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.
.png)
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.
.png)
Fig. 39: Identifying Turbocharging Components
READ NEXT:
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:
Removing And Installing/Replacing Inlet And Exhaust Adjustment Units On Left
Side (N62/N62TU)
Special tools required:
11 9 190
11 9 460
11 9 461
11 9 462
11 9 463
(cylinder bank 5 to 8)
Necessary preliminary tasks:
Read fault memory and make a documentary record.
Remove servomotor for left eccentric shaft.
Remove left cylinder head cover.
Remove all spark plugs on cylinder bank
Removing And Installing/Replacing Left Or Right Push Rod/Integral
Link
NOTE: If the integral link is detached from the wheel carrier or
swinging arm, it is
necessary after reinstallation to carry out a wheel/chassis alignment check.
Necessary preliminary tasks:
Remove rear wheel.
Tension coil spring (and leave on vehicle).
Version with ride-height control: Deacti
