Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
51 5 Highway Modes Simulation Modules 5.1 Common Elements to All Highway Vehicles The âBus-Simulationâ and âLDV-Simulationâ worksheets are structured in a similar way to one another. The main difference is due to the fact that intercity and commuter coaches do not vary significantly by manufacturer while light duty vehicles vary significantly by class and by manufacturer within specific classes. For bus simulations, only four representative coaches are characterized in the default dataset and one coach is selected for a simulation. The âLDV-Simulationâ worksheet is organized to simulate representative composite vehicles, including proportions of hybrid vehicles and non-hybrid CVT vehicles within the composite class being simulated. Functionally, the âBus-Simulationâ worksheet has one core simulation area while the âLDV-Simulationâ worksheet repeats the simulation area such that three separate variations of drivelines can be simulated for each vehicle (i.e. conventional, hybrid and non-hybrid CVT). In addition, the âLDV-Simulationâ worksheet uses higher performance drive schedules than does the âBus-Simulationâ worksheet. Figure 5 illustrates the layout of the highway simulation modules (âBus-Simulationâ and âLDV- Simulationâ). The top left corner of the spreadsheet contains vehicle characteristics as loaded by the âMacroâ, including the following: engine power, transmission loss coefficients, vehicle mass and coast-down resistance coefficients, auxiliary power, and onboard storage characteristics (for a hybrid vehicle). Below the basic vehicle characteristics, a default 6-speed transmission is defined (with fixed gear ratios and shift points for all coaches in the âBus-Simulationâ worksheet but with ratios and shift points varying with engine power for the âLDV-Simulationâ worksheet). After the âMacroâ loads the appropriate drive schedule and vehicle type, the core simulation proceeds in the following sequence: ï· Define the operating-mode (accelerate, cruise, decelerate, stop) in column H; ï· Select a gear (given the mode, speed and acceleration rate) in column J; ï· Determine the restive and inertial force/power on the vehicle (columns L â O); ï· Determine the engine speed (column P) and its fractional value in relation to the fuel map lookup table (column Q); ï· Determine the power required at the wheels (column R); ï· Determine the power provided by the engine (given any energy recovery from onboard storage and engine performance limits) (column S); ï· Determine the engine torque at the shaft (given the power provided at the wheels and the engine speed) (column W); ï· Normalize the engine torque and do a double interpolation of the engineâs normalized fuel map (in the âLDV-Engineâ or âBus-Engineâ worksheet); ï· Apply the fuel increment above the engineâs minimum bsfc and adjust the fuel for the generic engine fuel map with factors developed for the vehicle being simulated (column AF).
52 Figure 5. Highway Vehicle Simulation Sheets Layout color legend (primary purpose of Sheet): User input, Calculation processing Sheets/Macro; Optional User overrides of technical defaults; Output
53 The top part of the simulation area simulates vehicle performance at fixed cruise speeds (as input in the âBus-Routeâ or âLDV-Routeâ worksheet) in âcruiseâ mode with fuel output in kg/km- of-travel. The lower part of the simulation area performs a second-by-second movement of the vehicle over a drive-schedule (speed profile) brought in by the âMacroâ. The equations used in the step-by-step movement of the vehicle over the drive schedule are the same as those described for the rail vehicle pre-processed acceleration profile (see Section 4.1.3.1) with the exception of the locomotive tractive effort envelope and fuel efficiency equation which do not apply. The locomotiveâs properties are replaced by the highway vehicle engineâs torque/speed envelope and its fuel map of relative fuel efficiency for all torque- speed combinations within that envelope. The âBus-Simulationâ worksheet calculates the power flow and energy storage state of a hybrid vehicle (if one is being simulated) at columns âBus-Simulationâ!AN39:AO1187 while the âLDV-Simulationâ worksheet performs a separate simulation of the drive schedule for a hybrid version of the vehicle (on rows 1190 through 2339). The âLDV-Simulationâ worksheet also performs a separate simulation of a non-hybrid vehicle with a CVT (on rows 2341 to 3490). Either individual or composite LDVs can be simulated. The default is a composite vehicle (e.g. the 2011 CY driven fleet) with appropriate proportions of hybrid and non-hybrid CVT vehicles as specified on rows 44 and 45 of the âLDV-Resistâ worksheet. The resulting fuel intensity is the performance of the composite mix. If one wishes to simulate a sole- hybrid (or conventional or CVT) vehicle, either the proportion needs to be set to 100% in the input data column for that vehicle in the âLDV-Resistâ worksheet data table or the default mix can be temporarily overridden using the âEngine Optionâ selection available on the âAuto/LDV Type Selectionâ pop-up menu. Selecting âdefault mixâ will use the mix as defined in the âLDV-Resistâ data table while selecting the âHybridâ option sets 100% hybrid and 0% non-hybrid CVT or selecting the âNon-hybridâ option sets 0% hybrid and 100% non-hybrid CVT. The output from the simulation sheet is the fuel intensity (kg/vkm) for the particular drive schedule being simulated. The âMacroâ iteratively brings in each drive schedule and builds up the total trip fuel intensity in proportion to the allocated drive schedules as defined in the âLDV-Routeâ or âBus-Routeâ worksheets and the âLDV-Drive-Schedulesâ or âBus-Drive- Schedulesâ worksheets. Gradient influences are calculated at cells AM13:AO18 for the intercity leg of a trip and at cells AU26:AU118 for the drive-schedule part of a trip on both the âLDV-Simulationâ and âBus-Simulationâ worksheets.. Seasonal variations (temperature influence on aerodynamic drag and auxiliary power usage) are calculated on the upper right side of both the bus and LDV simulation worksheets (cells AP1:AS24). The âMacroâ selects the appropriate values for the season and region being simulated. 5.2 LDV Characteristics Sheet and Future-Year Preprocessor The âLDV-Resistâ worksheet contains the default characterization data for LDVs. Default data exist for different classes of 2011 vehicles as well as composite vehicles for the sales- weighted and driven fleets for the years 2011, 2012 and 2013.
54 The âLDV-Resistâ worksheet also includes a processor to generate data for fleet average composite vehicles in future years. The algorithm of the preprocessor assumes that 50% of the difference in fleet-average fuel economy of the new model year relative to the 2011 sales-weighted fleet is due to drive-train efficiency (engine and/or transmission efficiency is scaled by 50% of the fuel economy difference) and 50% is due to vehicle body design or fleet composition (the 2011 fleet average weight and resistance coefficients are scaled by 50% of the fuel economy difference). The lower part of the worksheet contains the necessary data and formulae. Use of the preprocessor is described in more detail in the User Guide (Sections A.6.8 and A.7.16). 5.3 Highway Drive Schedules A series of fixed drive schedules (speed â time) are used to represent urban travel. Speed is specified at 1-second intervals for each representative drive schedule. All are derived from EPA drive schedules, either as direct copies or with slight modifications. MMPASSIM simulates the movement of a vehicle over each drive schedule and scales the kg/Vkm fuel intensity output to the total distance for that road condition as specified by the user for a given trip. The model is responsive and thus, acceleration and braking rates are held within the capability of the vehicle rather than purely following the speed-time profiles. The drive schedules are derived from EPA drive schedules for Heavy Duty, Medium Duty and LDVs. Traffic congestion is typically characterized by the level of service (LOS) which is based on the level of reduction below free-running speed of the traffic. For a freeway with an average 110 km/h (68 mph) free flow speed, increasing congestion leads to decreasing average speed. LOS A through LOS D involve modest decreases, while LOS E depicts traffic at capacity conditions and LOS F depicts traffic beyond capacity covering a range of conditions from frequent slow-downs to full stop-and-go progress. Non-freeway travel involves intersection stops and idle periods. The bus and LDV modules use some common drive schedules and some performance- specific drive schedules for urban travel. There are seven drive schedules in each vehicleâs worksheet as illustrated below. A Creep drive schedule is used for queuing delays or fully congested travel and the output is presented in fuel consumption per unit time. Queue delays can be encountered at manual toll booths, some maintenance activities, congested arterial and city-street intersections and severely congested freeways. The Creep Schedule is composed of intermittent short advances and long idle periods as illustrated in Figure 6. The drive schedule is derived from the front end of EPAâs LOS-F drive schedule and is used by both the bus and LDV modules.
55 Figure 6. Creep Drive Schedule (0.9 km/h) Source: Derived from EPA Drive Schedules used in MOVES. There are two non-freeway drive schedules, with stops and speed variation from a shared- traffic in an urban environment. An arterial road (see Figure 7) is depicted by an average speed of about 40 km/h (25 mph) with stops at about 2 km intervals. The drive schedule is EPAâs non-Freeway HDD25 drive schedule. The user input specifies the total distance traveled on intermediate urban access roads (more for bus intermediate stops than for LDVs) for the intercity segment and as a proportional incurrence by time-of-day for the urban origin and destination. The same drive schedule is present in both âBus-Drive- Schedulesâ and âLDV-Drive-Schedulesâ. Figure 7. Urban Arterial/City Drive Schedule (40 km/h) Source: Derived from EPA Drive Schedules used in MOVES.
56 Figure 8 illustrates a congested traffic condition which could be encountered on either freeway or non-freeway roads. The LOS-F (14 km/h) is present in both the âBus-Drive- Schedulesâ and âLDV-Drive-Schedulesâ worksheets. Figure 8. LOS-F Stop and Go Drive Schedule (14 km/h) Source: Derived from EPA Drive Schedules used in MOVES. The âLDV-Drive-Schedulesâ worksheet also has a city street as depicted in Figure 9. Figure 9. City Street Drive Schedule for LDVs (25 km/ h) Source: Derived from EPA Drive Schedules used in MOVES.
57 Urban freeways have several drive schedules to simulate the degree of congestion. Each has an average speed associated with congestion conditions. The approximate average speeds involved for each drive schedule used in the âBus-Drive-Schedulesâ and âLDV-Drive- Schedulesâ worksheets are: Bus Freeflow 117 km/h (73 mph), (see Figure 10) LDV Freeflow 119 km/h (74 mph), (see Figure 11) LOS-B/C 105 km/h (65 mph), (see Figure 12) LOS-E 75 km/h (47 mph), (see Figure 13) LOS-E (Bus) 50 km/h (30 mph), (see Figure 14) Access/exit urban freeway 100 km/h (62 mph), (see Figure 15) New drive schedules can be used in place of the seven drive schedules in the middle of the Table. The creep drive schedule (col C) and cruise drive schedule (col K) cannot be replaced. The length limitation is a maximum of 1149 seconds duration and the active length of the intended drive schedule must be entered in row 29 at the top of the replacement drive schedule. The user can also manually introduce a speed governor for buses in the âBus-Drive-Schedulesâ by capping the maximum speed of the existing speed profiles with the appropriate speed limit. Thus for example, a 65 mph (25.058 m/s) governor setting would cap the maximum speed at 65 mph rather than the 79 mph (35.32 m/s) attained in the non-governed âBus Freeflowâ drive schedule of Figure 10 and the 67 mph (29.95 m/s) attained in the âLOS-E 75 km/hâ drive schedule of Figure 13. Figure 10. Urban Freeway Bus Free-flow - 117 km/h Drive Schedule Source: Derived from EPA Drive Schedules used in MOVES.
58 Figure 11. Urban Freeway LDV Free-flow - 119 km/h Drive Schedule Source: Derived from EPA Drive Schedules used in MOVES. Figure 12. Urban Freeway LOS-B/C - 105 km/h Drive Schedule Source: Derived from EPA Drive Schedules used in MOVES.
59 Figure 13. Urban Freeway LOS-E - 75 km/h Drive Schedule Note: This is the LDV drive schedule, the Bus drive schedule is the same except the speed peaks are capped at 65 mph (29 m/s). Source: Derived from EPA Drive Schedules used in MOVES. Figure 14. Urban Freeway â LOS-E 50 km/h Drive Schedule Note: This drive schedule is used in the Bus simulation. Source: Derived from EPA Drive Schedules used in MOVES.
60 Figure 15. Short Urban Freeway Access LDV Drive Schedule (EPA-US06) Source: EPAâs Fuel Economy Certification Drive Schedule US06. 5.4 Inter-City Road Maintenance/Weather Delays The congestion drive schedules described in the previous section are also used to depict maintenance delays for the intercity segment of the intercity long haul trip. The user specifies the distribution of trips by time-of-day congestion conditions and the model determines the average fuel intensity in relation to the input distribution. Long haul maintenance activity is also characterized by the same fixed duty cycles. The user specifies the distance and probability of occurrence for maintenance and/or weather delays. The LOS-E 75 km/h drive schedule is assumed to characterize these delays.