Boost pressure control - function

P09.40-2195-12

B5/1 Charge pressure sensor

B37 Accelerator pedal sensor

B60 Exhaust back pressure sensor (with DPF)

N3/9 CDI control unit

Y100/1 Right charge pressure positioner

Boost pressure control takes place dependent on the performance map and also dependent on the boost pressure and load requirement from the CDI control unit.

The CDI control unit actuates the boost pressure positioner (according to an input signal) to achieve boost pressure control.

The position of the guide vanes in the exhaust turbine is determined over the control linkages and thus the required boost pressure at the momentary current load condition of the engine.

Exhaust turbocharger protection

In order to prevent damage to the turbocharger from excessively high rotational speeds of the turbocharger (due to a strongly soiled air filter), the intake air pressure downstream of the air filter is monitored by the pressure sensor downstream of air filter (B28/5). If the intake air pressure s too low the CDI control unit reduces the boost pressure and the injection quantity to protect the turbocharger.

Engine and turbocharger protection (with DPF)

In order to prevent overheating damage (for major loading of the DPF) on the engine and turbocharger, the exhaust back pressure upstream of the turbocharger is monitored by the CDI control unit. At a high exhaust back pressure the CDI control unit reduces the boost pressure and the injection quantity to protect the turbocharger and engine.

P09.40-2194-76

Adjusting the charge pressure

110/1 Control linkage

110/2 Guide vane

110/3 Turbine wheel

110 A Exhaust turbine

110 B Fresh air compressor

Y100/1 Right charge pressure positioner

a Flow cross-section

b Adjustment angle of the guide vanes

A Boost pressure positioner actuated, guide vanes closed

B Boost pressure positioner not actuated, guide vanes opened

A: At low engine speeds, the guide vanes are increasingly closed and thus the flow cross-section is reduced. The result is that the flow rate of the exhaust gas at the turbine wheel is increased, which in turn increases the speed of the turbine wheel and the compressor turbine wheel. This increases the boost pressure and the engine torque increases.

B: At high engine speeds, the guide vanes are opened increasingly and thus the flow cross-section increased. This reduces the air flow velocity of the exhaust at the turbine wheel whereby the desired boost pressure is achieved for a lower exhaust back pressure. This reduces the fuel consumption.