CAN data systems

Wednesday, July 09, 2014

Tags :  test-equipment

A considerable amount of data can be obtained from factory-fitted engine sensors in a modern roadcar-based racer, and mining the data has become far easier in recent years thanks to the widespread adoption by mainstream manufacturers of CAN (Controller Area Network) bus wiring systems. There is a range of ways of interacting with and connecting to these sensors, but first it is worth looking at what exactly a CAN system is.

In simple terms, a CAN bus is a network of individual electronic controllers that communicate using a protocol which automatically gives important signals priority over less urgent ones. As vehicle electrical systems grew in complexity, CAN systems were developed to reduce the amount of wiring needed. This reduction is achieved owing to the fact that each controller needs only two wires to transmit signal data.

For example, if a car’s stability control system featured wheel speed, brake pressure and suspension displacement sensors on each wheel then, without CAN, each of them would need to be hardwired to the stability control ECU. With a CAN system, however, the sensors can input into individual control boxes located either at each corner of the car or, say, one front and one back, which then process the sensor signals and communicate with the main ECU via simple twin wires. In the old system, anything up to 20 individual wires would need to run to the ECU, while with CAN this can be reduced to just four if only two processing boxes are used.

From a data engineering perspective, these systems make it very easy to add or remove functionality from a particular data recording set-up. If properly implemented, CAN will also provide much better system redundancy in the event of components getting damaged.

There are two key ways of going about this with a production car already fitted with a CAN system. The first and easiest option is simply to connect to the factory ECU (if used) through the diagnostics port. With the correct interface and data logger, the information the ECU is receiving from its various sensors can be easily recorded. The alternative is to run a system piggybacked onto the existing wiring, sharing the CAN data signal being sent to the ECU.

“If you are doing a test and you want to add some functionality to the car, the CAN is very useful,” explains Steve Dunlop, an engineering and racecar constructor with the JRM team, which has extensive experience of running both rally cars and track machinery. “One particular area that that comes to mind is when you want to add a wideband lambda sensor instead of the narrowband type usually found in production cars; it is very easy to add it to the CAN stream and integrate it with your existing system. It also means you do not need to cut into the existing wiring looms, and the new additions simply run in parallel with the sensors already present.” 

The benefits of CAN-based vehicle electronics have also seen their growing adoption over the past five years in motorsport-specific engine control systems. For example, the Fiesta R5 rally car features a near-comprehensive CAN-based wiring system, with individual control modules designed specifically for the demands of motorsport sited throughout the car. The result is less cabling in the car, meaning simpler and thus cheaper and lighter wiring, combined with easier maintenance thanks to the improved fault diagnostics capability the CAN system has over a regular wiring loom.

Written by Lawrence Butcher

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