تجزیه و تحلیل هزینه چرخه عمر یک ماشین، انتقال قدرت یک اتوبوس شهری و اتوبوس های شهری برای سال 2005 و 2020

The international economy, in the beginning of the 20th century, is characterized by uncertainty about the supply and the price of oil. Together with the fast decrease of electrical propulsion component prices, it becomes more and more cost effective to develop vehicles with alternative powertrains. This paper focuses on two questions: Are alternative powertrains especially cost effective for specific applications?; How does an increased fossil fuel price influences the choose of powertrain? To assess these questions, a computer tool named THEPS, developed in a Ph.D. project, is used. Three applications and three scenarios are analysed. The applications, a car, a city bus and an intercity bus, are vehicles all assumed to operate in Sweden. One scenario represents year 2005, the other two year 2020. The two future scenarios are characterized by different fossil fuel prices. The study, presented in the paper, indicates that alternative powertrains can be competitive from a cost perspective, in some applications, already in year 2005. It is for example cost effective to equip a city bus, running in countries with a high fuel price, with a hybrid powertrain. The study also indicates that pure electric, hybrid and/or fuel cell cars will probably be a more cost effective choice than conventional cars in year 2020. Another indication is that it will not be clear which powertrain concept to choose. The reason is that many cost effective powertrain concepts will be offered. The best choice will depend on the application.

Increased energy demands, combined with limited fossil fuel sources and the environmental concern, are huge challenges for the humankind. The greatest increase in transportation energy consumption will occur in the developing world. Vehicles with an internal combustion engine (ICE), as single power source, have for a long time dominated the market. However, more energy efficient alternative powertrains,1 like hybrid powertrains, become more and more attractive. The major reasons are the reduced cost of electrical components and the risk of higher fossil fuel prices. Many design options are present when it comes to powertrain design. The powertrain components can be configured, chosen and sized in numerous ways. The most cost effective choice depends on factors like fuel price, application and interest rate. Especially, in future when many powertrain concepts will be offered, it will not be clear for a customer which powertrain to choose. Several papers deal with the economical impact of different fuels, in transportation, from a societal perspective, some examples are Specht et al. (1998), Azar et al. (2002), Hekker et al. (2003) and Ogden et al. (2004). These studies focus on comparing different fuel chains2 or technical aspects in the vehicle. Typically a cost model, that includes the capital cost of the vehicle and the fuel cost, is included. The powertrain models are normally very simple, in Specht et al. (1998) the energy conversion in the powertrain is modelled by a constant efficiency. The characteristics of the different powertrain types are derived from real vehicles or from computer simulation, in Hekker et al. (2003) it is assumed that hybrid powertrains have 50% lower fuel consumption compared to the conventional powertrains. There are also numerous papers that deal with detailed computer simulation of a given powertrain, some examples are Lyshevski (2000), Butler et al. (1999) and Wipke et al. (1999). By detailed computer simulation, virtual tests of powertrains can be performed to study technical aspects in a vehicle. Examples of earlier studies that focus on costs, connected with the use of a vehicle, are Cuenca et al. (2001), Lipman and Delucchi (2003), Cuenca et al. (1999), Burke (2003), Vyas et al. (1999), Mizsey and Newson (2001), Ekdunge and Råberg (1998) and Forsberg (2003). In this paper, a smaller set (2–5) of powertrains, are prescribed. Their performance, fuel consumption and other characteristics are typically determined from computer simulation. Comparisons for different parameter setups are then often made, fuel price can be the parameter varied. The purpose of this paper is to assess powertrain choices for different applications and scenarios. Two key questions are highlighted: (Q1) Are alternative powertrains especially cost effective for specific applications? (Q2) How does an increased fossil fuel price influence the choose of powertrain? The difference from similar studies, previously cited, is that the powertrain design is not prescribed. In this study, a computer tool automatically finds the lowest cost powertrain design, given constraints and prerequests. The author has not found any work that considers, in a systematic way, that the powertrain design highly depends on constraints and prerequests. In Section 2, different powertrain technologies are presented. A computer tool THEPS, developed in a Ph.D. project to optimize powertrains, is described in Section 3. Assumptions and limitations are presented in Section 4. The main contribution of the paper, a life cycle cost analysis of a car, a city bus and an intercity bus, is presented in Sections 5–7. In the end of the paper conclusions are drawn.

The design of a cost effective powertrain is a compromise between several aspects. One extreme case is a vehicle that is cheap to buy but has a high operating cost. The operating cost is highly influenced by the fuel consumption. An other extreme is a vehicle with a low operating cost and high purchase price. The powertrain in a cost effective vehicle is a trade off between these extremes. In contrast to similar studies, presented in Section 1, the method used in this paper automatically adapts the powertrain design with respect to prerequests. For example is a fuel efficient powertrain design proposed if the fuel prices are high. In a HEV, a large buffer normally means a fuel efficient design. If such an adaptation, corresponding to the location between the previously described extremes, is not performed, the result is debatable. The reason is that each powertrain configuration type must have a fair chance. This different approach, resulting in a systematic and extensive calculation procedure for powertrain comparison, is probably the most original contribution of the paper. The result of the study, in this paper, gives an answer to the first question Q1, presented in Section 1. HEVs are specially cost effective if following statements are true: the vehicle is operated in an urban environment, electrical power components are cheap, fuel prices are high and the vehicle is heavy. Hybrid powertrains are cost effective in heavy vehicles due to the long lifetime and high level of brake energy regeneration in such vehicles. The extra capital cost, of HEVs, is spread over more miles if the lifetime is long. Also the second question Q2, in Section 1, can be answered thanks to the study. Assuming non-cost effective fuel cell powertrains, an increased fossil fuel price will heavily increase the cost of intercity automobile transportation. Due to the high energy efficiency of HEVs in city traffic, urban transportation cost has a low dependency on fossil fuel prices.