A mild hybrid vehicle control unit capable of torque hole elimination in manual transmissions

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This thesis describes a new technique for eliminating the “torque hole” in conventional manual transmission-equipped vehicles (CV). This technique involves designing a hybrid control system for a hybridized powertrain, which was used in the development of the new control techniques. To develop a mild hybrid electric vehicle (MHEV) that is both relatively cheap to manufacture, and offers smooth torque transfer during a gear change, as well as a degree of damping against torque oscillation. It needs a small electric motor (EM) at the transmission output, in addition, clutch position measurement, and optionally, automatic actuation. The function of the motor is to eliminate or reduce the torque hole during gear changes by providing a tractive force when the clutch is disengaged, and also provide damping, particularly during gear changes and take-off. In another instance, the electric motor may act as a motor or generator in certain driving situations. The MHEV requires only a single EM in its powertrain to function as an electric motor or generator in different time intervals controlled by an energy management strategy (EMS). In other words, the motor of the vehicle act as an accelerator during acceleration to assist Internal combustion engine (ICE) and act as a generator during deceleration. This powertrain uses electric energy sources in the form of battery or ultracapacitors pack. In this work, through a power flow analysis of the powertrain, the main vehicle components were sized according to the vehicle parameters, specifications and performance requirements to meet the expected power requirements for the steady-state velocity of an average typical small 5-passenger light vehicle. After the sizing process, the components were selected based on the simulation, which was based on a 1990 Mazda MX-5 (Miata). Then, the model of individual components that make up the overall structure of the MHEV powertrain, are developed in Simscape/Simulink environment and the Simscape and SimDriveline tool boxes environment to study their operational performance in various drive cycles measured under real-life conditions. The accuracy of the model is verified and validated by a comparison between the simulation results from the CV and the Advanced Vehicle Simulator (ADVISOR) codes during a number of standard drive cycles. This project aims to develop a low-cost electric hybrid drive system for small vehicles as a proof of concept. The hybrid drive system being developed is such that in a mass-manufacturing situation the total extra cost of the system should not exceed 5% over the expense of the base vehicle as manufacture cost for hybridization to include motor, inverter, and battery. Such a system would be suitable for low-end cars typically sold in developing nations and would serve both to reduce fossil-fuel dependency in these regions as well as improve air pollution characteristics, which are typically poor owing to urban particulate matter. Extensive analysis has been conducted on the fuel economy, greenhouse gas (GHG) emissions, electrical consumption, operation cost and total lifetime cost computed for different standard drive cycles. Dynamic investigations of the system with numerous degrees of freedom are conducted in this thesis, and the resulting sets of equations of motion are written in an indexed form that can easily be integrated into a vehicle model. Lumped stiffness-inertia torsional models of the powertrain will be developed for different powertrain states to investigate transient vibration. The mathematical models of each configuration, using eight degrees of freedom (DOF) for the MHEV, compared to seven degrees of freedom for a CV. Free vibration analysis is undertaken to compare the two powertrain models and demonstrate the similarities in natural frequencies and mode shapes. The impact of motor power on the degree of torque hole compensation is also investigated, keeping in mind the practical limits to motor specification. This investigation uses both the output torque, vehicle speed as well as vibration dose value (VDV) to evaluate the quality of gearshifts at different motor sizes. A credible conclusion is gained, through different simulation phases in the form of Software-in-the-loop (SIL), Rapid prototyping, and hardware-in-the-loop (HIL) to support the MHEV scenario in the development. The strategies proposed in this thesis are shown to not only achieve shifting performance, driving comfort and energy recovery rate during all conditions but also to significantly reduce cost in both the short and long terms.
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