DIY Network

A Hybrid-Vehicle Technology Primer Bruce Bonebrake reaveals some of the reasons why a hybrid vehicle may be in your future. From "Weekend Mechanic" episode WKM-404

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There are some differences worth noting between a hybrid and conventional vehicle. Today's hybrid cars typically combine a gasoline engine with an electric motor and high-capacity battery. According to Honda specialist Jeff Keylon, the Civic Hybrid is essentially a regular Civic--but with the addition an integrated motor-assist and an ultra-thin brushless DC electric motor mounted between the gasoline engine and transmission.

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	The hybrid engine
	All high-voltage power lines in the vehicle are clearly marked by brightly colored orange shielding. The cables carry as much as 144 volts.

The Hybrid Advantage

The majority of the time, the vehicle is running off the gas engine, but it's given an added boost via electric motor assist mode during high demand situations like start-up or climbing a hill.

The DC electric motor provides the extra power needed for startup and acceleration, and also acts as a generator to supply energy to the hybrid's high-capacity battery. The motor turns into a generator during braking and converts the mechanical energy into electric energy which is stored in the battery. The electric generator also recharges the battery during deceleration, coasting and cruising.

All of this transitioning between gas and electric power is barely perceptible to the driver of the vehicle. With each stop the regenerative braking system kicks in and switches the electric motor into a generator to charge the battery system. Then seamlessly it changes back to assist mode for acceleration. When cruising speed is reached, or during coasting, the system also goes back to generator charging.

	Honda's integrated motor assist (IMA) unit helps give the hybrid extra boost in high-demand situations like acceleration from a stop and climbing a hill.

Actually, a hybrid vehicle has two separate batteries. The first is the standard 12-volt battery that powers items such as the lights, audio system, ignition and fuel injection. The other is a high-voltage battery that's stored in the intelligent power unit, on this model between the back seat and the trunk. Since the high-voltage battery is recharged by the generator portion of the electric motor, a hybrid car does not need to be plugged in, as some people think.

"It's basically a 1.3 liter single overhead cam motor, a small version of the normal Civic motor," says Keylon, "and then you've got the electric boost motor that kicks in when needed. . . When you first pull out, the electric motor kicks in. It'll boost up as much as 8 horsepower and then, when you begin coasting for example, or let off the accelerator, the electric motor kicks out."

Aside from the differences in engine and power train, efforts have been made to reduce the weight on the Honda as much as possible. The wheels, for example, are a special lightweight alloy. The sunroof, which adds weight, was eliminated, and the electric power-steering system is lighter than a conventional one. Additionally, aerodynamic features such as the rear spoiler reduce drag and help improve handling and gas mileage.

All of the hybrid's power and driving characteristics, combined with a lightweight aluminum alloy engine and an aerodynamic body design, mean better fuel efficiency, less gas consumption and lower emissions.

And there's one more potential advantage. Although maintenance on a hybrid is basically similar to that for a conventional vehicle, many hybrid owners report fewer service visits since the wear and tear on the gasoline engine and the brakes is less than on a conventional gas-only vehicle.

The High-Voltage Wiring Harness

Safety Alert: All of the high-voltage power lines in the vehicle are clearly marked and protected by strong orange-colored shields. It's important not to damage or work on high-voltage power cables as they carry 144 volts or more. Any service or repair on these high-voltage components should be performed by trained technicians.

The high-voltage wiring harness leads from the engine compartment to the battery compartment at the rear of the vehicle, is heavily shielded and is routed underneath the vehicle--down the center portion in the location where it would least likely be damaged in the event of a collision. In fact, all high-voltage components are completely insulated and isolated from the vehicle body.

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