Assessing the Accuracy of Vehicle Event Data based on CAN Messages

Transcription

1 Assessing the Accuracy of Vehicle Event Data based on CAN Messages Carsten Mueller Ph.D. Candidate in Computer Science Jeremy Daily Associate Professor (Select) of Mechanical Engineering Mauricio Papa Associate Professor of Computer Science Institute for Information Security (isec) University of Tulsa

2 Presentation Overview Networking Principles Description of Controller Area Networks (CAN) Example of Speed Display on Heavy Trucks Standardized CAN Data (J1939) Example from DDEC 10 Unknown CAN Data (Passenger Cars) Identification Procedure Example from Toyota Message Timing Analysis Data Synchronization Strategies 2

3 Networking Principles Multiple discrete devices need to communicate A Controller Area Network (CAN) enables communication Bosch developed CAN in 1980s Enjoys widespread use 3

4 Layered Network Model From SAE s J1939: 4

5 Example: Speed Display Goal: Take the tail shaft speed sensor and display data on the dash. Step 1: Application Layer in ECM Convert electrical pulses into km/h Step 2: Present Data to Network Send data from micro processor to CAN transceiver chip. 5

6 Example: Speed Display (cont.) Step 3: Construct a Message for the Network Done in the CAN Transceiver Requires: Message ID Data Length Code Data Calculates CRC value 6

7 Example: Speed Display (cont.) Step 4: Transmit Message All nodes have equal access to the physical media Message ID is used for collision detection and arbitration. 7

8 Example: Speed Display (cont.) Step 5: Voltage Encoded Data is on the Network 8

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11 Example: Speed Display (cont.) 120 Resistors on each end 11

12 Example: Speed Display (cont.) From J (Vehicle Application Layer): 10 Hz Signal Data contained in ID 0x18FEF100 Wheel Based Vehicle Speed has 2 bytes 2 bytes = 16 bits 2^16 = levels Data in bytes 2 and 3 Byte 3 = whole km/h Byte 2 = fractional km/h 12

13 Example: Speed Display (cont.) Also from J : Resolution: 1/256 km/h Data Range: This information can be interpreted and displayed on an instrument panel 13

14 Obtaining CAN Data Oscilloscope Inefficient Data Conversion DG Technology Gryphon S3 Vector CANCaseXL Log National Instruments Compact RIO Low-cost Arduino 14

15 Fundamental Premise We have hardware to extract CAN data from the network. Some of this data either: Sources Event Data Recorders (EDRs) Reflects Data with EDRs Comparing CAN data to external sources provides a comparison Data stored on the EDR cannot be better than CAN data EDR data is often truncated EDR date is often reported at lower frequency CAN Data is easier to obtain than EDR Data 15

16 Using Standardized CAN Data (J1939) Example: (not in paper) 2012 DD15 Powered (DDEC 10) Freightliner Cascadia 52 Box Van Trailer 1996 Cadillac Deville Truck pulls the Cadillac into the rear ICC Bar All CAN messages were recorded VBox 3i and Video VBox Data 16

17 Test Setup Split the CAN data from the Deutsch 9-pin connector Nexiq Vector CANCase XL Vbox 3i VideoVBox Record Data Download DDEC Reports 17

18 Results 18 Video is synchronized to CAN traffic (Wheelbased Vehicle Speed) Vbox 3i transmitted CAN messages onto J1939 DDEC Reports was obtained

19 DDEC Reports and J1939 Data 19

20 Front Axle Canalyser Speed Vbox 3i Speed Wheel-Based Vehicle Speed Air Brake Pressure Tape Switch CAN Brake Pedal 20

21 Data Discussion Demonstrates the concept of using CAN data to evaluate system performance Wheel-Based Vehicle Speed tracks closely with VBox 3i Synchronization of DDEC Reports data is still an issue Network traffic shows a lag of nearly 0.6 seconds on service brake application Beware of J1939 network saturation Vbox 3i floods the network. Bus utilization showed 99% 21

22 Dealing with unknown CAN Data Most OEMs keep CAN data confidential CAN Sources data to EDRs Vehicle Speed Engine RPM Brake Status Need a systematic way to identify message data 1. Record CAN data along with external measurements during a dynamic maneuver 2. Group messages by ID 3. Generate all probable combinations of data bytes 4. Plot the generated data interpretations 5. Determine the best fit 22

23 Automatic Plotting Routing Humans are good at pattern recognition Python code to generate graphs form hex data. Uses text output from CAN Logger DG Tech s Gryphon Vector CANCaseXL Log Performs basic timing assessments Inventories CAN message ID s and Data Length Codes Assembles and plots Byte-wise data Computer code is Available at 23

24 Example: Toyota Corolla Speed VBox Tools Graph Graphics from Automated Plotter 24

25 Individual Wheel Speeds 25

26 EDR Speed Source , Data is in raw km/h. Updates every ½ second Data is rounded down to lowest even number CDRTool says: km/h. 26

27 Message Timing CAN is asynchronous Jitter can be evaluated thought he timestamp differences For J1939, Wheelbased vehicle speed transmits at 100 ms. Observed Standard Deviation = sec. from messages Jitter seems irrelevant 27

28 Synchronization VBox to CAN to Data Logger Synchronized Speed Data for a Toyota Corolla Yaw Test CAN Speed ID:0x610 byte 2 VBox 3i Speed (GPS-CAN)*5 50 Speed, km/h Time (sec) 28

29 Main Points Description of Controller Area Networks Example of J1939 Speed Display Obtaining CAN Data using a logger Using CAN data based on standards J1939 defines message interpretation for Heavy Trucks Example of a DDEC 10 with a crash Decoding CAN messages Automatic Plotting for Pattern Recognition Example of Toyota Corolla data Periodic CAN data is generally on schedule Using the CAN to Synchronize Data Transmit VBox Speed data onto CAN while logging Beware of existing IDs and bus load Assessing the accuracy of synchronized and decoded CAN data is possible 29

30 For more information: Thankyou for your attention