Powertrain dynamic torque reduction using clutch slip control
The torque dynamic caused by the firing pulse from diesel engines set high robustness demands for gearboxes and final drives in today’s heavy duty trucks. If these dynamic loads could be eliminated or dampened, the driveline can be built lighter because of the lower demands which in turn would save fuel for the driver and material cost for the manufacturer. There exist solutions to this problem that include expensive and complicated hardware; for example the double mass flywheel, but there is one opportunity that is potentially for free to the manufacturer, namely clutch slip control.
The hypothesis of this thesis is that the torque oscillations from the engine can be reduced by controlling the clutch slip velocity. It is also evaluated if it is possible to control a slip using existing hardware in a Scania powertrain and if the control performance can be improved by changing one of the powertrain parameters. For the scope of this thesis, the wear rate and temperature of the clutch when slipping is not considered.
The first step of the thesis is to construct a MBS model of the powertrain in question. Further on, two control designs, namely fuzzy control and two degrees of freedom control are implemented using model based control design. Both control algorithms are implemented in a heavy duty truck and the performance is evaluated. To find the parameter that constrains the performance, a parameter variation is performed using the developed model to save both time and cost.
It is proved that the torque dynamics from the diesel engine can be dampened by forty to eighty percent in amplitude by slipping the clutch and that the implemented control design gives acceptable results for gears seven to twelve using existing hardware. The parameter variation shows that the actuation delay is the main limiting factor, enabling stable control at the first gear if removed completely.
The slip control concept shows potential but sets high demands for hardware specification, especially for actuation delays if all gears are to be used with slip control. Using existing hardware, the control is fully implementable for gears seven to twelve with good results.
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