Slashdot Mirror
Camless Internal Combustion and the Digital Age (hackaday.com)
szczys writes: The internal combustion engine is amazing, and it continues to evolve. Carburetors gave way to fuel injection, and a computer now monitors all kinds of sensors to ensure these engines operate at peak efficiency. But there is one thing that has remained largely unchanged: the cam shaft. This is a device responsible for mechanically timing the operation of the cylinders. It's possible to build an engine that uses digitally controlled actuators instead of a camshaft to decide when each cylinder should fire. These exist as prototypes — we have the technology, so why aren't we building with it? The answer is that change is hard, and as with the carburetor it could take an outside force (in that case mandatory efficiency benchmarks) to get automobile manufacturers to wager a bet on new technology.
It's possible to build an engine that uses digitally controlled actuators instead of a camshaft to decide when each cylinder should fire.
Camshafts don't control when cylinders should fire, that's an already replaced component called the distributor. Camshafts control the timing of inlet and outlet valves, and there are already formula one and other engines using electronically actuated pneumatic valve lifters.
The problem is that cam shafts are very reliable, and a single fault in valve timing, in an interference engine especially, results in catastrophic engine damage, so the software and hardware has a very high bar to meet for it to replace mechanical cams.
Also firstpost.
-puddingpimp
In doing a quick search for a mis-remembered car that I thought had an all-electric valve train, I came across some fellow's back-of-the-envelop calculations suggesting it would take about 20 KW to run a car's valvetrain electrically. That's a heapload of power.
Naturally, much of that power is likely dynamic (accelerate the valve mass, so put energy into it, then halt the valve mass, pulling energy back out, repeat indefinitely). Doing it efficiently is going to be a bear with wires of normal conductivity. It's also going to be a very nice radio transmitter.
Put my fist through my alarm clock with its ding-dong death inside my ear. - The Blackjacks.
The sparkplug of a gas engine requires... electricity.
A modern car engine uses an ECU which regulates spark timing and the transmission (usually called a PCU or Powertrain Control Unit nowadays) - it adjusts the spark timing and spark power based on the load of the engine. Lose battery power and the ECU goes dead. Depending on the vehicle, if you drop the battery, it may or may not continue running - the alternator will produce more than sufficient power to keep the engine running, but the battery provides voltage regulation of the entire system.
And there are still completely mechanically driven engines - small aircraft use them, and they're a PITA to manage because you have to manually adjust the mixture (fuel-air ratio) for optimum power as you change altitudes. Experimental avgas aircraft, and production diesels (running on Jet-A) use a FADEC (Full Authority Digital Engine Control) which runs off the ship battery and a backup battery that fully controls the engine. The pilot only has a lever that tells the FADECs (there are two of them for redundancy) how much power to develop - the FADEC figures out the optimum settings to achieve that. You get an increase in efficiency, a decrease in pilot workload and all around increases in efficiency.
Heck, Electronic Fuel Injection isn't on aircraft engines yet - yes, they've had fuel injection for around 25 years or so but it's generally of the continuous spray type.
As for this, it does have some advantages like extreme variable valve timing. Hybrid cars, for example, often use a modified Atkinson cycle engine (modified because it's really an Otto cycle engine, with the intake valve kept open well into the compression stroke to reduce the fuel charge). Atkinson engines are extremely efficient - they have a small intake and compression stroke but a large power stroke (the goal is at the end of the power stroke to have 0 differential between cylinder pressure and air pressure, thus ensuring you have extracted all the energy).. But at the same time, Atkinson engines don't develop as much power. Being able to switch operating modes on the fly can be useful in pure gas-only cars - switch to Atkinson during low power for maximum efficiency (idling, highway), while being able to switch to Otto when you need power (accelerating, for example)
http://www.motorauthority.com/news/1101737_video-shows-inner-workings-of-koenigseggs-camless
They call it a "Digital Cam" because when you graph valve lift vs time it literally looks like a square wave. The ramps really are that steep!
This compares to a conventional cam with a sudo-sinusoidal shaped wave lift profile (neglecting the effects of high RPM valve float).
Criticize as much as you want, but a truly functional electronically controlled camless engine would be the holy grail of internal combustion engine design. You can easily pick up 20 horsepower on many engines just by swapping to a performance cam, but you often compromise efficiency. But with a camless engine, in theory, you could have cylinder deactivation, low compression starts, the elimination of throttle plates (lower pumping losses), "full race-cam" profiles for performance, a cam profile for smooth idling, low emissions, etc....
Truly the best of both worlds!! That being said, there are disadvantages....
---
I read an interesting SAE paper 20+ years ago describing a working prototype camless engine. The performance gains were impressive, but as I recall, there were two main obstacles:
1) Noise, Vibration, and Harshness. (NVH)
2) The valves landed harshly leading to valve seat wear. The SAE paper suggested using a method for softer valve landings.
In general, solenoids are either on or off, but that is not intrinsic to their design. Opening and closing times can be altered either electrically or physically (for example, using soft iron to slow the magnetic field's change).
On some large diesel engines, the valves are driven hydraulically or pneumatically with solenoids just activating small control valves. On those, it's fairly easy to shape and position cylinder outlets to give it a (relatively) soft close.
The rest, as you pointed out is a cost/benefit analysis.
I can see some potential in the technology, but you won't see me buying a production car with it for the first few years after introduction.
One more MAJOR advantage of a camless design (if not the single greatest advantage) would be the ability to have extremely canted valve angles. Retrofitting an existing cylinder head design with camless engine technology is only scratching the surface. The biggest benefits would be gained by designing the cylinder head ports around the capabilities of the valve actuators. With cylinder head differences like this, we're literally talking about the difference between NASCAR horsepower levels and streetcar horsepower because cylinder head designs are the undisputed most important factor in making horsepower.
With traditional cylinder heads (on OHV engines), valve angles are limited by the rocker arms. Rocker arm rotation about one axis is trivial, but when the valve is canted it makes the valvetrain design exponentially more complex and prone to wear due to lateral loads as the angle is increased. A camless engine design wouldn't have this limitation. That being said, the camless designs have their own challenges, namely soft valve seat landings due to a nearly perfect square-wave lift profile.
Cam Timing - having a camshaft is a forced pick the optimum cam timing for the entire rev range - you get one choice - open at a particular degree in the cycle, and close. Further more, you cant adjust the ramp up and ramp down rates. The mechanicals have a limit on how quickly they'll ramp up and down - high rpm you'll get valve float and valve bounce.
You can play around with it a little. Nissan in the 90's started with an actuator to shift the cam timing forward slightly at higher rev ranges. Honda and their VTEC - shift the camshaft to a more agressive mode at higher RPMS. But still, this is only playing at the fringes.
Formula one has used pnuematic valve control for a while (camless). There is significant efficiency gains to allow higher revving engine, but more so to make sure the valve opening and closing timings are optmised for both the current engine rpm and load - which you can not do with a camshaft.
All of the easy gains have been made. To get further efficiency gains, we're going to have to look at the more complex options such as this.
In Soviet Russia the insensitive clod is YOU!
I just, I just can't see any benefit to this? ... What efficiency gains are here?
Follow the links and do some research? 30% fuel economy increase at low end, 30% increase in power at the high end, 50% reduction in emissions for standard driving, 4cyl engine in the same space as a 3cyl engine in the engine bay, a 20cm reduction in vertical height of the engine, reduction in engine weight (benefit increases with engine size).
Oooh and then you get into the really interesting things:
Ability to shutdown cylinders completely on demand by holding the valve open when not needed.
Eliminate engine breaking completely further increasing fuel efficiency by allowing an engine to freewheel without compression eating up efficiency.
And then you can do other things like using the back stroke of an engine to compress cylinder during engine breaking and sore it in a compressed vessel which can then be reused to boost power when needed either at take-off or at peak power.
Yep, no benefit at all.
Also this is not new. Not at all. Industrial compressors have had electronically diven continuous unloaders for the best part of 25 years now, and I guarantee that most of the compressors I've worked with have more rotations through their cylinders than any slashdot driver.