EPA testing methods for calculation of fuel economy label ratings, which were revised beginning in 2008, use equations that weight the contributions of fuel consumption results from multiple dynamometer tests to synthesize city and highway estimates that reflect average U.S. driving patterns. The equations incorporate effects with varying weightings into the final fuel consumption, which are explained in this thesis paper, including illustrations from testing. Some of the test results used in the computation come from individual phases within the certification driving cycles. This methodology causes additional complexities for hybrid electric vehicles, because although they are required to have charge-balanced batteries over the course of a full drive cycle, they may have net charge or discharge within the individual phases. The fundamentals of studying battery charge-balance are discussed in this paper, followed by a detailed investigation of the implications of per-phase charge correction that was undertaken through testing of a 2010 Toyota Prius at Argonne National Laboratory's vehicle dynamometer test facility. Using the charge-correction curves obtained through testing shows that phase fuel economy can be significantly skewed by natural charge imbalance, although the end effect on the fuel economy label is not as large. Finally, the characteristics of the current 5-cycle fuel economy testing method are compared to previous methods through a vehicle simulation study which shows that the magnitude of impact from mass and aerodynamic parameters vary between labeling methods and vehicle types. / Master of Science

Increasing environmental, economic, and political concerns regarding the consumption of fossil fuels have highlighted the need for more efficient and alternative energy solutions. Hybrid electric vehicles represent a near-term opportunity for reducing liquid fossil fuel consumption and green-house gas emissions in the transportation industry, and as a result, many automotive manufacturers have invested heavily in hybrid vehicle development. The increased complexity of hybrid electric vehicles over standard internal combustion engine-powered vehicles has subsequently placed significant emphasis on development of advanced control methods geared towards efficient energy management. Real-time optimization-based methods represent the current state-of-the-art in terms of hybrid vehicle control and energy management. This thesis summarizes the development of an optimization-based real-time control system – which determines the optimal instantaneous system operating point, including gear, traction split between front rear axles, and engine speed and torque – and its application to an all-wheel drive extended-range electric vehicle that uses a General Motor’s front-wheel drive 2-Mode electronic continuously variable transmission and an additional rear traction motor. The real-time control system was developed and validated using a plant model and preliminarily tested in the vehicle using a four-wheel drive chassis dynamometer. Results of simulation and in-vehicle testing demonstrate engine operation focused on high-efficiency operating regions and minimal use of the rear traction motor. Further testing revealed that a rule-based traction split system may be sufficient to replace the optimization-based traction split determination, and that the limited rear traction motor use was not a function of the motor itself, but rather an inherent result of the selected architecture. / Graduate

In the European Union the legislation governing fleet CO2 emissions is already in place with a fleet average limit of 130g/km currently being imposed on all vehicle manufacturers. With the target for this legislation falling to 95g/km by 2020 and hefty fines for noncompliance automotive engineers are working a pace to develop new technologies that lower the CO2 emissions and hence fuel consumption of new to market vehicles. As average new vehicle CO2 emissions continue to decline the task of measuring these emissions with high precision becomes increasingly challenging. With the introduction of real world emissions legislation planned for 2017 there is a development driven need to precisely assess the vehicle CO2 emissions on chassis dynamometers over a wide operating range. Furthermore since all type approval and certification testing is completed on chassis dynamometers, any new technology must be proven against these test techniques. Typical technology improvements nowadays require repeatability limits which were unprecedented 5-10 years ago and the challenge now is how to deliver this level of precision. Detailed studies are conducted into the four key areas that cause significant noise to the CO2 emissions results from chassis dynamometer tests. These are the vehicle electrical system, driver behaviour, procedural factors and the chassis dynamometer itself. In each of these areas, the existing contribution of imprecision is quantified, methods are proposed then demonstrated for improving the precision and the improved case is quantified. It was found that the electrical system can be controlled by charging the vehicle battery, not using auxiliary devices and installing current measurement devices on the vehicle. Simply charging the vehicle battery prior to each test was found to cause a change to the CO2 emissions of 2.2% at 95% confidence. Whilst auxiliary devices were found to cause changes to the CO2 emissions of up to 43% for even a relatively basic vehicle. The driver behaviour can be controlled by firstly removing the tolerances from the driver’s aid which it was found improved the precision of the CO2 emissions by 43.5% and secondly by recording the throttle pedal movements to enable the validation of test results. Procedural factors, such as tyre pressures can be easily controlled by resisting the temptation to over check and by installing pressure sensing equipment. Using a modern chassis dynamometer with low parasitic losses will make the job of controlling the dynamometer easier, but all dynamometers can be controlled by following the industry standard quality assurance procedures and implementing statistical process control tools to check the key results. The implementation of statistical process control alone improved the precision of unloaded dynamometer coastdown checks by reducing the coefficient of variation from 6.6 to 4.0%. Using the dynamometer to accelerate the vehicle before coastdown checks was found to approximately halve the variability in coastdown times. It was also demonstrated that verification of the dynamometer inertia simulation and response time are both critically important, as the industry standard coastdown test is insufficient, in isolation, to validate the loading on a vehicle. Six sigma and statistical process control techniques have shown that for complex multiple input single output systems, such as chassis dynamometer fuel economy tests, it is insufficient to improve only one input to the system to achieve a change to the output. As a result, suggested improvements in each noise factor often have to be validated against an input metric rather than the output CO2 emissions. Despite this, the overall level of precision of the CO2 emissions and fuel consumption seen at the start of the research, measured by the coefficient of variation of approximately 2.6%, has been improved by over six times through the simultaneous implementation of the findings from this research with the demonstration of coefficient of variation as low as 0.4%. Through this research three major contributions have been made to the state of the art. Firstly, from the work on driver behaviour an extension is proposed to the Society of Automotive Engineers J2951 drive quality metric standard to include the a newly developed Cumulative Absolute Speed Error metric and to suggest that metrics are reviewed across the duration of a test to identify differences in driving behaviours during a test that do not cause a change to the end of test result. Secondly, the need to instrument the vehicle and test cell to record variability in the key noise factors has been demonstrated. Thirdly, a universal method has been developed and published from this research, to use response modelling techniques for the validation of test repeatability and the correction of CO2 emissions. The impact of these contributions is that the precision of chassis dynamometer emissions tests can be improved by a factor of 6.5 and this is of critical importance as the new real world driving and world light-duty harmonised emissions legislation comes into force over the next two to five years. This legislation will require an unprecedented level of precision for the effective testing of full vehicle system interactions over a larger operating range but within a controlled laboratory environment. If this level of precision is not met then opportunities to reduce vehicle fuel consumption through technology that only has a small improvement on fuel consumption, which is likely given the large advances that have be achieved over the last few decades, will be missed.

The internal combustion engine (ICE) vehicle has dominated the transportation market for nearly 100 years. Numerous concerns with continued use of fossil fuels arise, however, and these concerns have created an impetus to develop more efficient vehicles that release fewer emissions. There are several powertrain technologies that could supplant conventional ICEs as the dominant technology, most notably electric and hybrid powertrains. In order to achieve the levels of performance and cost of conventional powertrains, electric and hybrid powertrain designers must use design techniques and tools such as computer modelling, simulation and optimization. These tools facilitate development of a virtual prototype that allows the designer to rapidly see the effects of design modifications and precludes the need to manufacture multiple expensive physical prototypes. A comprehensive survey of the state of the art of commercialized hybrid vehicle powertrains is conducted, and the term multi-regime in ICE hybrid vehicle (ICEHV) modelling is introduced to describe designs that allow for multiple configurations and operating regimes. A dynamic mathematical model of a power-split architecture with two modes (or configurations) introduced by General Motors Corporation is developed and a steady-state version is programmed into the ADvanced VehIcle SimulatOR (ADVISOR) simulation software package. This ADVISOR model is applied to a commercial delivery vehicle, and the fuel consumption of the vehicle undergoing a variety of drive cycles is determined. The two-mode model is compared to the ADVISOR models for the Toyota Hybrid System (THS), parallel hybrid, and conventional powertrains in the same vehicle. The results show that for this vehicle type, the two-mode design achieves lower fuel consumption than the THS and conventional powertrains, and only slighter greater fuel consumption than the parallel hybrid design. There is also considerable potential for improvement in performance of the two-mode model through the development of an optimal power management strategy. In the medium- to long-term, the necessity for zero-emission vehicles may position fuel cell systems (FCSs) to be commercialized as on-board energy conversion devices. FCSs are currently inordinately expensive with power density and durability issues, among other design problems. Fuel cell hybrid vehicle (FCHV) designers must use the available design techniques intelligently to overcome the limitations and take advantage of the higher efficiency capabilities of the fuel cell. As the first step in creating a virtual prototype of a FCS, a semi-empirical model of the system is developed and further enhancements such as transient response modelling are proposed. An optimization of the operating parameters to maximize average net power and average exergetic efficiency is conducted, and the technique is applied to the FCS model for the prototype fuel cell hybrid scooter (FCHS). The optimizations demonstrate that significant improvements in performance can be achieved, and that optimizations with more design variables are warranted. Models of a conventional battery scooter (BS) and of the FCHS are developed in ADVISOR. Simulations are conducted which compare the performance of the two models. Subsequently, performance tests of the BS and FCHS are conducted using a chassis dynamometer. Despite problems with the prototype FCHS, the tests confirm the theoretical results: the FCHS model achieves higher performance in terms of acceleration and power, while the BS model operates more efficiently and requires less energy. This study provides better understanding on the emerging FCHV and ICEHV technologies; introduced new and improved models for FCHV and multi-regime hybrid powertrains; developed FCHV and ICEHV performance simulation and design optimization methods using the new computer models; explored the methods for validating the computer models using prototype BS and FCHS on a research dynamometer; identified areas of improvements of the new experiment methods; and formed the foundation for future research in related areas.

Brake materials represent an important source of air pollution, especially in urban areas, where they can contribute to approx. 21 % of the traffic-related particulate matter emission. For this reason, the design of new brake materials with low emissions is a topical issue. In addition to low emissions, the design of new friction materials has to ensure excellent performance with stable coefficients of friction and low wear rate. Due to the several requirements that these materials need to fulfill, their development and testing are complex and intercorrelated. Good performance and low emission strongly depend on the mechanisms acting at the disc-pad interfaces. In this thesis, a brake dynamometer testing protocol is developed to better understand the relationships of the braking parameters with the brake performance and emission behavior, correlating them with the surface characteristics. The surface characteristics were investigated with a-posteriori analysis, in terms of extension of the contact area, degree of compaction of the wear particles and relevant composition. The work is focused on the bedding process and the influence of the braking parameters on the frictional, wear and emission behaviors. Regarding the bedding process, run-in, transition stage and steady states were identified as concerns the frictional, wear and emission behaviors. The frictional behavior gets stabilized by the extension of the secondary plateaus, whereas the wear and emission behaviors are stabilized as their degree of compaction increases. The influence of pressure and velocity under mild sliding conditions were studied for a low-met and NAO material, the two most common types of friction materials. The low-met material featured a more stable and higher friction coefficient and lower wear and emissions than the NAO material. The wear behavior is strongly affected by pressure for the NAO material, and for the low-met material, velocity is very influential. Emissions follow a cube relationship with velocity for both materials. The significant differences in the observed behaviors are explained in terms of the different features of the surfaces. The NAO material featured a smooth and uniform surface, with higher coverage than the low-met material, on which steel fibers play important adhesive and abrasive actions. From tests under mild sliding conditions of several friction materials sliding against cast-iron discs, a linear relationship is found between the specific wear rate and the emission factor. This relationship identifies a wear rate below 2.5 10-14 m2/N complying with the Euro 7 limitation of 3 mg/km/vehicle after 2034. Among the friction materials sliding against cast iron discs, the NAO material and only one friction material displayed an emission factor below the limit of 3 mg/km/vehicle. In addition, the emission factor of low-met material sliding against a cermet-coated disc was lower than this limit. These observations confirm that the NAO materials and coated discs are effective systems to mitigate emissions, whereas further efforts are required to improve the emission behavior of low-met materials. Interestingly, the low-met materials with a reduced presence of secondary plateaus featured higher wear and emissions. Regarding the brake performance, under severe sliding conditions, the NAO material displayed worse frictional and wear behaviors than the reference low-met material. For high-pressure ranges, the effect of pressure is to cause a monotonic decrease in the friction coefficient. The effect of temperature on the friction coefficient causes an increase in the friction coefficient when the tribo-oxidative processes are contained up to 300 °C. For combinations of high velocity and temperature, the tribo-oxidative processes are high enough to form a thick glaze layer on the surfaces. The glaze layers were correlated to a lubricating effect, or fade effect, at disc temperatures above 400 °C, especially when their extension covered the steel fibers. The cermet-coated disc displayed the same fade behavior at high velocity-temperature values, although at low velocities and high temperatures, friction instability was observed and related to larger but fewer patches originating to a significant extent from material transfer from the disc. The friction instability in the coated disc was ascribed to the different tribo-oxidative behavior in the formation of ‘glazes’ due to the low source of iron in the disc material.

Carbon fibre reinforced ceramic composites (Cf/C-SiC) have been explored as lightweight and durable disc in a friction brake. This composite was manufactured through infiltration of liquid silicon into a Cf/C perform. It has heterogeneous microstructure, composed of three key phases, silicon carbide, Cf/C, and un-reacted residual silicon. The development of the transfer layer on the friction surface of Cf/C-SiC was studied through microstructural image registration of the surface after a range of braking stops on a laboratory-scale dynamometer test rig. When an organic pad was used as the counter face brake pad, it was found that a steady transfer layer was developed in silicon regions right after initial stops; in carbon-fibre/carbon (Cf/C) regions and most of the silicon carbide region, the friction surfaces were unsteady and any possible friction transfer layers were hardly built up. Large voids and cracks/crevices likely became pools to quickly and efficiently collect the transferred materials generated by the friction, but the compacts formed inside the pools were susceptible to be stripped off by further braking operation. Three types of friction surfaces were generalized: type I, the friction transfer layer had a steady relationship with the matrix and respectable longevity; type II, the transfer layer had an unstable relationship with the matrix and poor durability; type III, the friction transfer layer had a steady relationship with the matrix but short lifetime. After testing against organic pads under the laboratory scale dynamometer testing condition, the friction surface of each key phase in Cf/C-SiC composites disc was studied by transmission electron microscopy (TEM). It was found that the transfer layer developed on Si consists of fine particles of metal silicides, silicates and minerals. The substrate damage of Si was not observed, while the precipitates having high oxygen content were found in the substrate. Formation of an interfacial bonding between transfer layer and silicon substrate is believed to be the key factor for the formation of a stable transfer layer on Si. However, the interfacial bonding between transferred materials and SiC was not detected. Kinks are common features developed on the friction surface of SiC. The interface between carbon fibre and carbon matrix was experienced mechanical damage, in form of microcracks, and the transferred material was developed in the interface. Instead of transfer layer, a thin amorphous film, produced by friction induced amorphisation of carbon fibre, was developed on top of carbon fibre.

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