Subframe Design General Information General Information the Subframe Can Be Used for the Following Purposes

Subframe design General information General information The subframe can be used for the following purposes:

• To distribute the load evenly over the chassis frame • To provide clearance for wheels and other parts which project above the frame • To connect the bodywork to the chassis frame • To provide rigidity and reduce the stress in the rear overhang • To protect the chassis frame • Contributes to dampening chassis oscillations The subframe should be torsionally flexible, when the bodywork allows this, in order for it to adapt to the torsionally flexible part of the chassis frame. Therefore, the side members and crossmembers of the subframe should consist mainly of open profiles, 334 113 e.g. U-profiles.

To make the subframe strong and rigid use high and strong side members, very torsionally rigid crossmembers and diagonal stays. Reinforcement is normally used only in the rear section of the truck.

More information on chassis frames is found in the document Selecting the subframe and attachment.

Refer to the document Forces and movements under Calculations and theory for

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The subframe can appear differently depending on the characteristics required. The subframe can be in one piece, in two pieces or divided into several sections. 347 749 Example of a divided help frame

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Side members Side members are usually manufactured like the chassis side members from U-profiles. An open profile allows twisting without being exposed to unnecessary stresses.

Crossmembers Crossmembers are made from open profiles, for example U-profiles, in order to ab- sorb lateral forces and hold the subframe together.

For the purpose of reinforcing the chassis, the crossmembers may be made of closed hollow profiles, such as tubes or square profiles.

If the chassis is exposed to recurring twisting motions it is not unusual to find cracks around the attachment to the side members. The design of the crossmember attachment to the side members is therefore particularly important. Scania recommends the 314 793 use of a folding beam or crossmember with end piece. Folding beam or crossmember with end pieces Place the crossmembers so that they connect to the body adaptation brackets to pre- vent the subframe from warping when under load from the body adaptation bracket.

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© Scania CV AB 2014, Sweden Subframe design Front part of subframe Front part of subframe Note: In order to dampen any frame oscillations, the subframe should be pulled forward and clamped to the chassis frame as close as possible to the front axle. This is particularly important on vehicles having a front axle with air suspension.

Maximum permitted distance between centre of front axle and front edge of subframe: 800 • Front axle with air suspension: 600 mm 600 327 097 • Front axle with leaf spring suspension: 800 mm Front end of vehicle with air suspension or leaf spring suspension

Distance between centre of front axle and first subframe attachment: • Air suspended front axle: as far forward as possible in the range of 550 to 700 mm. • Leaf spring suspended front axle: as far forward as possible in the range of 550 to 875 mm.

More information on the maximum distance between the front axle centre and the first subframe attachment is found in the documents for the relevant truck type under Trucks and in the document Bodywork attachment.

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Design and fit the subframe 1 Fit • Rest the subframe against the chassis frame so that any oscillations in the frame are dampened by the friction between the two frames. 45° • The subframe should have a large contact surface and so follow the outswing of 45° the frame at the front edge for the best damping. R5 R5 R5 • Fit the body adaptation brackets in the subframe front so that there is a gradual increase in the bending resistance. Do this by using flexible front brackets or a lower beam web height for the first 500 mm.

Front edge 347 750 1. Soft bending resistance curve at angles greater than 45 degrees. • Fit the subframe front end so that there is a gradual increase in the bending resistance. See the figure for examples of cuttings. • Round off the front lower edge to a smallest radius of 5 mm to avoid wear damage to the chassis frame's upper flange which will gradually form an incipient frac- ture. 2 Joins • If the subframe needs to be constructed with joins, these must be shaped so that a smooth surface lays against the chassis frame. Any welds must be ground down to a smooth surface. <45 °

R5 347 751

2. Cross bending resistance curve at angles less than 45 degrees.

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© Scania CV AB 2014, Sweden Subframe design Rear part of subframe Rear part of subframe For torsionally flexible bodies, it is often necessary to make the rear overhang torsionally rigid. This is particularly important on, for example, tipper trucks, mixer units, demountable body trucks and vehicles with a rear-mounted crane to obtain More information on the recommended reinforcements in the rear overhang is avail- good stability. A long overhang with a drawbeam also increases the requirement for able in the document Reinforcement. subframe rigidity.

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