Honda's new i-VTEC with IMA Engine

How does Honda's 3-stage i-VTEC with IMA work. Before we get into in-depth understanding of how the 3-stage i-VTEC system works in conjunction with Integrated Motor Assist (IMA) on the Honda Civic Hybrid, let us understand how an electric motor and an internal combustion engine are able to work in conjunction with each other. Essentially, an electric motor of a small capacity is attached at the flywheel side of the crank. Thus, at a very basic level, apart from the piston's power stroke, the electric motor also has the capability of turning the crank on its own.

At other times, for instance when the driver puts his foot down, making the engine work to its maximum capability, the electric motor can provide additional boost when needed. The reason they are able to do this in spite of their puny size is the fact that the max torque of any electric motor is available from anywhere above 0rpm to its max rpm, ie, it transverses a flat torque curve, unlike an internal combustion engine where the torque curve rises from initial, peaks at a certain rpm and then hits the redline.

The question now is, how does the battery pack, which powers the motor, recharge itself? This is achieved by several ways like regenerative braking which allows for the energy dissipated while braking to be used to recharge the batteries.

Honda 3-stage i-VTEC takes this principal further by employing three hydraulic pathways to couple and uncouple five rocker arm assemblies providing three stages of valve control depending on the driving conditions. The first mode is purely electric, where the combustion is stopped and cylinders are sealed shut and the crank is being driven solely off electric motor power.

During start-up and mild acceleration, the combustion is engaged and valves operate off the lower cam profile alongside electric motor assist.

During hard acceleration, the cam profile is switched to a 'wider' one via a solenoid, a somewhat similar mechanism seen on Honda's early VTEC engines. During low speed cruising, the combustion chamber is sealed again and the car is able to coast along on electric power only. The sealed chambers allow for 'pumping loss', simply put engine braking, to be eliminated, leading to increased efficiency.