It is rare to Wired make the headline with a subject rather accustomed to Defence news sites. Yet on May 13, it was the latest BAE (British Aerospace), the CV-90, equipped with “suspensions of formula 1” that was unveiled. We had already discussed the subject of the poor visibility of these massive machines with innovation from augmented reality to the driver. One of the other major research topics for this kind of “hardware” (in addition to protection and armaments that are classified confidential essentially) is to improve mobility. And it has not all to do with raw power.
Now this is a recurring feature of technological progress for this type of (very)hardware, much more massive than your car, and much more even than a heavy duty truck (38 tons loaded by definition), such as Leclerc and 54 tons, lighter in his category or the 70 tonnes American Abrams. The engineers were faced with these questions: How do we make these massive vehicles speeding at nearly 80 km/h do not spreading to the deck in pieces after jumping a an obstacle ?
How to ensure that the crew can endure running at 50 km/h on the worst terrains, jumping a fence to fall in a swamp, rolling on cars, tree trunks, or through a wall, crossing trenches, ditches and riverbeds, passing from desert to rocky terrain or wet grass in a few moments? How the driver can drive such a machine without any vibration and especially as the tanks scores a bullseye while rolling over evenen ground, hitting one or more targets several kilometers away, at full speed, and in the worst visibility?
A little history of suspensions
In addition to the stabilization systems that have made considerable progress, much of this “work” which consists of a stable chassis in all circumstances through suspension . And it comes from far away. As the airplane, the tank was born during the Great War, deadly laboratory numerous innovations. The car, designed in conjunction with the French and the English, was simply aims to pass the “no man’s land” by providing direct support to infantry, unlike artillery. Merely take on this very hilly and muddy terrain machines of several tons of artillery derived tractors, has already lean engineers on the problem. Initially, there was simply no suspensions. The tanks advancing “at no infantry” to 2-6 km/h on average, it was not a problem. These include the still-board comfort was very primitive and that we suffered from poisoning C02 even before they suffer from seasickness!
From the twenties, it seems clear that the speed remains insufficient. The next generation has leaf springs, tested, but which only allow for a limited speed. We already thought the cavalry tank concept, which to advantage against an armored car often confined to the road. English Officers as Lidell Hart theorize mechanized warfare (Heinz Guderian and De Gaulle did not lose a crumb) and already sees appearing three types of tanks with different vocations, and a different speed. Faster light tanks were the recognition and the industrial giant British Vickers Armstrong will be name with the spring suspension system (Of type Hotsmann) with tankettes line that lead in particular to the Universal Carrier, mass produced during the second World War.
In the United States, in 1928-1930, a named Walter Christie engineer adventurer had also noticed this problem and became the champions of cavalry tanks. His model was light, with an ultra-powerful aircraft engine and suspensions revolutionary lever (named after him). This system allowed to reduce the size of the springs by moving the contact energy while limiting vertical space. The concept will -made unmatched at the time, to reach almost 100 km / h at full speed. It will fail with the US Army who sulk concept, but a partial success internationally, with the clandestine sale of two “tractors” to the Soviets (who will copy and produce its mass model with the final famous T-34), and the British will buy the license to design their many “cruiser tanks” whose last Centurion was the first modern battle tank (1945). The French on their side with Renault, a pioneer of modern light tank with the small FT (1917), continue research to improve the speed of his armored with combined systems to complex and relatively fragile vertical springs, it will protect.
However during the second world war, in addition to tanks equipped with steel suspensions and finally have a few Christie suspension, universal suspension will also be created in the 30s and universally adopted for its numerous advantages: suspension torsion bar. This simple system uses a simple cross bar mounted under the chassis, which is connected to each side a lever arm on which the roadwheel swing freely. Each uneven ground is transmitted from the wheel to the lever connected to the bar that deforms -sent in torsion- and then regains its shape (hence the name). The system (with pioneers like Citröen with his front wheel and Tatra, then copied by Porsche) had the advantage of great simplicity and extreme ruggedness, in addition to being compact. So naturally destined to tanks, further to reduce their profile. Swedes and Germans were the first to adopt this system for their tanks, which will actually be used by all nations after the war.
It will then wait until the 70s for the first attempts to improve the system. Indeed, speed had been steadily improved through advances in engines, transmissions, and armour improvement in weight (using clever composites for example), and tanks were heading towards over fifty tons whereas still capable to reach 60 kp/h and more. In addition to the use of rubber shoes on tracks links and roadwheels, shock absorbers and bumpers, the torsion bar despite its merits had not the ability to actively control the suspension. This is a “passive system”. It is from there that came the use of hydropneumatic suspensions. French invention also (with the famous Citröen DS then taken by Rolls-Royce, Mercedes or Maserati) the first draft of this active suspension (also called oleo) had the advantage of being controlled by adjusting the pressure upstream.
Citroën hydropneumatic suspension (DS) – Wikipedia
And could in theory move from a “sport” mode (hard) to “all terrain” (soft) by pressing a button, without counting the self-adjustment of the system. The Swedes with their Strisvagn 103 were the first to adopt it for their “S-Tank” turretless in 1965, followed by other countries. It has now become the new standard for battle tanks of 50-70 tons class. Among other benefits for a tank, armored can finally lowered in a static position (defense or ambush), based in the environment, or on the contrary increase the ground clearance on rough terrain, but also use a vacuum/maximum elevation to the front or the back to enjoy the field and provide a depression/elevation extra barrel, in English called ‘hull down position which will be instrumental in the success of Israeli Centurions on the Golan plateau (Golan heights) in 1973.
The Innovation of BAE:
It would seem that the British reconnect again with innovation in a field for which they appeared as pioneers with their CV90 test, which uses for the first time “Formula 1” suspension systems. According to the press release this is a “new active damping suspension system” which result in a new damping system of active suspension. This system is actually derived from Formula 1, which after banishment in 1994 to eliminate driving aids found a new vocation in defense. This active suspension (computer-aided electronic management) allows vehicles to manage their ride height and stiffness of the suspension while in full speed and real time, either by activation of the driver, and/or automatically controlled power. This additional flexibility allows the CV90 increase its speed up to 40% at 65 kph off-road, and around 90 kph on flat. It seems paradoxical to return to performance already achieved by a 1929 tanks, but the technological gap between the two explains why it took so long to return to such performance. A 1929 Christie would have been virtually naked when facing a CV90. It is fair to remember though that the CV90 (originally created by Hägglunds/Bofors and currently used by Scandinavian countries) is not really a MBT but more a valorized IFV, weighing 35 tonnes and powered by a Scania diesel developing up to 810 horsepower (MBT figures are generally 70 tons for 1500 hp).
In detail, the active suspension system is obviously different from that of the formula 1: weight constraints have nothing to do indeed. It measures somehow the movements of the hull and calculates how much each point raised vehicle speeds (ie its ground clearance). When the movement reading exceeds predetermined thresholds, the system begins to stiffen the suspension. When the vehicle goes down, the dampers stiffen and absorb shock better than would a passive system, and even better than a conventional hydropneumatic suspension. This system (whose specificities are classified defense secrets) can handle three times better hull motion relative to the original system, with impacts on large and small reliefs reduced in real time, but also to anticipate the use of Antilock brakes.
The following video shows the vehicle trials, jumping an obstacle (in “free flight”) of 30 to 60 km/h on flat but with some bumpy trails.