Honda Accord -- Drivetrain
9/15/2000 9:27:02 PM
Three engines are available for the Accord: There is 3.0-liter, 200-horsepower, 24-valve V-6 and two 2.3-liter 4-cylinder engines. A 5-speed manual transmission is standard on 4-cylinder models and a 4-speed automatic transmission is available for the 4-cylinder engines and standard on V-6 models.
The 3.0-liter, 200-horsepower, 24-valve V-6 is the first V-6 engine to use VTEC (Honda Variable valve Timing and valve Lift Electronic Control system), Honda's variable valve timing system. VTEC helps give the V-6 a broader, more powerful torque curve. All engines and transmissions are built at Honda facilities in Ohio.
The Accord's 2.3-liter, in-line 4-cylinder engine is shared by DX, LX and EX models and features a 16-valve cylinder head and a vibration-canceling second-order balance system. Both LX and EX engines receive California Low-Emission Vehicle (LEV) certification, thanks in part to the application of VTEC technology.
- 200 hp
- 195 lb.-ft.
- 0-60 mph acceleration is about 8.2 seconds
- Compression ratio 9.4:1
- Uses regular unleaded gasoline
- VTEC cylinder heads with roller cam-follower rocker arms
- 20/28 mpg (EPA estimated Cty./Hwy)
- Electronically controlled EGR (Exhaust Gas Recirculation)
- 16-bit PCM (Powertrain Control Module)
- 60-degree V-angle
- Compact, lightweight engine (98-mm bore spacing)
- Separate camshaft holders allows for more compact cylinder head
- Lightweight pistons and connecting rods
- Full-floating piston pin eliminates piston slap during warm-up
- Cast-aluminum oil pan
- Twin-outlet exhaust system
- Horsepower:150 hp for EX and LX, 135 hp for DX. Torque increased to 152 lb.-ft. for EX and LX, 145 lb.-ft. for DX.
- VTEC (LX and EX models)
- Fuel economy: 23/30 mpg (EPA estimated Cty./Hwy.) (LX, EX w/AT), 22/29 mpg (EPA estimated Cty./Hwy.) (DX w/AT)
- EX and LX engines qualify as California LEV (Low-Emission Vehicles)
- EX with automatic transmission qualifies as ULEV (Ultra-Low Emission Vehicle) in California
- Stratified-charge VTEC
- Electronically controlled EGR (Exhaust Gas Recirculation)
- ULEV engine uses 32-bit ECU with individual cylinder air-fuel ratio control, lean air-fuel ratio during fast idle, high-efficiency catalyst and low heat-mass exhaust system
- Less radiated noise and vibration
- Quieter, less restrictive induction system with large, twin-chamber resonator
- New lightweight piston and connecting-rod design minimizes vibration
- More rigid crankshaft design
- Second-order balance system
- Redesigned cylinder block is more rigid with less vibration
- Aluminum engine stiffener between engine and transmission
- Direct-control automatic transmission is controlled by PCM (Powertrain Control Module) for smooth shifting
- Cruise control is controlled by PCM and AT Cruise ECU for smoother operation
- Reduced gear noise
- Manual transmission has reduced lining diameter for smoother shifting, with same level of fade resistance and durability
COMPACT, 3.0-LITER V-6 ENGINE
Accord V-6 sedans and coupes are powered by an aluminum-alloy, transversely mounted, 3.0-liter, 200-hp V-6 engine. The engine features 4 valves per cylinder (24 total), single overhead camshafts and VTEC.
The V-6 is quite compact and incorporates several innovative features that help minimize its size, weight, friction and vibration. The block is heat-treated, die-cast aluminum and is very compact and rigid, with a high natural frequency and minimal resonant vibration. In addition, its 60-degree V angle serves to minimize vibration. Bore and stroke are "square," each measuring 86 mm, for a total displacement of 2997 cc. The cylinder liners are cast-iron.
The V-6's narrow 98-mm bore spacing contributes to the engine's short over-all dimensions. The block-deck height (and piston compression height) is minimized by the use of ultra-short skirt pistons. The com-pression ratio is 9.4:1 and regular unleaded fuel is specified.
The pistons are 51.5 mm tall and use ultra-short skirts. In addition, the skirts are thicker and more rigid than those used on the previous engine, which helps to further minimize vibration and friction.The piston pins are a full-floating design whose small clearances result in less noise, especially during engine warm-up.
The pursuit of a lightweight, compact design mandated special care in crank-shaft and connecting-rod engineering. The engine's connecting rods don't use conventional nut-and-bolt type fasteners, but instead employ lighter bolts (without nuts) called plastic-region fasteners. These bolts are designed to operate in the plastic, not elastic, region of the steel material, unlike conventional fasteners. This allows downsized rod bolts to maintain relatively greater clamping force and handle operating stresses with normal strength margins. It also uses a special dual-mode crankshaft damper pulley. Overall engine width is 485.5 mm (as transversely installed in the car). That makes the power-plant narrower than the 3.0-liter V-6s in the Toyota Camry or Nissan Maxima.
COMPACT VTEC CYLINDER HEAD
Pressure-cast of aluminum alloy, the Accord's cylinder heads echo efforts visible throughout the engine to minimize weight and size. In the interest of simplicity, the single overhead cams are installed in the heads from the end, instead of being clamped in place from above with bolt-down caps.
The pentroof combustion chamber design is an evolutionary refinement of Honda 4-valve combustion chamber technology The 9.4:1 compression ratio allows the engine to operate on regular unleaded fuel.
The 4-valve-per-cylinder design offers several advantages over 2-valve arrangements, most notably the reduced reciprocating mass, which allows the engine to safely reach higher rpm and develop greater horsepower. Additionally, valve area is increased with the use of four valves, relative to conventional 2-valve systems, resulting in improved air flow. Remarkably, the Accord V-6 has comparable or better horsepower, and competitive fuel economy with other engines in its class, and meets California's strict standards -- all while burning regular unleaded fuel.
The Accord V-6's valves are actuated by roller followers and a single camshaft per cylinder bank. The U.S.-sourced camshafts are constructed of ductile iron, flame-hardened, then quenched to achieve the necessary hardness. The cams are turned by a glass-fiber reinforced, toothed belt, which is driven by the camshaft. An automatic tensioner compensates for belt-stress fluctuation.
The Accord V-6 engine uses Honda-programmed, sequential fuel injection. Air induction is via a cast-aluminum intake manifold with individual, tuned-intake runners. A tuned plenum and throttle body connect to the upper end of the manifold.
Honda engineers tuned the Accord 3.0-liter V-6 so that it would have sporty performance, but still be relaxed in everyday driving. Because of its VTEC valve train, the engine's powerband is exceptionally broad. Peak horsepower (200 hp @ 5500 rpm) and peak torque (195 lb.-ft. @ 4700 rpm) are both up by 18%. In addition, the torque curve remains within 90% of its peak figure, from 2,000 to 6,000 rpm. Zero-to-60-mph acceleration for the V-6 Sedan is around 8 seconds. Estimated fuel economy is expected to be around 20 mpg/city and 28 mpg/hwy.
Overall engine friction contributes about 4% to the Accord V-6's fuel economy.
Noise and vibration have also been reduced, thanks to the engine's rigid cylinder block, cast-aluminum oil pan, short crankshaft, hydraulic engine mount and rubber-isolated subframe.
2.3-LITER VTEC ENGINE
The 2.3-liter, 4-cylinder Accord engine has been engineered to meet the goals of more power, greater noise and vibration reduction, and lower emissions. Horsepower and torque figures for the engine are 150 hp @ 5700 rpm and 152 lb.-ft. @ 4900 rpm for the LX and EX models (ULEV EX is 148 hp). The DX model's engine produces 135 hp @ 5400 rpm and 145 lb.-ft. torque @ 4700 rpm for the DX model.
Acceleration (0-60) for the 4-cylinder models is improved (around the mid-9-second mark), with comparable fuel efficiency to its predecessor: 23 mpg/city and 30 mpg/hwy for LX and EX models with automatic transmissions.
Emissions of Non-Methane Organic Gases (NMOG), also known as unburned hydrocarbons, produced during engine warm-up are considerably lower. The LX and EX engines produce less than 0.0075 grams per mile, qualifying them for California LEV (Low-Emission Vehicle) status. In California, the Accord EX with the available automatic transmission will produce less than 0.003 grams per mile of NMOG, qualifying it as the first gasoline-powered vehicle to reach ULEV (Ultra-Low Emission Vehicle) status.
The five-main bearing block is high-pressure die-cast from aluminum alloy. The walls of the block extend below the centerline of the crankshaft, which helps stiffen the bottom end. FEM (Finite Element Method) computer analysis was used to arrive at optimum thicknesses for the block ribs and walls in order to minimize engine vibration.
Additional bottom-end rigidity comes from a larger, stronger bearing-cap beam that ties directly into the cylinder-block skirt.
An aluminum-alloy stiffener has been added between the transmission case and the block, just behind the bearing carrier. The stiffener serves to tie the block and transmission together into a single, reinforced unit. FEM was also used to design this stiffener so that it would not only stiffen the area, but also help minimize high-frequency engine vibration.
Finite-element analysis of the Accord's piston design by Honda engineers yielded a new ultra-short, lightweight skirt design, which is very rigid and resistant to vibration and piston slap. Like the V-6 engine the pistons are gravity-cast aluminum alloy and utilize full-floating wrist pins in order to minimize noise.
The engine's drop-forged single-plane steel crankshaft and connecting rods have been designed to be stronger and operate with less friction, much like the V-6 components.
The I-section, drop-forged steel connecting rods have a completely new design and are considerably lighter than their predecessors (475 g vs. 578 g), which helps to minimize vibration. Pin-journal (big end-bearing journal) diameter has been reduced from 48 mm to 45 mm. Rod thickness is down from 24 mm to 20 mm and the bolt size is smaller. Like the V-6 rod bolts, those of the 4-cylinder engine are torqued to the plastic region of the bolt material in order to ensure a solid union between the bearing cap and the connecting rod.
The engine block incorporates the Honda-designed second-order balance system that cancels the inertial forces common to large-displacement 4-cylinder engines. The system consists of two parallel shafts on either side of the crank-shaft, 81 mm (3.19 in.) above its centerline. Driven by a toothed belt, the balance shafts rotate in opposite directions at twice engine speed. Eccentric weights built into the shafts generate inertial forces that counteract the second-order forces created by the motion of the pistons and connecting rods. This Honda system minimizes vibration in the mid-to-high-rpm range.
The 16-valve, single-overhead-camshaft cylinder head features 4 valves per cylinder and pentroof combustion chambers. Individual valves are smaller and lighter in 4-valve heads, which allows the engine to be revved to a higher rpm, helping to extend the engine's power range. Valve actuation is via rocker arms and a hollow, belt-driven single overhead camshaft. The single-over-head-camshaft design requires less under-hood space than the more conventional dual overhead camshafts normally used with 16-valve, 4-cylinder engines.
The adoption of a sophisticated knock control system optimizes ignition timing and allows for a higher compression ratio (9.3:1 from 8.8:1). Unleaded regular fuel is specified.
REVISED INTAKE SYSTEM
The intake system was simplified in shape to reduce induction resistance and noise. A larger twin-chambered air box designed to dampen resonant intake tract noise replaces the previous Accord's smaller, single-chamber damper. The new box is 10.7 liters in capacity, compared to the older unit's 8.2 liters. The larger box also elimi-nates the need for a second resonant-frequency damper and an additional side branch
The 2.3-liter Accord 4-cylinder engine intake manifold has been redesigned to add more power and lower emissions. The individual cast-aluminum runners have revised dimensions to better take advantage of the different air-flow characteristics of the 2.3-liter engine. A larger plenum chamber reduces induction noise and the incorporation of EGR (Exhaust Gas Recirculation) ports into the plenum, upstream of the throttle plates, eliminates the need for a separate fitting and port in each intake runner.
V-6 AND 4-CYLINDER VTEC
Accord LX and EX engines (both 4-cylinder and V-6 models) utilize VTEC (VTEC stands for Honda Variable valve Timing and valve Lift Electronic Control system). The VTEC system helps these engines achieve their low emissions and broad torque curves.
During low-rpm operation, only one intake valve opens, allowing air and fuel into the combustion chamber. The other intake valve has only a slight amount of lift and its timing is staggered. As a result, the air-fuel charge drawn through the open intake valve undergoes a swirl effect. The swirl creates a stratified charge with a rich mixture near the spark plug (for good light-off), and a progressively leaner mixture toward its periphery. This stratified charge, combined with improved EGR control, results in lower emissions (especially during the critical warm-up period) and better fuel economy. Low-friction, roller-bearing rocker arms are used to help reduce friction and improve engine efficiency
Between 2300 and 3900 rpm (depending on manifold pressure) in the 4-cylinder engine, and at 3500 rpm in the V-6, the intake valve timing switches to a high-performance mode. The two intake-valve rocker arms are locked to a third rocker arm and cam follower located between them, via an electronically con-trolled, hydraulically actuated locking pin. Until now, this third rocker arm has been independently following the contour of a high-lift, long-duration camlobe. The two intake rocker arms are now actuated by this third rocker arm and a cam timing that more closely matches the intake-tract timing required for optimum torque at high engine speeds. The result is a broader, flatter torque curve, low emissions and smoother power delivery throughout the engine's entire speed range.
|6-CYLINDER VTEC ENGINE VALVE OPERATION|
|Valve Opens||24* ATDC||30* ATDC||5* ATDC||35* BBBC|
|Valve Closes||25* ABDC||72* BBDC||40* ABDC||15* BTDC|
|Lift||7.5mm||1.8mm||10.0 mm||9.5 mm|
|4-CYLINDER VTEC ENGINE VALVE OPERATION|
|Valve Opens||24* ATDC||26* ATDC||0* TDC||30* BBBC|
|Valve Closes||23* ABDC||76* BBDC||36* ABDC||15* BTDC|
|Lift||7.0mm||1.8mm||10.0 mm||9.0 mm|
AIR-ASSIST FUEL INJECTORS
Thorough atomization is critical for complete combustion. The smaller the fuel droplet size, the more effectively it mixes with the air, resulting in more efficient combustion. In order to improve fuel atomization, the Accord 4-cylinder and V-6 VTEC engines use an air-assist fuel-injector system.
MULTI-POINT PROGRAMMED FUEL INJECTION
The V-6 and 4-cylinder Accord engines use Honda Multi-Point Programmed Fuel Injection (PGM-FI). PGM-FI uses a new 16-bit powertrain control module (PCM), connected to sensors that monitor throttle position, engine temperature, cylinder~firing position, intake manifold pressure, atmospheric pressure, exhaust-gas oxygen content and intake air temperature. The PCM uses this information to determine the fuel requirements of the engine. It then activates each fuel injector at precisely the right moment. The result is outstanding driveability and power, with reduced emissions and better fuel economy
An additional advantage of PGM-FI is easier maintenance and repair. The PCM can sense when something is wrong with various parts of the system and flash a trouble code, which will tell a technician where the problem is located.
ELECTRICALLY CONTROLLED EGR
Both the V-6 and 4-cylinder engines use electrically controlled exhaust-gas recirculation valves, in place of the older vacuum-operated type. The new valve's rapid response and increased accuracy allows for more precise EGR control.