Editing Leaf spring (section)

==Operation and basic design==
[[File:マルチリーフスプリング概略図.svg|thumb|right|upright=1.5|Generic diagram of a leaf spring pack, without eyes; leaves are fastened together by the centre bolt, midway along the length of the spring, and lateral alignment is enforced by multiple clips]]	
A leaf spring takes the form of a slender [[Arc (geometry)|arc]]-shaped length of [[spring steel]] of a [[rectangle|rectangular]] cross-section.  In the most common configuration, the centre of the arc provides the location for the [[axle]], while loops formed at either end provide for attaching to the vehicle chassis. For very heavy vehicles, a leaf spring can be made from several leaves stacked on top of each other in several layers, often with progressively shorter leaves. The longest leaf is also known as the main, master, or No. 1 leaf, with leaves numbered in descending order of length.<ref name=IS1135-95>{{cite web |url=https://archive.org/details/gov.in.is.1135.1995/mode/2up |title=IS 1135(1995): Leaf Springs Assembly for Automobiles |date=1995 |publisher=Bureau of Indian Standards |access-date=13 October 2022}}</ref>{{rp|1–3}} The eyes at the end of the leaf spring are formed into the master leaf.<ref name=Sheldon/>{{rp|6}} In general, aside from the main leaf, the other leaves are tapered at each end.<ref name=Sheldon/>{{rp|8}} Sometimes auxiliary or rebound leaves are part of the main spring pack, in which case the auxiliary leaf closest to the main leaf is No. 1, the next closest is No. 2, etc.<ref name=IS1135-95/>{{rp|3}} The leaves are attached to each other through the centre bolt, which is at or near the mid-point along the length of the leaf spring.<ref name=Sheldon/>{{rp|8}} To ensure that leaves remain aligned laterally, several methods can be used, including notches and grooves between leaves or external clips.<ref name=Sheldon/>{{rp|9–12}}

Spring steels were discovered to be most efficient at approximately 1% carbon content.<ref name=Sheldon/>{{rp|13–15}} Individual leaf thickness is specified by the Stubbs or [[Birmingham gauge]], with typical thicknesses ranging between {{cvt|0.203|to|0.375|in}} (6 to 3/8 or 00 gauge).<ref name=Sheldon/>{{rp|16}} The material and dimensions should be selected such that each leaf is capable of being hardened to have a fully [[martensite|martensitic structure]] throughout the entire section. Suitable spring steel alloys include 55Si7, 60Si7, 65Si7, 50Cr4V2, and 60Cr4V2.<ref name=IS1135-95/>{{rp|6}}

===Characteristics===
[[File:Rear axle assembly, 1930s British motor car.jpg|thumb|right|upright=1.5|Each side of this rear axle is suspended by a leaf spring. The front eye of each leaf spring is secured to the frame; the rear eye is attached by a shackle that pivots to allow the spring to lengthen as it flexes.]]
The two ends of a leaf spring usually are formed into round eyes or eyelets, through which a fastener connects each end of the spring to the [[vehicle frame]] or [[Body-on-frame|body]]. Some springs terminated in a concave end, called a ''spoon end'' (seldom used now), to carry a swivelling member instead. One eye is usually fixed but allowed to pivot with the motion of the spring, whereas the other eye is fastened to a hinge mechanism that allows that end to pivot and undergo limited movement. A leaf spring can either be attached directly to the [[Frame (vehicle)|frame]] at both eyes or attached directly at one end, usually the front, with the other end attached through a shackle: a short swinging arm. The shackle takes up the tendency of the leaf spring to elongate when compressed and thus makes the suspension softer. The shackle provides some degree of flexibility to the leaf spring so that it does not fail when subjected to heavy loads. The axle is usually fastened to the middle of the spring by [[U-bolt]]s.<ref>{{cite book |last1=Stockel |first1=Martin W. |last2=Stockel |first2=Martin T. |last3=Johanson |first3=Chris |title=Auto Fundamentals |date=1996 |publisher=The Goodheart-Willcox Company, Inc. |location=Tinley Park |isbn=1566371384 |page=455}}</ref>

The leaf spring acts as a linkage to hold the axle in position and thus separate linkages are not necessary. The result is a suspension that is simple and strong. Inter-leaf friction dampens the spring's motion and reduces rebound, which, until [[Shock absorber|shock absorbers]] were widely adopted, was a very significant advantage over [[coil spring|helical springs]].<ref>{{cite journal |title=Springs – A simple study of car suspension |journal=The Automotor Journal |date=August 10, 1912 |pages=936–937 |url=https://archive.org/details/TheAutomotorJournal2ndHalf1904/page/n171/mode/2up}}</ref> However, because the leaf spring is also serving to hold the axle in position, soft springs—i.e. springs with low spring constant—are not suitable. The consequent stiffness, in addition to inter-leaf friction, makes this type of suspension not particularly comfortable for the riders.{{cn|date=February 2022}}

===Types===
[[File:Three-quarter-elliptic leaf spring.jpg|thumb|Three-quarter-elliptic leaf spring on a carriage.]]
There are a variety of leaf springs, usually employing the word "elliptical". "Elliptical" or "full elliptical" leaf springs, patented in 1804 by the British inventor [[Obadiah Elliott]], referred to two circular arcs linked at their tips. This was joined to the frame at the top centre of the upper arc, the bottom centre was joined to the "live" suspension components, such as a solid front axle. Additional suspension components, such as [[trailing arm]]s, would usually be needed for this design, but not for "semi-elliptical" leaf springs as used in the [[Hotchkiss drive]]. That employed the lower arc, hence its name. 

"Quarter-elliptic" springs often had the thickest part of the stack of leaves stuck into the rear end of the side pieces of a short ladder frame, with the free end attached to the differential, as in the [[Austin 7|Austin Seven]] of the 1920s. As an example of non-elliptic leaf springs, the [[Ford Model T]] had multiple leaf springs over its differential that were curved in the shape of a [[yoke]]. As a substitute for dampers ([[shock absorber]]s), some manufacturers laid non-metallic sheets in between the metal leaves, such as wood.

Elliot's invention revolutionized carriage design and construction, removing the need for a heavy perch and making transportation over rough roadways faster, easier, and less expensive.<ref>{{cite web|url=https://www.gutenberg.org/files/46216/46216-h/46216-h.htm#Page_119|title=Carriages and Coaches|page=205}}</ref>

<gallery mode="packed" heights="120" widths="200" caption="Examples of leaf springs">
File:Spring 3 (PSF).png|alt=Carriage with elliptic springs|{{visible anchor|Elliptic}}
File:Semi elliptic spring and mounting (Manual of Driving and Maintenance).jpg|alt=Vehicle suspension with semi-elliptic springs|{{visible anchor|Semi-elliptic}}{{anchor|Half-elliptic}}
File:Back axle suspension springs.jpg|alt=Car suspension with three-quarter elliptic springs|{{visible anchor|Three quarter-elliptic}}
File:Quarter elliptic spring mounting (Manual of Driving and Maintenance).jpg|alt=Vehicle suspension with quarter-elliptic springs|{{visible anchor|Quarter-elliptic}}
File:Transverse leaf spring (Manual of Driving and Maintenance).jpg|alt=Front suspension with transverse leaf spring|{{visible anchor|Transverse}}
</gallery>

[[File:テーパーリーフスプリング概略図.svg|thumb|Tapered or parabolic leaf spring diagram]]
A more modern implementation is the parabolic leaf spring. This design is characterized by fewer leaves whose thickness varies from centre to ends following a [[parabola|parabolic curve]]. The intention of this design is to reduce inter-leaf friction, and therefore there is only contact between the leaves at the ends and at the centre, where the axle is connected. Spacers prevent contact at other points. Aside from weight-saving, the main advantage of parabolic springs is their greater flexibility, which translates into improved [[ride quality]], which approaches that of coil springs; the trade-off is reduced load carrying capability. They are widely used on [[buses]] for improved comfort.

A further development by the British GKN company and by Chevrolet, with the Corvette, among others, is the move to composite plastic leaf springs. Nevertheless, due to the lack of inter-leaf friction and other internal dampening effects, this type of spring requires more powerful dampers/shock absorbers.

Typically when used in automobile suspension the leaf both supports an axle and locates/partially locates the axle. This can lead to handling issues (such as "axle tramp"), as the flexible nature of the spring makes precise control of the [[unsprung mass]] of the axle difficult. Some suspension designs use a [[Watts link]] (or a [[Panhard rod]]) and radius arms to locate the axle and do not have this drawback. Such designs can use softer springs, resulting in a better ride. Examples include the various rear suspensions of [[Austin-Healey]] 3000s and [[Fiat 128]]s.