Here’s How The Honda e:HEV Hybrid System Works

We simplify the workings of Honda’s latest self-charging hybrid system to be offered in the City sedan

The Honda City’s new hybrid variant will be the first mass-market hybrid in India. Ahead of its market launch in May, we’re here to explain the principle and workings of Honda’s e:HEV hybrid powertrain technology.

What is in the hybrid system?

• The key components of the e:HEV powertrain in the City are a petrol engine, two electric motors, and a battery.

• The 1.5-litre Atkinson engine is one of the most efficient in Honda’s lineup, rated to an output of 98PS and 127Nm. It is connected to an electric generator motor that powers the propulsion motor, or traction motor, to drive the wheels.

• The electric drive motor in the Honda City has a peak output of 109PS and 253Nm.

• The battery is small but has a high voltage capacity. It is connected to both the generator motor and the traction motor. 

• There is no gearbox in the conventional sense as the powertrain uses an electronic CVT system to regular performance delivery with a clutch that connects to the petrol engine.

How does it work?

• In Honda’s e:HEV hybrid system, the engine is not mechanically connected to the wheels. Instead, it is primarily used to power the generator motor.

• The generator motor converts the energy from the petrol engine into electricity that powers the traction motor that drives the front wheels.

• The battery gets charged by excess electricity from the generator motor and/or regenerative braking. It offers performance assistance to the traction motor along with the generator motor when needed.

• This system also allows the car to run in pure EV mode and engine-only mode apart from the hybrid mode.

Understanding the three modes

• The hybrid system autonomously switches between three drive modes depending on what is asked of it: pure EV, hybrid, and engine only.

• The hybrid mode functions as described above. It is the most efficient mode of the City e:HEV. It is most useful in urban driving situations and at high motoring speeds.

• In EV mode, the traction motor is powered solely by the battery and the engine remains off. This mode is used mostly at startup and pulling away, and for the slow sections of urban driving.

• The pure-engine mode kicks in when the power unit systems judge it to be more efficient in delivering performance than the hybrid mode. The clutch of the eCVT system is engaged in this mode allowing the engine to power the wheels directly. In other modes, the clutch remains disengaged.

What makes it more efficient?

• One might think that all these extra components would perhaps be less efficient than the wheels being driven directly by the combustion engine. However, that is not true. The City e:HEV has a claimed fuel economy of 26.5kmpl which exceeds the claimed figures of its petrol- and diesel-powered competitors.

• A combustion engine does not offer the same level of energy efficiency at every level of operation, as it is affected by many factors such as engine load and engine speed (rpm). 

• Honda’s engineers estimate that its engine is most efficient when under 70 percent load and at around 2000rpm. Let us call that peak efficiency zone the sweet spot of the engine.

• A normal combustion engine spends a lot of fuel trying to get close to that sweet spot but is constantly affected by driver input according to the driving scenario.

• In this hybrid system, the engine can be electronically told to operate primarily in the efficiency sweet spot to power the generator motor. Additionally, since the engine is not mechanically connected to the wheels, it can reach that sweet spot of load and revs with minimal friction or resistance, thereby achieving extreme efficiency.

• This makes Honda’s e:HEV hybrid system more efficient than a comparative combustion engine powertrain by up to 40 percent.

Related: Honda City Hybrid vs Rivals: Fuel Efficiency Compared

• Even when in engine-only mode, it focuses on efficiency of power delivery as well as fuel consumption. Since the system autonomously switches between modes, it will switch to hybrid mode as soon as it can to maintain peak efficiency in various driving scenarios.