Fuel cut-off

The fuel tank is made of plastic and is housed in a protected position in front of the rear axle.

The central locking control unit receives this signal simultaneously and unlocks the vehicle doors.

The hazard warning lights are activated automatically and the interior lighting is switched on.

A restart function enables the engine to be restarted after an accident and it can be moved from the danger zone under its own power.

The Audi TT Coupé is the ﬁrst Audi to be equipped with a fuel cut-off.
In connection with an airbag trigger mechanism (crash signal output), the Motronic control unit switches the fuel pump off.

Drive units TURBO

Charging

The turbocharging system comprises the following components:

– Exhaust emission turbocharger
– Charge air cooler
– Charge pressure control
– Air divert control in overrun

The ﬂow energy of the exhaust emissions is transferred to the fresh air entering the exhaust gas turbocharger. In the process, the air required for combustion is compressed and the volume of air entering the cylinders per working cycle is thus increased.

The air temperature, increased by compression, is again reduced in the charge air cooler. Since the density of the cooled air is higher, the amount of fuel-air mixture entering the engine is greater, too.

The result is an increase in power output for the same displacement and engine speed.

In the case of the 1.8-ltr. 5V turbocharged engine, turbocharging is also used to provide high torque from the bottom end to the top end of the rev band.

Charge pressure increases in proportion to the turbocharger speed. The charge pressure is limited to prolong the life of the engine. The charge pressure control performs this task.

The air divert control prevents the turbocharger slowing down unnecessarily if the throttle valve loses suddenly.

Charge pressure control

The engine control unit calculates the charge pressure setpoint from the engine torque request.

The engine control unit regulates the charge pressure as a function of the opening time of the solenoid valves for charge pressure limitation N75. For this purpose, a control pressure is generated from the charge pressure in the compressor housing and the atmospheric pressure.

This control pressure counteracts the spring pressure in the charge pressure control valve (vacuum box) and opens or closes the waste gate valve in the turbocharger.

In the de-energised state, the solenoid valve N75 is closed and the charge pressure acts directly on the vacuum box. The charge pressure control valve opens at low charge pressure.

If the control fails, the maximum charge pressure is limited to a basic charge pressure (mechanical charge pressure).

If the bypass is closed, the charge pressure rises.
In the lower engine speed range, the turbocharger supplies the charge pressure required to develop high torque or the required volume of air.

As soon as the charge pressure has reached the calculated charge pressure, the bypass opens and a certain quantity of exhaust gas is ducted past the turbine. The turbocharger motor speed
decreases, and so too does the charge pressure.

For more detailed information regarding charge pressure control, please refer to SSP 198.

The engine control unit calculates the charge pressure setpoint from the engine torque request.

The engine control unit regulates the charge pressure as a function of the opening time of the solenoid valves for charge pressure limitation N75. For this purpose, a control pressure is generated from the charge pressure in the compressor housing and the atmospheric pressure.

This control pressure counteracts the spring pressure in the charge pressure control valve (vacuum box) and opens or closes the waste gate valve in the turbocharger.

In the de-energised state, the solenoid valve N75 is closed and the charge pressure acts directly

Air divert control in overrun

When the throttle valve is closed, it produces a backpressure in the compressor circuit due to the charge pressure still present. This causes the compressor wheel to decelerate rapidly. When the throttle valve is opened, the speed of the turbocharger must again be increased. The air divert control in overrun prevents turbo lag, which would otherwise occur.

The air recirculation valve is a mechanically activated and pneumatically controlled spring diaphragm valve. It is also activated via an electrically activated air recirculation valve for turbocharger N249. This, in connection with the vacuum reservoir, enables the air recirculation valve N249 to operate independently of the intake manifold pressure. If the air recirculation valve fails, control takes place as a result of the engine vacuum downstream of the throttle valve.

As soon as the throttle valve is closed, the air recirculation valve brieﬂy closes the compressor circuit.

The vacuum counteracts the spring in the valve. The valve opens, and the compressor and intake sides of the compressor circuit close for a short period of time. There is no deceleration of the compressor wheel.

When the throttle valve re-opens, the intake manifold vacuum drops. The air recirculation valve is closed by the spring force. The compressor circuit no longer closes brieﬂy. Full charger speed is available immediately.

For more detailed information regarding the air divert control in overrun, please refer to SSP 198.

Quick-start sender wheel

The quick-start sender wheel is attached to the camshaft. It supplies a signal which enables the engine control unit to determine the position of the camshaft relative to the crankshaft more quickly and, in combination with the signal which the engine speed sender supplies, to start the engine more quickly.

On previous systems, it was not possible to initiate the ﬁrst combustion cycle until a crank angle of approx. 600˚ - 900o was reached. The quick-start sender wheel enables the engine control unit to recognise the position of the crankshaft relative to the camshaft after a crank angle of 400˚ - 480o.
This allows the ﬁrst combustion cycle to be initiated sooner and the engine to start more quickly.

The quick-start sender wheel comprises a twin-track sender wheel and a Hall sensor. The sender wheel is designed so that two tracks are located side by side. In the position where there is a gap in one track, there is a tooth in the other track.

The control unit compares the phase sensor signal with the reference mark signal and thus ascertains the working cycle currently taking place in the cylinder.

Low phase signal = Compression cycle

High phase signal = Exhaust cycle

The signal which the engine speed sender G28 supplies enables the injection cycle to be initiated after a crank angle of approx. 440o.

Electrical circuit

The Hall sender G40 is connected to the sensor earth terminal of the engine control unit.

The signal which the engine speed sender G28 supplies enables the injection cycle to be initiated after a crank angle of approx. 440o.

Even if the Hall sender fails, it is still possible to start the engine.

Charging 165 kW

To increase the power output and torque of the 1.8-ltr. 5V engine to 165 kW, it was necessary to make various design modiﬁcations to the basic engine of the Audi TT Coupé developing 132 kW.

A characteristic feature of the engine is its higher air demand, making it necessary to enlarge the diameter of the intake port and exhaust gas turbocharger.

Since the previous charge air cooler was no longer capable of effectively cooling down the increased air ﬂow through the exhaust gas turbocharger, it was necessary to accommodate a second, parallel charge air cooler on the left-hand side of the vehicle.

Secondary air injection valve N112

The secondary air injection valve is an electropneumatic valve. It is switched by the Motronic control unit and controls the combi-valve.
To open the combi-valve, the secondary air injection valve releases the intake manifold vacuum.
To close the combi-valve, the secondary air injection valve releases atmospheric pressure.

Secondary air pump V101

The secondary air pump relay J299 which the Motronic control unit drives switches the electric current for the secondary air pump motor V101. The fresh air which is mixed with the
exhaust gases is drawn out of the air ﬁlter housing by the secondary air pump and released by the combi-valve.

This valve also prevents hot exhaust gases entering and damaging the secondary air pump.

The combi-valve

The combi-valve is bolted to the secondary air duct of the cylinder head.
The air path from the secondary air pump to the secondary duct of the cylinder head is opened by the vacuum from the secondary air injection valve.