2AZ-FE Engine

Tech Briefs
Toyota's new inline four-cylinder engine

Toyota is accelerating hard on its "core" engine update. Significantly, these engines share the second character "Z," beginning with the type-ZZ that was first adopted in the U.S. Corolla and more recently in the revived mid-engine sports car MR-S. It was followed by the NZ-family propelling various small vehicles, including the Echo sedan.

The Z-gen engine for Toyota's mid-size cars and vehicles is the all-new type-2AZ-FE, making its first appearance in the second-generation Estima minivan (the first-generation Estima was the Previa). The 2.4-L 2AZ will power the next-generation Camry replacement as the base engine and other future mid-size vehicles. The
2AZ-FE incorporates many features of Toyota's dual-overhead-camshaft, four-valves-per-cylinder engines, including the slant-squish combustion chamber, offset cylinder and crank centers, and the VVT-i continuously variable intake valve timing system. The aluminum engine measures 626-mm (25-in) long, 608-mm (24-in) wide, and 681-mm (27-in) tall.

The 2AZ-FE obtains a total displacement of 2362 cm3 with 88.5-mm (3.5-in) bore and 96.0-mm (3.8-in) stroke. The cylinder block is now an open-deck, midi-skirt die-cast aluminum type with cast-in iron liners and a die-cast aluminum lower crankcase and a stamped oil pan. The forged steel crankshaft is fully balanced with eight
counterweights and supported by five main bearings. A helical gear pressed in No. 3 counterweight drives twin contra-rotating balance shafts in the shaft housing within the lower crankcase. The balance shaft geartrain includes
plastic Nos. 1 and 3 drive gears, meshing with steel gears.

The dual overhead camshafts are driven by a single-stage roller chain of 8.0-mm (0.3-in) pitch, enabling a narrow included valve angle of 27.5°. The camshafts act on four valves per cylinder via bucket tappets. As in the recent Toyota engine practice, no clearance adjusting shim is employed. Valve diameters are 34.0 mm (1.3 in) for intake and 29.5 mm (1.2 in) for exhaust, with 8.0-mm (0.3-in) lift for both intake and exhaust. The four-vane VVT-i device is fitted on the intake camshaft, altering timing by 50°. Fuel is injected sequentially via an ultra-fine-atomization injector with twelve small injection holes, each 0.18 mm (0.01 in) in diameter.

As in the smaller NZ engine, the new AZ adopts a plastic, built-up, and vibration-welded intake manifold integrating a large volume plenum chamber (3.5-L (214 in3) volume including a 1.3-L (79 in3) resonator). Twin three-way catalytic converters, each with a 0.84-L (51 in3) volume, are mounted immediately downstream of the stainless tubular exhaust manifold. The front exhaust pipe, collecting from the catalysts, has a separator in the
pipe that reduces exhaust gas interference and improves low- and mid-speed torque.

The type 2AZ-FE engine that powers the Estima minivan is rated at 118 kW (160 hp) at 5600 rpm
and 221 N•m (163 lb•ft) at 4000 rpm on a 9.6:1 compression ratio, requiring regular-grade, unleaded gasoline. A smaller version of this engine, the type-1AZ 2.0-L unit, powers the recently updated RAV4 light SUV. The Japanese version of this engine, designated 1AZ-FSE, features the fuel-efficient "D4" direct-injection head.

Jack Yamaguchi
AEI July 2000