Part 2 - Evolution of Electrical Systems
January, 2002by Cam Finnigan
This is the continuation of an article featured in a previous newsletter. It is a report from the fall 2001 technical session held at Don Docksteader Motors on Cambie Street in Vancouver. The presenter was Jason Leber.
Cars certainly have changed over the years and nowhere in the car are the changes more significant than in the electrical and control systems. Jason gave a comparison between a 1960 122 and a 1998 S70. The 122 came with 7 fuses (that was a lot compared to 2 in most British sports cars of the era), 83 metres of wire and CO of between 3% and 5%. The S70 has evolved to 54 fuses, 1200 metres of wire and 0.5% CO (at the engine). What is the downside of this much wire? Cost (design and manufacture), installation time (more cost), weight (fuel cost to the owner), many connections (reliability and cost), and difficult fault tracing (cost). So, basically, it comes down to cost. Don't forget that running all of those accessories such as rear window heater, headlights, seat heater, climate control and so on consumes electrical power. That power ultimately comes from fuel. Jason pointed out that an added load of 1 kW will cost you up to 1.7 litres extra per 100 km.
With more and more "things" in the newer car requiring control the number of electronic "controllers" has increased accordingly. Starting in 1999, a loaded Volvo S80 contains as many as 18 separate control units. These units are connected to a Controller Area Network or CAN system. This is not too dissimilar to the network that your computer at work might be connected to. It enables all of these modules to communicate with one another through a very simple medium using a special language. There are control modules in the instrument cluster, in the climate control, the radio, the rear lights and a dedicated system for the engine, automatic transmission, anitlock brake system and supplementary restraint system. There is no longer a headlight circuit running through your headlight switch, nor does the brake light wire run to your brake pedal. As scary as it may seem to some, there is no longer even a throttle cable! This control is strictly "drive-by-wire". The throttle pedal attaches to a position sensor which is connected through the network and controller to a servo controlled throttle body. This item, oddly enough, resembles an old 35 mm SLR camera. Some of us thought we were going to have our pictures taken.
Each of these control modules has a tiny computer inside that is frequently referred to, at least in my industry, as an MCU. This controller is designed and built to carry out a specific function based on inputs from sensors and provides some form of output based on software (or technically "firmware") which is commonly stored in Flash memory. These instructions are developed alongside the controller and are based on the desired functionality that the manufacturer wishes to achieve. The firmware is loaded to each module when the car is built. Each module has an indelible electronic serial number which uniquely identifies that part against all similar parts in other cars. When the car leaves the factory a record of the car is retained with the manufacturer identifying all of the modules that are contained in each car. The network communications protocol, message format and all decision algorithms are defined by this firmware. It is now possible to perform extremely complex tasks quickly and accurately at fairly low cost. Events can also be recorded and it is possible to have a controller "learn" so that future outcomes can be predicted by examining a record of previous outcomes.
The real beauty of controllers (and I know first hand) is that if you don't like the results that your current firmware is giving you, then you go to the firmware team and ask for a new revision to correct the problem. The best part is that you don't even have to open the cover. New firmware can be downloaded to the controller right over the network. This new firmware then replaces the old firmware and the controller then takes on new characteristics. The danger in upgrading firmware is that there is always a risk of being stuck in the event of an interruption in power or communications of the firmware. You may have erased the very firmware that will allow you to communicate further downloads. There are many ways of executing this download and designers normally build in some type of contingency against a total disaster.
Jason demonstrated a typically download into the automatic transmission control unit of a Cross Country using the Volvo Aftersales Diagnostic and Information System or VADIS . This looks a bit like a computer on a fancy shop cart. It comes with a really fancy price of about $60k. They currently have two, and given that they are nearly as essential as breathing, could use another one. Every time your car goes into the shop for an oil change, the VADIS is contacted to your car and scans your car for fault codes. In the case of the XC, the firmware was updated pro-actively to rectify a problem in the shifting algorithm that the customer may eventually complain about. The VADIS is a wealth of information. It also comes complete with parts information and step by step fault finding.
The VADIS communicates with the car, reads fault codes (if any), identifies the control modules and sends that information to the factory in Sweden. The factory then authorizes the download and 102 kilobytes of firmware is injected into the car through the OBD2 (On Board Diagnostic) connector, located between the front seats. This is an industry standard connector legislated for all manufactures to use. The same goes for the fault codes that the car communicates to the service computer. At the same time, the "adaption" is reset to zero. Now that the load is complete, the technician must then take the car out on the road for a series of specific exercises to retrain the adaption.
As a result of controller serial numbers and the possibility of having non-compatible firmware, it is no longer acceptable to buy used network components from the wrecker and expect them to work normally in your car. The next time the car is connected to VADIS, the question, "What are you doing in this car?" will arise.
Intermittent faults can result in the warning light going on and then off. Some faults, if occurring only once, will eventually extinguish the warning light after a number of driving cycles without any error. These faults will still be recorded in the controller and can be read out by the shop.
So, like it or not, your new car now comes complete with an array of computers that help with cost, serviceability and functionality. These are not too dissimilar to the small controllers that you find in your modern TV, VCR, furnace, cell phone, bread maker and child's toy. This really is the future of most products that are electronic or require intelligence. If you are uncomfortable with this concept then perhaps new cars are not for you.