So you want to know about suspensions?
The area of suspension design is a surprisingly complicated one, and one which has shaped tracked vehicle design--both of tanks and support vehicles--since their conception back before world war 1. The idea of a suspension system to dampen impacts on the chassis and to decrease the force on the tracks from terrain has been well known, with many approaches leading to many effects. Let's first look at the reason why a tank needs a suspension.
Tracked vehicles need suspensions for three primary reasons: comfort, traction, and track life.
The first of which is obviously the comfort of the crew. Going over shell craters, dips, rocks, bumps, etc, at high speed is a nerve-racking experience--bounced around in a steel can, surrounded by ammunition, with little visibility. This oscillation and bucking can damage tank components--much like sliding down too sharp a ravine in your T-50--and the crew can even pitch into the objects within the tank, literally being thrown about and even injured.
The second of which is traction. When a tank goes over a rut, if the tracks are perfectly flat--like that of most bulldozers--only a portion of the track will be in contact with the ground, and hence ground pressure goes up. Conversely, on a hill, the center of the tracks is under more pressure, and will dig in more readily. The second, and more critical, issue with this is that steering is affected. Tanks don't steer like cars, you don't simply turn a wheel and go X degrees. Most tanks of the WW1 through vietnam era used levers, which slowed one track; even modern tanks, by turning their tiller bar or wheels, apply X amount extra force to one side and subtract to the other. This means that steering is affected by traction. Ideally, for smooth turning, a tank should have fairly balanced ground pressure along its track length, gradually increasing as it reaches the center; the ends of the tracks at the front and back of the tank have to slide sideways to turn, with more sliding the further up the length of the tank you go. So having fairly uniform traction means the driver's control inputs are relatively steady, whereas without suspension and with unequal ground pressure, a turn that normally would have been a gentle slew to one side could spin the tank suddenly around, or not move it at all.
The third reason for a tank's suspension is track life. Tank tracks are not like car tires, they wear out fast and often need replaced. They are also very expensive. Some tanks in WW2 have been quoted as having tracks that only lasted as little as 250km. While the lifespan of hte tracks varied according to design and the weight of the vehicle, having a suspension that attempted to keep equal pressure from each bogie wheel was a necessity for any track life early in the war. This became less relevant later, as longer-travel designs such as that of the Panther and Pershing were introduced.
Tracked vehicle suspension is balance of factors: size, travel, longevity, and logistics.
First, the size of the suspension component is a big factor--a large, bulky system will add weight and has to be armored. More weight means a slower tank, exponentially so when you consider that usually these systems have to be armored if they are not particularly durable.
The travel of the suspension is incredibly important, adding to all three of the above-mentioned needs. More travel lets the tank cross more rough obstacles and gives it more flex. It also can usually add to the smoothness, and hence its top speed--I recall a certain British tank with a very high top speed from its engine, but which could never acheive it in practice due to shaking itself to bits over rough ground. It means that it also produces less sharp impacts on the tracks themselves, meaning they last longer (compare pushing on something with hammer, versus hitting it).
Longevity, or the lifespan of a suspension, was a relatively minor issue in regular use. Most of the suspension designs even in world war 1 were fairly effective in terms of lasting. The issue was combat damage. Two major approaches to suspension design emerged in the world during WW2, that of putting suspension under armor, and that of making the suspension easily removed and replaced. Both are, to an extent, used today, but under-armor suspension is generally the new norm.
Logistics, or the cost, was a relatively minor issue but one which showed up in a few instances. The infamous overlapping and interleaved roadwheels of the German big cats, for instance--not a design flaw, but a response to the lack of rubber available. Since rubber was necessary to reduce track friction with the wheels, the Germans instead used more roadwheels to reduce the wear of the roadwheels on the track, eventually using all-steel wheels with small internal shock absorbers. The Russian T-34, produced in great numbers, had a very poor and outdated track design which was prone to breaking, but was simple to produce and the only real option available to the soviet union. So we see a few unique examples of this.
So, enough about the needs and purpose. I want to see the facts! Let's see some suspensions!
The first is obviously that used in WW1 on the British tanks so well known--no suspension. This is fairly self-explanatory--roadwheels bolted directly to the hull. Interesting tidbit--if you look up bovington tank museums youtube, on the little willie they mention the tracks had guide rails but also flanges to prevent track slipping. Later variations had the tracks on big modules connected to the hull with a girder, like the Whippet. I won't go into the reasons why this was a bad system.
Coil Bogie (non-horstmann)
From the period of WW1 until WW2, this was a form of suspension often used, with a single or multiple coil springs carrying a bogie. This was a big improvement, but still only capable of very minimal travel. Later versions would be articulated, to allow it to pivot and help with interconnection and give travel. The system was limited by the size of the compressed spring, meaning that travel was fairly minimal. This suspension was fairly much phased out by the late interwar years, seeing its first use on some French WW1 tanks and the A7V.
While the first implementation of this I don't recall offhand, it was widely copied after being used, combined with high-strength steel tracks with very small links to reduce rotational friction, on the Vickers six-ton. In a nutshell, this system is a pair of wheels, carried on leaf sprigs or leaf sprung arms. When one wheel is raised like by hitting terrain, the other is lowered, and the average of the two--buffered by the springs--is carried to the body (I know that sentence is terrible English, I can't think of how to explain it). This also keeps fairly uniform track pressure, is rather light, easily removed and replaced, allows decent travel, and keeps the tracks from slipping. No shock absorbers are needed, since the friction of the leaves sliding over each other dampens oscillation. It is easy to see why this cheap and effective system was quickly copied and modified into various forms, from the Russian T-26 to the Czech 38t. A downside to this system was that the leaves were prone to breaking either under fire or from sharp impacts. Most tanks of the interwar period used small roadhweels to decrease individual point track wear and help keep from slipping a track, with this suspension system.
Rubber Scissor Spring
Much like the original Mini, the French developed a fairly standardized system of rubber springs used in their tanks, with (usually) a pair of wheels springing against each other. A bit heavier, using a lot of rubber, it was, from the little combat experience it saw and from general analysis of the system, a fairly good approach. Rubber has a natural dampening property, and is not prone to breaking like steel; however how it would have held up to things like flamethrowers or shellfire is questionable. Either way, we will never know, but similar systems are used today in vocational trucks and bulldozers.
Now we get into the more-seen systems! The volute spring was developed in the US, and is used only on US tanks. A very durable system, it consisted of suspension arms and coiled strips of metal. As the metal's layers glided over each other, it was a strong system and surprisingly resistant, while, due to the leverage the bogie arms provided, it allowed quite good travel. Later variants (the HVSS) used the springs sideways, springing one wheel off another, to interconnect, which, combined with the advanced and well-insulated American running gear design, contributed to surprisingly long track life. This system was also, like the leaf sprung bogie, easily removed if damaged by mines or shell fire, and was a bolt-on, modular solution.
A good video showing restoration of an early model volute spring bogie: http://www.youtube.c...h?v=E4-MkW4XMnI
If you drink tea and watch Top gear a lot, this might be a familiar sight for you. The horstmann bogie was broadly similar to the US VVSS bogie, but used a coil spring instead of a volute spring. This system was actually very comparable to torsion bars, being a tiny bit stiffer but also having better interconnection. Interestingly, after torsion bars became the norm in the 50s, this system was retained on the Chieftain tank and several other vehicles. Very simple, easy to replace, and a generally ideal solution in my personal opinion. Show below is an early version, later versions had more travel and a shock absorber.
Aka "America fuck yeah". Used a bell crank to transfer rotation of a springing arm's direction to allow very long springs to be used. Christie acheived much success with this system, but the Soviets were the only ones who bought it. They in turn copied it and his armor ideas and tracks, and threw them on the BT and T-34. This system is by far the best for ride quality except for MAYBE hydropneumatic; some vehicles could ahve as much as a meter of suspension travel, enabling incredible speed. Original Christie tanks also had a chain drive option, so they could run without their tracks on roads, because the concept of a dedicated tank transporter was apparently beyond 1930s America. A video of it in action: http://www.youtube.c...h?v=FWi1E-M9CtE
Simple system with a pair of wheels on a bell crank, each bogie connected by a short arm and lever to a central spring running the tank length. This version had actually too much interconnection, and, while having excellent travel, tended to make the tank sway back and forth a lot in motion. Only the Japanese ever used it. It is fairly heavy and large, and doesn't look particularly strong or durable.
Single Torsion Bar
A common, modern type of tank suspension, found today on many fast track layers. A steel bar runs under the bottom of the tank and twists; connected to it is a short trailing arm, carrying a wheel. As the wheels hit bumps, the bar twists. This system is compact, light, provides good travel, is simple to manufacture, and is generally a good solution. The downside is that tanks hit by mine damage may need to be cut open with a welding torch to repair--NOT fun, and a pain in the arse to do in the field. Virtually all modern fast track layers use this system. Tansk with torsion bars will have one sides' roadwheels slightly back from the other, noticeable upon close inspection, due to the packaging of the torsion bars.
Double Torsion Bar
Only the Germans...this is a fairly complex form of torsion bar, where apparently one bar pivots, and one both pivots and seems to skew. I can't explain it and only understand it partially. Only ever seen on the German big cats.
Video of an explanation: http://www.youtube.c...h?v=aS3rP7rLJN4
The current "new thing". Uses gas, whcih is very flexible and soft, as a springing medium in cylinders for each wheel. Also has shock absorbers which are connected through pipes, making all wheels interconnected to each other and providing a very smooth ride. Sometimes these shocks and the pipes are connected to the idler, as in the Chal2, to control tension as well. This is a very complex but effective and generally light system that promotes track life, crew comfort, and low mechanical damage due to terrain. The single drawback is that the system is not good in desert environments, as the sand can degrade the cylinders, hence its rejection from some custom-designed middle eastern tanks and the M1 Abrams. It is slightly less durable and much more complex than torsion bars, but again, promotes track life and crew comfort, as well as making the tank very easy to maneuver offroad and a generally excellent system.
That's it, folks, the basics of most tank suspension systems. Below I'm going to briefly touch on a few unique and experimental designs.
A short torsion bar on a bogie. The bogie is free to pivot with one wheel at the end of it, and the other wheel is sprung. Through the lever action, both wheels are actually sprung. The torsion bar appears to be actually inside the bogie itself, geared to the arm. Typical porsche, it's complicated but beautiful mechanically. But a picture of it fully compressed is worth a thousand words [edit: link broke somehow] Look here: http://www.tiger-tan...re/history2.htm
A torsion bar system, but with interconnected hydraulic shocks like a hydropneumatic. Only used by the Russians and in a few US arties I believe (not sure, don't quote me)
Belleville washers, little flat cones, were to be used on geared arms. I can't find a good schematic, and can't really explain it well. Used on the Swiss pz68 after the war and a few King Tigers.
Specialized coil-sprung two-wheel pivoting bogie, a modern approach to the concept of bogies. Very light, with a low center where the spring rests, springing against the hull at an angle and following the arm in its rotation. Used on the American Ripsaw MS1 & MS2. A similar system, with a single arm, is used on the Israeli Merkava; this has the TSAWS system where the coil spring can actually ride up off of the suspension arm, to allow the roadwheel to flop down unsprung held only by the shock down, as a method of increasing travel over very rocky terrain. This prevents track slipping.
A pivoting bogie assembly with two arms with two wheels each and an idler. Allows interconnection but no springing. The entire assembly is suspended on a leaf spring. Only ever used on Kegresse halftracks. The system, with no leaf spring, is used on low-speed construction equipment to increase ground contact and torque.
Single Wheel Leaf
A short arm sprung by a leaf spring clamped to it. Used on most variants of the Panzer II. Also used nowadays on Bobcat company's crawlers.
A short, half-length torsion bar. Used on the soviet T-64. Found to be very fragile as the bar had to be fairly soft to pivot sufficiently in such short space (more rotation per X amount of length), not used subsequently.
Others: if there are any, just give me a hollar. If this thread is well recieved, I might do a thread on caterpillar track designs. Until next time, have fun kids! --TheManWithNoName
Edited by TheManWithNoName, Nov 04 2012 - 13:27.