel crankshaft undergoes micro-polishing, which lowers internal friction. An internal balancer unit improves the smoothness throughout the rpm range and also lowers noise emissions.
Inline four-cylinder engines usually have an inherent second-order harmonic vibration characteristic. In this engine though, this trait has been controlled by using a pair of chain-driven counter-rotating shafts, located in the oil pan. Friction is further reduced by the cylinder bores being offset by 8 mm from the crankshaft, leading to lesser piston sliding friction. This also improves efficiency since the connecting rods have a more optimised angle during each power stroke, thereby lowering the side load on the piston.
Despite all the challenges surrounding hybrid technology, one cannot deny that it is one of the most viable technologies to act as a bridge to transition to other forms of propulsion. Barring few exceptions, hybrid vehicles haven’t been able to give fuel-efficiency gains large enough to offset the high buying cost over a few years of ownership. Honda’s new technology, however, has succeeded in setting new benchmarks, which can change the way people perceive the technology.
Priced between an approximate band of ` 17.8 lakh and ` 21.3 lakh in the US, the Accord Hybrid range isn’t prohibitive, considering the additional features offered in the hybrid range. Although there are no officially declared plans to bring this technology to India, it could still be on the cards in the medium-horizon. From a global technical perspective though, Honda has pushed the hybrid technology back into a zone of attractive numbers. What remain to be seen is how this technology performs in the real world over a period of time, and how long competition takes to push it further. Buyers, meanwhile, will continue to get rapidly improving hybrid technology over the next few years.
Text: Arpit Mahendra