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There's A Good Reason Semi Trucks Don't Use V8s:
V8 engines are among our favorites . They make big power and sound that is, in the vernacular of Boston, wicked awesome. It's only natural to think that such big engines would power the big semi trucks that transport most cargo in the U.S., but that isn't true. Instead, you're more likely to find an inline-6 under the hood of most modern semis.
There are some important reasons why V8s have fallen out of favor in trucking. A V8 makes great horsepower, but towing heavy loads is all about torque. The inline-6 engines powering most modern semis make between 400 and 600 horsepower. That's not much more power than a well-equipped pickup truck these days, and is likely all the horsepower you really need anyway . However, most pickups don't make anywhere near the 1,000 to 2,000 pound-feet of torque that semi engines do. Big displacement in the 13 to 16-liter range, turbocharging, and diesel power maximize torque, and it shows in those four-digit figures.
Another factor is that in the U.S., semis are typically limited to a maximum weight of 80,000 lbs. Scania makes a 16.4-liter V8 producing 2,350 lb-ft used in Europe, but many of those countries allow heavier loads than we do. A smaller inline-6 can handle lighter American loads just fine.
The fundamental nature of an inline-6 is simpler than a V8. There's only one cylinder head, not two, so it has fewer parts. It's also easier to access and work on, reducing both maintenance costs and the time the truck is off the road. All this, plus its low-revving nature, makes the engine slightly more fuel efficient than a higher-revving V8. It's not much more efficient, but when you're talking six to eight MPG, every little bit helps and makes a big difference over thousands of miles.
The final nail in the V8's coffin was increasingly strict emission regulations for semis. It's easier to get a smaller displacement inline-6 to comply than a bigger V8, so that's what most manufacturers chose to do. In contrast, some companies like Caterpillar simply quit producing semi-trucks, focusing instead on off-highway applications. While electric options like the Tesla Semi may play a role in the future, the inline-6 remains the workhorse of American trucking for now.
Read More: https://www.jalopnik.com/1906098/why-semi-trucks-use-inline-6-not-v8-explained/
(Score: 4, Interesting) by JoeMerchant on Monday May 04, @01:19AM (3 children)
Meanwhile, I have a perfectly mechanically functional V8 sedan that has been laid up for a month while an expert mechanic specialist in the particular (W220) model uses all the best factory CAN bus diagnostic tools and scratches his head about which $800 module needs replacement.
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(Score: 2, Informative) by Anonymous Coward on Monday May 04, @03:36AM (2 children)
Yeah, parent AC is shockingly wrong. Not sure how people can be so ignorant. He doesn't seem to understand how complex the newer cars are, and that flaky connectors can cause many incorrect trouble codes. Sometimes a flaky / weak / defective sensor can "throw" incorrect codes, or throw other things off such that you get incorrect codes and waste time and money replacing otherwise perfectly good sensors and / or modules.
Older pre-computer car: there are only a few things that can go wrong. I think a stretched / slipped timing (cam) chain was one of my more difficult diagnosis, only because I'd never seen it before.
One of my newer cars has two CAN busses. The high-speed one- the important stuff- had been wired incorrectly, badly violating CAN bus wiring rules. It is truly amazing that the car ever ran, let alone for 14 years. Corrected the wiring and my trouble codes are all but gone.
(Score: 0) by Anonymous Coward on Tuesday May 05, @12:52AM (1 child)
> Corrected the wiring and my trouble codes are all but gone.
Very interesting. We process data that comes off CAN bus systems that often have 500 data channels/sensors (people upstream from us build and run these data acq systems). Often there are problems with the data and the typical approach to diagnose is to look at the sensor. But maybe we need to look at the system wiring as well?
Any references you can recommend?
(Score: 2) by RS3 on Wednesday May 06, @01:02AM
I'm an EE, somewhat into cars, been doing all my own repairs, well, for a very long time. Aforementioned car is a 20 year old Volvo. It's all Bosch (German) electronics. Not sure who made the wire harnesses.
You can do a websearch on CAN bus wire rules, but I'll summarize. It's a differential signal, a bit asymmetrical, but like most differential communication mediums, it's to be twisted pair, with a bus terminator at each of the two ends. You're allowed up to 1 foot (30 cm) or so for a "stub" - a short branch off of the main bus to a device. (other differential examples: Ethernet, USB, RS485, ...)
I bought the car cheap knowing it had (many) problems. I had some difficulty reading the high-speed CAN bus devices, and could barely read from the electric power steering pump. It's down in the right front, just in front of the right front wheel.
Long story short, I tore into the wire harness and found what I suspected: the main CAN bus ran behind the engine, and they tapped in a "stub" to go to the EPS (Electric Power Steering) pump, at least 2 feet. Maybe just as bad, wire wasn't twisted very much.
Twisting a differential pair does interesting things. It causes "mutual shielding", and allows the wire to become more like a "transmission line"- much more stable and efficient at carrying high frequency signals. The main difference between CAT3, CAT4, CAT5, CAT6, is the higher the number, the more twists per unit of length. The more twists, the cleaner the signal will remain, so you can push the speed up.
Tearing into wire harnesses isn't fun, but I spliced in some wire to take the CAN bus down to the EPS, a very short stub tap, then more twisted pair up and spliced in where I cut it to add the correct loop of twisted pair. All made me wonder if there were other compromises with CAN bus wire, taps, etc.
It sounds like you might not have control over the physical wiring. Sounds like factory sensor / controller systems? I've done some of that too.
There are limits to the total length of a single CAN bus. That's a lot of devices, so I might wonder if they're all on one CAN bus? Or are there many busses connected to a multi-port hub (gateway / concentrator)?
There are CAN bus analyzers that can check for signaling problems, data errors, etc. In most communication systems there's the OSI model and layers. There are protocol layers at the hardware level that most upper layers might not see. For example, and Ethernet interface does hardware protocol / handshaking voltage timing verification, conditioning, error checking, etc., so you might need an analyzer to find where the problems are. You might be able to rent one.
Again, critical that there's a terminator resistor at each end of the CAN bus, normally 120 ohms. So anywhere along the bus, with things turned off, you should read ~60 ohms wire to wire.
Many times there will be a device at each end, and it might have a switch or jumper to enable an internal 120 ohm resistor. Maybe someone forgot to do that? An actual resistor would need to be added if the device doesn't have built-in terminator option.
This is interesting, LMK.