BMW X5: Exhaust Gas Turbocharging
The turbocharger is driven by the engine's exhaust gases, i.e. exhaust gases under pressure are routed by the turbocharger turbine and in this way delivers the motive force to the compressor, which rotates on the same shaft.
It is here that the induction air is precompressed in such a way that a higher air mass is admitted into the engine's combustion chamber. In this way, it is possible to inject and combust a greater quantity of fuel, which increases the engine's power output and torque.
The turbine and the compressor can rotate at speeds of up to 200,000 RPM. The exhaust inlet temperature can reach a maximum of 1050ºC. Because of these high temperatures, the N54 engine's turbochargers are not only connected with the engine-oil system but also integrated in the engine-coolant circuit.
It is possible in conjunction with the N54 engine's electric coolant pump even after the engine has been switched off to dissipate the residual heat from the turbochargers and thus prevent the lube oil in the bearing housing from overheating.
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Fig. 38: Identifying Exhaust Gas Turbocharging
- Compressor
- Cooling/Lubrication
- Turbine
Bi-turbocharging
Utmost importance is attached to turbocharger response in the N54 engine. A delayed response to the driver's command, i.e. the accelerator-pedal position, is not acceptable. The driver therefore must not experience any socalled "turbo lag".
This requirement is met in the N54 engine with two small turbochargers, which are connected in parallel.
Cylinders 1, 2 and 3 (bank 1) drive the first turbocharger (5) while cylinders 4, 5 and 6 (bank 2) drive the second (2).
The advantage of a small turbocharger lies in the fact that, as the turbocharger runs up to speed, the lower moment of inertia of the turbine causes fewer masses to be accelerated, and thus the compressor attains a higher boost pressure in a shorter amount of time.
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Fig. 39: Identifying Turbocharging Components
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Boost-Pressure Control
The boost pressure of the turbochargers is directly dependent on the flow of
exhaust gas which reaches the
turbocharger turbines. Both the velocity and the mass of the exhaust-gas flow
are directly
Load Control
Load control of the N54 engine is effected by means of the throttle valve and
the waste gate valves.
The throttle valve is the primary component in this process. The wastegate
valves are actuated t
Turbocharger Diagnosis
There are three "Golden Rules" to adhere to when diagnosing concerns on the
N54 engine:
1. When diagnosing cases of smoke from the exhaust, it is important to avoid
unnecessary replacement of
the tu
SEE MORE:
Flat Tire Monitor FTM
Principle
The Flat Tire display detects a tire pressure loss
while driving and issues a warning if the tire pressure
has dropped.
General information
The system detects tire pressure loss on the basis
of rotation speed differences between the individual
wheels while driving.
In the event of a tire
Removing And Installing Or Replacing Left Output Shaft
Special tools required:
31 4 170
Remove front wheel.
IMPORTANT: Expand turning lock sufficiently to avoid damaging thread
when releasing collar nut.
Release collar nut (1), press brake pedal to floor for this purpose.
Fig. 140: Identifying Collar Nut
Remove left microfilter housing cover.
IMPOR
