3.0 CL OVERVIEW
The 3.0CL is powered by a state-of-the-art, transversely
mounted,
single-overhead camshaft, all-aluminum 3.0-liter V-6 engine
created
jointly in the United States and Japan. The engine is built
exclusively at the Anna Engine Plant in Anna, Ohio, for worldwide
consumption. It's the first V-6 Acura has produced in America,
and
the first mass-produced V-6 built anywhere to incorporate VTEC
(Variable Valve Timing and Lift Electronic Control). The only other
current VTEC V-6 engine powers the limited-production Acura
NSX
sports car.
Typical of all Acura engines, the 3.0CL engine uses a cast aluminum cylinder block for lightness with cast iron cylinder liners for longevity. Employing the latest VTEC architecture, the engine has four valves per cylinder-two intake, two exhaust- operated by a single overhead camshaft (SOHC) per cylinder bank via friction-reducing roller followers. The lightweight, compact powerplant delivers a broad and full torque band (peaking at 195 pound feet at 4700 rpm) and the highest horsepower output in its class (200 horsepower at 5500 rpm). The 3.0CL achieves outstanding acceleration, and among the highest combined fuel economy of any competitive car using regular unleaded fuel. Programmed Fuel Injection (PGM-FI) handles fuel delivery, and is monitored by an OBD-II on-board diagnostic system. Consistent with Acura's tradition of engine design excellence the CL's new V-6 is designed to run for 100,000 miles before its first scheduled tune-up. (Likewise, the V-6 engines found in the Acura 3.5RL flagship luxury sedan, and 3.2TL touring luxury sedan, SLX luxury SUV and the 2.3CL also run for 100,000 miles before their first scheduled tune-up.)
As the first of a new series of V-6 powerplants, the 3.0CL's engine incorporates Acura's latest technology, which makes it physically the smallest and lightest in its displacement range. Additionally, its 60-degree V-angle, coupled with careful detail engineering, results in NVH characteristics that are among the best in class. It is paired with an advanced electronically controlled four-speed automatic transmission that attains new levels of shift smoothness and efficiency. For 1998, all CL models use a single powertrain control module (PCM) to control all engine and transmission functions, including the new immobilizer feature.
3.0CL ENGINE BLOCK
Key targets in the design of the 3.0CL powerplant were the
pursuit of
substantial weight savings and greater packaging efficiencies
relative to competitive V-6 engines. Working with a clean slate,
Acura engineers enjoyed wide design latitude. Though previous
Acura
V-6 engines have been a 90-degree configuration, the design
team felt
that a
60-degree angle was the best choice for the CL powerplant, given the car's snug fore and aft packaging constraints and the 60-degree angle's subdued vibration level.
The pressure-cast, heat-treated aluminum block uses cast iron cylinder sleeves, set at an unusually narrow 98mm bore-pitch (the distance between the cylinder bore centerlines, measured parallel to the crankshaft) to keep the transversely-mounted engine as narrow as possible. Bore and stroke are "square," each measuring out at 86mm, for a total displacement of 2997cc.
3.0CL CRANKSHAFT/CONNECTING RODS
The pursuit of lightweight, compact design mandated special
care in
crankshaft and connecting rod engineering. The 3.0CL engine
actually
has narrower connecting rods than the smaller V-6 that powered
the
first-generation Acura Legend (19mm in the CL, 22mm in the
Legend
2.7-liter V-6). The CL V-6 rod journals are slightly smaller in
diameter too (56mm in the CL, and 57mm in the Legend V-6).
The CL's
rods don't use conventional nut-and-bolt type fasteners, but
instead
employ lightweight bolts which thread directly into the connecting
rod. These bolts are designed to operate in the plastic, not
elastic,
region of the steel material, unlike conventional fasteners. This
allows the CL's downsized rod bolts to maintain relatively greater
clamping force, and handle operating stresses with normal
strength
margins. The CL also uses a special dual-mode crankshaft
damper
pulley to further cut overall engine width to just 485.5mm (as
transversely installed in the car). That makes the 3.0CL
powerplant
narrower than the 3.0-liter V-6s from either Infiniti or Lexus.
Minimizing overall engine height was also a top priority. With special compact pistons, cylinder deck height was kept to a minimum, and a special multi-part intake manifold allowed for the proper tuned runner length without compromising packaging. The result is an engine that is about 55mm shorter in overall height than the current Infiniti I30 V-6 and about 80mm narrower (as viewed from the side, installed in the car) than the Lexus ES 300 V-6.
3.0CL - THE LIGHTEST V-6 ENGINE IN ITS CLASS
The light weight of the new Acura V-6 is a key contributor to the
CL's exceptional handling, responsiveness and excellent fuel
economy.
The 3.0 CL engine is more than 15 pounds lighter than the ES
300 and
I30 powerplants. This, while producing more peak power than
either.
That lightness didn't come at the cost of strength. The CL V-6
has a
main-bearing cap that's constructed of a sintered powdered
metal
material for strength and accuracy, and it bolts in place between
deep skirts that lend stiffness to the block. The oil pan is made
from aluminum alloy instead of stamped steel, to further
increase
strength.
3.0CL CYLINDER HEAD/VALVE TRAIN
Pressure cast of aluminum alloy, the 3.0CL'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 sides, instead of being clamped in place
from
above with bolt-down caps.
The combustion chamber design is an evolutionary refinement of Acura technology, with four valves in each pent-roof combustion chamber. The 9.4:1 compression ratio allows the engine to operate on regular unleaded fuel.
The four-valve-per-cylinder design offers several advantages over two-valve arrangements, most notably reduced reciprocating valve-train 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 two-valve systems, resulting in improved air flow. Remarkably, the 3.0CL achieves greater peak horsepower, and competitive fuel economy with other engines in class, and meets California's strict TLEV (Transitional Low Emission Vehicle) standards-all while burning regular unleaded fuel.
The 3.0CL'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 that is driven by the crankshaft. An automatic tensioner compensates for belt stress fluctuation.
3.0CL VTEC SYSTEM
Keys to the 3.0CL's class-leading performance are its VTEC
(Variable
Valve Timing and Lift Electronic Control) cylinder heads. By
automatically altering the intake valve opening lift and duration
based on engine rpm, the engine can develop strong low speed
torque
without sacrificing high rpm power. Conventional fixed intake
valve
timing can't equal this broad-range flexibility. At its peak, the
3.0CL powerplant generates a substantial 195-pound-feet of
torque at
4800 rpm. More telling of the powerplant's usable response is
the
fact that it produces in excess of 150 pound-feet of torque from
1000
rpm through 6000 rpm-a broad 5000-rpm-wide band of
immediately
accessible power.
At low rpm, the VTEC intake valves follow a set of low-lift, short-duration cam lobes with timing that optimizes cylinder filling at low engine speeds. Additionally, the timing of the intake valves is staggered and their lift is asymmetric, creating a swirl effect within the combustion chambers. This increases burn speed, and improves combustion stability and EGR rate.
At 3500 rpm, the intake rocker arms transition to actuation by high-lift, long-duration cam lobes designed to optimize high-rpm output. The surprising flexibility of the 3.0CL's power characteristics, and the unique transformation of the engine note as the revs rise gives the 3.0CL a sporty character-without sacrificing a bit of day to day livability. Engineers at HRA-Ohio purposely tuned the intake sound to accentuate the dual nature of the engine-quiet for everyday driving at low rpm, with a pleasantly aggressive engine note that develops as the VTEC's high speed valve timing kicks in.
The 3.0CL engine's VTEC system benefits from U.S.-sourced components like the lost motion pistons that keeps the high lift rocker in check during low-rpm operation. Engineers at U.S.-supplier Eaton Corporation were able to come up with a much simpler design for the assembly. A further refinement, the engine has just one VTEC spool valve controller to handle hydraulic pressure switching for both cylinder banks-a job that in the past has required two controllers, along with their attendant weight and complexity.
3.0CL INDUCTION SYSTEM/PGM-FI
Intake tuning is critical to an engine's power characteristics.
Unfortunately, the conflicting requirements for intake runner
length
versus tight packaging make the intake manifold a complex
assembly on
the modern automobile. Additionally, since it ties the two cylinder
banks together, the manifold can impart unwanted stresses to
the
cylinder bores and crankshaft journals in the course of normal
thermal expansion. To avoid this problem the 3.0CL uses a four
piece,
built-up cast-aluminum manifold.
3.0CL NOISE, VIBRATION AND HARSHNESS
CONTROL
During the development of the 3.0CL powerplant, key competitive
engines were used to develop engineering targets for
smoothness and
noise control. The pursuit of subdued NVH (Noise, Vibration and
Harshness) runs right to the core of the new Acura V-6 engine.
Its
rigid cylinder block assembly has a high resonant frequency,
significantly higher (stiffer) than the quietest and smoothest
competitive V-6 engine. Point by point through the Acura V-6's
development, components were reviewed in an effort to
eliminate noise
and vibration at its source. As an example of this ongoing effort,
the acceptable variation in piston weight was tightened by
40-percent, and the range of connecting-rod-weight variation
narrowed
by 60-percent relative to previous Acura engines. With features
like
a highly rigid forged crankshaft, tight internal component
tolerances
and assembly clearances, die-cast accessory mounts, a stiff
cast
aluminum oil pan and many other features, the engine achieves
best-in-class performance in key measures of NVH.
3.0CL 4-SPEED AUTOMATIC TRANSMISSION
To complement the V-6 engine, a brand new four-speed
automatic
transmission was developed. With the focus placed on netting a
substantial improvement in shift quality under all circumstances,
the
transmission benefits from intelligent computerized control that
orchestrates torque converter lock-up, grade logic and clutch
pressure. The PCM monitors a variety of operating conditions
including throttle angle, coolant temperature, vehicle speed and
engine speed.
3.0CL DIRECT CONTROL TRANSMISSION
TECHNOLOGY
An advanced system called Direct Control employs linear
solenoids to
provide precise, real time control of the clutch on/off pressure in
the 3.0CL's four-speed automatic transmission. The system's
superior
clutch engagement accuracy allows the transmission to use
sophisticated logic to smooth operation under all conditions.
Working
in concert with this new system is a canceler mechanism built
into
the first and second gear clutches that "cancels" out the
detrimental
effects of rising fluid pressure caused by centrifugal force. This
fosters more precise clutch control. Another advancement: The
single
Direct Control first gear clutch is now able to modulate engine
braking forces along with acceleration forces, which has allowed
the
elimination of the first-gear one-way clutch used in conventional
designs. Its deletion has resulted in a weight savings of over five
pounds.
From a driver's standpoint, the new transmission is most notable for what it doesn't do. It doesn't impart driveline shock during upshifts, and it doesn't create the sensation of momentary hesitation (or split-second deceleration) during downshifts under power. Precise, real-time control of the clutches via linear solenoids lets the 3.0CL transmission take advantage of more complex and sophisticated clutch control logic than previous transmissions. The result is a new level of smoothness and refinement.
3.0CL GRADE LOGIC CONTROL SYSTEM
With its Grade Logic Control System, the 3.0CL "knows" when
it's on a
hill. By comparing throttle angle to vehicle speed, the Grade
Logic
Control System can determine the slope of a hill by comparing
this
information with a map stored in the engine computer. The shift
schedule is then automatically adjusted accordingly to hold the
engine in a lower gear for better climbing power or downhill
engine
braking.