Teardown of Toyota’s Flagship Sedan (3)

　This is a continuation of a series reporting on a teardown analysis performed by the Hiroshima Industrial Promotion Organization of the Toyota Crown Royal, a 2.5-liter V6 engine-powered rear-wheel drive model launched in Japan in December 2012. See Teardown of Toyota's Flagship Sedan (Part 1)  and Teardown of Toyota's Flagship Sedan (Part 2) for earlier reports.

　This report will focus on the Crown’s body structure, and acoustic insulation and absorption materials. The platform of the 14th-generation Crown inherits the basic platform originally developed for the 12th-generation Crown, which was launched in 2003. In spite of its age, the original platform already features well-thought-out technical considerations for high-end front-engine rear-wheel drive vehicles, from the large framework to the details of small components. A unique area of the Crown’s body structure is the linear layout of components including the side members and cross members, wherein they maintain large cross-sectional areas with little curving. Japanese cars often have framework components that have curves or small cross-sections among other features aimed at maximizing cabin space. In contrast with this, the components of the Crown are laid linearly as in frame-structured vehicles to increase rigidity. Moreover, this rational body structure results in a reduction in superfluous reinforcement that is intended to reduce weight. Another notable characteristic of the Crown is the use of sealing material at panel joints to increase the sealability of the body, and keep exterior noise from filtering into the cabin, while at the same time reducing the need for additional acoustic insulation and absorption material. An upcoming report (Part 4) will contain a photo gallery and list of suppliers to conclude this series.

Previous teardown reports:
Teardown of Toyota's Flagship Sedan (Part 1)(May 2016)
Teardown of Toyota's Flagship Sedan (Part 2)(May 2016)

4th-Generation Toyota Prius
4th-Generation Toyota Prius Teardown (Part 1)(Feb. 2016)
4th-Generation Toyota Prius Teardown (Part 2) (Mar. 2016)
4th-Generation Toyota Prius Teardown (Part 3) (Mar. 2016)
4th-Generation Toyota Prius Teardown: Photo gallery (132 parts) (Apr.2016)

　One characteristic of the Crown’s body structure is the extreme straightness of large components. This resulted from a basic theory for designing lightweight, highly rigid body structures. Generally, Japanese vehicles have little space allocated for mechanisms in order to make the cabin space roomier, and as a result of this many parts like the main framework components of the body structure and suspension members are bent or curved. In contrast with this approach, the Crown’s body structure has a smooth shape that eliminates unnecessary bends so that it can bear load without strain. The front side member, one of the main frameworks of the engine compartment, has a large cross-sectional area and a smooth shape transition. It stretches linearly from the front floor under the cabin to the rear end of the front floor.

Engine compartment

Front side members

　The right and left front side members are joined near the dashboard with the dashboard lower member, which have a large cross-sectional area. To bear load from both the left and right, the top of the dashboard member has a mild shape transition that straddles the floor tunnel. This type of design in which front side members are connected directly while a large cross-sectional area is maintained can be found in models such as the Mercedes-Benz C Class (launched in 2014) and E Class (launched in 2016) as well.

　European premium-class vehicles from makers like Mercedes-Benz and BMW use die-cast aluminum strut housings where the front suspensions are mounted. The Toyota Crown on the other hand uses a traditional steel panel instead.

　The front bumper reinforcements shown below are fitted via a front side member extension to the front edges of the side members. As a result, the large front side members and dashboard member are laid nearly on the same plane at the front and rear of the engine compartment to form a robust body structure.

Front bumper reinforcements and front side member extension

　The bumper reinforcements are made of extruded aluminum and have a constant cross-sectional area. The same structure is used in many recent models launched by Japanese, U.S., and European OEMs. Toyota uses extruded aluminum reinforcements fir the front, not only on the Crown, but on the Prius as well. At the same time, hot-stamped steel reinforcements are used in the rear. The front side member extension is made of steel with beads pressed at right angles with the travel direction of the vehicle. In normal driving conditions this design increases body rigidity and contributes to increasing handling stability while suppressing body vibration. When powerful force is exerted in the event of a collision, the front side member extension deforms like an accordion and absorbs the energy of the impact.

　The images below shows the radiator core supports. These are located at the front edge of the engine compartment and maintain the position of components including the radiator, condenser, and headlamps. The top edges connect to the hood ridge panel to increase the torsional rigidity of the engine compartment. Many other automakers are increasingly using plastic supports in their recent models, but Toyota uses the conventional steel-made components. It is conceivable that Toyota prefers steel supports on account of the cheaper cost and higher body rigidity.

Radiator core support disassembled

Radiator core supports in place

A-pillar, B-pillar side sill

Roof cross member, B-pillar, front floor cross member

　Components including the side sills, A- and B-pillars, and front floor cross members have rugged frames to minimize structural deformation in the event of an impact. The B-pillar, floor cross member and roof cross member are joined at the same point to form a robust loop-like structure specifically for resisting lateral force in a side collision.

Roof rail, roof bow

Rear-fender integrated body side panel

　The roof is made up of front and rear roof rails, a roof center cross member that connects the B-pillars,  roof bows, with in front and two behind the cross member. This design not only contributes to increasing the roof’s tensile rigidity, but improves the torsional rigidity of the body as well.

　The body side is one large panel made up of the A-pillar, B-pillar, side sill outer, roof side rail outer and rear fender. The dimensional accuracy of the door opening is kept high to increase the ease of door operation, acoustic insulation, and sealability.

Rear suspension member mounts in rear floor

Rear seat cross members

　The rear suspension member mounts are located under the rear side members. Cross members are used to form a rugged structure. Since the vertical offset is large, the addition of bracing under the suspension members increases the support rigidity of the suspension and handling stability of the vehicle.

Rear floor area with rear suspension in place

Rear floor area with bracing in place

Rear door inner panel

Front door inner panel

　The door panel has a conventional structure in which the regulator, door lock, speaker and other parts are assembled sequentially in the door inner panel.

Door guard bar (steel pipe)

Door guard bar (stiffener)

　The door guard bar for protection against side impacts has a steel pipe that is welded to the door inner panel with a bracket on the left and right sides. A steel panel stiffener is also used. Both of these components are installed so there is a slight gap with the door outer panel, and kept in place at several points using adhesives to maintain the surface rigidity of the door outer panel. This helps to increase the dent resistance of the door outer panel and reduce the vibration caused by door opening and closing.

Rear bumper reinforcement

Rear bumper reinforcement mounts

　The rear bumper reinforcement is made of steel. The rear side member is joined squarely behind the rear panel lower to which the rear bumper reinforcement is mounted.

Steering member, A/C unit

Steering member mounts to the A-pillar

　The steering member is straight pipe material that is welded at points where the cross-sectional area changes. The design does not bend, which leads to a lightweight, high-rigidity structure that contributes to a reduction in steering shudder and increased body rigidity. The steering member is mounted to the A-pillar using adjustable nuts that absorb dimensional tolerance relative to the body-side mount.

Engine compartment sealing

Sealing under rear floor

　The body joints of the Toyota Crown are tightly sealed off. Joints are coated with sealants and vibration damping coating. While this was done to water proof the body and prevent rust, it is also possible that the sealing was intended to improve quietness by blocking noise. Sealant is applied not only along the dashboard panel that isolates the engine compartment from the cabin, but also to the joints between the hood ridge, and the strut housing and side members. This is likely to keep external sounds from entering the cabin through the gaps between the hood ridge and the front fender. It is conceivable that the sealing of the body joints led to a reduction in the use of acoustic insulators.

Front floor

Rear floor, seatback panel

　The floor panel is almost entirely coated with damping material. Instead of the conventional damping sheet material called melting sheet, the Toyota Crown uses a robot-applied damping coat developed by Aisin Chemical Co., Ltd. It can be applied to areas such as vertical walls and under panels where it is difficult to attach sheet materials. In addition, the coating area can be specified precisely.

　Compared to conventional damping sheet materials, the damping coat can be applied to areas like body joints with variable thicknesses, and since it has improved damping performance, Aisin Chemical says weight can be reduced by 30% over conventional materials. The damping coat is also used as a sealant under the underfloor lower and at panel joints.
4th-Generation Toyota Prius Teardown (Part 3) Body structure based on TNGA, sound insulating, absorbing and damping technologies

Rear wheelhouse

Rear floor (front of spare tire pan)

Rubber sealing placed all around the engine room

Rubber sealing for the left, right, and rear sides

　Acoustic insulation in the engine room is intended not only to keep sounds from entering the cabin through the dashboard panel, but also to seal off the engine room completely (with the exception of the cooling vent passages) to make it so sounds don’t leak from around the engine room. The four sides at the top edge of the engine room are sealed with the hood panel and rubber seals.

Rubber seals and acoustic absorption material around the hood panel

Acoustic absorption material on the dashboard panel

　Acoustic absorption material is used on the engine room side of the dashboard panel. It is less than 10 mm thick and doesn’t have a vinyl or rubber-based acoustic insulation layer. This is a simple part with a similar structure to the hood insulator.

Engine cover

Sound absorption material (thinsulate) in back of the engine cover

　The engine cover is used for cosmetic reasons. It is covered with thinsulate in the back to keep high-frequency sounds from leaking out.

Sound absorption material on back of the engine undercover

Engine undercover under the vehicle

　Acoustic absorption material is also used in the engine room side of the engine undercover. The undercover seals the bottom of the engine room not only for aerodynamic reasons, but also to block off noise.

Thinsulate in back of the front inner fender

　Thinsulate is also applied to the rear side of the back of the inner fender inside the wheelhouse. It is used to keep the engine sounds, road noise and other high-frequency sounds from reaching the cabin from the hollow area in the front fender.

Front carpet lining

Floor carpet

　A small piece of acoustic insulation material is applied on the underside of the floor carpet, which is very thin for a high-end model like the Crown. The carpet itself is thin, and even with the acoustic insulator does not exceed 10 mm.

Acoustic insulation and absorption materials in the floor (front)

Acoustic insulation and absorption materials in the floor (rear)

　Felt of a width of around 10 to 20 mm is laid between the floor carpet and floor panel, which is very thin compared to the 30 mm or more of felt used in premium European vehicles. Acoustic insulation and absorption material is not used between the rear seat and the body. In premium European vehicles felt is integrated with the floor carpet to eliminate hollow spaces as much as possible, but it is conceivable that the use of acoustic insulation material in the cabin has been minimized in the Crown through the improvement in the sealability of the joints between the body and floor panel.

Acoustic absorption material behind the head lining

Foam urethane at center of A-pillar

　Felt and thinsulate acoustic absorption material are used on the underside of the roof trim. The center of the A-pillar is filled with foam urethane. It is used to keep noise from the engine room and wheelhouse from reaching the roof rail, which is located near the occupants’ ears.

Back of front door trim

Back of rear door trim

　Felt and thinsulate acoustic absorption material are used on the underside of the door trim.

Bottom view of underfloor

　Undercovers and aerodynamic diffusers are installed from the front to rear in the floor, resulting in a nearly flat bottom design. The bottom surface of the transmission oil pan and fuel tank were made flat in consideration of a diffusing effect. This design reduces the coefficient of drag and lift, which improves the handling stability of the vehicle on expressways. In addition, the use of diffusers, which were originally intended to improve aerodynamic performance, also insulate wind noise and various sounds from under the floor, making a significant contribution to creating a quiet cabin environment.

Engine undercover

Diffusers at front floor side

Diffuser at front floor center

Diffuser at rear floor rear edge

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