BMWs completely computerized?

[digitalwanderer]

I like the VDC on my 350Z, although I don't know what it stands for. It's like an acceleration governor that keeps my rear wheels from slipping, and it's very cool and a whole lot more useful than I thought.

Of course, it's only so cool because I have a button to turn it on and off....

 

[Frank]

Now you're talking about ESP, that's what it does when you drive the curves too fast Current ones can control three wheels(brakes) at once and have some very advanced algorithms.

That solution wouldn't work, since the torque would be going some 90+% on pushing against the brakes which will be engaged constantly if you're on ice, sand, mud - it's VERY slippery. And torque is what you want for forward movement

Whatever, you don't need brakes to reduce the torque. The engine control unit does it already for you much faster than any brake ever could.

Differential-lock leaves all the torque on the wheels. ESP signals every time a wheel starts slipping, engine control unit reduces the torque so that at least one wheel starts getting grip. As soon as the opposite wheel starts getting grip, you've won, since they spin simultaneously and thus will lead the car forward in a straight line more or less. It works very well actually. If you turn off the ESP, you can just go down to the metal and that might get you out of there as well. Or not.

Yes, that's what I mean. ESP is no substitute for a 4WD with real limited-slip differentials. But it is often sold as such, as most 4WD SUV's aren't supposed to be used in rough terrain anyway. They just have to look the part, and be able to handle parking on a construction site, or other short trails in good condition or a small bit of snow. And it's much cheaper to build them that way. Many SUV's do this (a lot doesn't even have 4WD), but they're no all-terrain vehicles, while they are often marketed as such when they do have a four wheel drive.

They just use ESP (or however that particular feature is called) as a cheap substitute for real limited-slip differentials. Because the buyer is unlikely to notice the difference. They are not supposed to drive on ice, serious mud or other places where you really need serious traction.

Mind you, I don't think there is anything wrong with that, as that is just what the average consumer wants and expects. But I think it's a bummer when you come into a situation where you expect your car to pull through, and it cannot.

But then again, those limited-slip differentials are quite expensive. So you get what you pay for, in most cases.

 

[Frank]

Btw, when cornering at high speed, a limited slip differential will prevent serious accidents, like when two of your wheels get next to the road because you went too fast. Or in a lot of other situations. The car is just much more responsive to your commands. So it is mostly about active safety, in being able to handle and survive dangerous mistakes.

While things like ESP can and will help you with that, they're no substitute for the real thing. But they do help with preventing the less serious driving errors causing the damage they would without it.

 

[swaaye]

The best vehicles for icey roads are not trucks or SUVs. They are small, light cars with AWD. Absolutely STUNNING superiority. My family has had a Eagle Talon AWD and a Audi A6 Quattro. Both were just awesome on ice, especially with some decent tires like Blizzacks.

I drive a Explorer AWD (wish it was 4WD) that is pretty kick ass on slick winter roads with decent tires. I've also driven Suburbans for years. They get the job done on snow ok. Heh up at the cabin I have the old rusted out '90 Burban with serious mud tires and man that thing rocks for snow and mud.... but stay off of ice for God's sake! Ice is scary shit and AWD cars wipe the floor with anything bigger. Unless you use chains or studs or something else illegal and crazy.

Once at school at MTU in Houghton, MI a few years ago I went to a crazy hick truck show called Tuff Trucks or something like that. Mud holes and crazy jumps, etc. I saw a little Mitsubishi mini-truck-thing wipe the floor with the big manly Chevy Tahoe/Fullsize Blazers. Lol! Never underestimate weight's damaging effects!

 

[digitalwanderer]

Eagle Talon AWD

I've always liked how those looked and thought they'd handle well.

 

[Frank]

The difference is between all-terrain stuff (SUV's and trucks, mostly), that have a lever that locks your differentials (4WD), and street-legal rally cars (AWD), like an Audi Quattro or a Subaru. I love the Subaru Impreza, as that is the easiest one to drive of them, and very forgiving. But an EVO or Quattro are very close, although (especially the EVO) harder to drive. They allow more, but you'll pay faster when you cross the line. So they're not as good when you mostly want a lot of active safety.

All-terrain driving is mostly about getting trough it at slow (walking) speed, while the rally cars can do the same, but at blistering speed. Although they won't be able to cross the really bad parts, while an all-terrain might. But the difference is not that great.

So, it's mostly about speed and handling. The all-terrain ones are build to stubbornly roll though, whatever happens, while the rally ones are all about agility and grip, and are supposed to scream through it all before they have a chance to get stuck.

 

[swaaye]

My uber-ancient rust heap Suburban has a limited slip rear diff (posi traction I believe it's called). You can literally feel it kick in as the rear slips when in 2WD. It's fun. Heh. But there's nothing like engaging those front tires to get some traction on a long vehicle with a light rear...

The worst part of AWD IMO is that you usually don't get a Low range. Really screws over the vehicle for getting through bad, deep, gooey stuff. I almost got stuck on a beach with my V8 Explorer AWD cuz of that....very disturbing. It was a black sand/pebble beach and down I was going. I was almost floored and it was obvious that a lower range would've helped immeasurably..

 

[Frank]

The whole trick to driving off-road or through snow or whatever is really simple, if you know how. I used to do that regulary with any car, at about 80 km/h. Even a simple 2WD one can do it (although it is much harder than with an AWD one, obviously).

It is like this: don't press the pedals or turn the steering wheel more than a bit at a time. And if you really have to brake to take a corner, do it before you enter it, and let go of the brake when you do. The braking will increase the grip of the tires quite a bit, and you will be able to round the corner at a much faster clip than without it. But when you try to brake inside the corner (and going really fast already), you will start to fly.

Your wheels will only start to spin when you push the pedal down deep. Don't do that. Just increase the power slowly, and you will be fine. The same goes for braking and steering.

Especially on ice, when you start to slide, you're lost. Unless you did it on purpose and knew exactly what you were doing, of course. Until you know, don't do that. At all. Handle those controls with a very soft hand.

That is the worst mistake you can make. Panic, and push the brakes or gas fully, or jerk the steering wheel. As long as you don't do those things, you keep control of the car. And that is the utmost important thing to be able to prevent making destructive accidents!

For example, you can take an all-terrain at a fair clip through deep mud, as long as you keep your wheels off the deep tracks and you stay away from making abrubt adjustments. Just keep on depressing the gas pedal steadily, and you will speed up. But when you push it down, you get stuck and stop. Strange but true. That's how I won a contest at one time: it had rained a whole lot, and I was the only one to finish.

On the other hand, if you know what you're doing, you can do the same at high speed, with the same considerations. If you want to slow down, hitting an obstacle at the side is probably better than pushing the brakes. At a good clip (~100 km/h or faster) and around corners, you're not so much driving as flying and hitting the right obstacles to stay inside the course...

 

[digitalwanderer]

Pffft, it's a whole lot easier than that. Just pop your drive into 4x4 mode and kick it down into ultra-low gear, always works for me.

 

[Frank]

Pffft, it's a whole lot easier than that. Just pop your drive into 4x4 mode and kick it down into ultra-low gear, always works for me.

Yes, exactly. Do that and go slow but steady, and your trusty all-terrain will save the day.

 

[_xxx_]

So what does the ECU on modern vehicles do to optimize the engine for the environment? And, how much does it influence shift patterns? This stuff is very fascinating but it's hard to figure out where to discuss it.

Lots of stuff!

The latest ones have a Motorola PowerPC @60MHz inside. What's being monitored the whole time: ambient temperature, several temperatures inside (oil, coolant, exhaust, gearbox), absolute geographic height, angle and spin of the car, throttle position, gasoline temperature and pressure and so on and so on. Other devices monitor their own sensors and actuators and send lots of stuff over the network (CAN bus). For instance, engine ECU calculates the vehicle speed with wheel rpm being sent over CAN from the ESP (which has wheel sensors hooked up to it).

But it would take like 20 pages just to explain the most basic functions, there are anywhere between 30 and 60 ECU's in a modern car (ECU being "Electronic Control Unit"), each of these with lots of stuff hooked up to them. There are different fallback-strategies in case of failure and a very advanced network management (all configured nodes have to be present and signal their state changes like awake, ready for sleep mode, power down,...). This is in another layer in terms of networking and is independant of "normal" communication although it all runs on CAN concurrently. And then there is a separate diagnostic bus going into the "Central Gateway", which has all the busses running through it and distributes different signals between them.

You have separate ECU's for pretty much everything. Let's take a usual S-class Merc: engine ECU, gear switch module, front/rear relais/switching module, door modules, seats with/without memory, airbag control unit, ABS/ESP/brakes, AC, switch modules, power management for the battery, gasoline pressure control driving the pump(s), ambient light control, rain/light sensors with a control unit for automatically managing the wipers/lights, air suspension ECU, Pre-Safe ECU, parametric steering, sound system, navigation, telephone unit, instrument cluster (is also a gateway), antenna amplifier module, and so on.

Lots of stuff happening in the car all the time. And the customer should never notice anything, just feel comfortable. I think people would think differently if they knew how much of what happens in the car is pure electronics.

 

[mustrum]

Computerisation is a nice thing. 150k € Merceds stop the engine on the highway because of electrosmog. No joke!
The more technical gimmics the better for the the machanics. You just pay and pay.

 

[_xxx_]

Computerisation is a nice thing. 150k € Merceds stop the engine on the highway because of electrosmog. No joke!
The more technical gimmics the better for the the machanics. You just pay and pay.

A thick wall will also stop a 150K car, but you don't stop building walls or start building cars like tanks, so what's your point? There is no way to realize even 30% of the functionality (which customers want, that's why it's in there in the first place) in modern cars without an insane amount of electronics...