|
|
|
Page 3
Lotus Service Notes
Section EH EH.1 - GENERAL DESCRIPTION; 2ZZ-GE The 1.8 litre, 16 valve four cylinder engine used in the Lotus 2005 model Elise is supplied by Toyota Mo- tor Corporation, and is designated '2ZZ-GE'. The engine number is stamped on the rear end of the cylinder block, exhaust side, and is followed by '2ZZ'. A full overhaul procedure for this engine family is contained in the separate Toyota publication under part number E120T0327J. The lightweight alloy cylinder block uses no separate cylinder liners, but has the integral cylinder walls constructed from MMC (Metal Matrix Composite). The forged steel crankshaft is supported in five cast iron main bearing caps which are integrated into a single piece alloy main bearing panel bolted to the bottom of the block. A pressed steel sump is fitted below the main bearing panel. The iron and tin coated pistons, fitted with three piston rings, are mounted via fully floating gudgeon pins to forged steel connecting rods which use two bolt big end caps around the crankpins. The cylinder head houses four valves per cylinder, with inlets arranged at 43° to the exhaust valves, and incorporates laser clad alloy valve seats welded into the cylinder head. At the front of the engine, a single row chain, automatically tensioned by spring and oil pressure, is used to drive the two overhead camshafts which incorporate VVTL-i (Variable Valve Timing and Lift-intelligent) to advance and retard the inlet camshaft timing under electro/hydraulic control, and increase the lift of both inlet and exhaust valves at high engine speed (see later). A trochoid type oil pump, driven directly by the front end of the crankshaft supplies an oil gallery along the left hand side of the crankcase, from which are fed the crankshaft main bearings, then the big ends, and via oil jets, the underside of the pistons. The gallery also feeds a drilling up to the cylinder head for the two camshafts, and the VVTL-i mechanism, with the chain tensioner fed from the exhaust cam drilling. The main gallery also feeds the oil filter, vertically mounted on the left hand side of the cylinder block. The timing chain is lubricated via an oil jet directly from the oil pump, and by oil draining down through the timing chest. The water pump is mounted at the left hand front of the block and is driven by a multi-rib serpentine auxiliary belt from the crankshaft. Coolant is pumped into the front of the cylinder block and head, and when the thermostat is closed, returns to the pump via a by-pass gallery in the cylinder head and block. When the thermostat opens, the by-pass route is closed off, and a greater volume of coolant flows via the heater matrix, and throttle body as well as through the engine cooling radiator. The die-cast aluminium intake manifold draws air from a single throttle body with cable controlled but- terfly valve, into a plenum chamber from which the four intake ports are fed by individual tubes. A twelve hole fuel injector is mounted in the top of each of the four intake ports in the cylinder head, with fuel supplied via a one-way flow system with a pressure regulator contained inside the fuel tank. The Direct Ignition System (DIS) uses separate high tension coils mounted directly onto each of the four spark plugs, with timing control by the engine management ECU. VVTL-i (Variable Valve Timing & Lift - intelligent) This system features two elements: Variable Valve Timing In order to allow the inlet valve timing to be advanced or retarded to the benefit of particular running condi- tions, the inlet camshaft is provided with a hydraulic hub connecting the chain sprocket to the inlet camshaft. The hub comprises a housing fixed to the sprocket and a four vane rotor fixed to the camshaft. The rotor is contained within the housing with the rotor vanes dividing each of the four chambers in the housing into two volumes, an advance and a retard side. Each of the chamber volumes is supplied with pressurised engine oil from a spool valve under ECU control. By varying the relative pressure of the two oil volumes, the positional relationship of the camshaft to the sprocket can be altered. The ECU monitors engine speed, intake air vol- ume, throttle position and water temperature to determine the optimum cam phasing for the particular running conditions, and modulates the duty cycle to the oil control (spool) valve until the desired timing is achieved, as determined by reference to the crankshaft and camshaft sensors. Duty cycles greater than 50% cause the timing to be advanced, and duty cycles less than 50% retard the timing. When the target timing is achieved, a 50% 'holding' duty cycle is applied. The oil control valve is mounted at the left hand front of the cylinder head and feeds oilways within the head connecting with the inlet camshaft immediately behind the hydraulic hub. When the engine is stopped, the inlet cam timing is set at full retard, to allow easy starting. To allow time for oil pressure to build after engine start up, a spring loaded lock pin engages at full retard to mechanically lock the hub, until normal oil pressure releases the pin automatically. The table shows the basic timing strategy for different operating conditions:
|