Why is volute spring Better?

The vertical volute spring suspension system is a type of vehicle suspension system which uses volute springs to compensate for surface irregularities. This type of the suspension system was mainly fitted on US and Italian tanks and armored fighting vehicles starting from throughout the s up until after the end of the Second World War in .

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Principle

The horizontal arms connected to the road wheels are cranks that drive the vertical arm up and down. The vertical arm connects to the volute spring in the box-shaped area above.

Development

During the s, many innovations in the components of light tanks would make US tanks considerably more reliable.[citation needed] These included rubber-bushed tracks, rear mounted radial engines and the vertical volute spring suspension.

A volute spring is a compression spring in the form of a cone (a volute). Under compression the coils slide over each other, affording a long travel. The result is more stable and powerful than any leaf, coil, or torsion bar spring in the same volume.[citation needed] Mounted vertically in a road wheel bogie for a pair of road wheels on a tank made a very compact unit.[1]

The suspension was developed in by Harry Knox, better known for his Knox Automobile Company, and was first tested on T2E1 light tank prototype in .[2][3]

The Rock Island Arsenal produced a small tank for the cavalry which used vertical volute spring suspension instead of leaf spring suspension. Standardized as the M1 Combat Car, it entered service with the US Army in .[4] The design was used in the M2 light tank and subsequent Stuart tank series. Design features of the Stuart were scaled up for use in the first M2 medium tanks which would evolve into the more successful M3 Lee and M4 Sherman, all using the VVSS.

Replacement

Battle experience showed that the service life of the original vertical volute spring suspension (VVSS) of the late model M4 was shortening due to the tank's increasing combat weight with larger guns and heavier armor. Beginning in mid-, M4A3 models of the Sherman adopted a newly developed Horizontal Volute Spring Suspension (HVSS).[5]

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Horizontal volute spring suspension

This type of a suspension system involved springing the pair of dual-mounted road wheels on each bogie against each other with a volute spring. First tried by Harry Knox on the Light Tank T6 project in , it was essentially a version of the British Horstmann suspension that replaced the Horstmann's coil spring with a pair of volute springs.

When the horizontally-affixed volute springs were placed in compression by either the front or the rear bogie wheel arm, the pressure from the load was transmitted onto the opposite arm, thus helping to maintain tension on the tracks. Compared to the VVSS system which it replaced on the M4, the HVSS system was heavier and stronger and allowed the changing of individual wheels aside from increasing wheel travel space.

See also

• Christie suspension – Suspension system for tanks
• Horstmann suspension – Type of tracked vehicle suspension
• Torsion bar suspension – Vehicle suspension that uses a torsion bar
• Continuous track – System of vehicle propulsion

Notes

Bibliography

A volute spring, also known as a conical spring, is a compression spring in the form of a cone (somewhat like the classical volute decorative architectural ornament). Under compression, the coils slide past each other, thus enabling the spring to be compressed to a very short length in comparison with what would be possible with a more conventional helical spring.

There are two typical types of volute spring:

• The first has a shape for the initial spring steel (or other material for the wound spring) as a "V", with one end wider than the other
• The second is the double volute, having two "V" shapes facing away from each other, which forms a distorted cylinder having a wider diameter at the centre than at the ends, forming symmetric attachment points

Double volute springs can frequently be found as a component of garden pruning shears. Short posts anchored in each side of the handles, and inserted into each narrow end of the spring, keep the spring in position.

However, the applications of volute springs are not limited to such light-duty purposes as gardening shears. For example, volute springs are used to cushion the impact between railway cars and as a core element of the suspension system of Sherman tanks. A volute spring buffer device for railway cars was invented by John Brown in .[1]

• A double volute spring mounted in pruning shears. Under compression, the coils slide over each other, so affording longer travel.
• A double volute spring
• A single-sided conical, or volute spring
• A volute suspension spring ()
• Diagram showing volute spring within the buffer assembly of a railway car (with dotted lines showing compressed position), invented
• Volute springs within buffer assemblies on a railway car
• Volute spring suspension on an M4 Sherman tank (in service –)