Powering Up the 2006 Civic Hybrid

3 February 2006

Honda used a combination of technologies to deliver the power and torque improvements in the 2006 Civic hybrid.

The Honda Civic Hybrid is the second top-selling hybrid vehicle in the US, posting 3,165 units in January. When Honda redesigned the platform for the 2006 model year, the company managed to provide a boost in power and driving performance as well as an increase in fuel economy.

Tatsuro Horie, Assistant Chief Engineer at Honda R&D in Japan, provided some insight into the different elements that contribute to the gains during the SAE Hybrid Vehicle Technology Symposium.

Compared to the 2005 hybrid, the 2006 Civic hybrid increases power by 12 kW and torque by 27 Nm, while increasing fuel economy to 50 mpg US (combined) and delivering acceleration from 0 to 60 mph in 11.5 seconds. Five major systems contribute to the gains:

1. The 3-stage i-VTEC engine reduces pumping loss and increase engine output at high engine speeds.

2. All-cylinder deactivation increases the amount of regeneration power and enables the addition of the all-electric drive mode (motor drive).

3. Cooperative regeneration brake control increases the amount of regeneration power.

4. Modified motor, battery and CVT components support the increased amount of regeneration power.

5. The adoption of a hybrid air conditioner expands the idle stop range, and the addition of a humidity parameter to the air conditioning controls expands the air conditioning stop range.

All-cylinder deactivation contributes to the gains. Click to enlarge.

3-Stage i-VTEC. The Civic Hybrid uses a 3-Stage i-VTEC valve control system that provides the different valve timings (high and low) and the cylinder idling functions. The previous generation system in the 2005 Civic Hybrid used a 2-stage VTEC that provides normal valve timing and 3-cylinder idling. The new 3-stage system adds high output valve timing and full-engine 4-cylinder idling.

The addition of all-cylinder deactivation reduces engine friction and increases the regeneration energy.

The three different valve timings—low-speed operation, high-speed operation, and deactivation—enable a new operation regime, illustrated in the diagram below. The all-cylinder deactivation and high-speed timing are new in the 2006 hybrid system.

Click to enlarge.

Cooperative regeneration braking system. Honda developed an advanced hydraulic booster to enable optimum control of brake pressure, which works in cooperation with regenerative braking.

Even with that enhancement, however, Honda’s IMA (Integrated Motor Assist) system can’t match the full regeneration capabilities of the Toyota or Ford systems because Honda can’t take the engine fully out of the circuit as can the other design.

Motor. Honda increased the power of the prior motor by 50% and more than doubled its torque output while retaining the same form factor. One of the technologies the company used was to switch to a flat wire coil in the stator, rather than the previous round wire. The use of the flat wire enables a higher torque constant and a reduction in copper loss.

In the rotor, Honda used high magnetic flux magnets (Nd-Fe-B).

Battery. Honda boosted the power density of the battery cell by increasing the thickness of the collecting plate, increasing the reaction surface area due to thinner and longer electrodes and by increasing the conducive electrolyte in the solution.

Honda also switched to a staggered layout of the cells, decreasing the volume of the pack by 12% while increasing the number of cells and increasing voltage from 144V to 158V.

The CVT. Click to enlarge.

CVT. The new Continuously Variable Transmission offers higher efficiency and higher power through a number of enhancements. For higher efficiency, the CVT has an extended belt ratio than increase drive radius; a double piston pulley to increase the pressured area, resulting in low hydraulic pressure; and a higher ratio final gear.

For higher power, the transmission offers increased forward clutch capacity (2 discs to 3 discs) and increased start-off clutch capacity (four discs to five discs).

Compared to the prior unit, the new CVT enhances cruise efficiency by 3.5%, and torque capacity by more than 17%.

Hybrid air conditioner. The air conditioning system is the same as in the Accord Hybrid—the hybrid compressor enables air conditioning even during idle stop.