Pressure-Regulated Fuel Filter
For the 1.8T engine, the fuel supply is routed through a pressure-regulated filter. This new design eliminates the need for a fuel return line from the engine fuel rail. Fuel in the tank is pressurized by the in-tank fuel pump and supplied through port “VL” to the filter. The pressurized fuel fills the chamber, flowing through the paper filter element and out through the port labeled “MOTOR” to supply the engine fuel rail. If the fuel pressure in the filter exceeds the filter pressure regulator threshold, the regulator valve opens and routes fuel through the plastic center tube and out at port “RL” to return to the tank. Fuel filter port “E” vents the pressure regulator to atmospheric pressure through the evaporative emission (EVAP) canister.
Exhaust Flap — 3.0-Liter V6
Front-wheel drive vehicles equipped with 3.0L V6 engines have an exhaust flap installed at one of the rear silencer outlets. This design ensures that legal restrictions on noise are met at engine idle and low engine speeds.
Exhaust Flap Operation
Exhaust flap operation is controlled by the Motronic Engine Control Module J220. When vehicle speed is above 3.1 mph (5 km/h) and engine speed is above 2000 rpm, there is no signal to the Valve for Exhaust Flap N220 and the flap is open to allow maximum flow of exhaust gases. When vehicle speed is below 3.1 mph (5 km/h) or the engine speed drops below 1800 rpm, the Motronic Engine Control Module J220 sends a signal to activate the Valve for Exhaust Flap N220 and the flap is closed to reduce exhaust noise to an acceptable level.
Effect of Failure
In the event of exhaust flap system failure, the default position is with the flap open.
Pneumatic Damping Control Shock Absorbers
Rear Axle Variable Load Recognition System
The Audi allroad quattro four-level air suspension employs a continuously variable load recognition system at the rear axle. This system enhances vehicle handling by maintaining suspension damping at a constant level whether the vehicle is partially or fully loaded. The use of air springs in combination with the natural vibration frequency of the body structure maintains virtually constant vibration characteristics regardless of the load on the system. The system adjusts to provide a comfortable ride with a light load and sufficiently firm damping under a heavy load. The pneumatic damping control (PDC) shock absorbers provide this capability. In PDC shock absorbers, the damping force is varied as a direct result of the amount of air pressure present in the air springs at any given moment.
The damping force is altered by a PDC valve integrated into the shock absorber. The PDC valve is connected to air spring air chamber pressure by a pneumatic hose. A variable throttle valve in the PDC valve is controlled by the internal air pressure in the air spring. This provides a continuously variable control of damping in direct proportion to the load on the suspension system. The movement of the throttle valve changes the resistance to hydraulic fluid flow in the shock absorber and thus the damping force during both compression and rebound. The air connector in the PDC valve includes a restricting orifice between the air spring side and the valve piston side. This air restriction reduces the influence of the dynamic pressure changes in the air spring on the shock absorber during compression and rebound.
Design and Function
The PDC valve affects the resistance to hydraulic fluid flow in the working cylinder on the piston rod side. The hydraulic fluid in the piston rod side of the working cylinder is routed to the PDC valve through holes in the side of the cylinder near the top and a jacket that encases the cylinder. The flow resistance of the PDC valve is directly proportional to the air spring air pressure. The PDC valve has a low flow resistance when the air spring air pressure is relatively low; when the vehicle is lightly loaded. Some of the hydraulic fluid gets past the PDC valve throttle valve, effectively reducing the damping force in the shock absorber. The total damping force in the shock absorber for compression or rebound damping is determined by the flow resistance of the piston valve, the bottom valve, and the PDC valve.
Function during compression at low air spring air pressure
During compression, the piston is pushed downward in the shock absorber working cylinder. Some of the hydraulic fluid flow is through the piston valve. Most of the fluid flows through the bottom valve, with a proportional amount flowing through the open PDC valve, the cylinder jacket, and through the holes in the side of the cylinder into the cylinder behind the moving piston. Since the air spring air pressure is low, the flow resistance at the PDC valve is low. More fluid can get past the PDC valve and the damping force is reduced.
Function during compression at high air spring pressure
Since the controlling air spring air pressure is high, the flow resistance at the PDC valve is high. Depending upon the control pressure, little or no fluid gets past the PDC valve. Most of the fluid must flow through the piston valve, and the damping force is increased.
Function during rebound at low air spring air pressure
During rebound, the piston is drawn upward. Part of the fluid flows through the piston valve, some flows through the bottom valve, and the rest flows through the holes in the side of the cylinder and through the cylinder jacket to the PDC valve. Since the air spring air pressure is low, the flow resistance at the PDC valve is low. More fluid can get past the PDC valve and the damping force is reduced.
Function during rebound at high air spring air pressure
Since the air spring air pressure is high, the flow resistance at the PDC valve is high. Depending upon the control pressure, little or no fluid gets past the PDC valve. Most of the fluid must flow through the piston valve, and the damping force is increased.
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