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Honda IMA Service and Repair

Honda’s Integrated Motor Assist (IMA) has been in production for nearly 15 years and chances are you have had some of these vehicles in your bays already.
Thursday, December 26, 2013 - 09:00
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Entering the realm of hybrid repair can be a daunting venture for many technicians and shop owners. Servicing Honda Integrated Motor Assist (IMA) vehicles is a great way to get your feet wet, as the technology on these vehicles is intentionally not as evolved as competing manufacturers’ hybrid platforms. Understanding the system’s operation and recognizing service and repair concerns will help you in your quest to become a hybrid-capable repair technician or facility.

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The IMA motor-generator is the heart of Honda’s IMA System.

Honda introduced its IMA system with the 1999 Insight and beat the competing Toyota Prius to the market by a margin of more than a year. Honda’s approach to the Hybrid Electric Vehicle (HEV) platform was to improve fuel economy by designing a lightweight, low-cost vehicle with an electrically assisted internal combustion engine (ICE). The IMA system utilizes a three-phase AC motor-generator (MG) sandwiched between the ICE and the CVT transmission.

This design is considered a simple or parallel hybrid and separates the IMA from its heavier Toyota counterpart that utilizes two motor-generators within a hybrid transaxle. The use of only one MG unit allows for the use of a fairly small HV battery, which also contributes to its weight reduction. The IMA has been used successfully in the Insight, Civic and Accord platforms, but because of increased EPA fuel economy demands, it will be replaced by a dual motor-generator hybrid drive, similar to Toyota’s Hybrid Synergy Drive system, in the 2014 Accord.

IMA Overview
Before you commit to servicing or repairing IMA vehicles, it is important to have a basic knowledge of system operation. The heart of the IMA system is a brushless three-phase AC motor-generator contained in a housing that bolts up between the ICE and the Constantly Variable (CVT) transmission. The rotor is a permanent magnet type that is bolted directly to the crankshaft, which means anytime the crankshaft turns, so does the rotor. The IMA motor provides power assist when needed, and also takes on the role of the conventional starter motor and alternator. The rotor includes a tone ring, and the IMA position sensor contained within the IMA housing monitors it.

Lineman’s gloves are essential personal protective equipment for HV repairs.

Control of the motor takes place in the Integrated Power Unit (IPU), which is located along with the HV battery behind the rear seat. The IPU is the brain of the IMA system and includes the Motor Control Module (MCM). The MCM monitors HV system data and controls the motor-generator through a series of contactors that act as oversized relays to allow the flow of high voltage to and from the IMA motor to either power the motor during assist or recharge the HV battery during deceleration. In addition to monitoring HV voltage output and input, the IPU also controls the high voltage air conditioning compressor and charges the 12-volt battery via the Motor Power Inverter (MPI).

The 12-volt battery, although not primarily used for starting purposes, still plays an important role in the vehicle, as it powers all control modules and related components including the HV system modules. It’s also required to provide power to the 12-volt backup starter motor. One other key player in the IMA system is the Battery Control Module, which we will discuss in further detail later. All of these components work together to give the IMA system several distinct modes of operation:

• Assist – Provides assist to the ICE by adding horsepower and reducing fuel consumption.

• Charging – Charging happens on deceleration, also known as regenerative braking.

• Auto Idle stop – ICE turns off when it sees the brake pedal depressed and restarts when the pedal is released. If the pedal is depressed for longer than 90 seconds the ICE will restart to continue charging the 12-volt system.

• Electric propulsion mode – Cylinders are deactivated via the V-TEC system. The ICE crankshaft continues to move with the IMA motor but all the valves are held closed as the pistons move in the cylinders.

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