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{{short description|Type of independent suspension}}
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A '''Corvette leaf spring''' is a type of ] that utilizes a ] (FRP) mono-leaf spring instead of more conventional coil springs. It is named after the ],<ref>{{cite book |url=https://books.google.com/books?id=WsjanO7xW58C&pg=PA81 |title=Corvette - The Great American Sports Car - Staff of Old Cars Weekly |page=81 |date=1975-10-02 |publisher=F+W Media |isbn=9781440217647 |access-date=2016-11-14 }}{{dead link|date=October 2019|bot=medic}}{{cbignore|bot=medic}}</ref> the American sports car for which it was originally developed and first utilized.<ref>{{cite web|url=http://www.corvetteonline.com/history-2/the-top-5-technological-advancements-in-corvette-history/ |title=The Top 5 Technological Advancements In Corvette History |publisher=Corvette Online |date=2015-05-16 |access-date=2016-11-14}}</ref><ref>{{cite web|url=http://www.edmunds.com/chevrolet/corvette/history |title=Chevrolet Corvette History |website=Edmunds.com |date= |access-date=2016-11-14}}</ref><ref name=CompWorld>{{cite web|url=http://www.compositesworld.com/articles/composite-leaf-springs-saving-weight-in-production-suspension-systems |title=Composite leaf springs: Saving weight in production suspension systems |publisher=CompositesWorld |date=2014-02-03 |access-date=2016-11-14}}</ref><ref>{{cite web |url=http://www.autocomposites.org/composites101/history.cfm |title=ACMA: Automotive Composites Alliance - Auto Composites 101: History of Automotive Composites |website=Autocomposites.org |access-date=2016-11-14 |url-status=dead |archiveurl=https://web.archive.org/web/20170117063725/http://www.autocomposites.org/composites101/history.cfm |archivedate=2017-01-17 }}</ref><ref name=CB>{{cite web |author=Chris Longhurst |url=http://www.carbibles.com/suspension_bible.html |title=The Suspension Bible |publisher=Car Bibles |date=2016-10-26 |access-date=2016-11-14 |archive-date=2007-02-06 |archive-url=https://web.archive.org/web/20070206034707/http://www.carbibles.com/suspension_bible.html |url-status=dead }}</ref> A notable characteristic of this suspension configuration is the mounting of the mono-leaf spring such that it can serve as both ride spring and anti-roll spring. In contrast to many applications of ]s in automotive suspension designs, this type does not use the spring as a locating link. While this suspension type is most notably associated with several generations of the ] the design has been used in other production ] cars, as well as vehicles from ] and ] van. ] produced cars with a similar configuration, using a multi-leaf steel spring in place of the FRP mono-leaf spring.
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== Design ==
This article is about ''']''' used on the ] ''']'''. While most other cars use ], the Corvette uses leaf springs.
] rear suspension]]


The leaf-spring suspension configuration is ], because the movement of one wheel is not determined by the position of the other.<ref name=CB/> ]s are utilized to define the motion of the wheel as the suspension is compressed. The usual coil springs are replaced with a single FRP spring, which spans the width of the car. As in independent suspension systems using coil springs, and unlike the common leaf-spring supported ], the suspension ] are defined only by the control arms.
In suspension designs where leaf spring systems are tasked to hold the axle and function as a spring (modern truck suspension), multi-leaf springs suffer from friction between the leaves as the system flexes. The inherently flexible leaf spring is being asked to work as a spring and a suspension arm. Springs (leaf, coil, torsion etc) are good at being springs. They are not good at being rigid links. To its credit, the leaf spring does this much better than a coil spring. For example a coil spring may be viewed as a bobble head doll in the same tasked assigned to truck-style leaf spring designs.


As in a coil-spring suspension design, the FRP mono-leaf spring supports the weight of the vehicle. However, the FRP leaf springs differ from steel coils and traditional steel multi-leaf springs in a number of significant ways. The FRP plastic springs have 4.3–5.5 times the ] storage per weight, compared to steel.<ref name=Yu>{{cite journal |last1=Yu |first1=W.J. |last2=Kim |first2=H.C. |title=Double tapered FRP beam for automotive suspension leaf spring |journal=Composite Structures |year=1988 |volume=9 |issue=4 |pages=279–300 |doi=10.1016/0263-8223(88)90049-9}}</ref> This results in a lighter spring for a given application. The single FRP mono-leaf front spring used on the ] is 33&nbsp;percent of the weight of an equivalent set of coil springs.<ref name=Lamm>{{cite book |last1=Lamm |first1=Michael |title=The Newest Corvette. Corvette from A to Z-15 |url=http://www.carbibles.com/images/fibreglass_spring.gif |date=1983 |archive-url=https://web.archive.org/web/20120219190009/http://www.carbibles.com/images/fibreglass_spring.gif |page=44 |edition=1st |publisher=Lamm-Morada Publishing |isbn=978-0932128041 |archive-date=February 19, 2012}}</ref> Comparing FRP to conventional steel leaf springs in similar applications, the weight saved is even greater. The ] offered an optional FRP mono-leaf spring as an alternative to the standard multi-leaf steel spring, the {{convert|48|lb|kg|0|order=flip|adj=on}} steel spring being replaced by a {{convert|7|lb|kg|0|order=flip|adj=on}} FRP spring.<ref name=McLellan>{{cite book |last1=McLellan |first1=Dave |title=Corvette from the Inside |date=2002 |publisher=Bentley Publishers |location=Cambridge, MA |isbn=0-8376-0859-7 |pages=86–87}}</ref> Volvo claims a weight savings of {{convert|10|lb|kg|0|order=flip}} by using a FRP spring in the rear suspension of its second-generation ], compared to designs using coil springs.<ref name=Volvo>{{cite web |title=Benteler-SGL mass-produces composite leaf springs for the new Volvo XC90 using Loctite Matrix resin from Henkel |url=http://compositesindustrynews.com/fullnews.php?ids=1298 |website=Composites Industry News |publisher=FRP Today |access-date=2015-07-30}}{{dead link|date=November 2016|reason=not at archive.org (as of May 2017)}}</ref>
The Corvette has double A-arm suspension like many other high end sports cars. The A-arms are used to fully control the movement of the wheels. The only difference between the Corvette and other cars with A-arms is the Corvette uses a leaf to pull the lower arm down rather than a coil spring to push it down. In both cases the spring is doing what it does best, being a only a spring.


The relative sliding movement of the leaves of a multi-leaf steel spring results in stiction-based hysteresis with respect to spring compression. This stiction reduces suspension compliance and can compromise both ride quality and handling.<ref name=Knowles>{{cite book |last1=Knowles |first1=Don |title=Today's Technician: Automotive Suspension & Steering |date=2010 |publisher=Cengage Learning |page=115}}</ref> Lacking individual leaves, the mono-leaf spring avoids stiction.<ref name=Lamm/>
Another problem with leaf springs arises from friction between the leafs. The Corvette however uses a single piece leaf in its design so there is no internal friction, just like a coil spring.


FRP springs are advertised as having exceptional cycle life and corrosion resistance.<ref name =Lamm/> A GM test comparing the third-generation Corvette springs found that failure of the multi-leaf steel springs was likely after 200,000 full-travel cycles. The replacement FRP leaf spring showed no loss of performance after two million full cycles.<ref name=McLellan/>
So the Corvette's leaf springs design is similar to double A-arm geometry just with a different type of spring.


Packaging is cited as both an advantage and disadvantage of the transverse FRP leaf spring, as compared to coil springs, depending on the application. The FRP spring is typically set low in the suspension, resulting in a low center of gravity. It also allows manufacturers to avoid tall spring mounts, thus resulting in a flatter load floor about the suspension.<ref name=Volvo/> James Schefter reports that, as used on the C5 and later Corvettes, the use of OEM coilover damper springs would have forced the chassis engineers to either vertically raise the shock towers or move them inward. In the rear this would have reduced trunk space. In the front this would have interfered with engine packaging. The use of the leaf spring allowed the spring to be placed under the chassis, out of the way, while keeping the diameter of the shock-absorber assembly to that of just the damper, rather than damper and spring.<ref name=Schefter>{{cite book |last1=Schefter |first1=James |title=All Corvettes Are Red |date=1998 |publisher=Gallery Books |isbn=978-0671685010}}</ref> However, in other applications, such as race car designs, the need to span the width of the vehicle resulted in significant design limitations. Coil and torsion springs present better packaging options for racing applications. FRP springs also have limited availability and selection as compared to coil springs.<ref name=Smith>{{cite book |last1=Smith |first1=Carroll |title=Engineer to Win |date=1984 |publisher=Motorbooks |isbn=9780879381868 |page=207 |quote=If I were involved in the design of a new passenger vehicle, however, I would give serious consideration to the use of a transverse composite single leaf spring of unidirectional glass or carbon filament in an epoxy matrix. This would be the lightest practical spring configuration and, although space constraints would seem to limit its use in racing, it should be perfectly feasible on road-going vehicles, from large trucks to small commuter cars. (Since I wrote this paragraph the new-generation Corvette has come out with just such a spring to control its independent suspension systems-at both end of the car.)}}</ref> Higher cost has also been cited as a disadvantage, when comparing FRP springs to coil springs on production road cars.<ref name="Edmunds-2014">{{cite web |last1=Edmunds |first1=Dan |title=2014 Chevrolet Corvette Stingray Z51 Suspension Walkaround |url=http://www.edmunds.com/car-reviews/track-tests/2014-chevrolet-corvette-stingray-z51-suspension-walkaround.html |website=Edmunds |access-date=2015-07-30}}</ref>
==Leaf springs on the Corvette==
GM began using a transverse leaf spring type suspension in the Corvette in 1984, replacing the traditional coil springs.


===Advantages=== == Properties ==
] model of a leaf spring under load. The initial, unbent shape of the spring is shown as a silhouette box. An upward deflection on the right side of the spring results in a smaller upward movement on the left side.]]
*Leaf spring suspension weighs much less than coil springs as a single leaf can replace two coils. The two coil springs weigh three times as much as the one leaf.
*Leaf springs help by lowering the ] of the vehicle by being placed at the bottom of the Corvette.
*Leaf springs act as an anti-roll bar allowing for lighter anti-roll bars because the springs perform part of that role.
*The leaf springs never wear out. The vendor of these springs has never had to replace one due to fatigue failure. Coil springs do wear out but you typically don't notice on smaller, lighter cars. You do see it more on old, heavy Caddies and such. The improved fatigue life was really evident compared to the C3's steel leaf spring. Thus this is an advantage over coils but not a big one.
*They are easy to adjust. One or two hand tools are all that's required to adjust ride-height, and some people are able to adjust the springs with the car on ramps and without removing the wheels.
*They allow the shock to be mounted as far out as possible. Coilovers allow it as well, but require the springs to be mounted at the top of the assembly, which is bad for the center-of-gravity. They also allow for a non-existent shock tower, which in turn allows for a lower fender/hoodline.


An advantage of the FRP transverse leaf springs—when supported with widely spaced, pivotable mounts—is the ability to replace the anti-roll bar. Typically springs that provide a sufficient ] need a supplemental spring (the ]) to increase the suspension ]. The coupling of the two sides of the transverse leaf spring across the vehicle results in an anti-roll bar like behavior. Corvette engineers have cited this property as enabling the use of a lighter anti-roll bar,<ref name=McLellan/> and even eliminating the rear anti-roll bar on some versions of the seventh generation Corvette.<ref name=Automobile>{{cite news |last1=Noordeloos |first1=Marc |title=Vette Engineering Manager Explains the C7 Chassis |url=http://www.automobilemag.com/features/news/2014-corvette-engineering-manager-dishes-on-the-c7s-chassis-206465/ |access-date=2015-08-01 |work=Automobile Magazine}}</ref>
===Drawbacks===
They are expensive. We normally don't think of leaves as the expensive suspension, but in the case of the Corvette, coils would be cheaper. Coils are usually easier to install as well. In the C5/C6, the lower ball joint must be popped on one side for the spring to be pulled out. It's also impossible to run stiffer springs left-to-right, so a transversely leaf sprung car would be a poor choice for oval tracks.


When either wheel is deflected upward, the center span of the spring (the portion between the pivotable mounts) deflects downward. If both wheels deflect upward at the same time (for example, when hitting a bump in the road) the center section bends uniformly between the pivot mounts. In a roll, only one wheel is deflected upwards, which tends to form the center of the spring into an S-shaped curve. The result is that the wheel rate of one side of the suspension depends on the displacement of the other side.<ref name =Lamm/><ref name=McLellan/><ref name=Smith/> The extent to which the spring acts as an anti-roll bar depends on the distance between the pivot mounts and their rigidity.<ref name =Lamm/>
The Vette already has all the parts a coil sprung double A arm suspension would use. Pull the leaf off, replace the shock with a coil over and you've converted the Vette. Since the rest of the system is the same, the cost comes down to the price of 2 coils or one spring. Well if it was a steel leaf spring it might be cheaper (remember truck suspension is cheaper because the leaves also act as links).


]
It is also susceptible to damage from chemicals and heat, so extra care must be taken that spilled fluids do not remain left on the springs long enough to eat thru the outer coating. The rear springs can be destroyed by heat from cutouts or catback removal. When these springs start to fail, they fail very quickly and completely!


A simplified flat, rectangular spring illustrates this principle. Deflecting the right side of the spring results in the left side rising. By comparison, a rigid central mount (2nd and 3rd generation Corvettes and other cars) shows no movement on one side when the other is deflected.<ref name=CB/>


== Applications ==
===Street cars===
A number of manufacturers have produced vehicles or concepts utilizing independent front or rear suspensions supported by transverse leaf springs that have an anti-roll effect.
#You must design them into the car in the first place. This seems obvious but consider these springs span across the bottom of the car. In the front they have to clear the engine oil pan and in the back they have to stay out of the way of the differential. Basically, you can retro fit coils on the Vette because the mounts can be shared with the shock mounts. For the most part you can't retrofit Corvette style leaves onto other cars because you would have to add mounts that don't exist on the regular car.
* Chevrolet Corvette: ] 1984–1996 (front only, centrally mounted rear spring did not have the anti-roll effect)<!-- this article is specifically about versions of this suspension that use the twin, widely spaced spring mounts, not the single central mount such as used on the C3 and C4 rear suspensions -->, C5–C7, 1997–2019 (front and rear).
#GM and their supplier spent a lot of time and money developing the Vette's composite spring. Currently they are the only manufacture with the knowledge and understanding to make the springs work. On the other hand, coil springs are common and well understood. Lots of vendors can make them in a wide variety of configurations. It's easier for the other manufactures to stick with what they know. Other manufactures would have to study the design and manufacture of composite leaf springs before they could pop them on the next Supra-NSX-Type-GT. GM did that work years ago. Toyota could certainly afford to develop their own composite springs if they wanted. The same may not be true for smaller companies like Ferrari and Porsche.
* ] cars: first generation (Lumina, Grand Prix, Regal, Cutlass Supreme).
#Engineers like to stick with what they know. Lots of suspension engineers are familiar with using coil springs. They could experiment with leaves if they wanted or they could stick with coils and get the job done. See the point about undertaking a research project.
* ] cars: (Eldorado, Toronado, Riviera, Reatta, Allante).<ref name=PopSci>{{cite news |last1=McCosh |first1=Dan |title=Luxury coupes: $24,000 a seat |url=https://books.google.com/books?id=zQAAAAAAMBAJ&q=GM+E-body+leaf+spring+transverse&pg=PA42 |access-date=2015-07-30 |work=Popular Science |date=April 1998}}</ref>
#Coils are cheaper. This automatically keeps them off lower cost cars (Miata, Civic) and cars that share platforms with lower cost siblings (Audi TT). Porsche isn't worried about saving every last dollar but there suspension and chassis design may not allow packaging a Corvette type leaf. Even if packaging isn't a problem they still have to pay for tooling to make the springs. Unlike the GM who spreads that cost over 30,000 Vettes a year, Ferrari would spread that over maybe 2000 cars a year. Conversely I can get coils made with relatively low setup cost and a cheaper per part cost. So not only would they have to spend more per car, they have to spend a lot more up front.
* ] (from model year 1995) renamed to S90 (sedan)/V90 (wagon) from model year 1997 to 1998.<ref name=Schulon>{{cite news |last1=Schuon |first1=Marshal |title=Behind the Wheel/1995 Volvo 960; A Box That's Well Rounded |url=https://www.nytimes.com/1994/10/23/automobiles/behind-the-wheel-1995-volvo-960-a-box-that-s-well-rounded.html |access-date=2015-07-30 |work=The New York Times |date=Oct 23, 1994}}</ref>
#Perception. Just like pushrods, the leaf spring has a stigma attached to it. The reasons for the stigma are legit (key component to heavy and typically poor handling suspension). However the reality is the sum of the older parts was the problem, not a specific part of it.
* ] and ] (second generation).<ref name=CandD>{{cite web |last1=Stoklosa |first1=Alexander |title=10 Things You Need to Know About the 2016 Volvo XC90 |url=http://blog.caranddriver.com/10-things-you-need-to-know-about-the-2016-volvo-xc90/ |website=Car and Driver |access-date=2015-08-01 |archive-date=2017-12-29 |archive-url=https://web.archive.org/web/20171229021116/https://blog.caranddriver.com/10-things-you-need-to-know-about-the-2016-volvo-xc90/ |url-status=dead }}</ref><ref>{{cite web |language=en |url=https://www.materialstoday.com/composite-applications/news/volvo-xc90-features-polyurethane-composite-leaf/ |title=Volvo XC90 features polyurethane composite leaf spring |author=Amanda Jacob |date=15 October 2014 |access-date=2018-02-02 |archive-date=2018-02-02 |archive-url=https://web.archive.org/web/20180202190441/https://www.materialstoday.com/composite-applications/news/volvo-xc90-features-polyurethane-composite-leaf/ |url-status=dead }}</ref>
#Some Do! Volvo used a transverse leaf spring on the 960.
* ] vans (front only, Hotchkiss in rear).<ref name=CW>{{cite web |last1=Wood |first1=Karen |title=Composite leaf springs: Saving weight in production suspension systems |url=http://www.compositesworld.com/articles/composite-leaf-springs-saving-weight-in-production-suspension-systems |website=Composites World |access-date=2015-08-01}}</ref>
* ]: 1969–1973 (Front only), Trailing arm with coil springs, panhard bar (Rear).
* ] Mk1-Mk3 (used with MacPherson Struts).<ref name=Smart>{{cite web |title=The Smart Fortwo Evolution |url=http://www.fq101.co.uk/data-a-reference/61-the-smart-evolution.html |access-date=2015-08-01}}</ref>
* ], prototype.<ref name=AutoIntel>{{cite web |title=Volkswagen : The 1-Litre Car |url=http://www.autointell-news.com/european_companies/volkswagen/vw_marke/volkswagen-concepts/volkswagen-1-liter/volkswagen-1-literauto-02.htm |website=Automotive Intelligence News |access-date=2015-07-30}}</ref>
* ], a Swedish made, low volume roadster. Due to the anti-roll properties of the transverse leaf-spring, the car does not employ a separate front anti-roll bar.<ref>{{cite web |url=http://www.lakritz.se/nyheter/INDIGO.PDF |title=The Successor: Indigo 3000 | archive-url = https://web.archive.org/web/20081216074553/http://www.lakritz.se/nyheter/INDIGO.PDF |archivedate=2008-12-16}}</ref>
* ], which used a similar system with a more traditional multi-leaf steel spring but configured with two pivots to provide the anti-roll effect.<ref name=Unique>{{cite web |title=How it Works: Suspension |url=http://www.uniquecarsandparts.com.au/how_it_works_suspension.htm |website=Unique Cars and Parts |accessdate=2015-08-01}}</ref>
* Some later models of ] and ] used rear transverse steel leaf springs with anti-roll pivot mounts.
* ].


== Recent patents and related research ==
===Race cars===
Several automotive companies have filed patents for suspension designs using a transverse composite leaf-spring supported in a fashion similar to that of the Corvette.
Not all race cars use coil springs, some F1 cars (Ferrari and others) use torsion springs instead. Years ago Indy and F1 cars DID use leaf springs but those days are long past.
* Ford Global Technologies, 2006, patent #7029017, ''Wheel suspension for a motor vehicle with a transverse leaf spring''.<ref>{{cite web |url=https://patents.google.com/patent/US7029017 |title=Patent US7029017 – Wheel suspension for a motor vehicle with a transverse leaf spring |access-date=2015-08-03}}</ref>
* Porsche AG, 2000, patent # 6029987, ''Front Axle for a Motor Vehicle''. Describes a strut suspension system supported by a transverse leaf-spring system largely the same as that used by the Corvette. The Porsche patent mentions the beneficial stabilizing effects of this arrangement.<ref>{{cite web |url=https://patents.google.com/patent/US6029987 |title=Patent US6029987 – Front axle for a motor vehicle |date=1997-05-26 |access-date=2015-08-03}}</ref>
* Honda, 1992, ''Transverse leaf spring type suspension'' patent #5141209.<ref>{{cite web |url=https://patents.google.com/patent/US5141209 |title=Patent US5141209 – Transverse leaf spring type suspension |date=1988-11-30 |access-date=2015-08-03}}</ref>
* DaimlerChrysler, 2004, patent #6811169, ''Composite Spring Design that also Performs the Lower Control Arm Function for a Conventional or Active Suspension System''.<ref>{{cite web |url=https://patents.google.com/patent/US6811169 |title=Patent US6811169 – Composite spring design that also performs the lower control arm function for a conventional or active suspension system |access-date=2015-08-03}}</ref>
* ] released a concept rear suspension design, in October 2009, using a composite spring-based rear suspension. The strut-based suspension uses a transverse leaf spring to function as both ride and anti-roll spring. The ZF concept differs from the system used on the Corvette by using the leaf spring as one of the suspension links.<ref>{{cite news |last1=Buchholz |first1=Kami |title=Composites take prime chassis roles at ZF |url=http://articles.sae.org/7840/ |access-date=December 22, 2016 |publisher=Society of Automotive Engineers |date=March 31, 2010}}</ref><ref>{{cite web |title=Lightweight Construction: Fighting the Fab |url=https://www.zf.com/corporate/en_de/magazine/magazin_artikel_viewpage_22131368.html |website=ZF Company corporate website |publisher=ZF Company |access-date=December 22, 2016}}</ref>


== See also ==
The current design of open wheel racecars places great restrictions on suspension packaging. The Corvette's transverse leaf spring must span from one side of the car to the other. Also, to be most effective the links between the spring and suspension arms should be under tension. This makes a bottom mount spring most effective. This packaging doesn't work well on an open wheel car because the spring would have to pass though the gear box around the dif (or the gear box would have to be raised and hurt the car's CG). At the front the driver's legs would get in the way. Additionally the spring is wide and would have to extend past the body work where it would hurt the car's aero package.
* ]


==References==
NASCAR rules dictate coil springs on the rear axle. They probably originally used leaves but given the option any car designer (modifier back in the day?) would have replaced the leaves with a multi-link set up. As I said before the multi-link offers better control of the rear suspension.
{{Reflist|30em}}


Another good reason is only a few companies understand the technology necessary to make the springs. Hypercoil is currently the top race spring manufacture. They can make very precise, matched spring pairs. The level of precise spring rate control and matching may not exist in the composite bow springs.

Coil race springs are not car specific. You select rates, diameters, length etc but you don't have a specific spring for a specific car. If you want to order a custom spring Hypercoil will wind it to your specifications on the same machine they use for the next custom spring. A custom Porsche, Formula Ford and LMP car spring can all be made on the same machine. By the time the C6 evolves into a C6-R (they don't start off with a production Corvette) the suspension geometry is so different that they couldn't just mount a C6 leaf spring. It's far too expensive to have a few custom leaf springs tooled up (you would have to buy the tooling as well as the springs) so they use readily available coil springs.

This type of universal tooling isn't availible for the composite leaf spring. Only the Vette currently uses the spring so you are making a Vette only part. This seriously reduces the market for aftermarket composite leaf springs (still there are after market leaf springs available for the Vette). The business case for custom equipment to make Vette springs is harder to justify since it's a smaller market.

Why don't other cars retrofit leaf springs? Well they also don't retrofit torsion springs despite the fact that F1 cars use them. Put simply it would be VERY difficult. The Vette was designed to have them. It has mount points under the car where the springs fit to the suspension sub frames. It's not easy to just add that to a car that was designed to use a coil spring. All of the cars you mentioned would have to be re-engineered to add leaf springs. Replacing the factory spring with a racing is easy by comparison.

The other VERY significant reason is racers will use what they know. They will put effort into learning about new technology (torsion springs in F1) but ultimately it is too there advantage to stick with what they know.

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Latest revision as of 16:59, 9 June 2024

Type of independent suspension

A Corvette leaf spring is a type of independent suspension that utilizes a fiber-reinforced plastic (FRP) mono-leaf spring instead of more conventional coil springs. It is named after the Chevrolet Corvette, the American sports car for which it was originally developed and first utilized. A notable characteristic of this suspension configuration is the mounting of the mono-leaf spring such that it can serve as both ride spring and anti-roll spring. In contrast to many applications of leaf springs in automotive suspension designs, this type does not use the spring as a locating link. While this suspension type is most notably associated with several generations of the Chevrolet Corvette the design has been used in other production General Motors cars, as well as vehicles from Volvo Cars and Mercedes-Benz Sprinter van. Fiat produced cars with a similar configuration, using a multi-leaf steel spring in place of the FRP mono-leaf spring.

Design

The C5 Corvette's rear suspension

The leaf-spring suspension configuration is independent, because the movement of one wheel is not determined by the position of the other. Control arms are utilized to define the motion of the wheel as the suspension is compressed. The usual coil springs are replaced with a single FRP spring, which spans the width of the car. As in independent suspension systems using coil springs, and unlike the common leaf-spring supported Hotchkiss rear axle, the suspension kinematics are defined only by the control arms.

As in a coil-spring suspension design, the FRP mono-leaf spring supports the weight of the vehicle. However, the FRP leaf springs differ from steel coils and traditional steel multi-leaf springs in a number of significant ways. The FRP plastic springs have 4.3–5.5 times the strain energy storage per weight, compared to steel. This results in a lighter spring for a given application. The single FRP mono-leaf front spring used on the fourth-generation Corvette is 33 percent of the weight of an equivalent set of coil springs. Comparing FRP to conventional steel leaf springs in similar applications, the weight saved is even greater. The third-generation Corvette offered an optional FRP mono-leaf spring as an alternative to the standard multi-leaf steel spring, the 22-kilogram (48 lb) steel spring being replaced by a 3-kilogram (7 lb) FRP spring. Volvo claims a weight savings of 5 kilograms (10 lb) by using a FRP spring in the rear suspension of its second-generation XC90, compared to designs using coil springs.

The relative sliding movement of the leaves of a multi-leaf steel spring results in stiction-based hysteresis with respect to spring compression. This stiction reduces suspension compliance and can compromise both ride quality and handling. Lacking individual leaves, the mono-leaf spring avoids stiction.

FRP springs are advertised as having exceptional cycle life and corrosion resistance. A GM test comparing the third-generation Corvette springs found that failure of the multi-leaf steel springs was likely after 200,000 full-travel cycles. The replacement FRP leaf spring showed no loss of performance after two million full cycles.

Packaging is cited as both an advantage and disadvantage of the transverse FRP leaf spring, as compared to coil springs, depending on the application. The FRP spring is typically set low in the suspension, resulting in a low center of gravity. It also allows manufacturers to avoid tall spring mounts, thus resulting in a flatter load floor about the suspension. James Schefter reports that, as used on the C5 and later Corvettes, the use of OEM coilover damper springs would have forced the chassis engineers to either vertically raise the shock towers or move them inward. In the rear this would have reduced trunk space. In the front this would have interfered with engine packaging. The use of the leaf spring allowed the spring to be placed under the chassis, out of the way, while keeping the diameter of the shock-absorber assembly to that of just the damper, rather than damper and spring. However, in other applications, such as race car designs, the need to span the width of the vehicle resulted in significant design limitations. Coil and torsion springs present better packaging options for racing applications. FRP springs also have limited availability and selection as compared to coil springs. Higher cost has also been cited as a disadvantage, when comparing FRP springs to coil springs on production road cars.

Properties

FEA model of a leaf spring under load. The initial, unbent shape of the spring is shown as a silhouette box. An upward deflection on the right side of the spring results in a smaller upward movement on the left side.

An advantage of the FRP transverse leaf springs—when supported with widely spaced, pivotable mounts—is the ability to replace the anti-roll bar. Typically springs that provide a sufficient ride rate need a supplemental spring (the anti-roll bar) to increase the suspension roll rate. The coupling of the two sides of the transverse leaf spring across the vehicle results in an anti-roll bar like behavior. Corvette engineers have cited this property as enabling the use of a lighter anti-roll bar, and even eliminating the rear anti-roll bar on some versions of the seventh generation Corvette.

When either wheel is deflected upward, the center span of the spring (the portion between the pivotable mounts) deflects downward. If both wheels deflect upward at the same time (for example, when hitting a bump in the road) the center section bends uniformly between the pivot mounts. In a roll, only one wheel is deflected upwards, which tends to form the center of the spring into an S-shaped curve. The result is that the wheel rate of one side of the suspension depends on the displacement of the other side. The extent to which the spring acts as an anti-roll bar depends on the distance between the pivot mounts and their rigidity.

A transverse leaf spring with a central rigid mount. The two spring halves are effectively isolated. Movements of one half of the spring do not affect the other half.

A simplified flat, rectangular spring illustrates this principle. Deflecting the right side of the spring results in the left side rising. By comparison, a rigid central mount (2nd and 3rd generation Corvettes and other cars) shows no movement on one side when the other is deflected.

Applications

A number of manufacturers have produced vehicles or concepts utilizing independent front or rear suspensions supported by transverse leaf springs that have an anti-roll effect.

Recent patents and related research

Several automotive companies have filed patents for suspension designs using a transverse composite leaf-spring supported in a fashion similar to that of the Corvette.

  • Ford Global Technologies, 2006, patent #7029017, Wheel suspension for a motor vehicle with a transverse leaf spring.
  • Porsche AG, 2000, patent # 6029987, Front Axle for a Motor Vehicle. Describes a strut suspension system supported by a transverse leaf-spring system largely the same as that used by the Corvette. The Porsche patent mentions the beneficial stabilizing effects of this arrangement.
  • Honda, 1992, Transverse leaf spring type suspension patent #5141209.
  • DaimlerChrysler, 2004, patent #6811169, Composite Spring Design that also Performs the Lower Control Arm Function for a Conventional or Active Suspension System.
  • ZF released a concept rear suspension design, in October 2009, using a composite spring-based rear suspension. The strut-based suspension uses a transverse leaf spring to function as both ride and anti-roll spring. The ZF concept differs from the system used on the Corvette by using the leaf spring as one of the suspension links.

See also

References

  1. Corvette - The Great American Sports Car - Staff of Old Cars Weekly. F+W Media. 1975-10-02. p. 81. ISBN 9781440217647. Retrieved 2016-11-14.
  2. "The Top 5 Technological Advancements In Corvette History". Corvette Online. 2015-05-16. Retrieved 2016-11-14.
  3. "Chevrolet Corvette History". Edmunds.com. Retrieved 2016-11-14.
  4. "Composite leaf springs: Saving weight in production suspension systems". CompositesWorld. 2014-02-03. Retrieved 2016-11-14.
  5. "ACMA: Automotive Composites Alliance - Auto Composites 101: History of Automotive Composites". Autocomposites.org. Archived from the original on 2017-01-17. Retrieved 2016-11-14.
  6. ^ Chris Longhurst (2016-10-26). "The Suspension Bible". Car Bibles. Archived from the original on 2007-02-06. Retrieved 2016-11-14.
  7. Yu, W.J.; Kim, H.C. (1988). "Double tapered FRP beam for automotive suspension leaf spring". Composite Structures. 9 (4): 279–300. doi:10.1016/0263-8223(88)90049-9.
  8. ^ Lamm, Michael (1983). The Newest Corvette. Corvette from A to Z-15 (1st ed.). Lamm-Morada Publishing. p. 44. ISBN 978-0932128041. Archived from the original on February 19, 2012.
  9. ^ McLellan, Dave (2002). Corvette from the Inside. Cambridge, MA: Bentley Publishers. pp. 86–87. ISBN 0-8376-0859-7.
  10. ^ "Benteler-SGL mass-produces composite leaf springs for the new Volvo XC90 using Loctite Matrix resin from Henkel". Composites Industry News. FRP Today. Retrieved 2015-07-30.
  11. Knowles, Don (2010). Today's Technician: Automotive Suspension & Steering. Cengage Learning. p. 115.
  12. Schefter, James (1998). All Corvettes Are Red. Gallery Books. ISBN 978-0671685010.
  13. ^ Smith, Carroll (1984). Engineer to Win. Motorbooks. p. 207. ISBN 9780879381868. If I were involved in the design of a new passenger vehicle, however, I would give serious consideration to the use of a transverse composite single leaf spring of unidirectional glass or carbon filament in an epoxy matrix. This would be the lightest practical spring configuration and, although space constraints would seem to limit its use in racing, it should be perfectly feasible on road-going vehicles, from large trucks to small commuter cars. (Since I wrote this paragraph the new-generation Corvette has come out with just such a spring to control its independent suspension systems-at both end of the car.)
  14. Edmunds, Dan. "2014 Chevrolet Corvette Stingray Z51 Suspension Walkaround". Edmunds. Retrieved 2015-07-30.
  15. Noordeloos, Marc. "Vette Engineering Manager Explains the C7 Chassis". Automobile Magazine. Retrieved 2015-08-01.
  16. McCosh, Dan (April 1998). "Luxury coupes: $24,000 a seat". Popular Science. Retrieved 2015-07-30.
  17. Schuon, Marshal (Oct 23, 1994). "Behind the Wheel/1995 Volvo 960; A Box That's Well Rounded". The New York Times. Retrieved 2015-07-30.
  18. Stoklosa, Alexander. "10 Things You Need to Know About the 2016 Volvo XC90". Car and Driver. Archived from the original on 2017-12-29. Retrieved 2015-08-01.
  19. Amanda Jacob (15 October 2014). "Volvo XC90 features polyurethane composite leaf spring". Archived from the original on 2018-02-02. Retrieved 2018-02-02.
  20. Wood, Karen. "Composite leaf springs: Saving weight in production suspension systems". Composites World. Retrieved 2015-08-01.
  21. "The Smart Fortwo Evolution". Retrieved 2015-08-01.
  22. "Volkswagen : The 1-Litre Car". Automotive Intelligence News. Retrieved 2015-07-30.
  23. "The Successor: Indigo 3000" (PDF). Archived from the original (PDF) on 2008-12-16.
  24. "How it Works: Suspension". Unique Cars and Parts. Retrieved 2015-08-01.
  25. "Patent US7029017 – Wheel suspension for a motor vehicle with a transverse leaf spring". Retrieved 2015-08-03.
  26. "Patent US6029987 – Front axle for a motor vehicle". 1997-05-26. Retrieved 2015-08-03.
  27. "Patent US5141209 – Transverse leaf spring type suspension". 1988-11-30. Retrieved 2015-08-03.
  28. "Patent US6811169 – Composite spring design that also performs the lower control arm function for a conventional or active suspension system". Retrieved 2015-08-03.
  29. Buchholz, Kami (March 31, 2010). "Composites take prime chassis roles at ZF". Society of Automotive Engineers. Retrieved December 22, 2016.
  30. "Lightweight Construction: Fighting the Fab". ZF Company corporate website. ZF Company. Retrieved December 22, 2016.
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