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Honda Civic Hybrid Technology

The latest in the petrol-electric stable

By Julian Edgar, Courtesy of Honda

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At a glance...

  • Sophisticated triple(!) VTEC engine
  • Dual-plug sequential direct ignition
  • Eight individually controlled coils
  • Battery electric motor assist
  • 4.6 litres/100
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Honda’s fourth-generation hybrid, the Civic Hybrid, combines a petrol-powered engine with an electric motor to boost power and cut fuel consumption and exhaust emissions. A Nickel-Metal Hydride (NiMH) battery pack is used to capture and store electricity for the electric motor.

The improved Integrated Motor Assist (IMA) system now allows the Civic Hybrid to drive on electric power alone, provided the vehicle is travelling at less than 40 km/h. The Civic Hybrid has a combined petrol/electric output of 85kW and develops 170Nm. Quoted fuel consumption is 4.6 litres per 100km, a saving of 0.6 litres per 100km over the previous model. The Civic Hybrid is equipped with a Continuously Variable Transmission (CVT).

During acceleration, the engine, or the engine working in tandem with the electric motor, propel the vehicle. During cruising, the petrol engine and/or the electric motor can propel the vehicle, depending on conditions. During braking, the petrol engine deactivates and the electric motor acts as a generator to replenish the battery pack. At a stop, the engine can enter an idle-stop mode to save fuel and reduce emissions, with the engine turned off until the brake pedal is released.

Engine Block Construction, Pistons and Connecting Rods

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The 1.3 litre aluminium engine block and its internal components create a lightweight package with extremely low friction qualities. To save weight, the block incorporates a thin sleeve construction. Friction-reducing measures include plateau honing, low friction pistons, low tensile force piston rings and an offset cylinder bore.

Thin sleeve cylinder wall construction results in a reduction of the total amount of aluminium used in the engine. Plateau honing lowers the friction level between the pistons and the cylinders by creating an ultra smooth surface. Plateau honing is a two stage machining process that uses two grinding processes instead of the more conventional single honing process. This also enhances the long-term wear characteristics of the engine.

Low friction pistons made of aluminium alloy are lightweight and have “micro-dimples” on the cylinder walls for improved lubrication. Offset cylinder bores help minimise friction by positioning the crankshaft axis in a more efficient alignment to the cylinder bore axis. This reduces friction caused by the side thrust of the pistons against the cylinder walls, just after top-dead-centre, as each piston begins its descent on the firing stroke.

Connecting rods are high strength forged steel units that have been treated with a special carbon process that hardens the surface and allows engineers to use a design that weighs less than a traditional connecting rod.

3-Stage i-VTEC with Variable Cylinder Management (VCM)

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The Civic Hybrid uses a 3-Stage i-VTEC valve control system that provides normal valve timing, high output valve timing and 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 3-stage system adds high output valve timing and 4-cylinder idling. Over the previous model, the high output valve timing contributes to the engine’s output increase of 9 percent, while the added cylinder deactivation reduces pumping losses by 66 percent 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 built-in rollers.

The compact valvetrain allows for a narrow angle (30 degrees) 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 optimises the air fuel mixture for a cleaner, more efficient combustion.

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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 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.

From a mechanical standpoint, the three stage VTEC switching capabilities are made possible by a rocker arm design with three hydraulic circuits that accommodates (a) low rpm VTEC switching on each cylinder’s intake and exhaust valve and (b) 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.

Dual & Sequential Ignition with Twin Plug Sequential Ignition Control

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The twin plug sequential ignition control is part of the i-VTEC system and helps facilitate an intense and rapid combustion process in the engine. 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. Honda’s patented twin plug sequential control system is programmed to respond to engine rpm and load conditions. Since the system has eight individual ignition coils, it can manipulate the ignition timing of each iridium-tipped spark plug.

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.

Electronic Throttle Control

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An electronic drive-by-wire system enhances the driving character of the Civic Hybrid. With smart electronics connecting the throttle pedal to the throttle butterfly valve in the intake manifold, the engine response and IMA operation can be optimised to suit the driving conditions and to better match the driver’s expectations. By eliminating the direct throttle cable connection to the engine, the ratio between pedal movement and throttle butterfly movement can be continuously optimised. This adjustable “gain” between throttle and engine is a significant step forward in driveability, which also allows for VCM to cut all cylinders and drive with the electric motor only during some cruising situations. A DC motor moves the throttle butterfly position in the intake manifold to change actual throttle position. To establish the current driving conditions, the system monitors pedal position, throttle position, vehicle speed, engine speed, calculated road slope and engine vacuum. This information is then used to define the throttle control sensitivity.

Programmed Fuel Injection (PGM-FI)

The Civic Hybrid is 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.

Lightweight Composite Resin Intake Manifold Chamber

Upstream from the aluminium intake manifold, the engine’s intake manifold chamber is constructed of a composite resin instead of aluminium alloy in order to save weight. The individual pieces that make up the manifold chamber are permanently connected with a vibration welding technique.

Dual Scroll Air Conditioning Compressor

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A dual scroll hybrid air conditioning system reduces the load on the petrol engine by using a combination of engine power and an internal electric motor to drive two air conditioning compressors. These compressors can act independently or together as dictated by the cooling needs of the Civic Hybrid’s automatic climate control system.

Under normal conditions, either of the two compressors cools the interior cabin individually depending upon cooling needs and the charge state of the IMA’s battery pack. On warmer days, the 75cc engine-mounted compressor acts as the sole source of air-conditioning, while the 15cc motor-driven compressor is in action when the climate control is maintaining a steady temperature or the car is idle-stopped. Under extreme ambient conditions, cooling is provided by the 75cc belt-driven compressor attached to the engine and the 15cc, 144V motor-driven by an internal electric motor. When the air conditioning system is forced to use both the petrol engine and electric motor, the Civic Hybrid’s idle-stop feature is temporarily disabled until cooling needs are reduced.

Engine Mounts

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A new torque rod damper system added to the subframe helps reduce rocking and isolate powertrain NVH from the passenger compartment. The engine mounts, one of which is hydraulic, and reinforcements in the engine compartment help further reduce engine noise and vibrations.

IMA System

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The 4th generation IMA system is the most powerful and most efficient to come out of Honda’s hybrid development program. (1st generation: Insight; 2nd generation: Civic Hybrid; 3rd generation: Accord Hybrid.) As with previous versions, the IMA system consists of an ultra-thin DC brushless electric motor mounted between the petrol engine and the continuously variable transmission, and an Intelligent Power Unit (IPU) that stores electric power in a battery and controls the flow of electricity to and from the electric motor.

IMA Electric Motor

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Providing a supplemental power boost to the 1.3-litre 4-cylinder engine and giving the Civic Hybrid the capability to cruise on its electric motor in certain situations, the IMA’s electric motor is designed to provide up to 15 kW and 89Nm of additional torque to the Civic Hybrid’s engine. Mounted between the engine and the CVT transmission, the IMA motor is a 70 mm thick DC brushless design and provides a substantial amount of low-end torque to aid acceleration, while also assisting in steady-state cruising and hill climbing.

In addition to providing supplemental motive power, the IMA motor acts as a generator during deceleration and braking to recapture kinetic energy and recharge the IMA’s battery pack during regenerative braking.

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For this fourth generation of IMA motor, a new internal permanent magnet was designed to increase output density and make the motor more efficient than previously. It also uses flat wire construction to increase wire density. The electric motor has increased output power by 46 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 percent (versus 94.6 percent efficiency of the 2005 Civic Hybrid IMA motor) of the available electricity into motive energy in assist mode.

IMA Intelligent Power Unit (IPU)

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Power for the IMA system is controlled through the Civic Hybrid’s Intelligent Power Unit. Located directly behind the rear seat, the IPU consists of the Power Control Unit (PCU) - the IMA’s command centre, a rechargeable Nickel Metal-Hydride battery module, and an integrated cooling unit.

The Power Control Unit (PCU) electronically controls the flow of energy to and from the IMA’s electric motor. Using the latest computer chip technology, the PCU’s response time is quicker than the previous versions, and a new inverter and DC/DC Converter help contribute to the IMA’s overall increase in power.

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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 12 percent smaller battery pack provides more cargo space.

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.

Cooperative Regenerative Brake System

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Hybrid-powered vehicles recapture kinetic energy via regenerative braking and store this energy as electricity in rechargeable battery packs. The Civic Hybrid is no different, as its IMA electric motor also acts as a generator that can recharge its battery pack during braking, steady cruising, gentle deceleration, or coasting. 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 percent more than the 2005 Civic Hybrid) and ultimately improved fuel economy.

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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 maximised 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.

Continuously Variable Transmission

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Honda’s Continuously Variable Transmission (CVT) is standard equipment on the Civic Hybrid and provides a 9 percent wider range between the maximum and minimum gear ratios to enhance acceleration and minimise engine rpm at high speeds.

Unlike a conventional transmission with four of five gears that change the final drive ratio in steps, a CVT uses a steel belt and a variable pulley to infinitely change the final drive ratio between a minimum and maximum setting. The variable pulley with its angled internal sides moves in and out by hydraulic pressure to expand or reduce the radius travelled by the steel belt.

Improvements to the new CVT include:

  • 9 percent wider ratio range of 2.52 - 0.421:1 (previously 2.36 - 0.407:1)

  • Final drive ratio of 4.94:1 (previously 5.58:1)

  • Expanded pulley axial distance from 143 mm to 156 mm

  • Expanded pulley ratio range to 6.0 mm from 5.8 mm

  • Double hydraulic piston used on variable pulley increases pressure by 170 percent

  • Improved low friction construction for overall efficiency increase

  • Torque handling capacity increases by 18 percent

Overall, a CVT provides a greater fuel economy benefit than a conventional automatic transmission with gears. It helps the engine stay in its most efficient operating range for both performance and economy, and the need to shift gears is eliminated.

2006 Civic Hybrid Specifications

Wheelbase (mm) - 2700

Length (mm) - 4550

Width (mm) - 1750

Height (mm) - 1430

Engine - 1.3-litre i-VTEC SOHC

Power @ rpm (combined) - 85 @ 6000

Torque (Nm) @ rpm (combined) - 170 @ 2500

Transmission - CVT

Tyre Size - 195/65 R15

Fuel consumption (litres per 100km) - 4.6

Weight - 1265

Next week: we road test the Honda Civic Hybrid

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