1AZ-FE Toyota engine

Introduction

Toyota’s 1AZ-FE was a 2.0-litre inline four-cylinder petrol engine. A member of Toyota’s AZ engine family, key features of the 1AZ-FE included its aluminium alloy block and cylinder head, double overhead camshafts, variable intake valve timing and 9.8:1 compression ratio.

For Australia, the 1AZ-FE was offered in the XA20 RAV4 and T250 Avensis Verso (see table below). In the Avensis Verso, the 1AZ-FE engine had a service weight of 123 kg for models with manual transmissions and 117 kg with automatic transmissions.

The 1AZ-FE was upgraded in late 2003, though no Australian-delivered models were offered with this engine. Upgrades for this post-2003 1AZ-FE engine included:

• The introduction of electronic throttle control;
• Revised valve timing; and,
• The adoption of a planar-type air:fuel ratio sensor (integrated with the oxygen sensor) and flat-type knock sensor.

1AZ-FE block

The aluminium alloy cylinder block of the 1AZ-FE engine had 86.0 mm bores and a 86.0 mm stroke for a capacity of 1998 cc. The 1AZ-FE engine had cast iron liners which were manufactured so that their casting exteriors formed large, irregular surfaces (‘spiny type’) for better adhesion between the liners and the cylinder block.

Other features of the 1AZ-FE cylinder block included:

• Air passage holes in the crankshaft bearing area of the cylinder block for better air flow and reduced back pressure at the bottom of the pistons;
• Water jacket spacers which suppressed water flow in the centre of the jackets and guided the coolant around the cylinder bores; and,
• Oil filter and air conditioning compressor brackets that were integrated into the crankcase.

 

Crankshaft, connecting rods and pistons

The 1AZ-FE engine had a forged steel crankshaft with five journals, eight balance weights and roll-finished pin and journal fillets. The 1AZ-FE’s crankshaft was offset by 10 mm to the thrust side of the cylinder bore centre line to reduce friction; according to Toyota, this design reduced fuel consumption by between one and three percent.

The connecting rods and caps were made of high-strength steel. To reduce mass, nut-less type plastic region tightening bolts were used.

The 1AZ-FE engine had aluminium alloy pistons. While the piston head had a taper squish shape, the piston skirt was coated with resin to reduce frictional losses.

Cylinder head

The 1AZ-FE engine had an aluminium alloy cylinder head which was mounted upon a steel-laminate type head gasket; to increase the sealing surface, a shim was used around the cylinder bore. To reduce mass, the 1AZ-FE engine had a magnesium alloy die-cast cylinder head cover.

Camshafts

The 1AZ-FE engine had double overhead camshafts (DOHC or Toyota’s ‘Twin Cam’) that were driven by a roller chain which had an 8 mm pitch and was lubricated by an oil jet. The chain tensioner used a spring and oil pressure to maintain chain tension; it also used a ratchet type non-return mechanism.

Valves

The 1AZ-FE engine had four valves per cylinder – two intake and two exhaust – that were positioned at a 27.5 degree included valve angle. The intake valves each had a diameter of 34.0 mm, while exhaust valve diameter was 29.5 mm. Furthermore, the 1AZ-FE engine used shimless type valve lifters that provided a large cam contact surface.

Variable Valve Timing – intelligent (VVT-i)

The 1AZ-FE engine featured Toyota’s ‘Variable Valve Timing – intelligent’ (VVT-i) system which varied intake valve timing according to driving conditions (based engine speed, vehicle speed, intake air mass and flow, throttle position and engine coolant temperature). The ECM used signals from the camshaft position sensor and crankshaft position sensor to detect the actual valve timing, thereby providing feedback control to achieve the target valve timing.

For the pre-2003 1AZ-FE engine, intake valve overlap ranged from -1 to 49 degrees relative to crankshaft angle, intake duration was 236 degrees and exhaust duration was 228 degrees.

For the upgraded 1AZ-FE engine that was introduced in late 2003, valve overlap ranged from 6 degrees to 46 degrees, a range of 40 degrees relative to crankshaft angle. Furthermore, intake duration was 243 degrees and exhaust duration 220 degrees.
The VVT-i system used:

• A camshaft timing oil control valve that was mounted adjacent to the inlet camshaft gear wheel; and,
• A VVT-i controller which had a four-bladed vane and was built onto the inlet camshaft timing gear.

The camshaft timing oil control valve was a spool-type valve that was controlled – via the ECU – by a coil and plunger; the ECU could signal ‘advance’, ‘hold’ or ‘retard’. When the ECU required a change in intake valve timing, it signalled the oil control valve to provide oil pressure to either the ‘advance’ or ‘retard’ side of the four vane chambers.

Inlet cam timing was set to the maximum ‘retard’ position for engine start-up, operation at low engine temperature, idle and engine shutdown. Furthermore, a locking pin in the controller locked the camshaft timing in the maximum ‘retard’ position for engine start-up and immediately after start-up (until oil pressure is established) to prevent any knocking noise.

Intake and throttle

The 1AZ-FE engine had a big bore, long-branch inlet that was made of plastic (to reduce heat transfer to the inlet charge), a resonator to reduce induction noise and vertical intake ports.

For XA20 RAV4 models with manual transmissions and all Avensis Verso models, the throttle body contained a spherical-plated throttle valve that, according to Toyota, provide greater pedal control and improved acceleration feel. The throttle had an additional spherical plate on one half of the butterfly valve to ‘spherical curve in the relationship between throttle opening angle and intake air volume to improve driveability in the initial phase of throttle opening’. Furthermore, the throttle body was water-heated.

From late 2003, the upgraded 1AZ-FE engine featured Toyota’s ‘Electronic Throttle Control System – intelligent’ (ETCS-i) which consisted of an electronic throttle body with a built-in contactless throttle position sensor and throttle control motor.

Injection

The 1AZ-FE engine had electronically controlled sequential fuel injection via 12-hole injector nozzles that were mounted in the inlet ports to prevent wall wetting and fuel adhesion to the walls of the port. The fuel injection system used a hot-wire L-type air flow meter to measure intake air volume, while two air:fuel ratio sensors in the exhaust headers were used to achieve a stoichiometric air:fuel mixture.

The 1AZ-FE engine had pentroof-type combustion chambers with a slanted (oblique) squish design to improve thermal efficiency and reduce the likelihood of engine knock (pre-ignition). Specifically, the squish angle was shaped obliquely along the wall surface of the combustion chamber to improve airflow, promote swirl and increase the speed of flame travel.

The 1AZ-FE engine had a compression ratio of 9.8:1.

Ignition

The 1AZ-FE engine had centrally located, iridium-tipped spark plugs. With the Toyota ‘Direct Ignition System’ (DIS) an ignition coil with an integrated igniter was used for each cylinder. Furthermore, the 1AZ-FE engine had Toyota’s ‘Electronic Spark Advance’ (ESA) which selected optimal ignition timing in accordance with inputs from sensors.

The firing order for the 1AZ-FE engine was 1-3-4-2.

Exhaust

The pre-2003 engine 1AZ-FE engine had:

• Double-walled stainless steel extractor-style exhaust headers;
• Three-way catalytic converters located downstream of the exhaust headers; and,
• A two-stage muffler.

For the upgraded 1AZ-FE engine introduced in late 2003, the two three-way catalytic converters were integrated into a single three-way catalytic converter and a three-way catalytic converter was added below the exhaust manifold and under the floor.