All variable geometry turbos have movable “nozzle vanes” on the exhaust, or hot side of the turbo. They also all have some mechanical means of moving them in sync with each other, typically a unison ring. They all use one of several types of actuators to move the ring; vacuum, electrical, hydraulic.
This is a view of the Holset VGT turbo used on the Cummins 6.7 L. The movable nozzle vanes are around the outer circumference. Because the VGT nozzle vanes are on the exhaust side, they all are subject to carbon fouling, and can bind or become stuck. Changes to the ECM software have made this less common, but have not eliminated it.
This is a generic drawing of a VGT, showing both the hot and cold sides, and a vacuum actuator for the nozzle vanes. I like this drawing because it shows the nozzle vanes in different positions. The nozzle vanes primary purpose is to make the turbo more responsive at various speeds. On Diesel engines, they can also be driven closed by the ECM to act as an exhaust brake.
PS- All of the nozzle actuator types are external to the turbo, so not in the exhaust stream. Each type tends to have their own strengths and weaknesses, and common failure points. Electronic actuators, like on the Holset VGT, tend to fail without much warning or apparent reason. It would take an engineering tear-down and analysis to determine the root cause of early life failures of an electronic actuator. But I would bet that the root cause would NOT be because you either did or did not engage the exhaust brake at every engine start.
:):)
This is a view of the Holset VGT turbo used on the Cummins 6.7 L. The movable nozzle vanes are around the outer circumference. Because the VGT nozzle vanes are on the exhaust side, they all are subject to carbon fouling, and can bind or become stuck. Changes to the ECM software have made this less common, but have not eliminated it.
This is a generic drawing of a VGT, showing both the hot and cold sides, and a vacuum actuator for the nozzle vanes. I like this drawing because it shows the nozzle vanes in different positions. The nozzle vanes primary purpose is to make the turbo more responsive at various speeds. On Diesel engines, they can also be driven closed by the ECM to act as an exhaust brake.
PS- All of the nozzle actuator types are external to the turbo, so not in the exhaust stream. Each type tends to have their own strengths and weaknesses, and common failure points. Electronic actuators, like on the Holset VGT, tend to fail without much warning or apparent reason. It would take an engineering tear-down and analysis to determine the root cause of early life failures of an electronic actuator. But I would bet that the root cause would NOT be because you either did or did not engage the exhaust brake at every engine start.
:):)
