A torsion bar suspension, also known as a torsion spring suspension, is any vehicle suspension that uses a Torsion spring as its main weight-bearing spring. One end of a long metal bar is attached firmly to the vehicle chassis; the opposite end terminates in a lever, the torsion key, mounted perpendicular to the bar, that is attached to a suspension arm, a spindle, or the axle. Vertical motion of the wheel causes the bar to twist around its axis and is resisted by the bar's torsion resistance. The effective spring rate of the bar is determined by its length, cross section, shape, material, and manufacturing process.
Manufacturers change the torsion bar or key to adjust the ride height, usually to compensate for engine weight.
Torsion bars reached the height of their popularity on mass-production road cars in the middle of the 20th century at the same time that unitary construction was being adopted. At a time when the mechanics of stress and metal fatigue in unitary body frames was poorly understood, torsion bars were very attractive to vehicle designers as the bars could be mounted to reinforced parts of the central structure, typically the bulkhead. Using to achieve independent front suspension with coil springs meant providing strong turrets in the frontal structure of the car.
A disadvantage is that torsion bars, unlike coil springs, usually cannot provide a progressive spring rate. In most torsion bar systems, ride height (and therefore many handling features) may be changed by simply adjusting bolts that connect the torsion bars to the frame cross member. In most cars with this type of suspension, swapping torsion bars for a different spring rate is usually an easy task. Longitudinal torsion bars extend under the passenger compartment, cutting into interior space by raising the floor, while in transverse systems, torsion bar length is limited by vehicle width.
In 1923 Parry-Thomas patented an updated design featuring a true torsion bar design with no leaf springs, however the inventor's death in a car crash in 1927 prevented its further development. Therefore the invention is often credited to the Porsche GmbH, which patented it in 1931 and later used in a lot of designs.
The front wheel drive Citroën Traction Avant from 1934 was the first to implement the idea in a serially produced car, featuring independent front torsion bar suspension and a flexible trailing dead axle, also sprung by torsion bars. The flexibility of the axle beam provided wheel location features like a twist beam axle. Also in the 1930s, Porsche's prototypes of the first Volkswagen Beetle incorporated torsion bars—especially their transverse mounting style. Czechoslovak Tatra's 1948 T600 Tatraplan employed rear torsion bar suspension, the only Tatra to do so.
The system first saw military use in the Swedish Stridsvagn L-60 tank of 1934. Its suspension was developed by German engineers, including Porsche employee Karl Rabe who also held patents on torsion bar suspensions personally. and others, see [1]
It was used extensively in European cars like Renault, Citroën and Porsche/Volkswagen, by less known producers like Mathis and Röhr in the 1930s, as well as by American Packard in the 1950s. The Packard used torsion bars at both front and rear, and interconnected the front and rear systems to improve ride quality. Morris Minor and Oxford from the late 1940s onwards used a front torsion bar system very similar to the Citroën, as did the Riley RM models. The revolutionary Jaguar E-Type introduced in 1961 had a torsion bar front suspension very similar to the Citroën and Morris Minor, and an independent coil spring rear suspension using four shock absorbers with concentric springs (coilover).
An early application of a torsion bar in an American car was by Hudson Motor Car Company of Detroit who had introduced the innovative front axle flex suspension in 1934 Hudson and Terraplane cars and realized for 1935 that a transverse torsion bar linked to the rear axle was needed as an anti-roll bar to stabilize the cars. The single torsion bar was mounted through the frame sides behind the rear axle and then attached by arms and links to the front side of the spring U-bolt plates. Axle flex was discontinued for the 1936 model year.
Gladeon M. Barnes and Warren E. Preston filed a US patent application for a torsion bar suspension in 1934, which was approved two years later. The original feature of the patent was what is now called tube-over-bar (TOB) design which only saw limited use in the 1960s (for example, on LVTP-7). Even though Barnes was employed by the US Army Ordnance Department, torsion bars were not used in American armor designs until the T70 GMC in 1943, which suspension was derived from Pz. III by GM engineer Robert Schilling.D.P. Dyer (2002). The Origins of Torsion Bar Tank Suspensions armorama.com
Post-war the use of torsion bar front suspension was a defining feature of British Morris Motors cars, starting with the Morris Minor of 1948, its larger Morris Oxford MO counterpart and the upmarket Morris Six MS, plus the Wolseley Motors-badged upmarket variants of the latter two models. The designer of these cars, Alec Issigonis, was inspired by the Traction Avant's suspension, although the Morris cars were rear-wheel drive and used conventional for their rear axles. The Minor used lever arm dampers with its torsion bars while the Oxford and the Six used innovative Shock absorber. The Minor remained in production largely unchanged until 1972 and was replaced by the Morris Marina which also used the torsion bar-lever arm damper system for its front suspension—one of the last new cars worldwide to be introduced with the system and which remained in production until 1984. The Oxford/Six platform was developed through several revised series which used Issigonis' torsion bar system until 1959 when the new Farina Oxford was introduced using front suspension with coil springs, lower wishbones and lever arm dampers.
The most famous American passenger car application of the torsion bar, was the Chrysler system used beginning with all Chrysler products starting with the 1957 model year in cars such as the Imperial Crown series, Chrysler Windsor, DeSoto Firedome, Dodge Coronet and Plymouth Belevedere although Chrysler's "Torsion-Air" suspension was only for the front axle; the same basic system (longitudinal mounting) was maintained until the 1981 introduction of the K-car. A reengineered torsion bar suspension, introduced with the 1976 Dodge Aspen, introduced transverse-mounted torsion bars (possibly based on the Volkswagen Type 3 passenger car) until production ended in 1989 (with Chrysler's M platform). Some generations of the Dodge Dakota and Durango used torsion bars on the front suspension.
General Motors first used torsion bars on their light-duty pickup trucks in 1960 until it was phased out in 1963 where traditional coil springs are used up front for their 2WD trucks. Its first use in a passenger car was in 1966, starting with the E-platform vehicles (Oldsmobile Toronado, Cadillac Eldorado), 4WD S-10 pickups and Chevrolet Astro vans with optional AWD, and since 1988, full size trucks and SUVs with 4WD (GMT400, GMT800, and GMT900 series).
Porsche used four-wheel torsion bar suspension for their 356 and 911 series from 1948 until 1989 with the introduction of the 964. They are also used in the front suspension of the 914 as well as the rear suspension of the 924, 944, and 968. Honda also used front torsion bars on the third generation Civic and other variants built on the same platform including the Honda Ballade and Honda CRX.
Many contemporary main battle tanks use torsion bar suspension, including the American M1 Abrams, German Leopard 2, and Chinese MBT-3000, though the newest generation of tanks such as the Russian T-14 Armata utilize an adjustable hydraulic suspension. Due to their small size, tremendous load capacity, and relative ease of service, torsion bar suspension has been ideal for tanks, though it is not without disadvantage. The large travel and high elasticity of the torsion bars results in a "rocking" motion when the tank is moving or coming to a sudden stop. A gun stabilizer must be used to compensate for the rocking motion. Due to the massive weight of a main battle tank, compared to an automobile, there is a much greater risk of breaking a torsion bar on sudden bumps or maneuvers, and if it is not replaced in short order the reduced suspension can affect the maneuverability of the vehicle, and in extreme cases risk immobilizing the vehicle as the reduced capacity of the suspension causes additional torsion bars to break.
|
|