HEADLINES

1999 Acura CL- Powertrain

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 Acura V-6 produced in America, and the first mass-produced V-6 built anywhere to incorporate Variable Valve Timing and Lift Electronic Control (VTEC).

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 exhaustoperated 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 lb ft at 4800 rpm) and is among the highest horsepower output in its class (200 horsepower at 5600 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 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, 3.2TL touring luxury sedan and the 2.3CL also run for 100,000 miles before their first scheduled tune-up.)

As the first of a series of V-6 powerplants, the 3.0CL's engine incorporates the 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 high levels of shift smoothness and efficiency. In addition, all CL models use a single powertrain control module (PCM) to control all engine and transmission functions, including the electronic immobilizer feature.

3.0 CL 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, 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 compact fore and aft packaging and the 60-degree angle's subdued vibration level.

The pressure-cast, heat-treated aluminum block uses cast iron cylinder sleeves, set at a narrow 98 mm 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 86 mm, for a total displacement of 2997 cc.

3.0 CL 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-generationAcura Legend (19 mm in the CL, 22 mm in the Legend 2.7-liter V-6). The CL V-6 rod journals are slightly smaller in diameter too (56 mm in the CL, and 57 mm 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 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 485.5 mm (as transversely installed in the car). That makes the 3.0CL powerplant narrower than the 3.0-liter V-6's 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 55 mm shorter in overall height than the current Infiniti 130V-6 and about 80 mm narrower (as viewed from the side, installed in the car) than the Lexus ES 300 V-6.

3.0 CL - The Lightest V-6 Engine In Its Class

The light weight of the Acura V-6 is a key contributor to the CL's exceptional handling, responsiveness and excellent fuel economy. The 3.0CL engine is more than 15 pounds lighter than the ES 300 and 130 powerplants. That lightness didn't come at the cost of strength. The CL V-6 has a main-bearingcap 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 and rigidity while reducing weight.

3.0 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 state-of-the-art 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 reciprocatingvalve-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 its 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 operated by a glass-fiber reinforced toothed belt that is driven by the crankshaft. An automatic tensioner compensates for belt stress fluctuation.

3.0 CL VTEC System

Keys to the 3.0CL's class-leading performance are its Variable Valve Timing and Lift Electronic Control (VTEC) 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 Ib ft of torque at 4700 rpm. More telling of the powerplant's usable response is the fact that it produces in excess of 150 Ib ft of torque from 1000 rpm through 6000 rpm-a broad 5000-rpm-wideband 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 bum 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 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 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 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.

From a driver's standpoint, the 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 transmission take advantage of more complex and sophisticated clutch control logic than previous transmissions. The result is a higher 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.

2.3CL Engine Block/Balancer

Like all other Acura engines, the engine block of the 2.3CL inline four-cylinder is an aluminum pressure casting with cast-iron liners, a design known for its light weight, high rigidity, and excellent long-term durability. The block is designed with a deep skirt and extensive webbing, adding rigidity and reducing engine noise and vibration. Additional bottom-end rigidity comes from a larger bearing-cap beam.

The engine block incorporates a 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 crankshaft, 81 mm (3.19 in) above its centerline. Driven by a toothed belt, the balance shafts rotate in opposite directions at twice the 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 system differs from other balancing systems in that it is designed to minimize vibration in the mid-to-high-rpm range, as this is the area where the engine operates much of the time.

2.3CL Crankshaft/Connecting Rods/Pistons

With an 86 mm bore and 97 mm stroke, the 2.3CL engine displacement is 2254 cc and utilizes an undersquare design to boost low rpm torque. The 2.3CL engine features lightweight gravity-cast aluminum alloy pistons with a highly rigid, ultra short skirt design and full floating wrist pins to minimize friction and reduce noise.

The engine's drop-forged single-plane steel crankshaftand connecting rods have been designed to be strong, lightweight and operate with less friction, much like the V-6 components. The I-section, drop-forged steel connecting rods are very light at only 475 grams, to help minimize vibration. To reduce friction, connecting rod journal diameter is only 45 mm and rod thickness has been kept to only 20 mm, without sacrificing strength or reliability. 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.

2.3 CL Cylinder Head/Valvetrain

The 2.3CL engine's cylinder head is pressure cast in aluminum, for light weight, increased accuracy and improved breathing due to more precisely formed ports and runners. The head features a 4-valve-per-cylinder valvetrain with pent-roof combustion chambers. Each valve is smaller and lighter than the valves in a 2-valve combustion chamber and therefore has less reciprocating mass. This allows the engine to be revved to a higher rpm, helping to extend the engine's power range. Two intake and two exhaust valves also have greater valve area than comparable two-valve designs, so engine volumetric efficiency improves. Valve actuation is via rocker arms and a hollow single-overhead camshaft, driven by a glass-fiber reinforced toothed belt. The compression ratio is 9.3:1. Unleaded regular fuel is specified.

2.3 CL VTEC System

For a superior blend of power, torque and fuel economy, the 2.3CL engine utilizes the innovative Variable Valve Timing and Lift Electronic Control (VTEC) system.

At low rpm, the intake valves of the engine follow a set of low-lift, short-duration cam lobes with timing that optimizes cylinder filling at low engine speeds. To ensure complete and rapid combustion, the timing of the intake valves is staggered and their lift is asymmetric, creating a swirl effect within the combustion chamber. This concentrates a richer fuel mixture near the spark plug for efficient combustion.

At engine speeds above 2300-3200 rpm (depending on engine load), the intake rocker arms are actuated by a high-lift, long-duration cam lobe designed to optimize high-rpm output. The result is an extremely efficient engine with a broader, flatter torque curve and smooth power delivery throughout the engine's operating range.

2.3 CL Induction System

The 2.3CL intake manifold has been designed to increase power and lower emissions. The individual cast-aluminum runners have been tuned to take advantage of the air-flow characteristics of the 2.3-liter engine.

The tuned air intake features a large twin-chambered air box to dampen intake tract noise by as much as 5 db.

2.3 CL Programmed Fuel Injection (PGM-FI)

Fueling the 2.3CL engine is a Programmed Fuel Injection (PGM-FI) system. PGM-FI uses a 16-bit microprocessor that monitors throttle position, engine temperature, cylinder firing position, intake manifold pressure, atmospheric pressure, exhaust gas oxygen content and intake air temperature. On the basis of these measurements, the microprocessor meters fuel at the correct fuel-air ratio for the best balance of drivability, power, fuel economy and exhaust emissions under each operating condition. It then activates each fuel injector at precisely the right moment. To improve fuel atomization, the engine also uses an air-assist fuel-injector system.

Exhaust System

The CL Series exhaust system was designed to offer minimal noise and vibration, light weight and excellent emissions control. The exhaust manifold uses thin-wall iron casting technology for weight savings. Optimized bracketry and rubber mountings reduce low-frequency vibrations and strengthen the system against impact damage.

Five-Speed Manual Transmission

A five-speed manual transmission is standard on the 2.3CL. In addition to gear ratios matched to the output of the 2.3-liter four-cylinder engine, the 5-speed manual transmission features a double-cone synchromesh second gear for improved shifting smoothness and feel. The cable operated 5-speed also utilizes a relatively small diameter friction disk to help reduce shift effort. The wear resistant friction material also improves clutch feel and helps prevent judder.

4-Speed Automatic Transmission

Like the 3.0CL, the 2.3CL benefits from a direct-control automatic transmission. The transmission shifts precisely with reduced shift shock, is compact and lightweight.

The automatic is constant-mesh type, with three parallel shafts: input intermediate and output. Shift management is controlled by a 16-bit micoprocessor operating two linear-shift solenoids. Since the control is linear, clutch engagement is more progressive than in other transmission. The result is smoother shifting under all conditions, whatever the driving style.

To increase fuel mileage, the lock-up torque converter helps minimize fluid-coupling slippage by mechanically coupling the engine to the transmission during certain driving models, such as steady-state cruising. The lockup feature works in third and fourth gears and also maintains lockup in third and fourth gears during deceleration. The design also reduces vibration and judder during engagement in addition to increasing efficiency.

Grade Logic Control System

The Grade Logic Control System is designed to minimize gear hunting on uphill and downhill driving, and to enhance engine-braking when traveling downhill. Drawing upon information supplied by the throttle-angel sensor and 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. Based on this information, Grade Logic Control modifies the shift schedule to hold the transmission in a lower gear for better uphill response or downhill engine braking. This system reduces gear hunting and reduces unnecessary shifting by as much as 50 percent, producing a more refined driving experience.

100,000-Mile Scheduled Maintenance Intervals

A reflection of the quality built into the powerplants, the engine's first scheduled tune-up occurs at 100,000 miles. During that time, only routine inspections and fluid changes are required. Auto-tensioning mechanisms compensate for any belt stress fluctuation on the accessory drive belt and the toothed cam-drive belt. The roller-follower design of the valve gear cuts friction and wear to the point that that the screw-type tappet clearance adjusters needn't be checked until the 100,000-mile mark. Long-wearing platinum-tipped spark plugs are scheduled for replacement at 100,000 miles. The CL engines represent two of the four Acura engines that require no scheduled tune-up for the first 100,000 miles.

Hydraulic Engine Mount

To minimize engine vibration both at idle and at high engine speeds, the engineers developed a special electronically controlled hydraulic engine mount for CL models equipped with the 4-speed automatic transmission. The mount features an exterior valve and two chambers filled with fluid. The chambers share the same hydraulic fluid by means of two sets of orifices--one large and one small.

At idle, the large set of orifices is used, allowing fluid to flow smoothly between the chambers. Above idle speeds, a signal is sent to the valve, which then engages the smaller set of orifices. Changing the orifices alters the resonant frequency of the engine mount and damps out excessive vibrations. The different vibration characteristics of the inline 4-cylinder engine equipped with the 5-speed manual transmission allows the use of a more conventional hydraulic engine mount.

Direct-Acting Cruise Control

For superior performance and smoothness, the CL uses a direct-acting cruise control system. When the cruise control is activated, a lost motion mechanism frees the throttle wire, allowing the throttle to be opened and closed without the friction of accelerator pedal movement. The system also helps reduce "hunting" when holding a preset speed. The convenient wheel mounted cruise control buttons allow the driver to tap-up or tap-down in 1 mph increments, in addition to normal functions.

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