Electronic boost pressure control- turbocharger actuator testing

The turbocharger actuator, also called control box or boost pressure regulator, is an electronic control device for adjustable turbochargers and is predominantly used for Variable Nozzle Turbine (VNT) and Variable Turbine Geometry (VTG) turbochargers.

In these turbochargers with variable turbine geometry, the actuator reliably and precisely controls the movement of the guide vanes. Through the adjustment of the guide vanes, the exhaust gas flow onto the turbine wheel is influenced, thus changing the boost pressure which can then be optimally adjusted to match all speed ranges. The required boost pressure is regulated according to a map stored in the engine control unit. The engine control unit sends the required boost pressure in the form of a signal to the turbocharger actuator via a data bus connection. The actuator adjusts the guide vanes accordingly in line with the required angle setting contained in the signal. 

Advantages of an electronic control device are:

• Faster response of the turbocharger already at low engine speeds
• Exact adjustment of the guide vanes in all speed ranges
• Improvement of the emission values

In the turbine housing, moving guide vanes are positioned in a circle on a carrier ring and connected with their shafts to the adjusting ring via guide pins. The adjusting ring is in turn connected to the turbocharger actuator via a rod. 

If the adjusting ring is moved by the actuator, all guide vanes are adjusted synchronously and in this way the turbine inlet area is either reduced or enlarged. This action has, in turn, an influence on the behaviour of the exhaust gas flow and consequently on the turbine speed. The result is that the boost pressure can be purposefully increased or reduced. 

The main function of the actuator is to bring the shaft into the position specified by the control unit or into that position calculated as a result of the map diagrams.

With the help of the contactless, inductive position sensor (CIPOS sensor), the position of the shaft is continuously determined and actively reported back. Angles are measured inductively using a non-contact and consequently wear-free method, thus guaranteeing high measuring precision throughout the entire lifetime. The insensitivity to magnetic fields and the high level of temperature stability, in particular, are the characteristic qualities of the CIPOS technology implemented here.

In addition to the CIPOS sensor responsible for precise positioning, the integrated electronics also include control of the electric motor and error diagnosis. In this way, errors can be detected, reported back and appropriate reactions automatically derived from them. The actuator has a flexible operating angle area and carries out controlled movement up to the limit stop. 

Depending on the model, communication in the vehicle is possible both via CAN bus and also via a pulse-width modulated signal (PWM).

Although many turbocharger actuators look the same on the outside, their design and configuration can differ as regards performance and alignment depending on the vehicle type and the turbocharger unit. In their respective combinations with the turbocharger and in accordance with vehicle manufacturer requirements, two types of HELLA turbocharger actuators can be installed. A distinction is made here between the "Smart" and "Simple" versions. Thanks to an integrated control unit, the "Smart" autonomously regulates the adjustment of the guide vanes, while the "Simple" is controlled by a higher-level engine control unit. Although similar in appearance, the technical design of the electronics, of the gearbox and of the housing configuration is fundamentally different.

Therefore repair work involving the exchange of various components, such as gears or electronics, taken from different actuators is not possible.