1990 Honda Accord -- Drivetrain

OVERVIEW/DESIGN OBJECTIVES
The 1990 Honda Accord's 2.2 liter, fuel-injected, 16-valve engine is an entirely new design. It has more horsepower and torque for improved performance, and incorporates innovative Honda technology that allows it to run smoothly and quietly.

The engine's high output is due, in part, to its increased displacement This is a dependable method of raising power but it presents significant design challenges in four-cylinder, in-line engines because of an inherent imbalance that causes vibrations to increase as displacement increases. To counteract these tendencies, Honda engineers pursued several strategies, including the design of an efficient secondary balancer system that differs conceptually from other designs based on the same principle.

To complement the engine's power curves and increased output, both automatic and manual transmission are newly designed. The automatic is based on a compact, three-shaft configuration. It is electronically controlled with a lockup torque converter and a Sport mode for spirited driving. The 5-speed manual transmission has been redesigned to increase rigidity and strength, and reduce noise and vibration.

The Accord's front-wheel-drive system is also redesigned in consideration of the engine's greater power and the car's larger size.

ENGINE
The Accord's new 2.2 liter in-line, fuel-injected, four-cylinder engine uses a single overhead camshaft and four valves per cylinder. It is compact and light weight with an aluminum block and cylinder head. The engine is transversely located and angled 10 degrees to the rear (as opposed to 15 degrees to the front in the 1989 Accord) for improved weight distribution and better under-hood packaging.

Though the engine is an undersquare design-with an 85 mm (3.35 in.) bore and a 95 mm (3.74 in.) stroke-its bore is relatively large, which permits the use of larger intake and exhaust valves. The engine's cam timing, induction and ignition systems are tuned to produce a steep, smooth horsepower curve with a wide torque band.

Among the engine's key features are a Honda-developed secondary balancer system that substantially reduces vibration, a tuned intake manifold with Multi-Point, Programmed Fuel Injection (PGM-Fl), and a fully electronic ignition system. A three-way catalyst provides emission control.

The output of the engine in Accord DX and LX models is 125 horsepower at 5200 rpm and 136.7 lb-ft. of torque at 4000 rpm. The engine in EX models is rated at 130 horsepower at 5200 rpm and 141.8 lb.-ft. of torque at 4000 rpm. The difference is attributable to the EX's four-into-two exhaust manifold and dual exhaust system, otherwise the engines are nearly identical.

SECONDARY BALANCER SYSTEM
To meet the power and performance criteria set for the new Accord, while improving its comfort and drivability, Honda engineers designed a secondary balancer system that significantly reduces vibration. It incorporates two unbalanced shafts turning in opposite directions at twice the crankshaft speed to dampen inertial forces.

The balance shafts are supported by three bearings and are crankshaft-driven by a toothed belt. A small gearbox is used to reverse the direction of the shaft that spins opposite the crankshaft. Both shafts are timed to rotate so that their imbalance is in direct opposition to the inertial forces created by the movement of the pistons and connecting rods. The two forces cancel each other, and the vibration level is cut to as much as one-tenth of what it would be without balance shafts.

The key difference between the Honda-designed system and other balance shaft layouts is the placement of the shafts. In most other systems the shafts are offset-the one that rotates in the same direction as the crankshaft is on a higher plane than the other shaft. Honda's design places the shafts on the same plane, 81 mm (3.19 in.) above the horizontal crankshaft centerline. The location of these shafts relative to each other determines the rpm range in which they are most effective. In other systems, this is the high-rpm range; in the Honda system it is in the mid- to high-range where most normal driving occurs.

ELECTRONICALLY CONTROLLED ENGINE MOUNT
In Accords equipped with automatic transmissions, a dual phase, electronically controlled rear engine mount smooths low-frequency vibration which can occur under high-load, low engine speed conditions, such as idling in gear with the air conditioner running.

The mount contains two fluid-filled chambers separated by a barrel valve. At low engine speeds, the valve is open so the full volume of both chambers can dampen the vibration. At 850 rpm, sensed by a computer which monitors ignition pulse, the valve is closed by a vacuum actuator, which takes one chamber out of the loop and makes the mount firmer.

ENGINE BLOCK
The cylinder block is die-cast aluminum alloy with integral cast iron cylinders. It saves 12.0 kg. (26.4 lbs.) versus the 1989 Accord's cast iron block. For added rigidity, it has a deep skirt which extends 50 mm (1.96 in.) below the crankshaft center line.

This block has the largest bore of any Honda 4-cylinder engine to date-85 mm (3.35 in.)-and a 95 mm (3.74 in.) stroke for a displacement of 2156cc (131.6 cu. in.). It uses five main bearings to support a forged steel crankshaft which carries forged steel connecting rods and forged aluminum pistons.

Mounting points for crank-driven components are on the front-facing side of the block which improves both under-hood packaging and maintenance access.

Particular attention was paid to reducing inertial mass and improving the vibration damping characteristics of rotating components by redesigning the torsional damper and pulleys for the camshaft and accessory drives.

CYLINDER HEAD
The Accord's engine uses an aluminum cylinder head with a flow-through design, large intake and exhaust ports, single overhead camshaft, and four valves-two intake and two exhaust-per cylinder. Its combustion chamber is of the highly efficient hemispherical design, modified to a pent roof shape. The compression is 8.8:1 and the chamber has a centrally located spark plug for even flame propagation.

The engine's increased bore permits the use of large valves- 34 mm (1.338 in.) intake and 29 mm (1.141 in.) exhaust-which further increase power and torque. By comparison, the new engine has 13.7 percent more intake valve area, and 19.0 percent more exhaust valve area than the three-valve 1989 Accord engine, even though it is only 9 percent larger in displacement.

The valves are at an included angle of 51 degrees and are actuated by forged steel rocker arms that pivot on two shafts located on each side of the camshaft, which is driven by a toothed belt.

INDUCTION SYSTEM
To raise low- and mid-range torque, the Accord's intake manifold uses long-430 mm (16.9 in.)-equal-length runners to increase intake velocity and pack a denser fuel/air charge into the combustion chamber. It is tuned to complement Honda's Multi-Point Programmed Fuel Injection (PGM-FI) system, which uses a microprocessor to control the fuel/air ratio and injection timing.

1990 ACCORD DRIVE TRAIN
The microprocessor monitors seven engine functions: throttle angle, crankshaft angle, coolant temperature, intake air temperature, manifold air pressure, atmospheric pressure, and exhaust gas oxygen content. It analyzes this information and continuously adjusts the injection system to maintain the optimum fuel/air ratio.

To reduce noise, the induction system has a two-stage air pre-induction system with two ducts connecting the air cleaner to the manifold. Since less air is required at low rpm, only one duct is open, keeping the air flow noise to a minimum. As engine speed increases, the second duct opens. Whatever additional noise this may create is not apparent to the driver because of the higher ambient noise levels that normally occur as engine speed increases.

IGNITION SYSTEM
The Accord's fully electronic ignition system is contained entirely within the distributor. This single, compact unit includes the coil and eliminates the wiring necessary with separate components. It is lighter, more space efficient and has fewer connections, which improves the system's reliability.

ELECTRONIC ENGINE MANAGEMENT SYSTEMS
The Accord uses two ECUs (Electronic Control Units), one for the engine and one for the automatic transmission. The engine ECU monitors sensors which read water temperature, air temperature, throttle position, exhaust oxygen, engine speed, air pressure, manifold pressure, top dead center and crankshaft angle. It processes this information and adjusts the air-fuel ratio, injection and ignition timing for the best possible efficiency and performance.

The automatic transmission ECU is programmed to control shift points and lockup according to the shift position and driving conditions.

MANUAL TRANSMISSION
The 1990 Accord has a new 5-speed manual transmission that's more rigid and durable to match the engine's increased power and torque. It has been refined to improve drivability and reduce noise and harshness. This was done by optimizing gear dimensions, improving the resonance characteristics of the housing, and using more precise parts manufacturing and assembly.

A spring-dampened clutch is actuated hydraulically and the shift mechanism is designed for short throws and positive engagement.

AUTOMATIC TRANSMISSION
The Accord's 4-speed automatic transmission is a new design that's compact, smooth-shifting and efficient. It is computer controlled and has a driver-selectable Sport mode, lockup torque converter and seven shift positions: Park, Reverse, Neutral, D4 and D3 with Sport mode, Second and First (Low-Hold).

Unlike most conventional transmissions, it uses three parallel axis shafts-a main shaft, a counter shaft and an additional secondary shaft-instead of two shafts. The unit is barely larger than a normal transmission (it is just 2 mm longer than the 1989 two-shaft automatic) yet permits the use of a fifth clutch so the transmission can be held in low gear until the driver moves the shift lever. This "low-hold" feature is useful when low-speed power or engine braking is needed, as when pulling a boat trailer out of the water or descending very steep inclines.

To improve efficiency, the new transmission has a lockup torque converter that engages in second, third and fourth gear when maintaining steady speeds, and third and fourth to provide engine braking when decelerating.

For smoother shifts, the transmission ECU signals the engine ECU to retard the spark between shifts, momentarily lowering engine torque, so that gear-change shock is reduced. For smoothing the upshift from third to fourth, and downshifts from fourth to third or second, there's an accumulator control system in the shift valve that maintains steadier hydraulic pressure and makes the shifts less abrupt.

The driver-selectable Sport mode is designed for sporty performance at partial throttle levels. With the shift lever in the D3 position, pushing the Sport mode switch on the shifter directs the transmission to shift at higher rpm points when going from first to second and second to third. Using Sport mode in the D4 position extends the function to the third-to-fourth shift. The Sport mode increases responsiveness and is useful on long grades to keep the transmission from "hunting" for gear ratios.

FRONT-WHEEL DRIVE
As with the engine and transmission, the Accord's drive components have been redesigned to complement its increased size and power. Also, important changes were made in the drive system geometry. Because the layouts of the new automatic and manual transmissions place the inboard constant velocity joints lower, the angle between the inboard and outboard joints is decreased, which helps to reduce torque steer.

Accords equipped with a manual transmission use equal-length halfshafts, which also helps reduce torque steer, and flat-roller, tripod constant-velocity joints. These were developed by Honda and reduce vibration at extreme joint angles. Unlike conventional joints, they incorporate roller bearings with a flatter surface and guide plates which maintain the bearing's alignment as it responds to axle motion. In bearings without these features, the maximum angle possible before friction and vibration sets in is six degrees; the newly designed joints permit an angle of 12 degrees.

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