Turbobrake, function

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Comparison diagram for turbobrake to engine brake flap

A Engine brake flap, constant throttle and retarder

B Turbobrake and constant throttle

C Engine brake flap and constant throttle

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1 Working cylinder

2 Setting cam

3 Housing

4 Guide vane

8 Vacuum cell

9 Purge element

10 Rotary valve

5 Clamp

6 Array

7 Turbine scroll

The turbobrake replaces the engine brake flap and is designed as a guide vane (4) that can be shifted axially within the turbocharger. As soon as an increased engine braking effect is required, the guide vane (4) is shifted into the annular port of the turbine inlet. This serves to reduce the flow cross-section of the annular port, as well as the flow angle of the exhaust gases onto the turbine. This in turn accelerates the exhaust gas and thus results in an increase in turbine speed, which then increases boost pressure.

The boost pressure thus generated also boosts the engine braking effect, i.e. the increased compression work corresponds to increased braking work.

The turbobrake acts as an engine brake flap.

Actuation is performed by pressing the engine control/permanent brake operating lever, which in turn actuates the working cylinder (1). At an engine oil temperature < 60 °C the constant throttle is also actuated.

To prevent any destruction of the turbocharger through overspeed, the turbine speed is forwarded by the turbine speed sensor in the turbocharger to the engine control (MR) and governed to 90,000 rpm. If required the engine control (MR) control unit regulates the electric-pneumatic converter, which actuates the vacuum cell (8) of the rotary valve (10) - similar to actuation of a waste-gate valve. This in turn restricts the boost pressure and the turbine speed.

The turbobrake responds within a period of 1 to 10 s, depending on the engine output speed and output load status. Almost spontaneously after actuation the constant throttle will set up a high braking power. This is perceived by the driver to be a smooth braking start up to max. braking power through the turbobrake.