Daihatsu Move Teardown (Part 3): Linear body structure optimizes space

Rigid body improves impact safety, handling, riding comfort and quietness

2015/03/11

Summary

Daihatsu Move Daihatsu Move

 The Daihatsu Move teardown was held on January 21 through 27, 2015, by the Hiroshima Industrial Promotion Organization. Part 1 of the teardown report about the mini vehicle (No. 1378 posted on February 19) focused on its equipment and components comparable to those in B-segment cars. Part 2 (No. 1380 posted on March 2) described the Move's high fuel economy and improved performance of the engine and transmission. This report focuses on the body structure of the fifth-generation 2014 Daihatsu Move X-turbo VS model (see Note 1).

 The fifth-generation Daihatsu Move has a linear body structure chosen to produce as much space as possible within the dimensional limits of the mini vehicle category in Japan (see Note 2). It is a rational structural design that ensures high body rigidity while keeping the vehicle weight to the minimum. As a result, the rigid body structure seems to contribute to improved impact safety, riding comfort and quietness.

 The front side member has a large cross-sectional area to maintain high strength and rigidity. However, the cross-sectional area changes near the front of the outer front wheel at the maximum steer angle so that the member yields under impact of collision to absorb the impact. The front pillar has a larger cross-sectional area around the front corner window than at other sections. This helps increase the rigidity at the joint between the engine compartment and the cabin. This design effectively reduces the cabin deformation in the event of a frontal collision. As discussed above, the high body rigidity appears to contribute to improved performance of the Move.

 (Note 1) The fully redesigned Move (sixth-generation Move) was launched in December 2014.
 (Note 2) The Japanese automobile regulations for mini vehicles require the overall length to be 3.4 meters or less, maximum width to be 1.48 meters or less, and maximum height to be 2 meters or less.


Previous teardown reports:

Daihatsu Move (Feb. 2015)
  (Part 1): Equipment comparable to B-segment cars
  (Part 2): High fuel economy and improved performance

VW Polo (Dec. 2014)
  (Part 1):Engine compartment and driver's seat area
  (Part 2):1.2-liter TDI diesel engine and suspensions

Nissan Note (Sep. 2014)
  (Part 1):Major safety technology and advanced driver
               assistance systems

  (Part 2):Drive unit and supercharger

Honda Accord Hybrid teardown (Feb. 2014)
  (Part 1): PCU and vehicle chassis components
  (Part 2):Battery components and brake system
  (Part 3):Sport Hybrid i-MMD drive unit

Honda Fit Hybrid teardown (Dec. 2013)
  (Part 1) Battery components and brake system
  (Part 2) Engine and transmission

Toyota Aqua (Nov. 2012)
  (Part 1) Part suppliers and battery components
  (Part 2) Hybrid systems behind the 35.4km/liter car

Nissan Leaf
  (Part 1) Benchmarking systems and components (Mar. 2012)
  (Part 2) Main components disassembled (Sep. 2012)
  (Part 3) Nissan Leaf body cutaway (Nov. 2012)

Specifications of the 2014 Daihatsu Move
Daihatsu Move Daihatsu Move
Vehicle
specifications
Model name/ Grade Daihatsu Move X-turbocharged VS grade,
special version with Smart Selection SA (Smart Assist)
Price JPY 1.33 million plus JPY 60,000 for optional Smart Assist
Dimensions Length: 3,395mm, Width: 1,475mm, Height: 1,620mm
Curb weight 820kg
Seating capacity 4
Engine KF-type water-cooled inline 3-cylinder intercooled turbocharger
Transmission CVT with a torque converter and lockup mechanism
Fuel efficiency (JC08 mode) 25.20km/liter


Engine compartment structure

Engine compartment Engine compartment
Engine compartment

 The engine compartment is formed by the dashboard panel that separates the engine compartment from the cabin, the front side members, strut housings and hood ridges. The front ends of the right- and left-side front side members are connected by bumper reinforcements to form space where the engine and the transmission are mounted. The photos above show engine compartment skeleton without the engine, transmission, suspensions, brake and other components. The front side member has a large cross-sectional area and is connected straight to the dashboard panel to form a very strong structure.

 

Front side member structure

Front side member Front side member
Front side member (seen from right-side of vehicle) Front side member (seen from under the vehicle)

 The front side member is the toughest of all components that form the body frame. It determines the strength and rigidity of the front half section of the vehicle. In the event of a frontal collision, the front side member absorbs the impact to prevent deformation of the cabin structure. It has a large cross-sectional area and extends longitudinally to maintain high rigidity.

 In the event of a frontal collision, the front side member of the Daihatsu Move yields midway to absorb the impact when it receives a large force from the front bumper. To make it yield easily, the cross-sectional area is large overall and small at midpoint.

 When the front wheels are turned to the maximum steering limit, the front of the outer wheel comes close to the side member. The front side member has a recess to allow steering space for the wheel. The cross-section of the front side member is 50 by 50mm overall but only 15 by 15mm at midpoint. The local strength at midpoint is made less so that the tough member bends at that point and absorbs the impact of collision. This also reduces the impact reaching the cabin and occupants.

 

Strut housing and front pillar joint structure

Strut housing Strut housing
Body structure near the front strut suspension and strut housing

 The next largest force acting on the body structure is the force from the suspension. When a jacking force caused by road bumps acts on the strut type front suspension of the Daihatsu Move, the large vertical force is transmitted from the upper end of the strut suspension to the strut housing. The housing is located at the rear end of the engine compartment and is supported by the adjoining front side member, hood ridge, dashboard panel and front pillar. The proximity of the strut housing to the dashboard panel and the front pillar helps increase strength and rigidity as it reduces the bending moment of the side member when it receives a large vertical force from the suspension.

 Another unique body structure of the Daihatsu Move is the front pillar that has a large cross-section along the front-to-rear direction of the vehicle. In many other vehicles, the front pillar adjoins the front door opening and is separated by about 100 to 300mm from the dashboard panel. The front pillar on the Move gets larger as it rises from the bottom toward the lower edge of the front corner window where it joins the forward-slanting dashboard panel.

 As a result, a large force reaching the strut housing is borne not only by the front side member and the hood ridge but also by the front pillar that has prominently large vertical strength. These rational design considerations in the Move's body structure seem to help eliminate the use of reinforcements while reducing the overall vehicle weight.

 

Front suspension member attachment

Front suspension member Front suspension member
Front suspension member and front side member attachment

 Longitudinal and lateral forces from the front suspension are transmitted from the transverse linkage of the front suspension to the front side member via the front suspension member. As reported in Daihatsu Move Teardown (Part 1), the front suspension member and its attachment are compact and simple in design as they are located nearly flush without an offset to the force reaching from the suspension. The rear end of the suspension member is attached directly to the bottom surface of the side member.

 The front attachment is also constructed with a minimal offset in the vertical direction of the suspension member. This helps increase the rigidity of the suspension member and the front side member while reducing their loads.

 These design considerations help block vibrations and sounds from the suspension and contribute to improved riding comfort and quietness. The high rigidity of the body attachments also helps reduce the fluctuation of suspension alignment and improve the handling stability.

 

Engine mount attachment

Engine mount Engine mount
Engine mount (mounted on right side of vehicle) Engine mount (mounted on left side of vehicle)

 An engine mount is attached each to the right and left front side members. The two engine mounts are attached nearly directly to the highly rigid front side members. This helps block vibrations and sounds from the engine and improve riding comfort and quietness.

 

Front bumper reinforcement

Front bumper reinforcement Front bumper reinforcement
Front bumper reinforcement Front bumper reinforcement attached to the vehicle

 The right and left front side members are connected to each other at the front edges by the front bumper reinforcement. In the event of a frontal collision, the input force from the front bumper is borne by the front bumper reinforcement and transmitted to the front side members. Connecting the right and left front side members increases the overall rigidity of the engine compartment. The simple structure formed by a single pressure molded steel sheet seems to improve rigidity effectively while reducing weight and costs.

 

Front cross member

Front cross member Front cross member
Front cross member Front cross member attached to the vehicle

 The front cross member is attached hanging down from the front edges of the right-side and left-side front side members. The front cross member is a structural component that supports the radiator and air conditioner condenser unit from bottom. In the event of a frontal collision, it supports the bottom of the front bumper and bears the input force from the front bumper jointly with the front bumper reinforcement.

 

 



Dashboard panel and front pillar structure

Dashboard panel and front pillar Front pillar
Dashboard panel and front pillar bottom Front pillar

 The Daihatsu Move has a small front corner window at the center of the front pillar. The front pillar starts as a single part at the top but branches off into two pieces at the midpoint to make room for the corner front window. The two pieces converge at the lower edge of the corner window. The front pillar forms a structure with a large cross-section extending in the longitudinal direction of the vehicle. This structural design ensures diagonally front visibility while contributing to substantially increasing the rigidity of the nearby structures.

 In other vehicles without a corner window, the front pillar forms part of the door opening and is longitudinally separated from the dashboard panel. The front pillar on the Daihatsu Move encloses the front corner window resulting in a cross-sectional shape having a large longitudinal span. This design ensures highly integral joint stretching from the door opening to the upper part of the dashboard panel.

 The upper part of the dashboard panel also has a rational structural design. In many other vehicles, the bottom edge of the windshield forms an arch when viewed from above as both ends are folded inward from the center. In the case of the Daihatsu Move, the front pillar is located further forward to make space for the front corner window. Therefore, the bottom edge of the windshield is nearly straight across the vehicle, and so is the dashboard panel that supports the windshield from below. Because of these structural designs, the upper portion of the dashboard panel has a very high rigidity.

 In other words, the high jointing rigidity of the engine compartment and the cabin is ensured by the large front pillars and the dashboard panel that connects them. This creates a body structure that ensures shock absorption in a frontal collision, handling stability, riding comfort and quietness.

 

 



Front floor and front seat attachments

Front floor Front seat
Front floor Front seat

 The seat cross members connect the right- and left-side sills and the central floor tunnel at the center of the front floor. The front end of the front seat rail is attached to the seat cross members.

 The seat rail inner rear is attached to the vertical wall of the floor tunnel. This allows large legroom under the front seat cushion for the rear seat occupant without being interfered by the seat rail bracket.

 

 



Rear floor, rear seat and rear suspension attachment structure

Rear floor Rear floor
Rear floor (under the rear seat) Rear floor (luggage room area)

 The rear seat cross member having a large cross-section is located in the front of the rear floor to connect the right and left sides of the vehicle. This area under the rear seat front is least crowded and therefore is used efficiently. The rear suspension trailing arm attachment to the rear side member (explained below) is located directly behind and under this area. Therefore, this floor area must have high rigidity to bear large forces from the rear suspension. The least crowded area is used to form a body structure with a large cross-section chosen to achieve both weight reduction and higher rigidity in a rational manner without using thicker sheets.

 The rear suspension shock absorber is attached to the rear wheel house inner. The rugged rear side member adjoins the inner bottom of the rear wheel house inner and the rear shock absorber attachment is located at a highly rigid position.

 

Rear seat Rear seat
Rear seat Rear seat (under side)

 The rear seat can slide up to 240mm. The front edge of the seat slide rail is attached to the seat cross member.

 

Rear suspension attachment Rear suspension attachment
Rear suspension attachment

 The rear suspension trailing arm is attached to the lower side of the rear side member. On vehicles equipped with a torsion beam type rear suspension such as the Daihatsu Move, the large longitudinal and lateral forces reaching the rear suspension are transmitted to the rear suspension attachment.

 Forces from the rear suspension spring are also transmitted to the lower side of the rear side member.

 The rear suspension shock absorber is attached to the top of the wheel house that adjoins the rear side member. This area also has high strength and rigidity.

 As illustrated above, the rear suspension is attached to the rear side member and adjacent sections having high rigidity. This design contributes to improving the handling stability, riding comfort and quietness.

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