Bringing home SAE J1939 Heavy-Duty Protocol Simulation

The J1939 standard for heavy-duty vehicles drafted by the SAE (Society of Automotive Engineers) in the mid-90s was driven originally by the "ECU trend" with the main objective of controlling exhaust gas emissions under increasingly tightening US and European regulations. Having gained wide acceptance ever since among diesel engine manufacturers, the SAE J1939 heavy-duty protocol has presently reached the stature of the de-facto standard for Truck and Bus manufacturers worldwide, for communication between various vehicle components and for diagnostics.

J1939 is a set of standards that includes a higher layer messaging protocol that works over CAN (Controller Area Network) protocol at the physical layer. The communication model supports both peer-to-peer and broadcast communication. The J1939 message format uses the Parameter Group Number (PGN) to label a group of related parameters, each of which may be represented by a Suspect Parameter Number (SPN). Continuously varying vehicle parameters (like Engine RPM etc.) are defined along with their valid range, offset, scaling etc. Besides, discrete (ON/OFF) parameters (like Brake Switch ON etc.) are defined separately. Commands to Enable/Disable specific vehicle functions (like Engine Fuel Actuator Control etc.) are defined.

Time based updates happen at 20 milliseconds (or lower) repetition rate, whereas the rate is significantly higher at higher Engine RPMs. Some periodic messages contain information that is of particular interest only when a specific state change occurs, and there is a defined range of repetition rates for these messages. Diagnostic messages (DMs) from various sub systems (like emission control etc.) are defined as per the Diagnostics Application Layer of the J1939 standard that includes services like periodic broadcasts of active DTCs (Diagnostic Trouble Codes), reading and clearing DTCs etc. Manufacturer specific parameter groups are supported that allow OEMs to define their proprietary message in addition to standard messages.

ECU design engineers of vehicle sub-systems at automotive OEMs, Tier-1 suppliers and R&D Service Companies routinely use J1939 Simulators for their product development, test and validation activities. In the early stages of development, a simulator comes handy for providing signals from other vehicle components exactly the same way as it would be in the real vehicle environment without the need for an actual vehicle in the lab. For instance a design engineer working on an ECU development program for Transmission Control would need signals from Engine Control system, Braking System etc. in order to validate his design functionality and performance. The ECU would get all these signals from the Simulator exactly as it would receive them in a vehicle environment, the physical connection provided by 2 CAN wires (CAN-HI and CAN-LO) and Ground (GND), taken out from the Simulator’s 16-pin OBD (or 9-pin D-Sub) connector using a custom wire harness to the mating connector of the ECU.

The J1939 simulator provides the design engineer with the ability to generate and vary individual parameters in order to check the response of the system under design/test. The required variations could be manually controlled using (rotary knob) potentiometers for continuously varying parameters. Some simulators automate the variation according to a pre-defined curve. A linear ramp that sweeps the full range (0-100%) of the given parameter, in increasing steps of 1%, is typical. Advanced simulators based on engine modeling data provide the ability to vary multiple parameters simultaneously in a specific relationship with reference to each other for better real-world simulation. A cost effective alternative to this would be to record multiple parameters of interest from the actual vehicle under standard test/driving conditions for the required duration, also known as the drive signature, and playing back the captured signature in the lab in the same time base, although with a lesser timing accuracy. Add on the simulation of actual vehicle hardware, like sensors, actuators etc. to create a fully Hardware-In-The-Loop (HIL) simulation and the full-extent of the simulation picture becomes complete.

Indian automotive R&D groups have traditionally banked on imported tools for J1939 simulation. Originating from USA, Canada, Germany etc. many of them come with pricey licenses although offering just an elementary 5-signal manual simulation. A few sophisticated ones with automatic ramp sweeps etc. are super-pricey, that even Indian R&D subsidiaries of multi-national OEMs have to contend with time-sharing the same simulator across multiple engineers/teams. It is in this context that a strong need is being felt for a high quality, cost effective J1939 Simulator that is indigenously designed and manufactured, that could provide many Indian customers the much-needed scalability for their R&D activities and reduce their dependence on imports.

Awareness on the availability of an indigenous product is the starting point however strict adherence to the standard is a hard requirement, including very strict timing considerations, in order to create a positive lean among automotive customers who always select and use only “proven technology”. Benchmarking data with reference to competing products could help customers get quantitative insights. Pilot trials could help them in familiarizing themselves with the indigenous product and to evaluate it against their experience with imported tools.

We at Deep Thought Systems design manufacture and supply J1939 simulators to Indian automotive customers, in addition to other offerings for CAN/J1939 logging, test/diagnostics, J1939 based displays and ECU manufacturing test automation. In our endeavors in bringing the above mentioned advantages to the Indian automotive R&D sector, we found that a customer's need many a time is a highly customized simulator for their specific application. And thanks to our expertise in automotive protocols like CAN, OBD-II and J1939, and being fully in control of the hardware design, component sourcing and manufacturing as well as the embedded firmware and application development, we find ourselves well placed to deliver to these custom needs.

Post Scriptum:

A later industry development has been that all the major European heavy-duty OEMs came together in 2000 to co-develop the Fleet Management Standard (FMS) which is based on J1939 that incidentally opened up possibilities for manufacturer-agnostic telematics applications. The J1939 simulator, combined with suitable GPS simulation having the required levels of performance, offer telematics product designers a proven means to quickly test and validate their design well before going for in-vehicle tests.