Unibody Vehicle frame

citroën traction avant body-chassis unit (1934)



1942 nash ambassador 600 cutaway drawing



saab 9000 safety cell in red , orange (2005)



backbone chassis of 1962 lotus elan

the term unibody or unit body short unitized body, or alternatively unitary construction design. engineering approach of vehicle describes of vehicle, one-piece frame , body structure a

type of body/frame construction in body of vehicle, floor plan , chassis form single structure. such design lighter , more rigid vehicle having separate body , frame.

traditional body-on-frame architectures has shifted lighter unitized body structure used on cars. last uk mass-produced car separate chassis triumph herald, discontinued in 1971.

integral frame , body construction requires more welding unstressed body conventional frame. in integrated body structure, entire car load-carrying unit handles loads experienced vehicle—forces driving cargo loads. integral-type bodies wheeled vehicles typically manufactured welding preformed metal panels , other components together, forming or casting whole sections 1 piece, or combination of these techniques. although referred monocoque structure, because car s outer skin , panels made load-bearing, there still ribs, bulkheads , box sections reinforce body, making description semi-monocoque more appropriate.

the first attempt develop such design technique on 1922 lancia lambda provide structural stiffness , lower body height torpedo car body. lambda though open layout, unstressed roof, made less monocoque shell , more bowl - 11,000 produced.

a key role in developing unitary body played american firm budd company, thyssenkrupp budd. budd supplied pressed-steel bodywork, fitted separate frames, automakers dodge, ford, buick, , french company, citroën.

in 1930, joseph ledwinka, engineer budd, designed automobile prototype full unitary construction.

citroën purchased unitary body design citroën traction avant. high volume, mass production car introduced in 1934 , sold 760,000 units on next 23 years of production. application first iteration of modern structural integration of body , chassis, using spot welded deep stamped steel sheets structural cage, including sills, pillars , roof beams. in addition unitary body no separate frame, vehicle featured other novelties such four-wheel independent suspension, , front-wheel drive. result of these innovations, traction avant had low-slung appearance futuristic era.

for chrysler airflow (1934–1937) budd supplied variation - 3 main sections airflow s body welded chrysler called bridge-truss construction. chrysler airflow unfortunately, method not ideal - panel fits poor. convince skeptical public of strength of unibody both citroën , chrysler created advertising films showing cars surviving after being pushed off cliff.

opel second european , first german car manufacturer produce car unibody structure - production of compact olympia started in 1935. larger kapitän went production in 1938, although front longitudinal beams stamped separately , attached main body.

the streamlined 1936 lincoln-zephyr conventional front-engine, rear-wheel-drive layout utilized unibody structure. 1941, unit construction no longer new idea cars, unheard of in [american] low-price field [and] nash wanted bigger share of market. single unit body construction of nash 600 provided weight savings , nash s chairman , ceo, george w. mason convinced unibody wave of future.

since more cars redesigned unibody structure, considered standard in industry . 1960, unitized body design used detroit s big 3 on compact cars (ford falcon, plymouth valiant, , chevrolet corvair). after nash merged hudson motors form american motors, rambler-badged automobiles continued exclusively building variations of unibody.

although 1934 chrysler airflow had weaker usual frame , body framework welded chassis provide stiffness, in 1960, chrysler moved body-on-frame construction unit-body design of cars.

most of american-manufactured unibody automobiles used torque boxes in vehicle design reduce vibrations , chassis flex, exception of chevy ii had bolt-on front apron (erroneously referred subframe). american motors (with partner renault) during late-1970s incorporated unibody construction when designing jeep cherokee (xj) platform using manufacturing principles (unisides, floorpan integrated frame rails , crumple zones, , roof panel) used in passenger cars, such hornets , all-wheel-drive eagles new type of frame called uniframe ... robust stamped steel frame welded strong unit-body structure, giving strength of conventional heavy frame weight advantages of unibody construction. design used xjc concept developed american motors prior absorption chrysler, later became jeep grand cherokee (zj). —including modern day sport utility vehicles (jeep grand cherokee et al.).

the unibody preferred construction mass market automobiles , crossovers. design provides weight savings, improved space utilisation, , ease of manufacture. acceptance grew dramatically in wake of 2 energy crises of 1970s , 2000s compact suvs using truck platform (primarily usa market) subjected cafe standards after 2005 (by late-2000s truck-based compact suvs phased out , replaced crossovers). additional advantage of strong-bodied car lies in improved crash protection passengers.