2UR-FSE Lexus engine

Introduction

Lexus’ 2UR-FSE was a 5.0-litre V8 petrol engine with a 90-degree ‘V’ angle. A member of the Toyota/Lexus ‘UR’ engine family, along with the 1UR-FE, 1UR-FSE, 2UR-GSE and 3UR-FE, key features of the 2UR-FSE included:

• Its aluminium alloy block and cylinder head;
• Double overhead camshafts (chain-driven);
• Dual VVT-i, including VVT-iE;
• Direct and indirect (port) injection (D-4S); and,
• An 11.8:1 compression ratio.

The 2UR-FSE was a development over the 4.6-litre 1UR-FSE V8 engine, with stroke increased from 83.0 mm to 89.5 mm. Offered solely in the Lexus XF40 LS 600hL, the 2UR-FSE engine was distinguished by its ability to shut down when the vehicle was stationary to reduce fuel consumption.

The 2UR-FSE engine had a service mass of 236 kg.

2UR-FSE block

The 4969 cc 2UR-FSE engine had a die-cast aluminium alloy block with 94.0 mm bores and an 89.5 mm stroke; bore pitch was 105.5 mm, while the cylinder banks had a 21.0 mm offset. Lexus used extensive computer aided design (CAD) analysis, including thermal deformation data from a running powerplant, to maximise rigidity in the cylinder block and oil pan structures.

Within the bores, the 2UR-FSE engine had spiny-type cast iron liners that were manufactured so that their casting exteriors formed large, irregular surfaces for better adhesion between the liners and the block – this improved heat dissipation and reduced heat deformation of the bores. To minimise the transmission of vibrations, the cross-hatched machining marks for the inner bore walls of the cylinder block were optimised at 30 degrees. Furthermore, Lexus used a bespoke three-dimensional inner cylinder wall measuring device to ensure the gap between cylinder lining and piston met design parameters throughout the stroke cycle.

The 2UR-FSE block and cylinder head were checked before assembly – using an X-ray inspection device and a CT (Computed Tomography) scan – to determine if cavity bubbles within the castings could absorb deformed metal under high temperatures. This information supplemented established thermal deformation data to ensure that, for each powerplant, engine deformation only occurred within design parameters.

Crankshaft, connecting rods and pistons

The 2UR-FSE engine had a forged steel crankshaft with six balance weights and five main bearing journals. For the 2UR-FSE engine, every area of the crankshaft, including the friction points and piston pins, was polished to a mirror finish to minimise piston friction and optimise rotational balance.

The crankshaft bearings were made of aluminium alloy, while the bearing lining surface was coated with resin to improve wear and seizure resistance. The crankshaft bearing caps had four plastic region tightening bolts of different sizes in the inner and outer sides to secure the journals; each crankshaft bearing cap was tightened laterally to improve reliability. To reduce noise and vibration, the crankshaft pulley had a torsional rubber damper.

For previously unreachable oil delivery passages – such as the crankshaft lubrication holes – Lexus used a specially developed high-pressure nozzle which sprayed a liquid that included ultra-fine alumina particles. The application of this liquid at high pressures removed burrs and reduced resistance for oil flow for superior lubrication.

The 2UR-FSE engine had forged connecting rods with resin-coated aluminium bearings. To minimise the shifting of the bearing caps during assembly, knock pins were used at the mating surfaces of the bearing caps. Furthermore, the connecting rods had plastic region tightening bolts.

The 2UR-FSE engine had aluminium alloy pistons that were cooled by four oil jets in the cylinder block. To reduce friction and improve wear resistance, the piston skirts had a resin coating, while the no.1 compression ring and oil ring had a Physical Vapor Deposition (PVD) coating. To reduce weight, the bottom of the piston head (near the pin bosses) had cast holes. Furthermore, the piston head for the 2UR-FSE engine had a taper squish shape.

Cylinder head

The 2UR-FSE had an aluminium alloy cylinder head that separated the cam journal portion (camshaft housing) from the cylinder head. The cylinder head was mounted on a three-layer steel-laminate type cylinder head gasket, while a shim was used around the cylinder bore of each gasket to enhance sealing and durability. Furthermore, the surface of the gasket was coated with heat-resistant fluoro rubber.

The 2UR-FSE had magnesium alloy cylinder head covers which included an oil delivery pipe for lubrication of the sliding parts of the valve rocker arms. Furthermore, fresh air was drawn from the right and left bank cylinder head covers to improve ventilation inside the engine and improve the deterioration resistance of the engine oil.

Like the 1UR-FSE, the 2UR-FSE is understood to have a new cooling technique, ‘Partial Head Pre-cooling’, whereby radiator coolant is fed into the cylinder head to cool the periphery of the combustion chamber. The heated coolant from the exhaust side – which had a tendency to gather the most heat – was then fed through the water jackets of the block for even heat distribution. According to Lexus, this cooling process reduced bore deformation and mechanical friction losses.

Camshafts and timing chains

The 2UR-FSE engine had hollow double overhead camshafts per cylinder bank. During production, the camshafts were cooled by liquid nitrogen before separate forged cam lobes were attached – this this process facilitated the machining and polishing of a more exact cam profile to enhance engine power output.

The 2UR-FSE used separate, primary timing chains for the intake camshafts, while each exhaust camshaft was driven by a secondary timing chain from the intake camshaft. Both the primary and secondary timing chains were roller-type chains with a pitch of 9.525 mm. Each primary timing chain and secondary timing chain had a chain tensioner that used oil pressure and a spring to maintain chain tension. A chain oil jet in the oil pump cover was used to lubricate the timing chains.

The timing chain cover had an integrated construction which consisted of a cooling system (i.e. a water pump and water passage) and a lubrication system (oil pump and oil passage).

Valves

The 2UR-FSE engine had four valves per cylinder – two intake and two exhaust – that were actuated by roller rocker arms with built-in needle bearings, the latter reducing friction between the cams and the valve rocker arms.

Unlike the 2GR-FSE and 4GR-FE engines, the 2UR-GSE did not have hydraulic valve lash adjusters. Instead, the roller rocker arms had a solid fixed pivot at the fulcrum end and a variable thickness valve lash cap on the top of the valve stem. A valve lash inspection procedure was recommended for 100,000 kilometre intervals to keep valve lash within specification.

As per the 1UR-FSE engine, the 2UR-FSE engine had intake valve lift of 10.9 mm and exhaust valve lift of 10.7 mm.

Dual VVT-i with VVT-iE

The 2UR-FSE engine had the Toyota/Lexus ‘Dual VVT-i’ system to control the inlet and exhaust camshafts and vary valve timing to optimise valve overlap according to engine and driving conditions to make full use of exhaust pulsation to enhance cylinder filling at high engine speeds.

For the inlet camshafts, the 2UR-FSE engine had ‘Variable Valve Timing – intelligent Electric’ (VVT-iE) which used an electric motor to vary the VVT-i controller vane and vary valve timing. In contrast, the exhaust camshaft had a conventional hydraulic VVT-i system in which the camshaft timing oil control valve controlled a spool valve that enabled hydraulic pressure to be applied to the advance or retard side of the VVT-i controller. In response, rotation of the VVT-i controller vane sub-assembly – relative to the timing chain sprocket – varied valve timing.

The VVT-iE system was developed because hydraulic VVT-i could not operate below engine speeds of 1000 rpm or when the engine was cold. VVT-iE, however, could operate at all engine speeds and temperatures, with a cam response speed of 50 degrees per second in the retardation phase and 150 degrees per second in the advance phase.

For VVT-iE, the 2UR-FSE engine featured a high-precision-finish plate and narrow pins at the interface of the speed reduction gear and phase converter to transmit the VVT-iE electric motor’s high rotation torque. Due to the hardness of these elements, a scroll machine – based on the mechanics of a tool used for cutting air conditioner parts – was used to achieve the required base-cutting precision.

For the camshaft motor control components, VVT-iE required:

• Uniform winding of the high density coils for matched magnetisation within each stator core;
• Precision milling of the motor shaft bearings so that VVT-iE could operate with minimal vibration; and,
• A new system that employed frictional resistance and speed-reduction gearing to hold the cam phase in the ideal position for engine start-up.

For the 1UR-FSE and 2UR-FSE engines, there was a four-degree variation in cam timing for four of the V8 engine’s cylinders – as per the table below, cylinder numbers 1, 2, 3 and 6 had inlet and exhaust timing that was always four degrees retarded from the timing of cylinder numbers 4, 5, 7 and 8. According to Lexus, this reduced vibration at idle and improved fuel economy. For the 2UR-FSE engine,

• Valve overlap could range from -29 degrees to 61 degrees (a range of 90 degrees) to make full use of exhaust pulsations and increase cylinder filling at high engine speeds;
• The intake camshaft had a 55 degree range of adjustment (relative to crank angle);
• The exhaust camshaft had a 35 degree range of adjustment (relative to crank angle);
• Intake duration was 248 degrees; and,
• Exhaust duration was 244 degrees.

Intake

The 2UR-FSE had an over-the-engine, dual-pipe air intake system with compact filter elements. The 2UR-FSE engine also featured the Toyota/Lexus ‘Acoustic Control Induction System’ (ACIS) which consisted of:

• A bulkhead to divide the intake manifold into two stages; and,
• An electronically controlled intake air control valve in the bulkhead which opened and closed to vary the effective length of the intake manifold according to engine speed and throttle valve opening angle.

When the engine was running at middle speed under high load, an actuator would close the intake air control valve to increase the effective length of the intake manifold and improve intake efficiency – at medium engine speeds – due to the effect of inlet pulsations. In any condition other than middle speed running under high loads, the intake air control valve was open to shorten the effective length of the intake manifold.

In contrast to a conventional throttle which used accelerator pedal effort to determine throttle angle, Toyota’s ‘Electronic Throttle Control System – intelligent’ (ETCS-i) used the ECM to calculate the optimal throttle valve angle and a throttle control motor to control the angle. The 2UR-FSE engine had a linkless-type throttle body that integrated the throttle position sensor and throttle control motor.

The 2UR-FSE engine had Siamese type intake ports whereby port diameter gradually decreased towards the combustion chamber to optimise air flow.

D-4S injection

The 2UR-FSE engine had ‘Direct-injection 4-stroke Superior’ (D-4S) which featured two injectors per cylinder: one injector in the combustion chamber and a second in the intake port. The 2UR-FSE engine could therefore use:

• Direct injection only; or
• Both direct injection and port injection.

The 2UR-FSE engine could also vary the injection timing phase of the two systems.

The 2UR-FSE engine had two fuel supply systems, low-pressure and high-pressure, for the port injectors and direct injectors, respectively. While the twelve-hole port injectors injected fuel at a maximum pressure of four bar, the direct injectors had twin 0.52 mm by 0.13 mm rectangular slits which produce a double-fan, 130-bar injection pattern.

With direct injection, the injection of petrol into the combustion chamber (during the downstroke of the piston) and its subsequent evaporation produced a cooling effect that increased intake air volume and improved charging efficiency. Furthermore, the intake air formed a vertical swirl current (tumble current) to promote improve air/fuel mixing and hence improve performance and emissions.

To resist deposits, the direct injectors had a special coating on their nozzles. Furthermore, the area where the injector body met the cylinder head had an insulator and the injector shaft had two Teflon seals to resist cylinder pressure, improve sealing performance and reduce vibration.

D4-S had the following operating scenarios:

• Under cold start conditions, D-4S used port injection during the intake stroke and direct injection during the compression stroke. This produced an air:fuel mixture of 15-16:1, generating a richer mixture around the spark plug and raising the temperature of exhaust gases for faster warm-up of the two thin-wall catalysts;
• At idle, the engine operated on direct injection alone due to its higher efficiency;
• At low to medium loads and lower engine speeds, both direct and port injection systems were used during the intake stroke. This created a homogeneous 12-15:1 air:fuel ratio to stabilise combustion, improve fuel efficiency and reduce NOx and HC emissions;
• Under heavy loads, direct injection alone was used with an 11.8:1 air:fuel ratio during the intake stroke. The use of direct injection at high engine loads created an intake cooling effect which improved the efficiency of each charge. The 2UR-FSE engine could therefore use a high compression ratio while reducing pre-ignition tendencies and improving engine output and performance.

Ignition

The 2UR-FSE engine had Toyota’s independent ‘Direct Ignition System’ (DIS) ignition system which used one ignition coil (with integrated igniter) for each cylinder. Ignition timing was determined by the ECM based on signals from sensors and adjusted in response to engine knocking. The 2UR-FSE engine had a dual knock control system.

The 2UR-FSE engine had long-reach, iridium-tipped spark plugs – poisoned in the centre of the combustion chamber – so that the surrounding cylinder head could be made thicker and the water jacket near the combustion chamber extended.

The 2UR-FSE engine had a compression ratio of 11.8:1 and firing order of 1-8-7-3-6-5-4-2.

Exhaust

The 2UR-FSE engine had stainless steel, ‘semi-dual’ exhaust manifolds which divided the traditional single manifold into two by connecting non-adjoining cylinders based on the engine ignition sequence. According to Lexus, the connection of cylinders with long ignition intervals minimised exhaust counter-pressure interference to ensure the smoothest possible flow of exhaust gases.

The 2UR-FSE engine had stainless steel exhaust pipes; the front exhaust pipe had two ceramic three-way catalytic converters on both the left and right exhaust pipe banks.