Turbocharged Combustion Engine Research Articles

𝓗∞ calibratable LPV control strategies for torque control in automotive turbocharged engines

This paper presents some outcomes of a recently completed research project aimed at developing torque control strategies for automotive turbocharged combustion engines with modern control design methodologies. Traditional torque control consists of maintaining some relevant signals close to certain set-points generated by a map representing the static inverse model of the engine, without any consideration for the optimality of the responses. The proposed model-based control strategy does not make use of any static map and all signals of interests are regulated at the same time by a unique centralised multivariable controller. A Linear Parameter Varying (LPV) optimal control design problem, formulated via Linear Matrix Inequality (LMI) feasibility conditions, is solved to generate the controller, whose main objectives are the reduction of fuel consumption while maintaining good torque tracking. The resulting regulator presents is gain-scheduled and is designed to be calibratable in real-time. Some numerical simulations demonstrate the effectiveness of the presented approach.

An Adaptive Frequency-Locked-Loop Approach for the Turbocharger Rotational Speed Estimation via Acoustic Measurements

Obtaining accurate measures of the turbocharger rotational speed is a key task to achieve good powertrain control performance in turbocharged combustion engines. However, direct access to the rotating parts of a turbocharger requires expensive sensors that present long-term reliability issues. In view of this, this article focuses on the design of measurement architectures for the estimation of the turbocharger shaft rotating speed via the numerical processing of the overall sound emissions acquired by a microphone placed in the vehicle hood. This kind of signal represents an extremely rich source of information about the operating conditions of all noisy powertrain subsystems. The core of the scheme is represented by an adaptive discrete-time nonlinear frequency locked-loop (FLL) filter that is properly designed to extract the useful frequency content from the acquired audio signal. The whole architecture is innovative, flexible, and extremely low cost by requiring, for its implementation, the additional installation of a single microphonic capsule only. Moreover, it exhibits such a modest computational burden to be directly implementable in commercial engine control units (ECUs) without requiring additional computing hardware. Reported experimental assessments show that the accuracy of the estimate is excellent in all allowed rotational speed regimes.

Reducing torsional vibrations by means of a kinematically driven flywheel — Theory and experiment

Modern turbocharged combustion engines induce high fluctuating torques at the crankshaft. They result in torsional crankshaft vibrations that are transferred both to the gearbox and the auxiliary engine systems. To reduce the torsional crankshaft vibrations, a kinematically driven flywheel (KDF) for compensating fluctuating engine torques has been developed. It comprises a flywheel that is coupled to the crankshaft by means of a non-uniformly transmitting mechanism. The kinematical transfer behaviour of the mechanism is synthesised in such a manner that the inertial flywheel torque compensates at least one harmonic of the fluctuating engine torque. The degree of non-uniformity of the mechanism has to be adapted to the actual speed and load of the engine. A novel geared double-crank mechanism with cycloidal-crank input and adjustable crank length is proposed and analysed. Parameter synthesis is achieved by means of a simplified mechanical model that calculates the required transfer function for a given engine torque. A multibody simulation of a three-cylinder engine equipped with the KDF demonstrates the efficacy of the system. A functional prototype has been built up and tested on an electrically driven test stand. Measurements confirm the simulated behaviour of the KDF thus demonstrating the potential of the device.

Unsteady Thrust Force Loading of a Turbocharger Rotor During Engine Operation

The bearing system of a turbocharger has to keep the rotor in the specified position and thus has to withstand the rotor forces that result from turbocharger operation. Hence, its components need to be designed in consideration of the bearing loads that have to be expected. The applied bearing system design also has significant influence on the overall efficiency of the turbocharger and impacts the performance of the combustion engine. It has to ideally fulfill the trade-off between bearing friction and load capacity. For example, the achievable engine’s low end-torque is reduced, if the bearing system produces more friction losses than inherently unavoidable for safe and durable operation because a higher portion of available turbine power needs to be employed to compensate bearing losses instead of providing boost pressure. Moreover, also transient turbocharger rotor speed up can be compromised and hence the response of the turbocharged combustion engine to a load step becomes less performant than it could be. Besides the radial bearings, the thrust bearing is a component that needs certain attention. It can already contribute to approximately 30% of the overall bearing friction, even if no load is applied and this portion further increases under thrust load. It has to withstand the net thrust load of the rotor under all operating conditions resulting from the superimposed aerodynamic forces that the compressor and the turbine wheel produce. A challenge for the determination of the thrust forces appearing on engine is the nonsteady loading under pulsating conditions. The thrust force will alternate with the pulse frequency over an engine cycle, which is caused by both the engine exhaust gas pressure pulses on the turbine stage and—to a smaller amount—the nonsteady compressor operation due to the reciprocating operation of the cylinders. The conducted experimental investigations on the axial rotor motion as well as the thrust force alternations under on-engine conditions employ a specially prepared compressor lock nut in combination with an eddy-current sensor. The second derivative of this signal can be used to estimate the occurring thrust force changes. Moreover, a modified thrust bearing—equipped with strain gauges—was used to cross check the results from position measurement and thrust force modeling. All experimental results are compared with an analytical thrust force model that relies on the simultaneously measured, crank angle resolved pressure signals before and after the compressor and turbine stage. The results give insight into the axial turbocharger rotor oscillations occurring during an engine cycle for several engine operating points. Furthermore, they allow a judgment of the accuracy of thrust force modeling approaches that are based on measured pressures.

Sensor Fault-Diagnosis in a Turbo-Charged Combustion Engine

In this work the principle of observer-based sensor fault detection and isolation is improved by the use of optimal parity relations. A parity check is performed on the observation errors such that even in the case of multiple simultaneous sensor faults correct fault detection, isolation and identification can be achieved. In contrast to previous observer-based approaches for sensor-fault-diagnosis the current method utilizes only one observer/Kalman-filter thus considerably reducing the computational workload of an FDI-system. In order to illustrate its applicability, the method is applied to measured input- and output-data of an industrial turbo-charged combustion engine power plant.