Problem Simplification

Although the argument has been made that ANN models may provide an extremely flexible tool to allow a range of stability control strategies, this will not be fully investigated here. Such a work, even considering the argument that ANN models simplify the controller development process considerably, is beyond the scope of this research. The reasons for this include:

 The state of Tasmania has no suitable test tracks for the thorough investigation needed to evaluate complicated stability controllers;

 There are no automotive manufacturers in Tasmania to be of assistance, and no assistance offered by interstate manufactures;

 The project budget precludes the use of expensive prototype controllers, sensors and actuators other than those already on hand;

 The provided test vehicle does not contain any method of electronic brake control;

 The University of Tasmania has extremely limited automotive engineering resources; and

 The work required to construct the controller hardware and software, and objectively evaluate their eventual performance, is considered beyond the scope of a single PhD investigation.

Instead, the investigation was planned to tackle the problem from another direction. It was observed that one of the principle benefits from the use of ANN models was their adaptability from system to system. With this in mind, it was therefore considered that proving the ANN model applicability and demonstrating controller performance for a simplified case would be sufficient to make a strong case for more complex controllers. Likewise, if no advancement could be made with this simple case, the usefulness of ANN controllers for stability control could be considered partially disproven.

Considering the points above, the use of a system requiring brake pressure control of any kind was considered impractical for this investigation. This was a relatively simple observation because the vehicle was not fitted with any form of electronic brake control and the addition of any such system would be difficult, expensive and raise some safety issues. Of particular concern was the possibility that such a modification would render the vehicle illegal for street use, as this would conflict with the goals of the “Intelligent Car” and hydrogen conversion projects. Unfortunately, this leaves very little room to investigate many different types of stability controllers, as brake control is absolutely necessary for slip regulation in ABS and the more advanced stability controllers. This leaves only traction control as a possible avenue for investigation.

Unlike ABS and the newer stability controllers, many traction controllers do not include electronic brake control as one of their controlled variables. Instead, driven wheel torque is often solely controlled by engine power reduction of some kind. Such systems can handle longer periods of traction control operation (as brakes often overheat very quickly), but suffer performance losses on “spit µ” and other surfaces. This is because the controlled variable is the torque transmission to both wheels through the differential, rather than torque control at individual wheel. Nonetheless, engine power can be reduced in a number of ways too. MoTeC traction control, for instance, utilizes electronic engine power reduction through injection and ignition control, with no brake control. Other systems incorporate throttle position control (or secondary throttle control) to limit airflow to the engine, and for power reduction control. The best performing systems, however, include both brake and engine power reduction control.

As discussed above, nonetheless, the implementation of brake control was not considered appropriate for this investigation. This, then, reduces the control problem to traction control using engine power reduction – and limited the choice to one between injection/ignition control, electronic throttle control, or a combination of both. This decision was influenced by the knowledge that the vehicle would be converted to hydrogen in the future, and therefore require the addition of a programmable aftermarket engine management system. The MoTeC ECU that was chosen through the course of this investigation had the ability to affect injection/ignition control based on an external signal, and so this was selected as the easier option. This decision was greatly influenced by the fact that the MoTeC ECU contained a traditional traction control function that would allow direct comparison with the ANN controller. In contrast, implementing

throttle control was considered a worse solution, in part because of its reduced response in limiting power. A more important factor in this decision was the difficulties in actually implementing the control as it was not considered wise within the scope of this investigation to directly electronically control the throttle for safety reasons. Likewise, the installation of a secondary throttle was not considered an appropriate course of action due to the possibility of extremely rich fuel mixtures and backfire during engine cut. Choosing to affect engine power reduction using the MoTeC ECU avoids these problems, although it was noted that injection/ignition cut has limitations. These include potential damage to the engine during extended periods of cut and a limitation in the amount of power that can be reduced without causing engine damage. Nonetheless, the MoTeC ECU contains the functionality for electronic throttle control, so the two methods of control could be combined in the future – but only with considerable knowledge of “drive by wire” systems, and at significant cost and effort.

Finally, although slip control forms the basis of the intended ANN controller, there are many other variables that can be controlled for significant benefit with the installation of appropriate hardware. As mentioned above, however, this hardware was not available, and as a result only slip control will be explored here. Nonetheless, the optimisation method that will be explored in this investigation is considered identical to the method required for any other relevant controlled variable.