|The 2006 Civic Hybrid|
Honda is rolling out its fourth-generation IMA (Intelligent Motor Assist) hybrid powertrain in the 2006 Civic Hybrid (earlier post), to be on display at the Frankfurt motor show.
Compared to the 2005 Civic Hybrid, the 2006 model with the new IMA is 18% more powerful than its predecessor while delivering a combined EPA estimated fuel economy of 50 mpg US compared to 47–48 mpg US of the 2005 hybrid. The new IMA also adds the ability to cruise only under the power of the electric motor.
|The new 2006 Hybrid delivers 110 hp (82 kW) and 123 lb-ft (167 Nm) torque with 50 mpg US.|
The fourth generation Honda IMA system consists of a 93-hp 1.3-liter i-VTEC 4-cylinder engine connected to a 20-hp electric motor and a Continuously Variable Transmission (CVT). Combined, the powertrain delivers 110 hp (82 kW) and 123 lb-ft (167 Nm)of torque.
A 158-volt, 5.5-Ah Nickel-Metal Hydride (NiMH) battery captures and stores electricity from regenerative braking for the electric motor.
The 2006 Civic hybrid powertrain has four basic modes of operation that are applied in different driving scenarios:
Engine off. This is when the vehicle is stationary, but powered on. The engine is turned off and fuel consumption is zero. The battery powers electric systems (including air conditioning).
Low-speed valve timing (LO-VT). The engine operates in low-speed valve timing mode, sometimes assisted by the electric motor. The Civic applies this mode for startup and acceleration with motor assist, and with engine-only operation for high-speed cruising and gentle acceleration at higher speeds.
High-speed valve timing (HI-VT). This mode is for rapid acceleration at higher speeds, and has the engine operating in high-speed valve timing mode with motor assist.
Cylinder Idle. The valves of all four of the engine’s cylinders are closed and combustion halted. The electric motor alone powers the vehicle. This is also the mode for deceleration, where the motor recovers a significant portion of the energy normally lost during deceleration and stores it in the battery.
|The different modes of the 2006 Civic Hybrid IMA under appropriate operating conditions.|
Engine Valve/Cylinder Management, Ignition and Fuel Injection.. 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 uses 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 high output valve timing contributes to the engines increase in output of 9%, while the added cylinder deactivation reduces pumping losses by 66% to help improve electrical regeneration capability by 1.7 times.
The Civic Hybrid’s single overhead camshaft (SOHC) cylinder head uses a compact chain drive and a compact, low friction VTEC system. It uses a common rocker shaft for both the intake and exhaust rocker arms. Placing all the rocker arms on one shaft eliminates the need for a second rocker-arm shaft, so the valve mechanism can be lighter and more compact. To reduce friction, the rocker arms have rollers built-in.
The compact valvetrain allows for a narrow 30º angle between the intake and exhaust valves, which helps supply a more powerful direct charge into the cylinder chamber. The narrow angle valvetrain also allows for a more compact combustion chamber. The intake ports create a swirl effect in the cylinder chamber that promote a well balanced and even air fuel mixture as it enters the engine. This optimizes the air fuel mixture for a cleaner, more efficient combustion.
The new VCM (Variable Cylinder Management) system is an advanced form of the three-cylinder Cylinder Idling System used on the previous generation. VCM allows the regenerative braking system to reclaim as much energy as possible during deceleration, while also allowing the electric motor to propel the vehicle in certain steady state cruising situations.
Since the electric motor, which also acts as an electric generator, is attached directly to the crankshaft of the engine, the engine needs to provide as little resistance as possible during deceleration to allow the generator to produce high levels of electricity and charge the batteries. In a traditional engine, the pumping action of the cylinders will actually provide a moderate amount of resistance, or engine braking, during deceleration. VCM virtually eliminates that effect.
|The 3-stage VTEC valve switching capabilities are enabled by three hydraulic circuits in the rocker arm.|
From a mechanical standpoint, the 3-stage VTEC switching capabilities are made possible by a rocker arm design with three hydraulic circuits that accommodates:
low-rpm VTEC switching on each cylinder’s intake and exhaust valve
high speed switching on the [intake] valve
Three oil passages inside the rocker shaft receive oil from an external spool valve (controlled by the ECU based mostly on throttle and rpm). The oil pressure from one of the three passages activates a combination of push pins inside the rocker arms for each of the intake and exhaust valves. By moving the pins, the intake valve rocker arms can follow one of two lobes on the camshaft (normal or high profile). Or, to deactivate the valves and leave them closed, the pins are pushed in a direction that allow part of the intake and exhaust rocker arms to move with the camshaft and not move the closed valves.
Each cylinder in the iVTEC engine has twin sparkplugs for sequential ignition control. The ignition control has eight ignition coils that are independently controlled according to a dynamic engine map program. The benefits are more power, less fuel consumption and reduced emissions.
When the air/fuel mixture enters the combustion chamber, the first plug located near the intake port ignites. Shortly thereafter, the second plug located near the exhaust port ignites, accelerating the combustion process by forcing the flame to more rapidly propagate. The spark plugs can also ignite simultaneously under certain circumstances. This process results in a more complete combustion compared to a single plug system.
The Civic Hybrid is also equipped with a Programmed Fuel Injection (PGM-FI) system. The system monitors throttle position, engine temperature, intake-manifold pressure, atmospheric pressure, exhaust-gas oxygen content, and intake-air temperature. It controls fuel delivery by multi-holed injectors mounted in the plastic intake manifold. The ECU also tracks the operation of the engine with position sensors on the crankshaft and camshaft.
The Electric Motor. The ultra-thin (70 mm) DC brushless electric motor is mounted between the gasoline engine and the continuously variable transmission and provides up to 15 kW (20 hp) and 66 lb-ft of additional torque to the engine. An Intelligent Power Unit (IPU) that stores electric power in a compact battery box and controls the flow of electricity to and from the electric motor is in the rear of the car.
A new internal permanent magnet increases output density and makes the motor more efficient than previous motors. It also uses flat wire construction to increase wire density. The electric motor has increased output horsepower by 50 percent and maximum torque by 14 percent compared with the 2005 Civic Hybrid IMA motor. The electric motor is also more efficient, now converting 96% (versus 94.6% efficiency of the 2005 Civic Hybrid IMA motor) of the available electricity into motive energy in assist mode.
Energy Storage and Management: the IPU. Located directly behind the rear seatback, the IPU consists of the Power Control Unit (PCU), a rechargeable Nickel Metal-Hydride battery module, and an integrated cooling unit.
The PCU’s response time is quickened over previous versions, and a new inverter and DC/DC Converter help contribute to the IMA's overall increase in peak power.
The battery pack stores electricity in a bank of Nickel Metal-Hydride cells. This bank of 132 1.2-volt units stores up to 158 volts of electrical energy for the IMA motor compared to 144 in previous versions. A new Panasonic dual module casing reduces weight from previous hybrid battery packs and also allows it to increase efficiency of the electrical flow. The battery pack is also 12% smaller in volume than the prior.
The Integrated Cooling Unit offsets the heat generated by the constant flow of electricity to and from the battery pack with an integrated cooling system mounted directly on the battery pack’s outer box. Interior cabin air is continually flowed over the battery pack and re-circulated via a small vent placed on the rear seat shelf.
Regenerative Braking. New for 2006, a cooperative regenerative braking system debuts on the Civic Hybrid with the added capability to intelligently proportion braking power between the hydraulic brakes and the electric motor to extract even more electricity from the vehicle’s kinetic energy. Less reliance on the traditional braking system and reduced engine pumping losses translate into greater electrical regeneration (170% more than the 2005 Civic Hybrid) and ultimately improved fuel economy.
When braking, a brake pedal sensor sends a signal to the vehicle's IMA computer (IPU). The computer activates a servo unit in the brake system’s master cylinder that proportions braking power between the traditional hydraulic brakes and the electric motor to maximize regeneration. Previous versions of Honda’s IMA systems proportioned braking power at a pre-set rate below the maximum regeneration threshold and with no variable proportioning.
The Continuously Variable Transmission. Honda’s fourth generation of Continuously Variable Transmission (CVT) is standard equipment on the Civic Hybrid and provides a 9% wider range between the maximum and minimum gear ratios to enhance acceleration and minimize engine rpm at high speeds. The transmission provides smooth and predictable transitions and helps keep the IMA system operating at its peak efficiency.
|Honda Civic Hybrid 2006 vs. 2005|
|Engine||1.3-liter i-VTEC SOHC||1.3-liter VTEC SOHC||+ i-VTEC|
|Electric Motor hp @ rpm||20 @ 2000||13 @ 4000||+ 7|
|Cylinder Deactivation||4-cylinder||3-cylinder||Full Engine Deactivation|
|Power||110 hp (82 kW)||93 hp (69 kW)||+17 hp (+13 kW)|
|Torque Nm @rpm||167 @ 1000-2500||142 @ 3000 (CVT)||+ 25 @ - 500|
|Transmission||CVT||CVT or MT||CVT standard|
|Tire Size||P195/65 15||P185/70 15||Larger tire|
|Fuel Economy city/hwy mpg||50 / 50||47 / 48 (CVT AT-PZEV)||+ 3 / +2|
|Emissions||AT-PZEV (50 State)||AT-PZEV (CA +)||50-State AT-PZEV|
|Passenger Volume (cu. ft.)||90.9||91.4||-0.5|
|Front/Rear Leg Room (in.)||42.2 / 34.6||42.2 / 36.0||0/-1.4|
|Front Hip Room (in.)||51.8 / 51.0||51.3/ 49.8||+0.5/+1.2|
The 2006 Civic is incrementally larger, definitely more powerful but still more efficient than its predecessor. It’s good to see a new hybrid platform rolled out that leans more toward the efficiency end of the scale rather than the performance hybrids of late.
Honda’s market timing is impeccable. It will be very interesting to see how rapid the uptake is on this car, given the surge in sales of the current Civic hybrid last month. (Earlier post.)