Turbocharger (TC) Control System

Courtesy of VOLVO CARS CORPORATION

Boost pressure control 

The boost pressure in the inlet manifold is controlled via the wastegate valve, which has a pressure box (1) that is affected by the pressure from the turbocharger (2).

The Engine Control Module (ECM) (8) receives information about the current throttle position via the throttle position sensor for the throttle unit (3), engine load, knocking, etc. This affects the boost pressure that is permitted. The boost pressure is measured by the boost pressure sensor (9).

The control module controls the boost pressure using the turbocharger control valve (4), which controls the pressure to the wastegate valve so that the control is adapted to the desired pressure.

See also DESIGN  

When the pressure rises, the wastegate valve's pressure box is affected. When the boost pressure has increased to the maximum permissible value, the wastegate valve opens, and some of the exhaust gases pass the turbocharger's turbine rotor, limiting the boost pressure.

Turbocharger (TC) control is governed continually by the Engine Control Module (ECM).

When a higher boost pressure is permitted, the control module opens the turbocharger (TC) control valve further. Some of the boost pressure which affects the wastegate valve's pressure box is released back into the intake manifold. This lowers the control pressure, the wastegate valve opens later and the boost pressure increases.

Because the control module calculates the boost pressure using the signal from the boost pressure sensor and the temperature sensor, there is automatic compensation of boost pressure control when driving at altitude and at different temperatures. As a result engine power will not be noticeably affected by the air density or temperature.

The Engine Control Module (ECM) can diagnose the turbocharger (TC) control function.

Relief valve 

In case of overpressure in the intake manifold (turbo pressure) and when the accelerator is let up quickly, an increasing pressure is generated which may cause noise (pulsations). The relief valve's (7) function is to lead back this pressure to the turbocharger's inlet side to limit the sound.

Usually, a mechanical relief valve (dump valve) is used, built up around a diaphragm (directly affected by pressure differences) and a piston to handle control of the overpressure, but this developed variant is electrically controlled by Engine Control Module (ECM).

Since the pressure that is controlled away already is measured by the mass air flow sensor (6), the pressure cannot be released to the atmosphere, instead it is returned again between the mass air flow sensor and turbocharger.