Honda's parallel lines

Jan. 1, 2020
There was a time that hybrid cars were unusual enough that people would turn their heads and point them out to their friends as one passed by. Those were the days when folks were undecided as to whether this hybrid idea was even going to stick. Of co
The 2010 Honda Insight uses the fifth generation of Honda’s Integrated Motor Assist (IMA). Note that the high-voltage battery and the associated electronics are located at the rear of the car.

There was a time that hybrid cars were unusual enough that people would turn their heads and point them out to their friends as one passed by. Those were the days when folks were undecided as to whether this hybrid idea was even going to stick.
 
Of course, times have changed and hybrid cars are now commonplace. Many hybrid cars now are based on conventional models and don’t look very much different from them. Past that, much of the social stigma that came with owning a hybrid has diminished. In a recent Johnson Controls survey, 90 percent of the respondents say they are open to the idea of buying a hybrid car, and 24 percent say they would buy one even if it cost more than a conventional model. It would appear that the hybrid-electric vehicle (HEV) is moving quickly into the mainstream.

Even while our nation’s familiarity with hybrid cars continues to grow, many technicians still are on the steepest part of the learning curve. If you have yet to perform service on an HEV, you still might be eyeing these technological wonders with some fear and trepidation. It turns out that many hybrids (especially Honda) have a great deal in common service-wise with their conventional cousins. Let’s take a look at what makes Honda hybrids unique and some things to keep in mind when performing service on them.

The 2006 Civic hybrid doesn’t look very much different under the hood than the non-hybrid version. Note the orange high-voltage cables and the “Integrated Motor Assist” emblem on the ICE cover.

Integrated Motor Assist
Honda HEV technology was introduced to American roads in December 1999. In fact, the 2000 Honda Insight was the first production HEV to be sold in the U.S. While Honda’s newest HEV designs have a different look about them than these earlier models, the essential hybrid system remains the same.

The foundation of the Honda hybrid system is the IMA, also known as Integrated Motor Assist. Now entering into its sixth generation, the IMA is essentially an electric motor installed in between the internal combustion engine (ICE) and the transaxle. Because a hybrid vehicle utilizes two or more power sources, a hybrid-electric vehicle uses an ICE in conjunction with an electric motor to move the car. The primary power source still is the ICE, but the Honda IMA has a single electric motor installed in parallel with the ICE to increase torque output to the transaxle.

Thus, the Honda IMA is known as a parallel hybrid system. This same basic design has been used in all Honda hybrids to date, including:
• 2000-2006 Insight
• 2010 Insight
• 2003-2010 Civic hybrid
• 2005-2007 Accord hybrid

Honda hybrids use an electric motor-generator located between the ICE and the transaxle. Honda calls this a “DC Brushless Motor,” but it is powered with 3-phase alternating current.

The IMA rotor is attached directly to the ICE crankshaft. The rotor, in turn, acts as a mounting surface for the flywheel (early models with manual transmissions) or the damper (CVT-equipped models). The rotor is a permanent magnet design, so no electric current is required to generate its magnetic field. Using permanent magnets on the circumference of the rotor also means that no brushes are required, leading Honda to call this a “DC brushless motor.” A more accurate descriptor would be “AC synchronous motor,” as the IMA is actually powered by three-phase alternating current. The IMA stator (stationary field coils) has three separate windings and is powered by the Intelligent Power Unit (IPU), which is located at the back of the car. The IPU consists of a number of components, including:
• the high-voltage battery pack.
• an inverter which converts DC voltage from the high voltage (HV) battery to three-phase AC for powering the IMA motor.
• a DC-DC converter for powering the vehicle’s 12-volt electrical system.
• ECMs for control of hybrid drive and battery management functions.
• a cooling fan.

The Intelligent Power Unit (IPU) on a 2006 Honda Civic hybrid is located behind the rear seat back.

While the IMA can provide torque to assist with moving the car, it can also be used as a starter motor. Reliability is much improved due to the fact that no starter drive mechanism is required. The IMA is capable of spinning the ICE at 600 rpm or more (two to three times faster than a conventional starter), making for very quick starts. The IMA is also used to restart the ICE after the car goes into “idle stop” mode. When stopped at an intersection or in traffic, a Honda hybrid can go into idle stop, where the ICE shuts off and minimizes fuel use during extended idling. Honda hybrids use the IMA for starting the majority of the time, but are also equipped with a conventional 12-volt starter motor. This redundant starter is only used when the HV battery is discharged, a failure takes place in the IMA, or ambient temperatures are low.

The IMA can also be operated as a generator. When in this mode, the IMA can recharge the HV battery and also provide power to the vehicle’s electrical system using the DC-DC converter located in the IPU. When acting as a generator, the IMA receives its energy either from the ICE or from the kinetic energy of the vehicle as it decelerates.

Service Tip
One of the hallmarks of Honda hybrid technology is air-cooling. All electrical and electronic components related to the hybrid drive system are air-cooled, which reduces weight and makes the system simpler overall. Having said that, there is very little (if any) scheduled maintenance that needs to be performed on the IMA system itself.

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The plastic shield under this 2010 Honda Insight’s engine compartment is designed to enhance vehicle aerodynamics. Take it easy when removing it for undercar service.

Regenerative Braking
The primary efficiency advantage that an HEV has over a conventional vehicle is because of regenerative braking. When a vehicle is moving, it possesses kinetic energy (the energy of motion), which gets converted to heat when its brakes are applied. Of course, this waste heat then dissipates to the atmosphere and cannot be recovered. The idea with regenerative braking is to recover some of the kinetic energy that otherwise would be lost and use it to recharge the high-voltage battery pack. The energy stored in the battery pack can then be used to help the vehicle accelerate again, reducing fuel consumption when in stop-and-go traffic.

With a Honda hybrid, regenerative braking is accomplished by switching the operation of the IMA from a motor to a generator, then using it to help slow the car. The brake pedal doesn’t apply the brakes during the first part of the pedal stroke. Instead, it signals the IPU to switch the IMA to generator mode and controls vehicle deceleration that way. The brakes will apply, but only if the driver presses harder on the pedal and requires more braking than the IMA can provide. Interestingly enough, it is common for HEVs to suffer brake failures that are related to atrophy (lack of use) as opposed to simple wear and tear.

It pays to use the right tool when removing the plastic shield’s fasteners. Customers don’t like seeing broken shields or missing fasteners after their car has been serviced.

Because the IMA motor is attached directly to the ICE crankshaft, the ICE will absorb some kinetic energy during regenerative braking. Drivers of conventional vehicles know this as “engine braking.” This potentially recoverable energy is wasted due to the pumping action of the ICE cylinders as they take in air, compress it, and send it out the exhaust. Regenerative braking efficiency can be increased if the “pumping losses” of the ICE are minimized. In the case of Honda hybrids, this is accomplished by closing both the valves on several (or all) of the ICE cylinders, which then allows the cylinders to idle. With less energy being absorbed by the ICE, more can be directed to the IMA for conversion into electricity and storage in the HV battery pack. Reducing internal friction in the ICE can further increase efficiency. This can be achieved using techniques such as special cylinder honing or the use of low viscosity motor oil such as 0W-20.

High Voltage Operation
The electric motors in most HEVs are powered with high-voltage (100-plus volts) electric current. These high voltage systems have the potential to be much more dangerous during service than a conventional 12-volt automotive electrical system. So, why wouldn’t engineers make the systems safer by using low-voltage motors? The bottom-line answer is that the higher the voltage, the greater the efficiency that can be realized. The key principle here is that electric motors are powered by wattage, which is a function of voltage and amperage.

Power (in Watts) = Voltage (in Volts) x Current (in Amperes)

Newer Honda hybrids are calling for 0W-20 motor oil, where 5W-20 used to be the norm. Lower viscosity oils reduce engine friction, which also enhances fuel economy and starting performance.

Let’s say that you have a 1,440-watt electric motor, and you plan on powering it with 12 volts. Using the formula above, we can see that the motor will draw 120 amperes of current. This high current draw will require large cables to transmit the current in order to limit voltage loss. Now, what would happen if we were to power this same motor with 144 volts? The motor now would only draw 10 amperes, making it possible to use much smaller cables as well as thinner windings in the motor. This saves money in raw materials and also saves weight, a key factor in lowering fuel consumption. Some HEVs are using up to 650 volts to power their electric motors, which further increases efficiency gains and the potential for greater fuel economy.

Honda hybrids use high-voltage (HV) battery packs made up of dozens of cylindrical nickel-metal hydride (NiMH) cells. These are about the size of a D-cell flashlight battery and are rated at 1.2 volts apiece. Typically, six of these cells are joined end-to-end to build a module, and the modules are connected in series to form the high voltage battery pack. The output voltage of the battery pack can be determined by multiplying the number of NiMH cells by 1.2 volts. In the case of the 2006 Civic hybrid, there are a total of 132 NiMH cells used in the HV battery pack for a rating of 158 volts.

All HEVs use a 12-volt auxiliary battery which requires some level of attention. Honda hybrids also have a conventional 12-volt starter motor that is used as a backup to the IMA.

Service Tip
The high-voltage system on a HEV can be identified by the color orange. Orange-colored cables that run underneath the car or through the engine compartment should not be touched unless the system has been disabled using recommended service procedures. Online factory service information for Honda hybrids is available for purchase at http://techinfo.honda.com. Also available (for free) at this website is the current Emergency Response Guide (ERG), which outlines safety procedures to be used when Honda hybrid vehicles are involved in an accident. This information can be very useful for automotive technicians, because it outlines in detail what threats are present on the vehicle and what can be done to mitigate them.

Final Words
The trademark of Honda HEVs is that they are more like regular cars than the majority of other hybrids. Many of the bread-and-butter service items on a conventional Honda are also found on the hybrid version (for example, coolant, transmission service, brakes, etc.). This means that making the transition to Honda hybrid service does not have to be particularly daunting. In fact, it could be downright fun as you learn about new approaches in personal mobility.

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