This online tool calculates the road load energy necessary to propel a vehicle along a selected driving cycle. It also estimates the fuel economy the vehicle would achieve for the average powertrain efficiencies you specify. You can also specify a regenerative braking efficiency if it is a hybrid vehicle.

• The background information below explains more about what this tool does and how it works.
• Consult the modeling methodology for detailed information about the vehicle equation of motion.
• See the parameter definitions for information about the terms used below.
• See the example code to see how Wheels calculates the equation of motion.

 Driving cycle: Urban Dynamometer Driving Schedule (UDDS) Highway Fuel Economy Test (HFET) Supplemental FTP (US06) Unified Dynamometer Driving Schedule (LA92) Federal Test Procedure (FTP) New York City Cycle (NYCC) UN/ECE Elementary Urban Cycle (ECE-ELEM) UN/ECE Extra-Urban Driving Cycle (ECE-EU) UN/ECE Extra-Urban (Low Powered) Driving Cycle (ECE-EULP) 30 mi/hr trip 60 mi/hr trip    What is a driving cycle?   See data in (sec, mi/hr): UDDS HFET US06 LA92 FTP NYCC 30 mi/hr 60 mi/hr See data in (sec, km/hr): ECE-ELEM ECE-EU ECE-EULP Cd: Frontal area: m2ft2 Crr: Curb mass: kglb Payload: kglb Rotational inertia factor: Wheel diameter: mftin Air density: kg/m3lb/ft3

 Fuel heating value: btu/gal Ave. engine efficiency: percent (0-100) Ave. drivetrain efficiency: percent (0-100) Ave. regen efficiency: percent (0-100) Target mi/gal:Calculates the necessaryengine efficiency to achievethis mi/gal for given regenand drivetrain efficiencies. mi/gal What would you like on your plot? Velocity Rolling resistance power Aerodynamic drag power Braking power Inertia power Total power Cumulative rolling resistance energy Cumulative aero energy Cumulative braking energy

Background

Moving any vehicle consumes energy in the form of aerodynamic drag and rolling resistance. Energy must also be invested in inertia, some of which will be lost when the brakes are used. These losses are collectively referred to as road load, or the tractive energy demand, or the energy demanded "at the wheels".

Unfortunately, any powertrain that can deliver this energy to the wheels will lose a lot of energy on the way - primarily in thermodynamic losses in converting fuel to work, and also in transmitting the work through downstream mechanical components. You must account for these losses, too, if you want to compute fuel economy.

This tool

Wheels lets you define a vehicle by specifying its road load parameters, and then computes the total energy needed at the wheels to propel it along a specified urban or highway driving cycle. The energy usage is broken down among drag, rolling resistance, and braking.

You can also account for powertrain losses in an approximate manner by specifying the average efficiency of the engine and of the drivetrain (the transmission and other mechanical driveline components). You may also specify a regenerative braking efficiency, which represents the percentage of total braking energy successfully captured and used again (applicable only to a hybrid vehicle).

In practice, average efficiencies of the engine and other components are rarely known accurately, but are commonly estimated for modeling purposes. Even when known, they would be valid only for a specific driving cycle. The miles-per-gallon figure this tool returns is therefore not exact, but is useful for comparing the efficiency of hypothetical vehicle configurations with respect to a specific driving cycle.

Methodology