Search

The legislation limits for pollutants emissions are strongly pushing OEMs to electrification of their vehicle fleet. Even high performance car manufacturers are taking on the challenge of using electrification - a trend also observed for premium and exotic vehicles. This electrification job is seen from some manufacturers as an opportunity to increase the vehicle performances while moving to more “green” powertrains. It means that the installation of electric power on the vehicle should certainly not affect the performances of the vehicle models with only an internal combustion engine, but increase the performances while cutting the pollutants emissions during driving. As such it is no easy task, since the hybrid system (battery, inverter, and electric motor) affects strongly the overall vehicle weight and thus its driving dynamics as well as system cost. On top of this most manufacturers look for synergies between hybrid and standard versions in order to minimize cost and investments of the overall vehicle platform. All the arguments above weigh even stronger focussing on high performance cars due to the challenges posed by low to medium production volumes. Because of this, modularity of the specific subsystems plays a key role during the concept selection.

Torque-fill capability during gearshifts is an important customer requirement in automated transmission systems. This functionality can be achieved through transmission system layouts (e.g., based on dual-clutch technology) characterized by significant mechanical complexity, and hence with relatively high cost and mass. This paper describes a parallel hybrid electric drivetrain concept, based on the integration of an electric motor drive into a relatively simple six-speed automated manual transmission. The resulting hybrid electric drivetrain actuates the torque-fill function through control of the electric motor torque during the gearshifts on the engine side of the drivetrain. An optimal controller, based on the off-line computation of the control gain profiles, is presented for the clutch re-engagement phase. The novel controller allows computationally efficient consideration of clutch energy dissipation during the clutch re-engagement phase of the gearshift. The performance with the optimal controller is contrasted with that of two conventional clutch engagement controllers, along a set of gearshifts simulated with an experimentally validated vehicle model.

The main benefits of dual clutch transmissions (DCTs) are: (i) a higher energy efficiency than automatic transmission systems with torque converters; and (ii) the capability to fill the torque gap during gear shifts to allow seamless longitudinal acceleration profiles. Therefore, DCTs are viable alternatives to automated manual transmissions (AMTs). For vehicles equipped with engines that can generate considerable torque, large clutch-slip energy losses occur during power-on gear shifts and, as a result, DCTs need wet clutches for effective heat dissipation. This requirement substantially reduces DCT efficiency because of the churning and ancillary power dissipations associated with the wet clutch pack. To the knowledge of the authors, this study is the first to analyse the detailed power loss contributions of a DCT with wet clutches, and their relative significance along a set of driving cycles. Based on these results, a novel hybridised AMT (HAMT) with a single dry clutch and an electric motor is proposed for the same vehicle. The HAMT architecture combines the high mechanical efficiency typical of AMTs with a single dry clutch, with the torque-fill capability and operational flexibility allowed by the electric motor. The measured efficiency maps of a case study DCT and HAMT are compared. This is then complemented by the analysis of the respective fuel consumption along the driving cycles, which is simulated with an experimentally validated vehicle model. In its internal combustion engine mode, the HAMT reduces fuel consumption by >9% with respect to the DCT.

The paper describes the advantages due to the adoption of multi-speed transmission systems within fully electric vehicles. In particular, the article compares a conventional single-speed transmission layout, a 2-speed layout based on a novel gearbox architecture capable of seamless gearshifts, and a Continuously Variable Transmission layout. The selection of the optimal gear ratios for the 2-speed system has been based on an optimization procedure, taking into account the efficiency characteristics of the components of the whole vehicle powertrain. The control system for the Continuously Variable Transmission system has been designed with the aim of maximizing the efficiency of the operating points of the electric motor. The results show that there is a significant advantage in adopting a 2-speed transmission system over the single-speed layout, and, despite a reduction in motor losses, the typically lower efficiency characteristics of Continuously Variable Transmissions do not result in lower energy consumption for the four case study vehicles.

This paper deals with the simulation of the low frequency drivability of through-the-road parallel (TTRP) hybrid electric vehicles (HEVs). The current literature relating to HEVs is predominantly focused on energy efficiency optimisation. However, the drivability of this HEV typology can be particularly critical, due to the interaction of the front and rear axle dynamics. The article presents an experimentally validated non-linear model of a TTRP HEV, consisting of a front axle driven by an internal combustion engine (ICE) with a six-speed transmission, and a rear axle powered by an electric motor with a prototype two-speed transmission. The simulated TTRP HEV is then considered with both driven axles, and drivability manoeuvres in conditions of constant gear are carried out. The results are analysed to study acceleration and jerk profiles, and understand the anti-jerk control system fundamentals through linearisation methods.

Fully electric vehicles and range-extended electric vehicles can be characterised by a multitude of possible powertrain layouts, many of them currently under investigation and comparison. This contribution presents a novel clutchless seamless four-speed transmission system which can be concurrently driven by two electric motor drives, for use in fully electric vehicles or electric axles for through-the-road parallel hybrid electric vehicles. The transmission system allows the electric motors to work in their high efficiency region for a longer period during a typical driving schedule. This paper describes the layout of the novel transmission system, the equations for modelling its dynamics and the criteria for the selection of the best gearshift maps for energy efficiency. Finally, an energy consumption and performance comparison between the novel drivetrain, a conventional single-speed electric drivetrain and a double-speed electric drivetrain is discussed in detail for two case study vehicles.