@@stianmathisen4284 most of the surfaces in an engine never contact one another, they ride on a thin film of oil and any amount of metal-to-metal contact should be considered a mechanical failure. larger contact surfaces = way more oil shear forces = more losses. the main reason modern car engines are moving to thinner and thinner oils is because the engine oil viscosity contributes a huge portion of the total frictional losses
The sliding box section of the yoke design would make lubrication a lot more difficult to achieve effectively than with standard plain bearings on a normal crank pin.
as a new comer marine engineer cadet, i have to say that the sliders that are being used on the 2 stroke low rpm diesel engines, are made of white metals, that are cheap and are the first to wear out, so damaging of the engine can be avoided. In those engines are vertical, but yoke sliders are on the side, something that will incise friction and wearing out. Because of that i am very interested to see with what they came out to stope that problem.
Not really, it would be feeding oil to the crank and thus the square itself through feed holes, exactly like normal cranks. And voila. Have it squirt oil just before and after the lead and end corners of each slide surface of the square, the same way we use piston skirt squirters. Just have it squirt the slides instead. Bam done. The early Scot design probably only relied on paddle oiling like push mowers so it's no wonder it failed.
@@ShogunAutoworks it slows the wear out, but yes, if it is lubricated properly, then the life spend will be increased to that of a piston' s spring, or even more then that.
There could be needle bearings the same that are used in some high horsepower cam applications. However, there could be a round design instead of a square crank design.
There is still significant friction against the cylinder of the scotch yoke design: the off-centre force from the crank pin on the yoke causes a torque, just like in the connecting rod, which in turn torques the piston inside the cylinder. The force on the cylinder wall can be reduced by increasing the piston length, similar to how the lateral forces are reduced by lengthening the connecting rod.
No , the short edges of the scotch yoke's "square" run up and down linear bearings ( 9:40 648 & 650 in the diagram are bearings) in the crankcase walls. This eliminates side loads on the piston. i.e. The square also acts as a crosshead , as used in steam engines and large (ship size) diesels For some reason most commenters fail to understand this
I think you are missing the fact that the off-axis force still exists. So you will need restraint against rotating of the yoke due to the moment (torque).
@@paulgee-i7j Got it, so you have more reciprocating sliding surfaces and more reciprocating mass. You also have much more difficulty in maintaining tolerances which is why such designs have only been used commercially in low speed applications such as diesel ship engines. You just moved the problem (which has long ago been solved) to a more problematic location. YAY! I love designs that rattle themselves apart due to problematic tolerancing requirements!
I am a pilot. Although I spent most of my career flying jets, perhaps my favorite piston aircraft engine is the Lycoming IO-360. It is a 6 liter, 4 cylinder engine. How do they manage to make a smooth 4 cylinder engine that big? It's an air cooled boxer. The secondary balance problem was solved a long time ago, 23 million Volkswagen Beetles can't be wrong.
boxers are very suitable for larger displacement due to their inherent good balance. vw beetles were built to spec so are not the pinnacle of engineering, just good enough. a boxer 6 is even better than a boxer 4, ie porsche.
lol i was thinking the same thing, this design but in boxer engine would get rid of many problems he talks about, and if you make lets say, a 8 cyl boxer, with two pistons per rod assembly, you get rid of the weakness in the bottom rod cap
You not only have sliding friction but also every moment of movement places a different direction of sheering force on that slot as you convert circular motion into lateral motion.
We had a horizontally-opposed Scotch-yoke engine designed three decades ago. Each piston was double-ended (you still need to keep that yoke from moving, there _are_ side forces!) with the yoke in the middle. We never got around to building it, but in my retirement I may do so. Gotta make it a four to keep the balance even close enough to live with!
@@klausbrinck2137 And it's added friction... That whole thing about no sideloading on the piston is unfortunately not true in the configuration that was shown in all the animations. Adding linear bearings to keep the yoke from moving sideways would take out a lot of that, but it would add friction at yet another point. It's a case of saving friction in one place and loosing it in three others. So sorry, but I can't see how this would be able to revolutionize engine design. People have tried it before, and will try again as everyone is certain that no one else understands just how great their particular idea is. And there's nothing wrong with people trying to refine ideas, but it become stupid when you have to ignore science for your idea to make sense.
Scotch yoke engines make more sense as a boxer engine I remember reading a article on how it would change engines forever and that was 20years ago still waiting.
As mentioned in the video, there are still inherit issues with the Scotch/Yoke engine that is still keeping it in engineering development. Until then, a conventional piston mechanism is still the preferred choice for mass production and applications.
The Scotch crank has been arround for ages . It's ONLY advantage is that the piston moves sinusoidaly . Greater reciprocating mas more sliding friction , a total non starter that should remain a historic curiosity .
The most important part is getting rid of the far more severe sliding-friction in the cylinder/piston -interface... High combustion temperatures let metals get soft, and ease the destructive effects of sliding friction. Friction doesn´t come from nowhere, it simply leaves the cylinder, and goes somewhere, where the situation is far more under control, cause it´s cooler.
You get the benefit of longer dwell at tdc and a few other things on top of that. Scotch yoke engines aren't exactly a new thought, the first ones built were the Bourke engines iirc. They're quite interesting, and it's without doubt a feasible concept. Iirc some larger companies experimented with some such rather recently because the longer dwell time/slower movement around TDC was supposed to have advantages for HCCI engines or something like that.
The slider bracket would have to have a guiding groove andthe guide square have guide nub. Starting this would require a starter on the crank and timed firing. It seems rather extensive withmore draw backs for mass production. The lower crank case would need testing as well
Funny in 1976 my father and I built a 2 cylinder apposed Brouke scotch yoke engine. We used a roller bearing on the crankshaft, but on our first crankshaft the rod journal was to small and it sheared off. Second try we used a Kawasaki 100cc crankshaft. I believe that an apposed 4 cylinder may solve some of the balance issues. We were able to get 10,000 rpm underload but were unable to spin it faster due to it having a carborator and a distributer out of a 1960's VW. Using modern direct injection and ignition this may actually work.
The yoke needs a tail guiding section below the connection to the crank to overcome piston ossilations within the bore from the forces of power stroke and compression strokes. The line of force moves from one side of the yoke/crank connection on every cycle.
Came here to write a similar thought. The forces on that large "see saw" will cause huge friction on the piston to bore area. Adding more stabilisation to counter that just makes the friction elsewhere increase .
if you like new engine ideas, you may like the liquid piston engine. It seems to have a lot of potential, by being able to run in a variety of fuels, with high efficiency, and being simple and light weight. There is not much videos about it, so if you find it interesting, you could make a video about this engine, and at the same time help the engineers by making their job known.
It does sound interesting, but at the same time the company and people there have too many... "questionable" stuff behind them. I'd love to be proven wrong, but there're too many signs that it's an intentional scam, just to grab investors' money.
@@dirtyclanner2250 they are developing the engine from 2004, with the final design been made in 2016. From then, they are involving it, trying to make it more efficient and more powerful. They have a small museum with their previous designs and fully workable prototypes, and in their website, their looking for new engineers, so calling it a scam is a huge claim for which there are no evidences.
@@reedhanson5945 they have relish. It is all in their website. Also don't say that something is a crap before it get tested. The LP engine doesn't need more lubrication oil then a usual engine, because the friction that is experiencing is mostly rolling friction.
The LP engine would be great for small aircraft but I am skeptical if they will ever make an engine that does not need overhauled frequently. The Achilles heel of the design is the seals, not at the tip like on a normal rotary but on the sides of the rotor.
Just looking at the scotch yoke design, I would expect it to be a better proposition in horizontally opposed engines, simply becaues each cylinder will support the straight movement of the yoke assembly, also able to optimise the strength of the yoke on both thrust surfaces without adding extra material. I would also expect this layout to reduce any balance issues. Surprised the likes of Porsche and BMW (Motorcycles) havent tried this in their boxer engines.
To have no side loading, there would have to be another sliding guide below the crankshaft for the piston assembly to slide in which means even MORE friction
Yes it seems that triangle would otherwise rock x degrees if it wasn't supported in some sort of guide... If the connection to the piston is solid, to keep the triangle moving I a vertical plane, rather than the usual wrist pin, seems there would be rotational forces there, that would end up cracking the connection to the piston... unless it's heavily reinforced, but that would be more reciprocating weight....
It seems one would want roller bearings inside the slot. Is there a hidden problem with that? And maybe a hydraulic mechanism to keep contact with both sides of the slot (kind of like hydraulic lifters) as it wears?
I love this guy. I love that he spent time explaining to people the realities of developing an engine as a segue from his analysis on the engine. Such a great channel.
I see a torque at the piston in that configuration. Much more than in the traditional design. I would guess that this would greatly increase wear an the potential of engine failure. In the traditional design, the piston is pushed against one side. But in the here presented design, the piston will get tilted. Seems like a bigger problem to me.
Yup, not only that but you might need a longer piston head to reduce the moment-induced forces at the corners, increasing the contact area of the piston walls and increasing friction. Then there's the arm which would probably need to be much wider to survive the bending moment without fatiguing. Then he also says there are fewer parts because there's no hinge between the head and the arm, conveniently forgetting that those extra parts have just been shifted down to the sliding block connection. In general mechanical engineers like to say that they prefer rotation over sliding wherever possible for reliability. There's so many practical reasons why this theoretically better engine just isn't better. Engine builders haven't just been ignorant this whole time, they've converged on the conventional design for good reasons.
@@excrubulent In addition to that, bearings, or anything round, is easier and cheaper to manufacture. Sorry for spelling errors, i usually speak german ^^'
To mitigate the "small thin" section weakness, make the entire area ROUND. Not flat. A flat surface is more friction. You can make the shape using a cylinder all the way around, and this increase strength (since cylinders are stronger) and also less surface area contact yet same result.
I think the Scotch yoke rod should slide between rails, to keep it straight and in linear motion. Now the force of combustion will try to tilt it and the piston, which is much worse than pushing into the cilinder wall. Great idea though!
Yes, real Scotch yoke engines do have rails to constrain the "big end" of the yoke, which are omitted in this video. They are visible in the small model engines shown in this video, and in the Alfadan patent drawings also shown in this video.
The Scotch yoke actually tends to _degrade_ efficiency in practice. Since the piston spends more time being near TDC, and the sliding motion between the yoke and guide, more energy is lost as heat.
@@darysparta9676 first of all "piston axial torque" isn't a thing. Not sure what you are referring to. Regardless he said the secondary forces are "much less pronounced". He did not say anything was eliminated.
I'd say that it's dangerous to croudfund any engineering endeavour unless you know exactly what you're building, how it's going to be built, with minimal unknowns. This is why we see other things like software struggling. People don't realize that there are things that we don't know that we don't know and it directly impacts everything about a product. Not just cost, but timeline, design, and required resourcing at the time, forget macro-economic conditions.
Plenty of stuff is crowd funded at the start. The difference here is the crowd is the general public. I think this is a bad investment but I don't think there's anything nefarious or reckless in this offering
Very interesting. So Alfadan didn't actually "reinvent the connecting rod" (their words not the video presenter's), they refined an existing design. I hope they succeed in bringing their technology to market.
@@nenume00 Alfadan is a scum 100%. They just want investors to give them money. The owner will take all those money and deliver nothing. The money will go to his own pocket to finance his car, his boat, his mistress etc. Thus the mentioned in marketing material engine will never happen. Never.
Scotch yoke.... I'm in Perth Western Australia and two different local companies made versions of an engine known as the Bourke Engine (USA 1960's). Bottom line frictional losses were too high, as was wear. LOL. I typed this as your video started... You covered most of it in your video. However.... One was Sarich Technologies...Circa 1987. I forget the other, but That company was owned by a then friend's dad. This was 43 years ago. Just Saying ! P.S. I enjoy your videos. Thank you for making them!
Thanks! As always you manage to explain things in a manner that it makes them look simple even if I know they are not. The best automotive channel from my point of view.
It would make sense to use the scotch yoke in an opposed cylinder design to get around some of the strength issues the yoke has. Also, a plain rotational bearing has the same sliding friction as a linear sliding bearing (apart from the direction reversal). Making it work efficiently is just a matter of getting the fluid dynamics of the lubrication right. They make it work for piston rings.
Lubrication nowadays involves much more than just the fluid and basic surface treatments. There are nanoparticles for coatings, solid lubricants, electromagnetism, all sorts of bizarre alloys and ceramics, self-lubrication, ... (search for anything about tribology for more info) but the technology used in mass production is still lagging behind.
@@panvomacka9079 Modifying the Scotch Yoke in order to improve its problems with friction and structural issues seems to be more important than this. For example the inner slider could use a gear that rolls over a "serrated" surface and its shape could be slightly elliptical so it only touches one side at any moment. Another example is the article "Design of Scotch yoke mechanisms with improved driving dynamics" which proposes the use of springs to regularize the input torque.
do you have any concrete evidence that their claims of the superiority of their engine is not baseless, and they aren't just sitting around twiddling their thumbs saying "working on it" while drawing a wage until the invested money runs out?
I don't and neither does anyone but society is built on the concept of innocent until proven guilty. No one has said proof for thousands of different companies but we can't go arresting based on assumptions without proof. Ps it goes the other way too. Do you have concrete evidence they're doing what you claim? Or any other company. You also don't have concrete evidence that I'm not a thief but you can't barge into my house because you can't get a search warrant based on a hunch that I'm a thief.
That's the way most startups work. They have an idea and maybe a few patents, and they burn through capital until they have something worth selling. It's a speculative investment; most of them fail but some make it big or at least get bought out profitably. If you don't like the idea, don't invest in them.
I have an early Bosch power saw that uses that arrangement to drive the blade back & forth. It was my granddads then my dad's now I've got it ! Still working perfectly. They definitely don't make them to last like back then, has to be around 90 years young.
The main advantage I see with this design is balance and harmonics. Wear rates are very good on conventional piston engines that are 'properly' designed, due to advancements in materials/chemical engineering and manufacturing processes. Small engines are pushing loads of turbocharger boost and surviving (like AMG mercedes 4 cylinders), while milder engines (like Toyota's newer 2.5 liter) survive many miles of abuse and minimal maintenance.
In large diesel engines, side-loading on the piston walls is eliminated by having a straight intermediate shaft between the piston and crank, which allows the side-loading to be shifted to a separate bearing set. Can't do that on small engines since it adds a bit more than a piston stroke length to total crank case height.
Hater's gonna hate. You don't have to explain yourself. Thank you for the interesting and informative videos. The vast majority of us appreciate you sharing your knowledge and cool new technologies.
Having watched 25mm thick steel rip like tissue paper, as well of having connecting rods blast new channels through engine blocks, I would suggest that scotch yokes remain with the early low power toys of yester years.
This rod design is interesting, but I have a suggestion. Instead of the slot being a hole through the rod, it should be a sold face with a slot on each side. Then, instead of a single crank shaft passing through the slot, the slot on each side would interface with a 'knob' attached to a crank shaft segment, with the segments rotating in opposite directions. This way, the rod is much stronger, and the compression and tensile forces between the rod and the crank knobs would always be horizontally symmetrical.
I remember back in the day, the original Alfa Romeo GTA from the 1960s and 1970s had a sliding block rear end (might have be an option for racing use) to help locate the rear axle. From my understanding wear and maintenance issues were the main problems. This video reminded me of that setup.
Neat theory, but more moving parts = more things that could break. I also think that would add a lot of weight the rotating assembly. Not to mention packaging inside the block, I don’t think a rod that wide would clear the bottom side of sleeve or other parts of the block when piston is at TDC, at least on a larger stroke engine. I could see the square inside the rod wearing out very quickly as well.
The force angle is there on both types. If you take for example the moment when the crank shaft is at 90°, the little square which the force acts upon is not directly below the center of force. Therefore the twisting force still remains. This does not solve anything.
There will be a side friction anyway, not on cylinder walls but on "rod" outer walls. It will be necessary to prevent a rod-cylinder assembly from tilting. Bourke cross was preventing that by placing two cylindrs in oposing positions.
I always love your work, and great job as always. I especially love your break down of what is and isn't a scam because of just how bad it really is out here. Free idea for the next April Fool's day: explain breathing and then add blinking so people know how to do both at the same time.
The combustion forcing the piston to one side of the cilinder will not be completely gone on this desighn. The "rod" is still only supported by one side when combustion pushes down on it, so there is going to still be some torke generated.
Just from looking at this configuration, it apears to me that there is still a torque force where the piston and con rod join, since there is only resistance on one side of the slot; probably mitigated by constraint of the cylinder barrel, but that would then create piston:cylinder friction again... I'd also think the sliding friction under load might be a great deal more difficult to overcome than it it seems... Obviously thpugh, this is just eyeball impressions, so could be completely wrong. 🤷♂️
This does nothing to reduce piston side forces, they're still there just the same as the geometry is still the same. It does dramatically increase reciprocating mass though, so I guess that a plus? Quite literally the only 'benefit' I can see here is better balance, but there's much better ways to resolve that problem.
Give an engine more points of possible failure, it will possibly fail more frequently. Always interesting to see anything innovating, whether it's old or new, revisiting them is always a good experience! Especially with evolving machining and tech!
8:43 i knew this would be Alfadan's new engine tech since back then they said "we revolutionized the connecting rod" while they where working with Mahle but not showing anything to it before they get enough validation data just the "soon TM" glad to know this thing was still trucking along and thanks for the follow up mate!
Hey, I think you should analyze and do a video about the Commer ts3 Engine, a really unique op two stroke diesel like no other, and talk about the benefits and drawbacks about its design!
I am glad you present these alternative technologies. We have to accept that most of them won't pan out. You can't be an entrepreneur without having unreasonable faith in your product. Sometimes it works, mostly it doesn't. Either way, it is nice to see what is out there.
2 counter rotating cranks in the one yoke would even it up, a double ended yoke for 2 cylinders strengthens both sides of the slides in the rod as well.
Where can I give you 100 thumbs up? In all seriousness, this video is great. Many people don't understand the complexities of developing anything. This is sometimes a failure of the press. On a related note, I would like your take on things like Liquidpiston or the Omega 1 engine. Purely from a technical standpoint.
Nice video as always, keep it up and don't mind the people that complain ilogically after barely understanding what your videos explain, and for free. Someones do only see what they want. Thanks for the content.
I think you would still get the cylinder wear/friction problem because the force of the piston will still be sideways. Think of it like holding a long 2 by 4 horizontally against your abs, and trying to push on a box with one end. The force will still be transfered at the angle. It doesn't matter what you do in-between.
I'm wondering if the rectangular slot is a modeling simplification, or if changing it to rounded ends (like a pill) would make the slot a bit stronger x) Unless the square bit slams into the slot's sides and a flat surface is desirable ?
A partial solution is to make this engine a boxer design, thus, the surface in the bottom of the rod & piston will no longer be thin. This doesn’t resolve the sliding motion, but it does solve the strength issue. The triangle is the strongest shape and this would make a diamond shape piston rod combo.
So, much higher friction losses, much more reciprocating mass, and the need for many more bearing faces, that have to be positioned relative to each other very accurately. Furthermore, the expectation is that we use technology to try and mitigate a problematic engine design, but conventional engine designs arent allowed to have these advances (for some reason)? Sounds like complete trash.
Wow! I actually dropped an email 2 years ago or so to D4A to cover balance in case a Scotch yoke would be used exactly after watching the Alfadan video. No idea if it had any impact but still nice that it's actually here ;-)
What about adding multiple rollers to the top and bottom of the square part of the crankshaft journal and pressurizing oil the same way from the inside of the crank.
It's amazing that I've watched enough of your videos and learned enough about IC engines that I was able to tell why that engine is inherently better than a traditional engine just by looking at the thumbnail. Of course I will still watch to hear your in depth explanation. Thanks for the video!
Removing the offset that way just transfers the problem elsewhere. Increasing the need for perfect lubrication and adding friction/heat in a less favorable location. Using weighted rotating camshafts will always come with wear and tear. No matter where you force it to happen.
The dewalt dcs 369 recip saw also use the scotch yoke drive system and it is really smooth, no rotational vibration at all. The side effect is, due to how the yoke accelerate at TDC and BDC, it produces such an ear piercing metallic sound.
It doesn't eliminate the connecting rod and wrist pin. The little arm on the crank replaced the connecting rod. The wrist pin and crank bearing are replaced by the channel and the pin that connects the arm to the slider. The crank bearing and wrist pins are fairly easy to lubricate. The sliding block in a channel looks far more difficult.
Without wristpin the yoke rod will force piston skirt into cylinder wall. Add a wristpin and the piston can truly float but the long slot rod is a big problem. Clearance, lubrication, assembly and reliability.
Another typical problem with sliding friction is dirt buildup. The sliding surface is very large open area where engine gunk lands easily. It is then wiped by the sliding block to the corners of the system, eventually blocking movement. For this reason linear movements as such are often avoided in machinery that has to operate in dirty environments.
Longer rods, offset crank, and ultimately a crosshead like in marine diesels are partial or total solutions to lateral piston forces, but all have their respective drawbacks.
Some type of roller bearing design in the scotch yoke would dramatically reduce sliding friction and beefing up the underside, thin part of the yoke would help much. However, with the increased friction area of the yoke, premature wear and knocking is inevitable.
This video got me thinking about the problem of transferring linear motion into rotational motion without causing angular stresses. At first i thought of a ratcheting mechanism that has a wheel with teeth on it that would engage with a pall on the piston rod. It would reduce angle of attack significantly. But then i realized that such a system operating at those speeds and loads would most likely wear out or fail quite prematurely. Then i thought about what a 2 stroke engine is. It's essentially a pump that sucks and bangs on one side of the piston but also sucks and pushes with the other side of the piston. And a steam piston pushes in both directions effectively making them 1 stroke engines. So here's my second idea, a conventional valve driven engine that runs in 4 stroke. But where the piston rods only job is to return the piston to TDC. It's not meant to carry the load of combustion at all. Instead, the sump side of the piston has some really low viscosity hydraulic oil that, on the combustion stroke, is directed to any hydraulic motor in the system which is super high torque that can be geared over to high RPM as necessary. The sump side of the piston would operate like a 2 stroke with one modification, on the exhaust and intake cycle it would "idle" and just keep a neutral load of hydraulic oil. But on the combustion stroke it would pressurize an accumulator and on the exhaust stroke it would pull in fresh oil from the low pressure side. I have no engineering skills and it's just an idea but it would be really cool to see if that was viable in any way. It would practically remove all imbalances in an engine though. I also assume it would be a very low "RPM" engine that instead focuses on extremely high compression ratio and torque.
Conventional design transfers the power through 2 frictional bearings; piston to rod and rod to crank. However scotch yoke solves this problem by still using two frictional bearings; one is from crank to the square sliding block and the other is from square block to the rod, also one of them is sliding friction now. brilliant.
Rotating crank journals are still sliding friction, they just are sliding in a circle. The reason early designs failed is their rods sliding surface wasn't being pressure oiled, as modern cranks and thus rod journals are. Lastly, we could build these and eliminate PRIMARY IMBALANCES if we combined this design in a BOXER engine. You're welcome ;)
The wrist pin friction losses are just moved to the sliding square and the piston is obviously still loaded at an angle
Yeah i was thinking the same thing
Yes I see a lot friction there.
Would that sliding square be set in roller bearings, both top and bottom?
there is also a lot more weight.
@@rob5944 Even if, that would add more moving parts and reliability would probably suffer.
It can be a balance king but at the same time it become friction king. The contact surface is enormous
Large friction surface means lower friction!
@@stianmathisen4284explain please
@@stianmathisen4284 most of the surfaces in an engine never contact one another, they ride on a thin film of oil and any amount of metal-to-metal contact should be considered a mechanical failure. larger contact surfaces = way more oil shear forces = more losses. the main reason modern car engines are moving to thinner and thinner oils is because the engine oil viscosity contributes a huge portion of the total frictional losses
Why not put four bearings, one at each corner of the slider. That would eliminate the sliding friction.
The contact surface is smaller. 2-times diameter vs 3.1415926535... times
The sliding box section of the yoke design would make lubrication a lot more difficult to achieve effectively than with standard plain bearings on a normal crank pin.
Mitigation through soaking the crank in the oil sump halfway or more? Yes more detergent and stringent oil change intervals I believe
as a new comer marine engineer cadet, i have to say that the sliders that are being used on the 2 stroke low rpm diesel engines, are made of white metals, that are cheap and are the first to wear out, so damaging of the engine can be avoided. In those engines are vertical, but yoke sliders are on the side, something that will incise friction and wearing out. Because of that i am very interested to see with what they came out to stope that problem.
Not really, it would be feeding oil to the crank and thus the square itself through feed holes, exactly like normal cranks. And voila. Have it squirt oil just before and after the lead and end corners of each slide surface of the square, the same way we use piston skirt squirters. Just have it squirt the slides instead. Bam done.
The early Scot design probably only relied on paddle oiling like push mowers so it's no wonder it failed.
@@ShogunAutoworks it slows the wear out, but yes, if it is lubricated properly, then the life spend will be increased to that of a piston' s spring, or even more then that.
There could be needle bearings the same that are used in some high horsepower cam applications. However, there could be a round design instead of a square crank design.
There is still significant friction against the cylinder of the scotch yoke design: the off-centre force from the crank pin on the yoke causes a torque, just like in the connecting rod, which in turn torques the piston inside the cylinder. The force on the cylinder wall can be reduced by increasing the piston length, similar to how the lateral forces are reduced by lengthening the connecting rod.
No , the short edges of the scotch yoke's "square" run up and down linear bearings ( 9:40 648 & 650 in the diagram are bearings) in the crankcase walls. This eliminates side loads on the piston. i.e. The square also acts as a crosshead , as used in steam engines and large (ship size) diesels
For some reason most commenters fail to understand this
@@paulgee-i7j Ok, so they just shifted the uneven force and friction from the cylinder wall to the crank case wall. My point still stands.
It would probably not be a 1 cylinder engine.
I think you are missing the fact that the off-axis force still exists. So you will need restraint against rotating of the yoke due to the moment (torque).
@@paulgee-i7j Got it, so you have more reciprocating sliding surfaces and more reciprocating mass. You also have much more difficulty in maintaining tolerances which is why such designs have only been used commercially in low speed applications such as diesel ship engines. You just moved the problem (which has long ago been solved) to a more problematic location. YAY! I love designs that rattle themselves apart due to problematic tolerancing requirements!
I am a pilot. Although I spent most of my career flying jets, perhaps my favorite piston aircraft engine is the Lycoming IO-360. It is a 6 liter, 4 cylinder engine. How do they manage to make a smooth 4 cylinder engine that big? It's an air cooled boxer. The secondary balance problem was solved a long time ago, 23 million Volkswagen Beetles can't be wrong.
boxers are very suitable for larger displacement due to their inherent good balance. vw beetles were built to spec so are not the pinnacle of engineering, just good enough. a boxer 6 is even better than a boxer 4, ie porsche.
lol i was thinking the same thing, this design but in boxer engine would get rid of many problems he talks about, and if you make lets say, a 8 cyl boxer, with two pistons per rod assembly, you get rid of the weakness in the bottom rod cap
@@daos3300 porsche makes flat sixes, not boxer sixes.
@@midnight.a3 how so?
@@midnight.a3 nope
You not only have sliding friction but also every moment of movement places a different direction of sheering force on that slot as you convert circular motion into lateral motion.
We had a horizontally-opposed Scotch-yoke engine designed three decades ago. Each piston was double-ended (you still need to keep that yoke from moving, there _are_ side forces!) with the yoke in the middle. We never got around to building it, but in my retirement I may do so. Gotta make it a four to keep the balance even close enough to live with!
Use rails on the right+left of the yoke.
Could it be possible to use gears to increase the strength and reduce sliding friction?
What engine was that? I've only heard of a 2 stroke design and that it never made mass production.
Bourke engine, look it up.
@@klausbrinck2137 And it's added friction...
That whole thing about no sideloading on the piston is unfortunately not true in the configuration that was shown in all the animations. Adding linear bearings to keep the yoke from moving sideways would take out a lot of that, but it would add friction at yet another point.
It's a case of saving friction in one place and loosing it in three others. So sorry, but I can't see how this would be able to revolutionize engine design. People have tried it before, and will try again as everyone is certain that no one else understands just how great their particular idea is.
And there's nothing wrong with people trying to refine ideas, but it become stupid when you have to ignore science for your idea to make sense.
1.7m investment, nothing to show, the only 2 employees taking a 100K a year salary. No seems legit.
Scotch yoke engines make more sense as a boxer engine
I remember reading a article on how it would change engines forever and that was 20years ago still waiting.
As mentioned in the video, there are still inherit issues with the Scotch/Yoke engine that is still keeping it in engineering development. Until then, a conventional piston mechanism is still the preferred choice for mass production and applications.
Not a boxer, you mean a flat engine - a boxer, by definition, needs to have separate rods
It’s vapour ware.
I read about the scotch yoke in 1974, still waiting. 😅
The Scotch crank has been arround for ages . It's ONLY advantage is that the piston moves sinusoidaly . Greater reciprocating mas more sliding friction , a total non starter that should remain a historic curiosity .
Have you heard of the Wankel rotary engine it is cool and people are working on making it more efficient with better seals
im not convinced the complexity of the sliding friction interface is worth a minor improvement in vibrations.
You're underestimating harmonics and balance
The most important part is getting rid of the far more severe sliding-friction in the cylinder/piston -interface... High combustion temperatures let metals get soft, and ease the destructive effects of sliding friction. Friction doesn´t come from nowhere, it simply leaves the cylinder, and goes somewhere, where the situation is far more under control, cause it´s cooler.
You get the benefit of longer dwell at tdc and a few other things on top of that.
Scotch yoke engines aren't exactly a new thought, the first ones built were the Bourke engines iirc.
They're quite interesting, and it's without doubt a feasible concept. Iirc some larger companies experimented with some such rather recently because the longer dwell time/slower movement around TDC was supposed to have advantages for HCCI engines or something like that.
if it was worth it, it would be used all over the place
The slider bracket would have to have a guiding groove andthe guide square have guide nub. Starting this would require a starter on the crank and timed firing. It seems rather extensive withmore draw backs for mass production. The lower crank case would need testing as well
Funny in 1976 my father and I built a 2 cylinder apposed Brouke scotch yoke engine. We used a roller bearing on the crankshaft, but on our first crankshaft the rod journal was to small and it sheared off. Second try we used a Kawasaki 100cc crankshaft. I believe that an apposed 4 cylinder may solve some of the balance issues. We were able to get 10,000 rpm underload but were unable to spin it faster due to it having a carborator and a distributer out of a 1960's VW. Using modern direct injection and ignition this may actually work.
The yoke needs a tail guiding section below the connection to the crank to overcome piston ossilations within the bore from the forces of power stroke and compression strokes. The line of force moves from one side of the yoke/crank connection on every cycle.
The yoke runs on rails on its left and right (not shown in the animations here)...
It's called a crosshead but yeah
Came here to write a similar thought. The forces on that large "see saw" will cause huge friction on the piston to bore area. Adding more stabilisation to counter that just makes the friction elsewhere increase .
Another piston seems like the ideal "stabilizer".... it's other shortcomings, not withstanding...
@@jamesgeorge4874 an additional piston is probably best, a flat 8 seems like the most logical configuration
Fascinating that the source of secondary imbalances in a standard layout are clearly visible as the two models reciprocate.
if you like new engine ideas, you may like the liquid piston engine. It seems to have a lot of potential, by being able to run in a variety of fuels, with high efficiency, and being simple and light weight. There is not much videos about it, so if you find it interesting, you could make a video about this engine, and at the same time help the engineers by making their job known.
It does sound interesting, but at the same time the company and people there have too many... "questionable" stuff behind them. I'd love to be proven wrong, but there're too many signs that it's an intentional scam, just to grab investors' money.
LP is just another crap ass rotary engine with high SA/vol and low efficiency. theres a reason they havent published any efficiency numbers yet
@@dirtyclanner2250 they are developing the engine from 2004, with the final design been made in 2016. From then, they are involving it, trying to make it more efficient and more powerful. They have a small museum with their previous designs and fully workable prototypes, and in their website, their looking for new engineers, so calling it a scam is a huge claim for which there are no evidences.
@@reedhanson5945 they have relish. It is all in their website. Also don't say that something is a crap before it get tested. The LP engine doesn't need more lubrication oil then a usual engine, because the friction that is experiencing is mostly rolling friction.
The LP engine would be great for small aircraft but I am skeptical if they will ever make an engine that does not need overhauled frequently. The Achilles heel of the design is the seals, not at the tip like on a normal rotary but on the sides of the rotor.
I'll never tire of your presentation style, broad vocabulary, and ability to convey complex concepts. So cool! Bravo!
Just looking at the scotch yoke design, I would expect it to be a better proposition in horizontally opposed engines, simply becaues each cylinder will support the straight movement of the yoke assembly, also able to optimise the strength of the yoke on both thrust surfaces without adding extra material. I would also expect this layout to reduce any balance issues.
Surprised the likes of Porsche and BMW (Motorcycles) havent tried this in their boxer engines.
To have no side loading, there would have to be another sliding guide below the crankshaft for the piston assembly to slide in which means even MORE friction
Yes it seems that triangle would otherwise rock x degrees if it wasn't supported in some sort of guide...
If the connection to the piston is solid, to keep the triangle moving I a vertical plane, rather than the usual wrist pin, seems there would be rotational forces there, that would end up cracking the connection to the piston... unless it's heavily reinforced, but that would be more reciprocating weight....
It seems one would want roller bearings inside the slot. Is there a hidden problem with that? And maybe a hydraulic mechanism to keep contact with both sides of the slot (kind of like hydraulic lifters) as it wears?
I love this guy. I love that he spent time explaining to people the realities of developing an engine as a segue from his analysis on the engine. Such a great channel.
I see a torque at the piston in that configuration. Much more than in the traditional design. I would guess that this would greatly increase wear an the potential of engine failure. In the traditional design, the piston is pushed against one side. But in the here presented design, the piston will get tilted. Seems like a bigger problem to me.
Needs a cross head to control the rotation of the yoke.
Yup, not only that but you might need a longer piston head to reduce the moment-induced forces at the corners, increasing the contact area of the piston walls and increasing friction.
Then there's the arm which would probably need to be much wider to survive the bending moment without fatiguing.
Then he also says there are fewer parts because there's no hinge between the head and the arm, conveniently forgetting that those extra parts have just been shifted down to the sliding block connection.
In general mechanical engineers like to say that they prefer rotation over sliding wherever possible for reliability. There's so many practical reasons why this theoretically better engine just isn't better. Engine builders haven't just been ignorant this whole time, they've converged on the conventional design for good reasons.
@@excrubulent In addition to that, bearings, or anything round, is easier and cheaper to manufacture.
Sorry for spelling errors, i usually speak german ^^'
To mitigate the "small thin" section weakness, make the entire area ROUND. Not flat. A flat surface is more friction. You can make the shape using a cylinder all the way around, and this increase strength (since cylinders are stronger) and also less surface area contact yet same result.
nice scotch yoke, next: geared piston
Why bother with geared pistons. Wankel engines is where it's @ m8!
@@markusluftner8418 a Wankel is basically 3 geared pistons in one
@@hansdietrich83 No, its' 3 very inefficient geared pistons in one.
@@markusluftner8418 So 3 geared pistons in one, then.
@@Ijusthopeitsquick no 3 oilfillercaps in 1 scavege pump
I think the Scotch yoke rod should slide between rails, to keep it straight and in linear motion. Now the force of combustion will try to tilt it and the piston, which is much worse than pushing into the cilinder wall. Great idea though!
Yes, real Scotch yoke engines do have rails to constrain the "big end" of the yoke, which are omitted in this video. They are visible in the small model engines shown in this video, and in the Alfadan patent drawings also shown in this video.
The Scotch yoke actually tends to _degrade_ efficiency in practice. Since the piston spends more time being near TDC, and the sliding motion between the yoke and guide, more energy is lost as heat.
As a mechanical engineer I can say this channel is top notch. Those animations just incredible. Visualization is the key to teaching. Amazing work!!!
as a mechanical engineer you should recognise this design doesn't remove the piston axial torque he mentions initially
@@darysparta9676 first of all "piston axial torque" isn't a thing. Not sure what you are referring to. Regardless he said the secondary forces are "much less pronounced". He did not say anything was eliminated.
I'd say that it's dangerous to croudfund any engineering endeavour unless you know exactly what you're building, how it's going to be built, with minimal unknowns. This is why we see other things like software struggling. People don't realize that there are things that we don't know that we don't know and it directly impacts everything about a product. Not just cost, but timeline, design, and required resourcing at the time, forget macro-economic conditions.
Exactly!
Plenty of stuff is crowd funded at the start. The difference here is the crowd is the general public. I think this is a bad investment but I don't think there's anything nefarious or reckless in this offering
@@d4a USE WHEELS!
Very interesting. So Alfadan didn't actually "reinvent the connecting rod" (their words not the video presenter's), they refined an existing design. I hope they succeed in bringing their technology to market.
They did?? Where? We all would love to actually see something
@@nenume00 Alfadan is a scum 100%. They just want investors to give them money. The owner will take all those money and deliver nothing. The money will go to his own pocket to finance his car, his boat, his mistress etc. Thus the mentioned in marketing material engine will never happen. Never.
Scotch yoke.... I'm in Perth Western Australia and two different local companies made versions of an engine known as the Bourke Engine (USA 1960's). Bottom line frictional losses were too high, as was wear. LOL. I typed this as your video started... You covered most of it in your video. However....
One was Sarich Technologies...Circa 1987. I forget the other, but That company was owned by a then friend's dad. This was 43 years ago. Just Saying ! P.S. I enjoy your videos. Thank you for making them!
Hello Neighbour- keep cool
Thanks! As always you manage to explain things in a manner that it makes them look simple even if I know they are not.
The best automotive channel from my point of view.
Thank you so much for your support. I sincerely appreciate it.
It would make sense to use the scotch yoke in an opposed cylinder design to get around some of the strength issues the yoke has.
Also, a plain rotational bearing has the same sliding friction as a linear sliding bearing (apart from the direction reversal). Making it work efficiently is just a matter of getting the fluid dynamics of the lubrication right.
They make it work for piston rings.
Lubrication nowadays involves much more than just the fluid and basic surface treatments. There are nanoparticles for coatings, solid lubricants, electromagnetism, all sorts of bizarre alloys and ceramics, self-lubrication, ... (search for anything about tribology for more info) but the technology used in mass production is still lagging behind.
@@vitordelima don't believe the spiel on an oil bottle , Castrol Magnetec 🙄
Indeed, but opposed cylinders mean 2 heads, which already complicates the engine a lot, so it could ruin the "game changer" potential of the engine
@@panvomacka9079 Modifying the Scotch Yoke in order to improve its problems with friction and structural issues seems to be more important than this. For example the inner slider could use a gear that rolls over a "serrated" surface and its shape could be slightly elliptical so it only touches one side at any moment. Another example is the article "Design of Scotch yoke mechanisms with improved driving dynamics" which proposes the use of springs to regularize the input torque.
Someone has never heard of a hydrodynamic wedge...
Wow brate, the knowledge and the visuals, very very informative and well put together! Svaka čast!
That Scotch Yoke design will be forcing the piston to rock in the cyclinder, thus trying to grip it.
A lot
The way you explained scam and what is not scam was amazing. I love you! Lmao 😂🤣😂🤣
Gives a whole new meaning to forcing a square peg in a round hole
There is force pushing the piston to both sides of the cylinder depending of the offset of the sliding part to the vertical axis of the rod.
do you have any concrete evidence that their claims of the superiority of their engine is not baseless, and they aren't just sitting around twiddling their thumbs saying "working on it" while drawing a wage until the invested money runs out?
I don't and neither does anyone but society is built on the concept of innocent until proven guilty. No one has said proof for thousands of different companies but we can't go arresting based on assumptions without proof. Ps it goes the other way too. Do you have concrete evidence they're doing what you claim? Or any other company. You also don't have concrete evidence that I'm not a thief but you can't barge into my house because you can't get a search warrant based on a hunch that I'm a thief.
That's the way most startups work. They have an idea and maybe a few patents, and they burn through capital until they have something worth selling. It's a speculative investment; most of them fail but some make it big or at least get bought out profitably. If you don't like the idea, don't invest in them.
I have an early Bosch power saw that uses that arrangement to drive the blade back & forth. It was my granddads then my dad's now I've got it ! Still working perfectly. They definitely don't make them to last like back then, has to be around 90 years young.
The main advantage I see with this design is balance and harmonics. Wear rates are very good on conventional piston engines that are 'properly' designed, due to advancements in materials/chemical engineering and manufacturing processes. Small engines are pushing loads of turbocharger boost and surviving (like AMG mercedes 4 cylinders), while milder engines (like Toyota's newer 2.5 liter) survive many miles of abuse and minimal maintenance.
In large diesel engines, side-loading on the piston walls is eliminated by having a straight intermediate shaft between the piston and crank, which allows the side-loading to be shifted to a separate bearing set. Can't do that on small engines since it adds a bit more than a piston stroke length to total crank case height.
This is called a cross head, also seen on steam engines where it is mandatory in most cases because the cylinder is double acting.
Hater's gonna hate. You don't have to explain yourself. Thank you for the interesting and informative videos. The vast majority of us appreciate you sharing your knowledge and cool new technologies.
This is brilliant. Less the additional material needed to make a triangle versus a rod.
Having watched 25mm thick steel rip like tissue paper, as well of having connecting rods blast new channels through engine blocks, I would suggest that scotch yokes remain with the early low power toys of yester years.
Friction: Im gonna have to stop you right there
I can't believe this man just had to explain to people what scam means
This rod design is interesting, but I have a suggestion. Instead of the slot being a hole through the rod, it should be a sold face with a slot on each side. Then, instead of a single crank shaft passing through the slot, the slot on each side would interface with a 'knob' attached to a crank shaft segment, with the segments rotating in opposite directions. This way, the rod is much stronger, and the compression and tensile forces between the rod and the crank knobs would always be horizontally symmetrical.
I remember back in the day, the original Alfa Romeo GTA from the 1960s and 1970s had a sliding block rear end (might have be an option for racing use) to help locate the rear axle. From my understanding wear and maintenance issues were the main problems. This video reminded me of that setup.
Neat theory, but more moving parts = more things that could break. I also think that would add a lot of weight the rotating assembly. Not to mention packaging inside the block, I don’t think a rod that wide would clear the bottom side of sleeve or other parts of the block when piston is at TDC, at least on a larger stroke engine. I could see the square inside the rod wearing out very quickly as well.
The force angle is there on both types. If you take for example the moment when the crank shaft is at 90°, the little square which the force acts upon is not directly below the center of force. Therefore the twisting force still remains. This does not solve anything.
I’m excited to see this! I’d love to see you cover other alternatives to traditional engine configurations.
There will be a side friction anyway, not on cylinder walls but on "rod" outer walls. It will be necessary to prevent a rod-cylinder assembly from tilting. Bourke cross was preventing that by placing two cylindrs in oposing positions.
I always love your work, and great job as always. I especially love your break down of what is and isn't a scam because of just how bad it really is out here.
Free idea for the next April Fool's day: explain breathing and then add blinking so people know how to do both at the same time.
The combustion forcing the piston to one side of the cilinder will not be completely gone on this desighn. The "rod" is still only supported by one side when combustion pushes down on it, so there is going to still be some torke generated.
Became a financial advice video from an engineering video 😂😂
I need a car guy friend like you! I love the way you talk and think and disect everything to do with cars! Good video as always!
Just from looking at this configuration, it apears to me that there is still a torque force where the piston and con rod join, since there is only resistance on one side of the slot; probably mitigated by constraint of the cylinder barrel, but that would then create piston:cylinder friction again... I'd also think the sliding friction under load might be a great deal more difficult to overcome than it it seems... Obviously thpugh, this is just eyeball impressions, so could be completely wrong. 🤷♂️
This does nothing to reduce piston side forces, they're still there just the same as the geometry is still the same. It does dramatically increase reciprocating mass though, so I guess that a plus? Quite literally the only 'benefit' I can see here is better balance, but there's much better ways to resolve that problem.
I love it when armchair internet engineers get triggered by an engine design outside the norm
Give an engine more points of possible failure, it will possibly fail more frequently. Always interesting to see anything innovating, whether it's old or new, revisiting them is always a good experience! Especially with evolving machining and tech!
8:43 i knew this would be Alfadan's new engine tech since back then they said "we revolutionized the connecting rod" while they where working with Mahle but not showing anything to it before they get enough validation data just the "soon TM" glad to know this thing was still trucking along and thanks for the follow up mate!
Hey, I think you should analyze and do a video about the Commer ts3 Engine, a really unique op two stroke diesel like no other, and talk about the benefits and drawbacks about its design!
I am glad you present these alternative technologies. We have to accept that most of them won't pan out. You can't be an entrepreneur without having unreasonable faith in your product. Sometimes it works, mostly it doesn't. Either way, it is nice to see what is out there.
2 counter rotating cranks in the one yoke would even it up, a double ended yoke for 2 cylinders strengthens both sides of the slides in the rod as well.
Where can I give you 100 thumbs up? In all seriousness, this video is great. Many people don't understand the complexities of developing anything. This is sometimes a failure of the press.
On a related note, I would like your take on things like Liquidpiston or the Omega 1 engine. Purely from a technical standpoint.
A boxer configuration where 2 cylinders share the same rod will considerably improve the rigidity of the lower part of the rod.
Nice video as always, keep it up and don't mind the people that complain ilogically after barely understanding what your videos explain, and for free. Someones do only see what they want. Thanks for the content.
If only someone redefined rotary engine to work perfectly with no flaws
The flaws in all engines is what makes them so interesting.
There is no absolute perfection; only levels of staving off inevitable impending failure.
Always happy to see you upload. I always learn so much from your videos. Great job!
I think you would still get the cylinder wear/friction problem because the force of the piston will still be sideways. Think of it like holding a long 2 by 4 horizontally against your abs, and trying to push on a box with one end. The force will still be transfered at the angle. It doesn't matter what you do in-between.
Maybe so, but it would be fractions of the force of a conventional piston/rod/crank arrangement
I'm wondering if the rectangular slot is a modeling simplification, or if changing it to rounded ends (like a pill) would make the slot a bit stronger x)
Unless the square bit slams into the slot's sides and a flat surface is desirable ?
The ends of the slot aren't contacted and are purely structural.
@@TheShamefurDispray okay, thanks !
A partial solution is to make this engine a boxer design, thus, the surface in the bottom of the rod & piston will no longer be thin. This doesn’t resolve the sliding motion, but it does solve the strength issue. The triangle is the strongest shape and this would make a diamond shape piston rod combo.
Scotch yokes are widely used in mechanical engineering, maybe there is something that uses it under similar conditions already.
it feels illegal to be this early
You'll be arrested and jailed unless you deposit some bitcoin to a suspicious wallet 😂😂😂
Maybe some kind of needle/roller bearing setup in the rod big end would be the way to go?
So, much higher friction losses, much more reciprocating mass, and the need for many more bearing faces, that have to be positioned relative to each other very accurately.
Furthermore, the expectation is that we use technology to try and mitigate a problematic engine design, but conventional engine designs arent allowed to have these advances (for some reason)?
Sounds like complete trash.
It's a "solution looking for a problem".
Wow! I actually dropped an email 2 years ago or so to D4A to cover balance in case a Scotch yoke would be used exactly after watching the Alfadan video. No idea if it had any impact but still nice that it's actually here ;-)
Maybe you shouldnt shill financial advice and just stick to the facts.
A flat 8 is balanced perfectly and gives the smoothest power.
This guy lost all engineering credibility when he backed Alfascam.
What about adding multiple rollers to the top and bottom of the square part of the crankshaft journal and pressurizing oil the same way from the inside of the crank.
Thanks for the really bad explaination on what investments are, and what a scam isn't.
I feel like if we had the technology to mitigate the friction from this thing we would already have better engines at that point lol
This video is wrong in every way.......
It's amazing that I've watched enough of your videos and learned enough about IC engines that I was able to tell why that engine is inherently better than a traditional engine just by looking at the thumbnail. Of course I will still watch to hear your in depth explanation. Thanks for the video!
Removing the offset that way just transfers the problem elsewhere. Increasing the need for perfect lubrication and adding friction/heat in a less favorable location.
Using weighted rotating camshafts will always come with wear and tear. No matter where you force it to happen.
The dewalt dcs 369 recip saw also use the scotch yoke drive system and it is really smooth, no rotational vibration at all. The side effect is, due to how the yoke accelerate at TDC and BDC, it produces such an ear piercing metallic sound.
7:57 correction: the piston rings are sliding the walls, and sometimes the piston skirts do that too
It doesn't eliminate the connecting rod and wrist pin. The little arm on the crank replaced the connecting rod. The wrist pin and crank bearing are replaced by the channel and the pin that connects the arm to the slider. The crank bearing and wrist pins are fairly easy to lubricate. The sliding block in a channel looks far more difficult.
Without wristpin the yoke rod will force piston skirt into cylinder wall. Add a wristpin and the piston can truly float but the long slot rod is a big problem. Clearance, lubrication, assembly and reliability.
I agree with you on balance, however machining cost and wear are going to be an issue.
i have one downside, friction, there are two extra friction surfaces where oil can't realy come without verry complicated oil channels
Finance 101. You just explained an entire semester of investment risk in a few minutes. Nicely Done!
Seems rollers could alleviate the friction issue. Very interesting video! Complements!
Thanks for the video... Please do a video on roller rod bearings like on the honda s600... thanks
Another typical problem with sliding friction is dirt buildup. The sliding surface is very large open area where engine gunk lands easily. It is then wiped by the sliding block to the corners of the system, eventually blocking movement. For this reason linear movements as such are often avoided in machinery that has to operate in dirty environments.
Longer rods, offset crank, and ultimately a crosshead like in marine diesels are partial or total solutions to lateral piston forces, but all have their respective drawbacks.
Some type of roller bearing design in the scotch yoke would dramatically reduce sliding friction and beefing up the underside, thin part of the yoke would help much. However, with the increased friction area of the yoke, premature wear and knocking is inevitable.
The rod may not be assuming an angle, but the forces do, so it's not quite so different as you say, regarding cylinder wall friction.
This video got me thinking about the problem of transferring linear motion into rotational motion without causing angular stresses.
At first i thought of a ratcheting mechanism that has a wheel with teeth on it that would engage with a pall on the piston rod. It would reduce angle of attack significantly.
But then i realized that such a system operating at those speeds and loads would most likely wear out or fail quite prematurely.
Then i thought about what a 2 stroke engine is. It's essentially a pump that sucks and bangs on one side of the piston but also sucks and pushes with the other side of the piston.
And a steam piston pushes in both directions effectively making them 1 stroke engines.
So here's my second idea, a conventional valve driven engine that runs in 4 stroke. But where the piston rods only job is to return the piston to TDC. It's not meant to carry the load of combustion at all.
Instead, the sump side of the piston has some really low viscosity hydraulic oil that, on the combustion stroke, is directed to any hydraulic motor in the system which is super high torque that can be geared over to high RPM as necessary.
The sump side of the piston would operate like a 2 stroke with one modification, on the exhaust and intake cycle it would "idle" and just keep a neutral load of hydraulic oil. But on the combustion stroke it would pressurize an accumulator and on the exhaust stroke it would pull in fresh oil from the low pressure side.
I have no engineering skills and it's just an idea but it would be really cool to see if that was viable in any way. It would practically remove all imbalances in an engine though.
I also assume it would be a very low "RPM" engine that instead focuses on extremely high compression ratio and torque.
Conventional design transfers the power through 2 frictional bearings; piston to rod and rod to crank. However scotch yoke solves this problem by still using two frictional bearings; one is from crank to the square sliding block and the other is from square block to the rod, also one of them is sliding friction now. brilliant.
Rotating crank journals are still sliding friction, they just are sliding in a circle. The reason early designs failed is their rods sliding surface wasn't being pressure oiled, as modern cranks and thus rod journals are.
Lastly, we could build these and eliminate PRIMARY IMBALANCES if we combined this design in a BOXER engine.
You're welcome ;)