Integrated Motor Assist

Integrated Motor Assist (IMA) is a hybrid vehicle powertrain technology developed by Honda, first introduced in 1999 with the launch of the first-generation Honda Insight. IMA is a type of parallel hybrid system that incorporates an electric motor positioned between the vehicle's internal combustion engine and transmission. The electric motor serves multiple functions, including acting as a starter motor, generator, engine balancer, and providing power assist during acceleration.

Honda Insight IMA, 1999.

Honda Insight IMA, 2009.

Overview

The first-generation IMA system was a mild hybrid system designed to operate exclusively in conjunction with the gasoline engine and was not capable of powering the vehicle using electricity alone. In later versions, such as the 2006 Honda Civic Hybrid, the electric motor could propel the vehicle during coasting under certain conditions without engaging the internal combustion engine. However, unlike systems such as Toyota's Hybrid Synergy Drive or the Global Hybrid Cooperation platform developed by General Motors and DaimlerChrysler, Honda's IMA features a less powerful electric motor that limits its ability to independently decelerate or move the vehicle without engine assistance.

Regenerative braking

IMA incorporates regenerative braking, which captures kinetic energy during braking that would otherwise be lost as heat. This energy is stored and later used to assist acceleration. The system offers several benefits: it enhances acceleration, reduces engine workload, and extends the life of braking components by decreasing mechanical brake usage. The ability to supplement engine output allows the use of smaller, more fuel-efficient gasoline engines, contributing to improved highway fuel economy compared to conventional vehicles.

Start-stop functionality

The IMA system also provides start-stop capabilities. When the vehicle comes to a complete stop, the gasoline engine automatically shuts off to reduce idling emissions and fuel consumption. The electric motor restarts the engine quickly when the driver releases the brake pedal (or, in manual transmission models, engages a gear). IMA-equipped vehicles also include a conventional starter motor as a backup, allowing the vehicle to operate without the high-voltage hybrid system active. In such cases, the car functions like a conventional gasoline-powered vehicle. However, since the IMA system also replaces the alternator, prolonged operation would eventually discharge the 12 volt accessory battery, requiring an external recharge.

List of vehicles using IMA

IMA-equipped Honda Civic Hybrid

• Honda J-VX (1997 concept car)
• Honda Insight (1999-2006, 2010-2014)
• Honda Dualnote (2001 concept car)
• Honda Fit Hybrid (2010-2014)
• Honda Fit Shuttle Hybrid (2010-2015)
• Honda Civic Hybrid (2003-2015)
• Honda Accord Hybrid (2005-2007)
• Honda Freed Hybrid (2008-2016)
• Honda CR-Z (2010-2016)
• Acura ILX Hybrid (2013-2014)