On or around Wed, 23 Feb 2005 13:42:03 +0100, Erik-Jan Geniets enlightened us thusly:
used on one of the modern Range Rovers, is it the P38 or the new one?
instead of wires running all over the vehicle carrying current, you have a power supply, earth and data connection to (e.g.) yer rear light cluster, and when you want the rear lights on, instead of switching the current and sending it down a wire, the BECM or equivalent sends a message to the rear light cluster telling it to switch the rearlight on.
OWTTE...
has advantages, but then again, it's far less easily fixed.
I suspect that the odd size pipes are due to their using (for a while, anyway) an accumulator type brake system - also used by Rolls Royce for quite a while too (the Citroen system, that is).
Ah! My favourite subject! I was Feature Owner for the CAN bus on the "Medium Size Bentley".....
The great advantage of CAN (or VAN etc) Bus systems is that it removes the need for all those nasty wires (the harness) runing round the vehicle, thus reducing design complexity, vastly increasing realiability and flexibility. Bearing in mind the harness is one of the most expensive, heavy and (to an extent) unreliable components of a vehicle, then:
The entire harness can be done away with and replaced by four wires that visit each "electrical point" in the vehicle. This uses standard connectors, standard cable, wieghs almost nothing and costs buggger all. However, each electrical point increases in complexity - a bit. Although we had a Jag doing just this about 8 years ago, no one has *fully* implemented yet - there's still a lot of cable about.
So, for example, the rear light cluster. A message is broadcast from the Body Controller ECU (could be straight from the brake light switch if it had a bus controller). A standard IC in the rear light cluster spots the message and says "Ah ha! Thats for me" and then decodes the contents of the message.... "switch on the brake light on" - which it does. So far it's no different to cable, but now the good stuff kicks in. The brake light bulb is blown. The light cluster controller (which is electronic, no relays) can now do things like : Use the tail light instead if the lights are not on, or flash the tail light rapidly as a back up if the lights are on. It also broadcasts a message telling the rest of the vehicle ECU's (if they are interested) that the failure has occured. Most likely in this case, the Body Controller would tell the driver that the bulb (or more than a given percentage of LED's) has failed, and could then log the fault for the next service or whatever. If an ECU "disappears" from the bus through damage or something, then the message originator can re-try for a while, and getting no response, tell other ECU's to act accordingly.
If you extrapolate this functionality throughout the vehicle, then the possibilities are endless. When the car is built, the ECU's attached to the system can determine automatically what features are attached to the vehicle - no different harnesses for different spec vehicles. Upgrades can be truly plug-and-play, or even enabled using a code when the extra dosh is handed over. If the keys have different codes, then as well as seats, mirrors etc being moved for that person, the performance of the vehicle can be modified - e.g. Daddy can have full blown sports mode, young Rebecca can have much reduced performance to save on insurance - all with no extra cable. You can log all this to give info leading up to an accident - even who's key was being used - if Rebecca was using Daddy's key then the insurance could be invalidated etc.
Compared to the above, the tradition harness doesn't even get a look in! We had an entire Jag on a 6x4ft bit of chipboard for demo purposes (as well as a real car!) - the real cars harness would have taken (at least) two of us to carry it.
Personaly, I drive a 200Tdi 110 - not an ECU in sight. but then I don't want fancy toys anyway...... There are two flavours of CAN - high-speed and low-speed, the high speed flavour is for engine management etc, and low-speed for lower demand systems. It is an amazingly robust system, originaly designed for machine and factory automation and remote control. There were other contenders (VAN being one), but unless things have changed recntly, CAN has won the day.
On or around Wed, 23 Feb 2005 13:06:37 +0000 (UTC), beamendsltd enlightened us thusly:
The BX, CX and probably Xantia and XM too use a single high-pressure hydraulic system for suspension, brakes and steering. On the BX at least, the front brakes are supplied from the high-pressure supply, while the back brakes are supplied from downstream of the rear suspension, thus making them load-dependant, in rather a neat way which doesn't require a complicated gadget with linkages to go wrong.
'course, instead, it has a CGWLTGW that adjusts the ride height...
and yes, the system has an accumulator. Mind, so does the ABS on my sierra, except that the ford has an electric, rather than engine-driven, pump.
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