25
5V Turbo
N249
J220
N75
G70
G28
G69
Charge pressure control
If the control fails, the maximum charge pres-
sure 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 turbochar-
ger 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 com-
pressor 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.
SSP207/22
energised
de-energised
Waste gate valve
