Gearbox ECU Override Unit

Judging by the search terms leading to the blog, as well as the popularity of the post Diagnosing the Transmission Anomaly, many of you are interested in our experiences trouble-shooting the problems we had with the transmission before leaving for Tunisia.

This weekend, we had a chance to take the Scania (EM-1) out for a drive, and we filmed a short sequence demonstrating the switches we installed on the gearbox monitoring unit that enable us to manually force a gear change if the ECU fails to send a command to the gearbox. The switches are mounted in parallel to the ECU, so that we can engage a gear if the ECU fails to do so. However, if the ECU has engaged the gear, then the switch will have no effect.

Since we first encountered the transmission problems only a few weeks before our departure to Tunisia, we did not have time to find a more comprehensive solution before the trip. This unit was designed to be an emergency override to make sure that we would not remain stuck in the desert in case of an ECU failure. Driving for an extended period of time while manually changing gears using the switches would not be easy, but in an emergency, it would be feasible.

We are still working on a more permanent solution and are investigating both repairing the ECU and designing a new micro-controller to replace it.  We’ll post an update once we’ve made more progress.

Diagnosing the Transmission Anomaly

We spent some time this weekend making a micro-controller test platform to develop a new control unit for the EM-1 (Erg Machine 1) transmission. We’ll be reporting on that once we’ve made more progress, but now seems like a good time to describe our diagnosis of the gearbox error and the steps we took to make sure we didn’t have any problems because of the transmission while in Tunisia.

During the road test we experienced an intermittent problem with the transmission; from time to time when accelerating or decelerating the gear would not engage.

One of the nice things about the Scania SBA 111 is its automatic transmission. This makes it a good vehicle for a first big truck experience, since the driver can concentrate on driving and doesn’t have to worry about shifting the gears. It’s also great for dunes (as we learned), since there’s no worry about losing momentum when shifting gears. However, the downside is that the automatic transmission adds complexity to the maintenance and increases the number of potential failures. Read more of this post