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Turbocharger testing is a time consuming process, and as rapid-prototyping technology advances, so must other areas in the development chain. As an example, in one study a compressor map took over 34 hours to measure. In this paper, an effort to combat the main bottleneck of turbocharger testing, namely the thermal inertia, is made. When changing operating point during the measurement process, several minutes can be required before the turbocharger components reach temperature steady state. In an earlier paper, a method based on non-linear trajectory optimization was developed that significantly reduced the testing time required to produce compressor performance maps. The time was reduced by a factor of over 60, compared to waiting for the system to reach steady state with constant inputs. However, the method required a model of the turbocharger. This paper extends the method with system identification and model predictive control (MPC). This is an important step in order to use the optimal control method when only geometric information of the turbocharger is known, such as new prototypes. To demonstrate the effectiveness of the combination of system identification, non-linear trajectory optimization and MPC, the control strategy is applied to a virtual gas-stand implemented as a Simulink model, based on data from a Mitsubishi TD04 turbocharger. The data that was used to create the model was originally collected at Saab Automobile in Trollhättan, 2011. The results show that system identification captures the turbocharger behavior. Trajectory optimization finds a set of time optimal input trajectories. MPC successfully tracks the generated references. Real time implementation of the Matlab/Simulink based algorithm is planned for experimental testing.

The assembly of threaded fasteners may seem straightforward. However, there are many factors to consider to achieve quality tightened joints, including the joint material, threaded fastener, and coatings. Additionally, there are many assembly tool types and torque application strategies to choose from. This investigation studies the tightening speed dynamics when using torque as a control method. The clamp force obtained in the joint changes when tightening at high speed or when the speed varies greatly during tightening. This type of tightening is called highly dynamic. Highly dynamic torque control tightening strategies are studied, such as impact, pulse, and inertia-controlled methods, and compared with the continuous drive strategy, which is a standard dynamic torque tightening method. The clamp force and its scatter caused by the torque accuracy in the assembly tool type are investigated for the abovementioned torque application strategies. The study also focuses on the different results obtained from the International Organization for Standardization’s (ISO) 16047:2005 (Fasteners-Torque/clamp force testing) standard compared to a production-like setup., SAE Technical Paper 2021-01-5073

Modelbased systems engineering is becoming an important tool when meeting the challenges of developing the complex future vehicles that fulfill the customers and legislators ever increasing demands for reduced pollutants and fuel consumption. To be able to work systematically and efficiently it is desirable to have a library of components that can be adjusted and adapted to each new situation. Turbocharged engines are complex and the compressor model serves as an in-depth example of how a library can be designed, incorporating the basic physics and allowing fine tuning as more information becomes available. A major part of the paper is the summary and compilation of a set of rules of thumb for compressor map extrapolation. The considerations discussed are extrapolation to surge, extrapolation to restriction region, and extrapolation out to choking. Furthermore the compressor diameter is coupled to the maximum performance of the compressor such as maximum speed, mass flow, and pressure ratio. All this is a result of an analysis of a database of more than 300 compressors. The paper uses the compressor modeling to discuss how wishes for extendability and reuse of component performance influences the library design. A Modelica library named Vehicle Propulsion Library VehProLib has been developed to meet these goals by including basic components that give a starting point for modeling and at the same time allows reuse and extendablility.

When electrifying the powertrain, there arises an opportunity to revise the traditional turbocharging trade-off between fuel-economy and transient performance. With the help of electrification, it might be possible to make the trade-off in favor of fuel economy, since transient response can be improved by the electric machine. The paper investigates this trade-off by looking at three turbocharger selections. A conventionally dimensioned turbocharger, an efficiency optimized turbocharger with maintained flow capacity, and an efficiency optimized turbocharger with increased flow capacity. The concepts are evaluated on the following cases: stationary operation, engine tip-in performance, vehicle acceleration performance, and on road fuel economy performance. The investigation is based on a validated mean value engine model of a six cylinder inline CI engine, and on a validated driveline and vehicle model of a heavy-duty truck. The evaluations are made with the help of simulations and numerical optimal control. The results show that there is a fuel saving potential, and that the transient response is improved by the electric machine.

Turbocharging plays an important role in the downsizing of engines. Model-based approaches for boost control are going to increasing the necessity for controlling the wastegate flow more accurately. In today’s cars, the wastegate is usually only controlled with a duty cycle and without position feedback. Due to nonlinearities and varying disturbances a duty cycle does not correspond to a certain position. Currently the most frequently used feedback controller strategy is to use the boost pressure as the controller reference. This means that there is a large time constant from actuation command to effect in boost pressure, which can impair dynamic performance. In this paper, the performance of an electrically controlled vacuum-actuated waste-gate, subsequently referred to as vacuum wastegate, is compared to an electrical servo-controlled wastegate, also referred to as electric wastegate. Their performance is investigated with the two actuators installed on a turbocharged inline four gasoline engine in an engine test bench. Furthermore, different control synthesis designs for these different actuators are investigated. A state-feedback controller with standard models for the electric wastegate is described and implemented, which gives a position-controlled wastegate. One main difference between vacuum and electric wastegate is that the latter has a position sensor. To make an extended comparison between the solutions, the vacuum wastegate is also equipped with a position sensor and controller using standard controller design methods. The controllers are implemented and compared both in a simulation environment and evaluated in an engine test bench. In addition, for the electric wastegate, both soft-landing and tightening features are also implemented and investigated. Their aim is to improve the lifetime and behavior at or near the closed position.

Today’s need for fuel efficient vehicles, together with increasing engine component complexity, makes optimal control a valuable tool in the process of finding the most fuel efficient control strategies. To efficiently calculate the solution to optimal control problems a gradient based optimization technique is desirable, making continuously differentiable models preferable. Many existing control-oriented Diesel engine models do not fully posses this property, often due to signal saturations or discrete conditions. This paper offers a continuously differentiable, mean value engine model, of a heavy-duty diesel engine equipped with VGT and EGR, suitable for optimal control purposes. The model is developed from an existing, validated, engine model, but adapted to be continuously differentiable and therefore tailored for usage in an optimal control environment. The changes due to the conversion are quantified and presented. Furthermore, it is shown and analyzed how to optimally control the engine in a fuel optimal way under steady-state conditions, and in a time optimal way in a tip-in scenario.

Rollover has for long been a major safety concern for trucks, and will be even more so as automated driving is envisaged to becoming a key element of future mobility. A natural way to address rollover is to extend the capabilities of current active-safety systems with a system that intervenes by steering or braking actuation when there is a risk of rollover. Assessing and predicting the rollover is usually performed using rollover indices calculated either from lateral acceleration or lateral load transfer. Since these indices are evaluated based on different physical observations it is not obvious how they can be compared or how well they reflect rollover events in different situations. In this paper we investigate the implication of the above mentioned rollover indices in different critical maneuvers for a heavy 8×4 twin-steer truck. The analysis is based on optimal control applied to a five degrees of freedom chassis model with individual wheel dynamics and high-fidelity tire-force modeling. Driving scenarios prone to rollover accidents are considered, with a circular-shaped turn and a slalom maneuver being studied in-depth. The optimization objective for the considered maneuvers are formulated as minimum-time and maximum entry-speed problems, both triggering critical maneuvers and forcing the vehicle to operate on the limit of its physical capabilities. The implication of the rollover indices on the optimal trajectories is investigated by constraining the optimal maneuvers with different rollover indices, thus limiting the vehicle's maneuvering envelope with respect to each rollover index. The resulting optimal trajectories constrained by different rollover indices are compared and analyzed in detail. Additionally, the conservativeness of the indices for assessing the risk of rollovers are discussed.

Green zones are challenging problems for the thermal management systems of hybrid vehicles. This is because within the green zone the engine is turned off, and the only way to keep the aftertreatment system warm is lost. This means that there is a risk of leaving the green zone with a cold and ineffective aftertreatment system, resulting in high emissions.A thermal management strategy that heats the aftertreatment system prior to turning off the engine, in an optimal way, to reduce the NOx emissions when the engine is restarted, is developed. The strategy is also used to evaluate under what conditions pre-heating is a suitable strategy, by evaluating the performance in simulations using a model of a heavy-duty diesel powertrain and scenario designed for this purpose.The results show that, for the studied vehicle, pre-heating of the aftertreatment system is an effective strategy to reduce NOx for engine-off events shorter than two hours, and is most effective for engine off events of around 1.5 hours. The results also show that for engine-off events longer than two hours, pre-heating quickly becomes an inefficient strategy. At this point, ammonia storage when the engine is turned off is more important, and pre-heating can even make the results worse, since an increased SCR temperature results in lower ammonia storage before turning off the engine, which is detrimental for NOx conversion during the restart.

To investigate the optimal controls of a diesel-electric powertrain during a torque controlled gearshift, a powertrain model is developed. A validated diesel-electric model is used as the power source and the transmission dynamics are described by different sets of differential equations during torque phase, synchronization phase and inertia phase of the gearshift. Using the developed model, multi-phase optimal control problems are formulated and solved. The trade-off between gearshift duration and driveline oscillations are calculated and efficient gearshift transients for a diesel-electric and pure diesel powertrain are then compared and analyzed.

A method for determining turbocharger performance on installations in an engine test bench is developed and investigated. The focus is on the mapping of compressor performance but some attention is also given to the turbine mapping. An analysis of the limits that an engine installation imposes on the reachable points in the compressor map is performed, in particular it shows what corrected flows and pressure ratios can be reached and what these limitations depend on. To be able to span over a larger region of the corrected flow a throttle before the compressor is suggested and this is also verified in the test bench. Turbocharger mapping is a time consuming process and there is a need for a systematic process that can be executed automatically. An engine and test cell control structure that can be used to automate and monitor the measurements by controlling the system to the desired operating points is also proposed. In experiments, used for constructing the compressor speed lines, it is virtually impossible to control the turbocharger to the exact corrected speed that is postulated by the speed line. To overcome this two methods that compensate for the deviation between measured speed and the desired speed are proposed and investigated. Detailed data from a gas stand is used to evaluate the measurements compared to those that are generated in the engine test cell installation. The agreements are generally good but there is more noise in the engine data and there are also some small systematic deviations.

Hybridization and velocity management are two important techniques for energy efficiency that mainly have been treated separately. Here they are put in a common framework that from the hybridization perspective can be seen as an extension of the equivalence factor idea in the well known strategy ECMS. From the perspective of look-ahead control, the extension is that energy can be stored not only in kinetic energy, but also electrically. The key idea is to introduce more equivalence factors in a way that enables efficient computations, but also so that the equivalence factors have a physical interpretation. The latter fact makes it easy to formulate a good residual cost to be used at the end of the look-ahead horizon. The formulation has different possible uses, but it is here applied on an evaluation of the size of the electrical system. Previous such studies, for e.g. ECMS, have typically used a driving cycle, i.e. a fixed velocity profile, but here the extra freedom to choose an optimal driving pattern is added., CADICS

In modern Diesel engines Exhaust Gas Recirculation (EGR) and Variable Geometry Turbochargers (VGT) have been introduced to meet the new emission requirements. A control structure that coordinates and handles emission limits and low fuel consumption has been developed. This controller has a set of PID controllers with parameters that need to be tuned. To be able to achieve good performance, an optimization based tuning method is developed and tested. In the optimization the control objectives are captured by a cost function. To aid the tuning a systematic method has been developed for selecting representative and significant transients that excite different modes in the controller. The performance is evaluated on the European Transient Cycle. It is demonstrated how weighting factors in the cost function influence control behavior, and that the proposed tuning method gives a significant improvement in control performance compared to standardized tuning methods for PID controllers. Further, the proposed tuning method and the control structure are applied and validated on an engine in a test cell, where it is demonstrated that the control structure achieves all stated control objectives.

The objective is to investigate models of the specific heat ratio for the single-zone heat release model, and find a model accurate enough to introduce a modeling error less than or in the order of the cylinder pressure measurement noise, while keeping the computational complexity at a minimum. Based on assumptions of frozen mixture for the unburned mixture and chemical equilibrium for the burned mixture, the specific heat ratio is calculated using a full equilibrium program for an unburned and a burned air-fuel mixture, and compared to already existing and newly proposed approximative models of γ. A two-zone mean temperature model, Matekunas pressure ratio management and the Vibe function are used to parameterize the mass fraction burned. The mass fraction burned is used to interpolate the specific heats for the unburned and burned mixture, and then form the specific heat ratio, which renders a small enough modeling error in γ. The specific heats for the unburned mixture is captured within 0.2 % by a linear function, and the specific heats for the burned mixture is captured within 1 % by a higher-order polynomial for the major operating range of a spark ignited (SI) engine.