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In Detail: Honda Integrated Motor Assist

By / 5 years ago / Features / No Comments

IMA has since been found not only in the second-generation Insight, but also in the Jazz Hybrid, the now discontinued Civic Hybrid and with a larger engine in the sporty CR-Z coupe, as well as other models worldwide.  Honda says the 1.3-litre engine used in the Insight allows the car to drive like a 1.6-litre petrol engine with an automatic gearbox, while assistance from the electric motor reduces load on the engine and helps bring efficiency in line with smaller units.

And the Insight has grown, too, now with five doors and hatchback styling aimed at netting European customers, while CO2 emissions of 96g/km in the recently revised version offer low running costs for business and retail customers alike. Here’s how Honda’s IMA helps owners save fuel.

Components:

-          Petrol engine – The Insight uses an 87bhp 1.3-litre petrol engine, derived from the unit found in the conventional Honda Jazz hatchback. For use with the IMA system, this has lower friction internals and dual spark plugs for maximum efficiency, can be slowed to idle irrelative of vehicle speed when not under load and switches off completely when the car is stopped.

-          Electric motor – Fitted between the engine and transmission, the 14bhp electric motor is only 35.7mm thick, compared to 61.5mm for the unit found in the Civic Hybrid. As well as providing power to the wheels, it acts as a starter motor, recharges the battery while decelerating and helps boost power while accelerating, reducing load on the petrol engine.

-          CVT gearbox – Honda’s hybrid vehicles use a Continuously Variable Transmission (CVT) gearbox, which varies the engine speed based on the load required and always keeps it in its most efficient rev range. Although there are no gears or clutch, this allows the car to be driven like a conventional automatic and the Insight features steering wheel paddles to allow the driver to take control.

-          Intelligent Power Unit – The Insight’s IPU is located under the boot floor, and includes the DC/DC converter and a nickel-metal hydride battery which now recharges faster than in the previous model. This packaging offers a low centre of gravity for high speed stability, and Honda has used a torsion bar rear suspension setup to save space, leaving a large boot. The IPU weighs 38kg, 15kg lighter than the Civic Hybrid’s, and is cooled through air ducts on either side of the rear bench.

How it works:

-          Acceleration – The Insight uses both power sources while accelerating, depending on available battery power, with the electric motor providing a power boost to reduce the load on the petrol engine. Combined, the two power sources offer 97bhp, with power delivery governed by the ECON mode selected on the dashboard. This softens throttle inputs, except when the pedal is fully depressed, to improve efficiency further.

-          Low-speed cruising – Unlike some hybrid systems, the Insight can’t use electric power independently. At low loads, IMA can coast using its electric motor between 10 and 22mph, slowing the engine to idle by controlling the speed of the valves. This reduces the energy used to pump air in and out of each cylinder (pumping loss) and allows the motor to regenerate more electricity, charging the battery quicker than it would with the engine running normally.

-          Decelerating – The electric motor not only provides additional power when accelerating. When decelerating or driving downhill it functions as a generator, using energy that would otherwise be lost as heat to recharge the battery. By doing so, the battery has more electricity in reserve for use to assist the engine. Because the engine isn’t under load, IMA slows it to idle speed.

-          Idle stop – A common feature on modern cars, the Insight switches off its engine when stopped in traffic, saving fuel and reducing harmful exhaust emissions. The electric motor can be used to quickly and smoothly restart the engine when the brake pedal is released, and shut-off only happens if on-board systems such as climate control are able to function without. When driving in ECON mode the car will switch off the petrol engine more readily to save fuel.

Alex Grant

Trained on Cardiff University’s renowned Postgraduate Diploma in Motor Magazine Journalism, Alex is an award-winning motoring journalist with ten years’ experience across B2B and consumer titles. A life-long car enthusiast with a fascination for new technology and future drivetrains, he joined Fleet World in April 2011, contributing across the magazine and website portfolio and editing the EV Fleet World Website.

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