What is a Drive Cycle?

A drive cycle is time series data that describes how a vehicle is driven. At minimum, it includes speed over time, but can also include road grade, ambient air temperature, or other time-varying quantities.

FASTSim simulates a vehicle model over each time step of the drive cycle to compute the vehicle’s response, including speed, acceleration, and power demand. This makes FASTSim a backward-looking model.

Loading a Drive Cycle from Resources¶

This example uses HWFET (Highway Fuel Economy Test), a regulatory drive cycle used to evaluate highway fuel economy.

For more information on HWFET and other regulatory drive cycles, see:
https://www.epa.gov/vehicle-and-fuel-emissions-testing/dynamometer-drive-schedules

The NLR DriveCAT page has a variety of cycles available for download as well:
https://www.nlr.gov/transportation/drive-cycle-tool

A full list of drive cycles available in FASTSim’s resources can be printed:

Visualizing a Drive Cycle¶

FASTSim has convenience functions for visualizing drive cycles.

In FASTSim, drive cycles represent all data that vary over time.

The following are inputs to FASTSim drive cycles:

• Time

  • time_seconds

• Vehicle speed

  • speed_meters_per_second

• Road grade

  • grade

• Ambient air temperature

  • temp_amb_air_kelvin

  • Only affects thermal vehicle models

FASTSim automatically derives the following from a drive cycle:

• Distance

  • dist_meters

  • Accumulated from vehicle speed

• Elevation

  • elev_meters

  • Accumulated from grade and distance

  • Initial elevation

    • init_elev_meters defaults to 121.92 m (400 ft)

Defining Custom Drive Cycles¶

Drive cycles can be loaded from a variety of file types:

• .csv CSV files (like the above example)

• .json JSON files

• .msgpack MessagePack files

• .toml TOML files

• .yaml YAML files

Here is a small example of a custom drive cycle file:

custom_cycle.csv

time_seconds,speed_meters_per_second,grade
0,0,0
1,0,0
2,0,0
3,0,0
4,0,0
5,0.5,0
6,0.75,0
7,1,0
8,1.25,0
9,1.5,0
10,1.75,0
11,2,0
12,3,0
13,4,0
14,6,0
15,8,0
16,10,0
17,12,0
18,14,0
19,16,0
20,14,0
21,12,0
22,10,0
23,8,0
24,6,0
25,4,0
26,2,0
27,0,0
28,0,0
29,0,0
30,0,0

To load this, you can use fastsim.Cycle.from_file:

cyc_custom = fastsim.Cycle.from_file("custom_cycle.csv")

Accessing Drive Cycle Fields at Runtime¶

Drive cycle fields can be accessed at runtime by converting the Cycle object to a Python dictionary. Each key corresponds to a field name, and many values are lists of data points over time.

Editing Drive Cycle Fields at Runtime¶

After making changes to the cycle dictionary, be sure to convert it back to a FASTSim Cycle before using it in simulation.