Intake Air Distribution and Filtering
Intake Air Distribution and Filtering - 3.2L
COMPONENT LOCATION
OVERVIEW
The air intake system has been designed to:
^ make available the appropriate air supply to the engine,
^ while providing a wade-proof system to ensure vehicle off-road durability
Fresh air is supplied into the system, through the Left Hand (LH) vent located on the front fender. The vent is positioned above the vehicle's wade line to minimize the risk of water entering the system. This positioning of the vent also prevents hot air from the engine-compartment being drawn into the engine.
A polyfibre porous duct providing low intake noise, directs air into the base of the rigid injection-molded air filter housing. The filter housing is supported on 4 elastomer mountings to minimize noise transmission to the vehicle's body structure. A one-way drain valve, incorporated in the base of the filter housing, releases any water that may have entered the system. Intake air is cleaned as it passes through an oil-soaked filter element which offers minimal obstruction to the flow of air.
Clean air passes through the Mass Air Flow (MAF) sensor and along a sealed polypropylene duct to the throttle body and intake manifold. The clean air duct features a single quarter-wave resonator tube to enhance engine sound quality during intake manifold tract switching events.
Computational fluid dynamics were extensively used in the design and refinement of the system to minimize air-pressure drop.
The intake manifold is capable of varying both intake tract length and plenum volume. Two separate valves control these features:
^ the variable tract valve, and
^ the variable plenum valve
Intake Manifold
At low engine speeds, long intake tracts are functioned to provide optimum engine torque; shorter tracts are used at medium speeds, again to optimize engine torque for the existing engine speed range.
At higher engine speeds the benefits of optimizing the tract lengths are outweighed by necessity of maintaining an appropriate supply of air to meet the engine's requirements. Therefore, the plenum valve is opened to create a single, large plenum volume to provide the maximum quantity of air to charge the engine's cylinders.
Variable Induction System Functionality
PRINCIPLE OF OPERATION
Low Engine Speed
NOTE: Both throttles closed. The air is routed the long way.
At engine speeds up to 2100 rpm, optimum filling is achieved by how the exhaust gases leave the cylinders. When the exhaust gases leave the cylinders, a empty chamber is created behind the exhaust gases, whereupon a low pressure is created in the cylinders.
By also making adjustments when the intake valves open/close, positive pressure differences are obtained between the cylinder and intake manifold. The intake air is drawn into the cylinders resulting in optimum cylinder filling.
Engine Speed Up To Approximately 3700rpm
NOTE: Both throttles are closed.
The pulsations, which increase at speeds over 2100 rpm, are forced the long way round. When the pulsation speed is constant and the engine speed is relatively low, the pulsations have a long time to reach the cylinders at the correct time.
However, certain losses occur when a proportion of the pulsations disappear the back way to the air filter (and add to the engine's sound pattern).
Engine Speed From 3700 To 4700rpm
NOTE: The lower throttle is open whilst the upper one is closed.
The pulsations must have access to a shorter route to make it to the cylinders in time. The shorter route is obtained by allowing the lower throttle to be open, which means that the pulsations reach the cylinders in time.
Certain losses occur, however, when a proportion of the pulsations take the long way round and a proportion take the back way round to the air filter.
Engine Speed Over 4700 rpm
NOTE: Both the upper throttle and the lower throttle are open.
In this position, the pulsations are only determined by the short intake pipe's geometry.
The total volume for all cylinders now accessible is necessary to have sufficient access to air.
Torque Development
By combining the throttle's position, in principle, three different torque curves are produced, which combined, give a flat torque curve for a naturally aspirated engine.
Throttle Units (Actuators)
The throttle units consist of throttle, Direct Current (DC) motor, worm gear and internal electronics.
The Engine Control Module (ECM) controls the position of the throttle by modulating the relevant throttle unit's control signal. If the signal shifts from low (approximately 1 volt) to high (approximately 10 volts) the internal electronics interpret it as the throttle must close. If the signal shifts from high to low, the throttle must open.
If an actuator fails and the flap is in the open position, it is not possible to remove the actuator and flap assembly from the inlet manifold. A small indentation on the body of the actuator allows for a 3 mm Allen key to be pushed through the thin membrane wall of the actuator housing. The Allen key can be engaged in the spindle of the actuator motor, which allows the flap to be turned to the closed position and consequently the actuator and flap assembly can then be removed from the intake manifold.