2005 Honda Odyssey Powertrain - Part 2

VCM Operation

The Odyssey's i-VTEC V-6 engine (available on EX with Leather and Touring models) features a Variable Cylinder Management (VCM) system that improves fuel economy by idling three of the Odyssey's six cylinders during cruising and deceleration. VCM deactivates the rear bank of cylinders by using the VTEC (Variable Valve-Timing and Lift Electronic Control) system to close the intake and exhaust valves while cutting fuel at the same time.

The rear bank of cylinders was chosen for deactivation because the front bank is best positioned for cooling performance. Idling the rear bank also helps to maintain the temperature of the catalytic converter beneath the cylinder heads, helping to maintain optimum environmental performance.

The Odyssey's spark plugs continue to fire even when the cylinders are deactivated. This minimizes plug temperature loss and prevents fouling-induced from incomplete combustion during cylinder re-activation. Further, sparking in air alone results in higher voltages than in a fuel-air mixture because of the higher insulation resistance. Therefore, iridium-tipped spark plugs are used for their high resistance to wear at high voltages.

i-VTEC VCM System Designed for Rapid Switching at Low Engine Speeds

In a conventional VTEC system, hydraulic pressure pushes a single synchronizing piston, which is in turn pressed back by a return spring. The VTEC system locks the valvetrain's rocker arms to allow additional valves to open and increase engine breathing. Such systems require relatively high engine speeds since hydraulic pressure is used to push the spring. VCM, however, demands switching at low rpm. This is achieved by creating a hydraulic circuit with two systems, each capable of providing the hydraulic pressure required to push the synchronizing piston in the required direction. This design thereby allows switching from six cylinders to three cylinders in low-speed ranges. To achieve responsive switching to six cylinders when the driver operates the accelerator pedal, the system employs a new three-way solenoid spool valve to control the oil pressure for switching. These enhancements result in highly responsive VCM switching regardless of engine speed.

VCM monitors throttle position, vehicle speed, engine speed, automatic-transmission gear selection, and other factors to determine if the vehicle is cruising or decelerating. During cruising and deceleration, VCM deactivates three of the cylinders on the rear bank of the engine. To further enhance control, the system also simultaneously determines whether engine oil temperature is suitable for VCM switching and whether catalytic converter temperature will remain in the proper range. While idling the cylinders, the system controls ignition timing, adjusts throttle position via Drive-By-Wire, and turns the torque converter lock-up on and off, thereby suppressing torque-induced jolting during the switch from six to three cylinder operation. The result is a smooth, seamless switch between three and six cylinder modes that is nearly unnoticeable to the driver.

For cylinder deactivation operation, the synchronizing piston moves to isolate the valve-lift rocker arms from the deactivated cylinders' rocker arms. The deactivated cylinder rocker arms are operated by zero-lift cams that deactivate the cylinders by closing the intake and exhaust valves.

Engine Mounts

Odyssey LX and EX models use a special liquid-filled engine mount and an Electronically Controlled Mount (ECM) to help absorb vibration from its already smooth V-6 engine. Odyssey EX with Leather and Touring models (with VCM) use an advanced Active Control Engine Mount system to counteract any vibrations.

Due to the inherent increase in engine vibration when VCM has deactivated the rear cylinders, an Active Control Engine Mount system (ACM) is used to minimize the effects of engine vibration. The system uses sensors that alert the Electronic Control Unit (ECU) to direct ACM actuators to move in synch with the vibration, thereby eliminating the vibration being transmitted to the passenger compartment. Additionally, an Active Noise Control system (ANC) works in cooperation with the ACM. An ANC controller with a microphone detects the booming noise associated with cylinder deactivation and instructs the audio system's speakers to emit "anti-noise." See the interior section for more information on ANC.

Dual-Stage Induction System (i-VTEC Engine)

Designed specifically for the Odyssey's i-VTEC engine, the induction system works in concert with the valvetrain to significantly boost torque across the engine's full operating range. Internal passages and two butterfly valves commanded by the powertrain control module are configured to provide two distinct modes of operation. The valves are closed at lower rpms. In this mode, the three cylinders on each bank draw air from only the nearer half of the manifold's internal chamber, or plenum. The volume of the plenum and the length of inlet passages are both tuned to maximize the resonance effect, wherein pressure waves are amplified within each half of the intake manifold at certain rpm ranges.
The amplified pressure waves significantly increase cylinder filling and the torque produced by the engine throughout the lower part of its rpm band. Funnel-shaped intake ports - similar to those used on racing engines - are built in at the uppermost end of each intake runner to improve air flow.

Exhaust System

A low-restriction, high-flow exhaust system is crucial to efficient power and torque production. The Odyssey features a high efficiency system that incorporates several key elements that work in concert with the engine's uniquely designed cylinder heads to help boost performance, reduce tailpipe emissions and trim weight. Major system components include two close-coupled catalytic converters, a secondary underfloor catalytic converter, a centrally positioned, high-flow resonator and a silencer. The close coupled catalytic converters mount directly to the cylinder head to reduce light off time, thereby allowing the catalyst to begin cleansing the exhaust as soon possible.

The catalysts, muffling element, and piping are all sized for high flow and low restriction. High-chromium stainless steel is used throughout the exhaust system for excellent durability.

Linear air-fuel and oxygen sensors installed in each of the close-coupled catalytic converters make possible precise control of the air-fuel ratio. These sensors and the precisely controlled high-atomizing multi-hole fuel injectors help achieve almost complete combustion, for cleaner emissions. The result is compliance with California's LEV2-ULEV standards as well as Federal Tier 2-Bin 5 emission requirements.

ENGINE ELECTRONICS
Drive-By-Wire Throttle System

The Odyssey features an innovative drive-by-wire (DBW) throttle control system. This DBW system replaces a conventional throttle cable arrangement with an all-electronic system that senses the accelerator pedal position and relays that information to a computer. The computer then performs the actual throttle activation instantaneously.

The Odyssey electronic throttle control system works by means of a accelerator pedal sensor, a throttle angle sensor, a control unit built into the power control module and a DC motor to control throttle opening and provide fail-safe throttle operation. This system allows for throttle control to be integrated into the VSA and VCM systems, and also incorporates the cruise control function. To improve shifting smoothness, the automatic transmission shifting has been enhanced, and the electronic throttle control system controls the throttle during transmission shifts. To optimize driving feel, accelerator pedal characteristics are calibrated to be smooth and linear during start up, and when driving on ice or other low traction surfaces, and more responsive during acceleration. During cruise control, throttle operations are smoothed out to maximize idled-cylinder operation. This not only enhances fuel economy but also helps eliminate unnecessary switching, making for a smoother ride.

Programmed Fuel Injection (PGM-FI)

Fuel is delivered in sequence and timed to each cylinder's induction stroke by six injectors mounted on the lower portion of the intake manifold. The Odyssey features innovative orifice-type injectors instead of pintle-type injectors. These injectors optimize the fuel spray pattern, and improve fuel atomization for increased fuel mileage and reduced emissions. A 32-bit, 40MHz central processor unit (CPU) within the Odyssey's powertrain control module calculates injection timing and duration after assessing an array of sensor signals; crankshaft and camshaft position, throttle position, coolant temperature, intake manifold pressure and temperature, atmospheric pressure, and exhaust-gas oxygen content. The CPU controlling the Odyssey's Programmed Fuel Injection (PGM-FI), VCM, VTEC valve train, dual-stage intake manifold, the drive-by-wire throttle, and the transmission also communicates with CPUs that regulate the Vehicle Stability Assist (VSA) and meters, and interacts with the ACM.

Direct Ignition and Knock Control

Maintaining the correct ignition timing throughout all operating conditions is essential to producing maximum power, using fuel efficiently and minimizing emissions. A powertrain control module (PCM) examines various engine functions as well as a block-mounted acoustic knock sensor to determine optimum ignition timing. In the event the engine is supplied with fuel lower in octane than the specified unleaded premium, the PCM retards ignition timing as needed to forestall detonation. As a result, the engine constantly operates at the point of peak efficiency. Spark is supplied to iridium-tipped, long-life spark plugs by six coil units positioned directly over the plugs in the cylinder-head access bores.

Smart Maintenance Tune-Up Intervals

The new Smart Maintenance System allows the Odyssey to become an active participant in alerting its owner to pending service requirements. This feature takes the guesswork out of determining how severe or normal road conditions may affect oil service intervals by displaying the percentage of remaining oil life before the need for an oil change. Smart Maintenance also monitors driving conditions and prescribed mileage, and displays corresponding codes that indicate the need for tire rotation, air cleaner element replacement, automatic transmission service, a coolant change, and spark plug and timing belt replacement. This system anticipates soon-to-be maintenance needs and groups them together with those more urgently required. This allows an owner to take care of everything at one time and reduce their number of visits to the service department.

The only maintenance necessary is routine inspections and fluid and filter changes. At 105,000 miles, the valves should be adjusted, the timing belt should be replaced, the water pump should be inspected and the iridium-tipped spark plugs should be replaced.

5-Speed Automatic Transmission Overview

The Odyssey features a compact 5-speed automatic transmission that utilizes a 3-shaft design layout. The SOHC VTEC V6 transmission provides both smooth startup and outstanding fuel economy when cruising at high speed. The SOHC V6 i-VTEC with VCM transmission makes use of a lower ratio for fourth and fifth gears, boosting acceleration during high-speed travel. These ratios expand the range of the three-cylinder mode that dramatically enhances fuel economy, thereby realizing both powerful acceleration and low fuel consumption.

A lock-up torque converter is provided to maximize fuel efficiency. Torque-converter lock-up and shift timing are both managed by a PGM-FI ECU that maintains a communications link with the engine's CPU. Lock-up continues even during downshifting from fifth to fourth and from fourth to third gear, making continuous fuel cutoff possible. The specially designed springs used for the lock-up dampers employed with the VCM system feature a low spring coefficient during three-cylinder mode, effectively absorbing changes in speed.

Creative use of clutched idler gears permits the transaxle to provide five forward speeds with little more weight or bulk than a typical four-speed automatic. A one-way clutch is provided for first gear to smooth upshift quality. An extra-capacity transmission fluid cooler is offered with the Odyssey's optional tow package to maintain acceptable lubricant temperatures during heavy-load conditions.

A direct-control strategy provides real-time pressure management of the transmission's clutches. Various safety and control strategies coordinate engine and transmission operation. For example, driveline shocks during up- or downshifts are minimized by momentarily reducing engine torque during the shift. In neutral and park, engine rpm is automatically limited to 5000 rpm.

For driving through hilly terrain, a Grade Logic Control system monitors throttle position, vehicle speed, acceleration and deceleration to avoid hunting and excessive shifting. A lower gear is held for a longer-than-normal period to provide better climbing ability on hills and more engine braking on downhill grades. On i-VTEC models, the 2005 Odyssey is equipped with an intelligent cruise control system that works in combination with the transmission to provide downshifts from fifth to fourth or from fourth to third as required on downhill grades, making effective use of engine braking to control the vehicle's speed.

Half-Shafts

Equal-length, front-wheel half-shafts use a plunger joint at their inboard end and a ball-type universal joint at the wheel end.

Gear Ratios (VTEC and i-VTEC)

Towing

The ability to haul pop-up campers, medium-sized boats, and recreational vehicle trailers can be a priority to some minivan owners. Ultimately, the engineers concluded that a casual or weekend towing capability was most appropriate for the Odyssey. Customer feedback helped set the towing limit at 3500 pounds for trailers. The Odyssey's 3500-pound rating is calculated to include up to two passengers and their cargo.

In support of safe towing, Odyssey's tow hitch and other hardware needed for the job are factory engineered for dealer installation. The dealer-installed trailer hitch is a Class III receiver-type design that bolts on with no drilling, cutting, or bumper-cover modifications. An external transmission cooler and a separate power-steering fluid cooler is also included along with a harness to provide electrical power to trailer lights that plug into a connector provided at the rear of the vehicle.