4 ms·

Car gearboxes are a spectacular cause of power loss (in the order of 20% IIRC), so probably better to come up with a simple gear reduction or a belt-driven pull

by lloeki 3y ago

Car gearboxes are a spectacular cause of power loss (in the order of 20% IIRC), so probably better to come up with a simple gear reduction or a belt-driven pulley system.

dylan604 3y ago
They didn't say use the car's transmission. The suggestion of a 2:1 gear reduction could easily be a simple gear reduction or a belt-driven pulley. You've tried to inject something on your own accord for possibly a misunderstanding??
- cduzz 3y ago
  Yeah, they didn't mention many specifics; I also imagine that they're just pulling the power off the engine using the accessory belt connected to their existing alternator -> inverter setup. Similarly -- the concerns about how to cool the device if it s putting down 100hp -- that's 74570 watts; it's unlikely they're using a harbor freight generator's alternator to generate that kind of power.
- lloeki 3y ago
  I read "gearbox" as, well, an automotive gearbox, which would hardly be surprising in the context of the article. 2:1 could easily mean crank the gearbox into a gear that approximately produces that ratio. > You've tried to inject something on your own accord for possibly a misunderstanding?? WTH is that supposed to mean? If I misunderstood anything it was a honest mistake. GP suggested a RPM reduction for fuel efficiency reasons, it would be counterproductive to offset that efficiency gain with a high-loss mechanical device. There was neither ill intent nor hidden agenda.
polishdude20 3y ago
What about them makes them so inefficient?
- bluGill 3y ago
  If the torque converter doesn't have a lock that is a big loss. Those same transmissions also tend to have low efficiency hydraulic pumps internally to select the gears. Modern automatic transmissions tend to be much better than older ones.
  - lloeki 3y ago
    > Modern automatic transmissions tend to be much better than older ones. I seem to recall improvements in that area around 2015 (probably driven by emissions regulations) but don't know the implementation details. One change was also a marked increase in available ratios (7, up to 10) which combined with better logic drives mpg down overall, sometimes lower than stick or dual clutch on standardised tests.
- lloeki 3y ago
  Automotive gearboxes prime goal is to: a) expand the workable range of the IC engine (1000-5000rpm for Diesel, 1000-9000 - at best - for NA petrol, turbocharging dials it down) b) solve the zero-to-low rpm problem that causes stalling due to nonexistent torque It results in a complex device where many parts are still spinning even on the non-engaged gear. Look at a cut out of a manual transmission. The irony is that an epicyclic automatic transmission is mechanically efficient, up to the torque converter which uses fluid coupling. Efficiency is a secondary goal to the ones above, without which the car would be useless.
bluGill 3y ago
Some car gearboxes are that bad. However others are much lower. Are we talking about a "slushbox" automatic without a locking torque converter, or an all gear manual transmission - there is a big difference. I didn't specify what type of gear box because there are many different options. Belts of the front pulleys would work. You could rig up a chain drive system as well. there are pros and cons to each.
- lloeki 3y ago
  > Are we talking about a "slushbox" automatic without a locking torque converter, or an all gear manual transmission - there is a big difference. Correct. IIRC again (numbers from 2010ish, probably there were some improvements since but I bet physics limit those) the best stick were 15%-20%; slushboxes were 25%-30%. Such loss is justified by making the car able to operate on a much wider range, from standstill to highway speeds, and solve the ~zero torque at <1000rpm problem. IOW without a gearbox the car is useless. Without that requirement a simple reduction would be much more efficient. One of the huge benefits of going electric is that - in addition of having stellar electric to mechanical energy conversion efficiency (90-95%, vs a very lousy number I can't recall for chemical to mechanic energy) - the engine can basically be put on direct drive because torque is immediately available starting at 0rpm and all the way to max rpm, so no additional loss. > I didn't specify what type of gear box because there are many different options. Belts of the front pulleys would work. You could rig up a chain drive system as well. there are pros and cons to each. Totally fair! I didn't want to sound dismissing, only complementary.
ehaliewicz2 3y ago
I'm curious what the loss for a typical constant-mesh manual gearbox would be. I assumed 90% or more efficiency.

by lloeki 3y ago

Car gearboxes are a spectacular cause of power loss (in the order of 20% IIRC), so probably better to come up with a simple gear reduction or a belt-driven pulley system.

dylan604 3y ago

They didn't say use the car's transmission. The suggestion of a 2:1 gear reduction could easily be a simple gear reduction or a belt-driven pulley. You've tried to inject something on your own accord for possibly a misunderstanding??

cduzz 3y ago
Yeah, they didn't mention many specifics; I also imagine that they're just pulling the power off the engine using the accessory belt connected to their existing alternator -> inverter setup. Similarly -- the concerns about how to cool the device if it s putting down 100hp -- that's 74570 watts; it's unlikely they're using a harbor freight generator's alternator to generate that kind of power.
lloeki 3y ago
I read "gearbox" as, well, an automotive gearbox, which would hardly be surprising in the context of the article. 2:1 could easily mean crank the gearbox into a gear that approximately produces that ratio. > You've tried to inject something on your own accord for possibly a misunderstanding?? WTH is that supposed to mean? If I misunderstood anything it was a honest mistake. GP suggested a RPM reduction for fuel efficiency reasons, it would be counterproductive to offset that efficiency gain with a high-loss mechanical device. There was neither ill intent nor hidden agenda.

polishdude20 3y ago

What about them makes them so inefficient?

bluGill 3y ago
If the torque converter doesn't have a lock that is a big loss. Those same transmissions also tend to have low efficiency hydraulic pumps internally to select the gears. Modern automatic transmissions tend to be much better than older ones.
- lloeki 3y ago
  > Modern automatic transmissions tend to be much better than older ones. I seem to recall improvements in that area around 2015 (probably driven by emissions regulations) but don't know the implementation details. One change was also a marked increase in available ratios (7, up to 10) which combined with better logic drives mpg down overall, sometimes lower than stick or dual clutch on standardised tests.
lloeki 3y ago
Automotive gearboxes prime goal is to: a) expand the workable range of the IC engine (1000-5000rpm for Diesel, 1000-9000 - at best - for NA petrol, turbocharging dials it down) b) solve the zero-to-low rpm problem that causes stalling due to nonexistent torque It results in a complex device where many parts are still spinning even on the non-engaged gear. Look at a cut out of a manual transmission. The irony is that an epicyclic automatic transmission is mechanically efficient, up to the torque converter which uses fluid coupling. Efficiency is a secondary goal to the ones above, without which the car would be useless.

bluGill 3y ago

Some car gearboxes are that bad. However others are much lower. Are we talking about a "slushbox" automatic without a locking torque converter, or an all gear manual transmission - there is a big difference. I didn't specify what type of gear box because there are many different options. Belts of the front pulleys would work. You could rig up a chain drive system as well. there are pros and cons to each.

lloeki 3y ago
> Are we talking about a "slushbox" automatic without a locking torque converter, or an all gear manual transmission - there is a big difference. Correct. IIRC again (numbers from 2010ish, probably there were some improvements since but I bet physics limit those) the best stick were 15%-20%; slushboxes were 25%-30%. Such loss is justified by making the car able to operate on a much wider range, from standstill to highway speeds, and solve the ~zero torque at <1000rpm problem. IOW without a gearbox the car is useless. Without that requirement a simple reduction would be much more efficient. One of the huge benefits of going electric is that - in addition of having stellar electric to mechanical energy conversion efficiency (90-95%, vs a very lousy number I can't recall for chemical to mechanic energy) - the engine can basically be put on direct drive because torque is immediately available starting at 0rpm and all the way to max rpm, so no additional loss. > I didn't specify what type of gear box because there are many different options. Belts of the front pulleys would work. You could rig up a chain drive system as well. there are pros and cons to each. Totally fair! I didn't want to sound dismissing, only complementary.

ehaliewicz2 3y ago

I'm curious what the loss for a typical constant-mesh manual gearbox would be. I assumed 90% or more efficiency.