4 ms·

Thanks to the 'heartbleed' mess I was passed several collections of design documents (for then-current and then-future production) from an european carmaker aft

by kw71 9y ago

Thanks to the 'heartbleed' mess I was passed several collections of design documents (for then-current and then-future production) from an european carmaker after some less than scrupulous colleagues got into their vpn. Specification: Engine design lifetime = 2000 running hours. CAD and FEA are great, but the above spec ruins it. You get parts made of light alloys and plastic, made of the minimum amount of material possible. They happen to be mostly fine when everything is perfect but any unintended load or crack in the plastic due to aging results in a catastrophe.

nether 9y ago
At least in aerospace, the 2,000 hr spec comes up often as a reasonable service life. We could make everything last forever, but that usually means beefier, heavier parts. How much more in fuel per flight hour are you willing to pay for a product that lasts longer? What about decreased range? Also, how much of a unit cost increase will you accept to pay for larger chunks of aerospace aluminum? Tradeoffs are necessarily driven by consumer demands.
- saiya-jin 9y ago
  I will happily accept extra 20 kg weight on my 1500 kg car, if it means 10 most mechanically stressed parts in engine, suspension, transmission etc. will last much longer. that maximum 0.1l/100km consumption increase will be perfectly fine with me too, most people don't drive for fuel efficiency anyway (that would mean 90 kmh on highway for example).
mattsouth 9y ago
At an average speed of 50mph, 2000 running hours comes out at 100000 miles. If the spec aims for all engines to last this long then you'd expect a good majority of them to last a lot longer. This doesnt seem too bad a goal to me.
- michaelmrose 9y ago
  Why on earth would you imagine 100,000 is an ok goal? My 2004 Toyota Carolla has around 150k miles on its original engine and supposing you keep maintaining it 250k is not unreasonable. It seems odd that you would accept a design lifetime that is 40% of a car made 13 years ago. I'm also not clear why you would expect the majority to perform above spec? Wouldn't a significant number fail under spec? Isn't a care which may become a total loss in 60-80k miles basically tissue paper quality?
  - rplst8 9y ago
    Manufacturers often use a term MTBF or "mean time between failure". I'm not sure if the 2000 hours spec is an MTBF or not, but essentially that is an average life with some standard deviation. Personally, I think a pretty big swath of engines make it well past 100,000 miles now - there are usually other issues with cars at about the 10 to 15 year mark with most makes and models that have to do with rust. Designing engines that last significantly longer on average (say 250,000 miles) would require either a beefier design, which will add weight and reduce efficiency, or exotic materials that will significantly increase the cost. Automobiles are pretty amazing for what they are. I agree with many others that they have gotten ridiculously complex, but this is mostly because of the emissions requirements - and that said I do enjoy the fact that smog is not much of an issue (at least in the US) these days.
  - adrianN 9y ago
    He said "if the spec aims for all engines to last this long", implying enough safety margins to make the average engine last longer.
  - mattsouth 9y ago
    My main point was that 2000 hrs sounds quite short, at least to me, but 100K miles sounds considerably longer. I suppose that if a manufacturer's goal is that all their vehicles last at least that long, and they can reach that goal then most will last much longer, especially with some TLC.
- johnbrodie 9y ago
  I think your average speed of 50mph is incredibly unrealistic, unless the car is driven almost exclusively on the highway.

by kw71 9y ago

nether 9y ago

At least in aerospace, the 2,000 hr spec comes up often as a reasonable service life. We could make everything last forever, but that usually means beefier, heavier parts. How much more in fuel per flight hour are you willing to pay for a product that lasts longer? What about decreased range? Also, how much of a unit cost increase will you accept to pay for larger chunks of aerospace aluminum? Tradeoffs are necessarily driven by consumer demands.

saiya-jin 9y ago
I will happily accept extra 20 kg weight on my 1500 kg car, if it means 10 most mechanically stressed parts in engine, suspension, transmission etc. will last much longer. that maximum 0.1l/100km consumption increase will be perfectly fine with me too, most people don't drive for fuel efficiency anyway (that would mean 90 kmh on highway for example).

mattsouth 9y ago

At an average speed of 50mph, 2000 running hours comes out at 100000 miles. If the spec aims for all engines to last this long then you'd expect a good majority of them to last a lot longer. This doesnt seem too bad a goal to me.

michaelmrose 9y ago
Why on earth would you imagine 100,000 is an ok goal? My 2004 Toyota Carolla has around 150k miles on its original engine and supposing you keep maintaining it 250k is not unreasonable. It seems odd that you would accept a design lifetime that is 40% of a car made 13 years ago. I'm also not clear why you would expect the majority to perform above spec? Wouldn't a significant number fail under spec? Isn't a care which may become a total loss in 60-80k miles basically tissue paper quality?
- rplst8 9y ago
  Manufacturers often use a term MTBF or "mean time between failure". I'm not sure if the 2000 hours spec is an MTBF or not, but essentially that is an average life with some standard deviation. Personally, I think a pretty big swath of engines make it well past 100,000 miles now - there are usually other issues with cars at about the 10 to 15 year mark with most makes and models that have to do with rust. Designing engines that last significantly longer on average (say 250,000 miles) would require either a beefier design, which will add weight and reduce efficiency, or exotic materials that will significantly increase the cost. Automobiles are pretty amazing for what they are. I agree with many others that they have gotten ridiculously complex, but this is mostly because of the emissions requirements - and that said I do enjoy the fact that smog is not much of an issue (at least in the US) these days.
- adrianN 9y ago
  He said "if the spec aims for all engines to last this long", implying enough safety margins to make the average engine last longer.
- mattsouth 9y ago
  My main point was that 2000 hrs sounds quite short, at least to me, but 100K miles sounds considerably longer. I suppose that if a manufacturer's goal is that all their vehicles last at least that long, and they can reach that goal then most will last much longer, especially with some TLC.
johnbrodie 9y ago
I think your average speed of 50mph is incredibly unrealistic, unless the car is driven almost exclusively on the highway.