4 ms·
Unfortunately the explanation of the A/C fluid cycle is haphazard and the description of how forces relate to crankshaft position is completely wrong. The cran
by jcims 5y ago
Unfortunately the explanation of the A/C fluid cycle is haphazard and the description of how forces relate to crankshaft position is completely wrong. The crankshaft actually applies maximum force to the piston while approaching top and bottom dead center, when the mechanical advantage is greatest, and the least at mid stroke, where the torque of the motor is most directly opposed by the pressure of the gas against the face of the piston. This is good, however, because it marries well to the available power through an alternating current system.
The design described does seem to have fewer moving parts, which is good. But the advantage of linear vs rotary motion with respect to forces seems sketchy. Field strength in the linear system is likely to vary across the travel and would still need to be synchronized to the alternating current to prevent motor stalls. (Edit 50 of this comment: this effect is actually illustrated directly in the video here: https://youtu.be/2TFiL5BM3ss?t=348 https://youtu.be/2TFiL5BM3ss?t=348 Imagine the field lines directly correlate with force applied, and mentally plot the quantity of field lines over time as you watch the animation. Turns out it looks precisely like the force chart of a rotary compressor.)
The primary advantage of this pump, to me, seems to be reduced weight/complexity and lower friction losses. For it to operate with low starting load it would likely need to essentially vibrate its way to full travel (confirmed at 7:47 in the video), something rotary compressors can’t really do. If you try to restart rotary compressors too quickly after stopping, the high head pressure will stall the motor. This causes it to effectively be a dead short minus winding resistance, pulling much more current than average (known as LRA or locked rotor amps) with no cooling. This will heat the motor quickly until it thermally trips or burns up. This is why you will frequently see restart delays in A/C systems.
For what its worth, scroll compressors have been around forever and share some of these advantages, but aren’t dominant in the industry because of the additional complexity in manufacturing. They have an additional advantage of somewhat continous output pressure, which *significantly* reduces ambient noise and vibration. They also have fewer moving parts and are generally more reliable.
All of these advantages convey to standard air compressors by the way, something I'm a little surprised they didn't mention.
- phnofive 5y agoYou sound like you have expertise, so could you have a look at his patents? I couldn't make much of them other than they looked familiar in some aspects and impractical/impossible in others: https://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=0&f=S&l=50&d=PTXT&RS=IN%2F%22helmreich%22&Refine=Refine+Search&Query=IN%2F%22helmreich%22+AND+IN%2F%22martin%22 https://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=... I assume that this is pretty common in trying to improve linear motors - I am trying to get my hands on a small one to drive an air pump and it's just inscrutable to me.
- jcims 5y agoI just have experience rather than expertise, hoping someone with actual expertise shows up to correct me where I'm wrong. :) I love the idea of low hanging fruit in every dimension of technology, but the reality is that linear pumps have been around for quite some time and aren't dominant in any high (sales) volume application that I'm familiar with. That tells me there are likely some tradeoffs here that are not being explained. Vibration would be one obvious area, but could be handled with a harmonic balancer or an additional pump operating 180 out of phase (unfortunately increasing cost/complexity). The other potential issue is that the motor needs to be built for the application for the most part. With rotary compressors, you can incorporate pulleys to gear the system up or down in accordance with the cheapest motor you can put to use. With this system the motor is the pump, so it's harder to add some kind of lever to gear it up or down. (This is less applicable to small A/C systems which tend to use hermetically sealed compressor systems, but for larger systems this can come into play.)
- ironmagma 5y agoThe cost is likely to be less important as time goes on and consumers become more aware (and caring) of the external cost to having inefficient machines.
- jcims 5y agoNot to be trite, but cost is always important to the manufacturer. Tesla, for example, has been able to build a vertically integrated company through sheer will of its leadership. However, this is highly unusual and most product companies are going to want to invent as little as possible in order to ship a product. In this case a company wanting to sell an HVAC system based on this tech would have to develop the manufacturing pipeline to build these compressors vs. buying them from Copeland. Now Copeland may choose to build these, but they are going to have to build the motor vs. buying them from one of hundreds of companies that build AC motors to spec. Now one of those companies might decide to build these linear motors, but they are going to have to license the IP to do so, putting them at a distinct cost disadvantage vs. standard rotary motors. They are also going to be a sole supplier for some time, something manufacturers are very wary of unless it's a major differentiator. These are likely to cancel out.
- y04nn 5y agoThank for the explanation, what about screw compressor? Are they too expansive to manufacture and need too much maintenance? How would you compare them to scroll compressor? I know they have industrial use, but I'm not sure why they are not more widespread.
- jcims 5y agoScrew compressors are more well suited for high volume applications (like superchargers) than high pressure. This is because the geometry of the screws is difficult to sustain with very high tolerances. Small leaks aren't a problem when you're talking 10-50psi, but the 'high side' pressure of an A/C system is typically over 200psi.
- mech422 5y agoMy Dad made the screws for screw compressors back in the 70-90s... He primarily worked for joy/lovejoy, but also made screws for ingersall and a few others. It was amazing to me how small the screws were for say, a shopping mall unit.. and how PRECISE the machining was. The math behind the profiles was insane to, it was a 'self generating' curve.. You calculated a point on the curve, and that was fed in to generate the next point. Generating a new profile shape was a HUGE process... Wonder what it would be like with today's computers :-P
- jcims 5y agoThat's awesome! Seeing how wholly dependent modern manufacturing is on CNC makes me respect those early machine operators even more. They were constantly innovating on how to apply physical geometry and minimize incremental errors in order to build parts with tolerances that would still hold up today.
- mech422 5y agoMy Dad used to do a 'trick' where he would zero out a 6 decimal place readout on the big ground glass comparator.. You could then move the table anywhere you wanted in X/Y, cover the display, and he would bring it back to 0.0000X by eye :-) He actually went to some institute in Sweden that did ultra-accurate measurements to show them how he did it. I think the 'trick' was, he moved the shadow till it was just past the blueprint, and back it off till a sliver of light shone thru, rather then trying to 'walk' the shadow up to the blueprint.. Neat stuff - but I decided on a tech career when I was mucking out the Holyroyd mill and he turned the cutting pumps on :-P Being drenched in cutting oil convinced me I liked computers better :-P
- rozap 5y agoVW mass produced scroll superchargers 30 years ago for the G60 and they were unreliable but super efficient. Kind of surprising that with 30 years of manufacturing advances they're not more common. Such a cool design.
- ip26 5y agoModern turbos more or less killed off superchargers. Largely thanks to advances in computer fuel injection managing all of the tricky parts of turbos. (Superchargers are simpler, but cost ~10% engine power to drive)
- deleted 5y ago[deleted]
- ants_a 5y agoThe comparison to a turbo got me thinking if some of the compression energy could be recovered in the expansion stage. Turns out the answer is yes, but the energy recovery is limited to 7% at best: https://www.sciencedirect.com/science/article/pii/S1876610215027897 https://www.sciencedirect.com/science/article/pii/S187661021...
- danans 5y ago> If you try to restart rotary compressors too quickly after stopping, the high head pressure will stall the motor. This causes it to effectively be a dead short minus winding resistance, pulling much more current than average (known as LRA or locked rotor amps) Inverter based heat pumps and ACs that are already available on the market today have low LRAs as a consequence of their ability to operate at continuously variable speeds.
- deleted 5y ago[deleted]
- jhallenworld 5y agoI'm worried about vibration. Maybe they should have two masses operating in opposite directions at once to balance out the vibrations. Maybe they will license my idea..
- flavius29663 5y agowouldn't that effectively double the cost of production? It might be cheaper and easier to invest in some spring based dampening. Anyway, even in their video, the vibration is out of control, moving the pipes around and making it look like it won't last too much in real life applications.
- jcims 5y agoYou could probably do some kind of damped harmonic balancer with a simple mass on the end of a damped spring tuned for the expected operating range. Still increases cost but not as much.