Air flow meter. The air mass meter is located between the air filter and the throttle valve. It registers not only how much air enters the engine, but also the density of the air. The proportion of oxygen, which plays a decisive role in the process of fuel combustion, depends on the air density. The amount of air filling is used in calculating the amount of fuel injected, the ignition timing and the current engine torque output.
The Audi A4 uses a hot-film air mass meter. An electrically heated sensor plate is positioned in an intake air stream that cools the plate. The control circuit regulates the heating current so that the temperature of the plate is a certain amount higher than the air temperature. The heating current value is used by the control device as a measure for measuring the air mass flow.
Air mass meter located on the air filter housing: 1 - electrical outlets, 2 - electrical connections, 3 - block for processing measurement results, 4 - inlet, 5 - sensor element in hot-film air flow meter, 6 - outlet, 7 - housing.
Intake manifold pressure sensor. This sensor is pneumatically connected to the intake manifold and senses the absolute pressure in the intake manifold. The sensor can be built into the control device, it can also be located directly in the intake gas line or near it.
Throttle position sensor. This sensor determines the angular position of the throttle, that is, it provides information on how the driver throttles. If the air mass meter fails, the control device uses the signals from this sensor to determine the load on the engine.
Speed sensor. This sensor not only provides information about the engine speed, as its name suggests, the position of the sensor on the crankshaft serves as a starting point that allows the control device to determine the position of the crankshaft, and at the same time the position of each cylinder.
Inductive speed sensor. This sensor is located above the ferromagnetic ring gear on the crankshaft. Rotation affects the magnetic flux in the permanent magnet of sensor 1 north (N) and southern (S) pole. 2 - case, 3 - engine crankcase, 4 - soft iron core, 5 - winding (interacts with the sensor magnet), 6 - Gap gear: The absence of two teeth on the sensor wheel is matched to a specific crankshaft position for cylinder #1.
The position of the camshaft is also important, data on which are obtained using a phase sensor, which is also called hall sensor. Thanks to this sensor, the control unit receives information about which cylinder is currently in the compression stroke, on the basis of which the individual ignition coils receive an ignition signal from the control unit.
Ambient air pressure sensor (altimeter). This sensor is located directly above the control unit. It allows you to accurately determine the density of the surrounding air, this information is used in numerous diagnostics.
Also used in turbocharged engines boost pressure sensor.
Oxygen sensor. The oxygen sensor must be located in the exhaust manifold. Modern powerful engines have multiple sensors (before and after the catalytic converter). Based on the composition of the exhaust gas, the oxygen sensor measures the excess air ratio - a numerical measure of the ratio of air and fuel in a new portion of the working mixture. For complete combustion of one kilogram of gasoline, approximately 14.5 kilograms of air is needed, which corresponds to an excess air ratio of 1. A ratio of more than 1 means a lean mixture with a lot of air, and a ratio of less than 1 means a rich mixture.
The catalytic converter works optimally only when the excess air ratio is 1. If this ratio is not achieved, then the digital engine control by changing the amount of fuel injected, accordingly changes the ratio between the amount of air and fuel in the mixture. The oxygen sensor only works from 350'C, so there is no regulation immediately after a cold start. To shorten this phase, a heated oxygen sensor is used.
Oxygen sensor in the exhaust pipe: 1 - special ceramics, 2 - electrodes, 3 - contact, 4 - contact with the housing, 5 - exhaust pipe, 6 - (porous) ceramic protective layer, 7 - exhaust gas, 8 - outside air. U - voltage.
Fuel detonation sensor. This sensor is built into the cylinder block and detects uneven (detonation) combustion and regulates the ignition timing accordingly.
Engine temperature sensor. Located in the coolant circuit, transmits fluid temperature data to the control device.
Intake air temperature sensor. Located in the inlet.
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