Analysis of connection element classes and locations and of some structural requirements for the mounting of different superstructure types on transport vehicles

• Main Authors: Zoran Đ. Majkić, Novak S. Vukčević
• Format: Article
• Language: English
• Published: University of Defence in Belgrade 2011-04-01
• Series: Vojnotehnički Glasnik
• Subjects: request; truck superstructure; type; connection; torsion; elasticity; manufacturer; location; construction
• Online Access: http://scindeks.ceon.rs/article.aspx?artid=0042-84691102120M

The paper presents the basic requirements for transport vehicles. A special request regarding the adaptation of transport vehicles for the transport of various types of cargo was taken into consideration. Superstructures and the situation arising after mounting superstructures on wheeled transport vehicles were analyzed and the following was described: console coupling, stirrups, simplex elastic coupling, two-way elastic and rigid connection elements. Vehicle torsional elasticity is provided by a proper choice of the type of connection between the superstructure and the vehicle chassis. Applying the instructions of vehicle manufacturers for using appropriate connections between the truck superstructure and the vehicle chassis provides positive torsional elasticity of the vehicle. The paper gives the general recommendations of the Volvo, Mercedes and Renault transport vehicle producers for the use of particular connection types of locations as well as structural requirements for the mounting of concrete mixers, tippers and truck tanks on their vehicles. Introduction Achieving a high level of transport effectiveness depends on a number of factors. One of the most important ones is the possibility to increase the payload share in the gross vehicle weight. This share depends on the net vehicle weight, a method of coupling the truck superstructure with the chassis frame as well as on the truck superstructure construction. Realization of this requirement is of significant importance, particularly for large business systems since it results in the reduction of number of necessary vehicles, more economic fleet maintenance and the fleet capacity increase. It is also relatively easy to adapt the vehicle for the transportation of other loads, depending on user's current needs. The adaptation is correctly performed if manufacturer's recommendations are followed during the mounting of the superstructure on the chassis. This paper gives the analysis of the types of coupling used for particular truck superstructures. Types of truck superstructure A truck superstructure is generally a torsionally stiffer structure of the vehicle chassis and by its mounting on the vehicle main frame the torsion stiffness of the whole vehicle increases. In order to retain the vehicle torsional elasticity because of its positive reaction to strain, it is necessary to apply a particular type of coupling for a particular type of truck superstructure. Regarding the torsional stiffness, truck superstructures can be divided into three groups: 1. Torsionally elastic 2. Torsionally semielastic 3. Torsionally rigid Connection of the chassis and the truck superstructure In order to retain the vehicle torsional elasticity because of its positive reaction to strain, it is necessary to apply a particular type of coupling for a particular type of truck superstructure: Panel connection Panel connection allows longitudinal motion and prevents lateral or vertical motion of the chassis runner in relation to the main vehicle frame. Stirrup (U bolt) connection Stirrup connections enable longitudinal motion of the chassis runner in relation to the main frame but they cannot accept lateral forces, so additional leading plates are mounted for that purpose. Simplex elastic connection Simplex elastic connections enable vertical motions of the automotive frames due to the effect of longitudinal torsion moments as well as longitudinal motion of the chassis runner due to the effect of longitudinal forces and frame flexion moments. Two - way elastic connection This kind of connections is used to connect the truck tank with the vehicle automotive frame. The connection supports lateral and longitudinal forces and enables vertical motion of the automotive frame in relation to the truck tank, during the torsion and lifting of the vehicle. Stiff connection (connection plates, sheets) This type of connections enables rigid connection of the automotive frame and the chassis runner thus making them behave as a whole. Connection plates transfer longitudinal, lateral and vertical forces. They are mounted from the front of the anterior support of the rear suspension to the end of the automotive (chassis runner) frame. The upper part of the plate is welded for the chassis runner, while the lower part of the plate is bolted for the automotive frame. Guidelines for the application of particular truck superstructures A truck superstructure must not prevent the chassis movement; therefore, it is important to choose a proper type of connection between the chassis and the truck superstructure. Chassis twisting is most expressed in the area behind the driver's cabin and it should decline towards the rear of the vehicle. If a rigid superstructure is mounted on the basic frame and the coupling is also rigid, the twisting of the main frame is not gradual but sudden and restricted to a limited area where high levels of torsion stress occur. The principal rule regarding the rigidity of superstructures is: the stiffer superstructure is, the more elastic connection must be. Manufacturer's recommendations for particular types of truck superstructures Manufacturer's recommendations for concrete mixer superstructures The truck superstructure of a concrete mixer is an example of torsionally flexible mounting. Figs. 7, 8, and 9 show types and cites of connections as well as some structural requirements of Volvo, Mercedes and Renault transport vehicles [2, 3, 4, 5]. In a 6x2 Volvo (Fig. 7), the first three couplings are cantilevered and five other connections are achieved with midfielder plates. The mixer is mounted on 6x2 vehicles with suspension or on 4x2 or 6x2 vehicles with air damping. All twin - shaft trucks could be loaded with 13t on the rear axle. Mercedes does not give much information related to the concrete mixer superstructure. To ensure stability and reduce strain of truck frames, the chassis runner is stiffened in the rear. Fig. 6 shows that the Mercedes chassis runner bends outwards, because of the possibility of embedding a larger drum or because of lowering the existing one in order to lower the focus down and thus increase the stability of the entire vehicle. Recommendations of the body tipper manufacturer A body tipper is an example of a torsionally flexible superstructure. Fig. 10 shows some types of sites and links, as well as some structural requirements of Volvo and Mercedes tippers [2, 3, 4]. Linking the main frame with the mounting one is performed using the console connection in the front part while near the axles connecting plates are used. To ensure the stability of the vehicle when unloading and to reduce stress, the frames are stiffened in the rear (Fig. 8). Recommendations of the manufacturer for mounting tanks Tank compartments are usually of circular or elliptical cross section, and as such they have large shaft, polar or torsion inertional moments. If the theories of material resistance and construction resistance are applied, it can be easily shown that the bending and torsion rigidity directly depend on the size of the moment inertia; x x c ~ I ; ϕ ϕ c ~ I , from which it can be concluded that the tank is a very rigid structure regarding bending and twisting. To connect the superstructure to the vehicle base, two-way elastic connections are used. Fig. 9 shows a twin-shaft Volvo tank with the number and types of connections used in connecting the main frame with the tank compartment. Three-axle tanks and four-axle tanks with the type and number of links of the main vehicle frame with the tank compartment are also shown. Similarly to the case of the tipper MB [3], there is no much information about linking the basic frame with the tank. Fig. 9 shows only a simplified method of coupling, without defining the number of connections and a more detailed description of connections. However, an important difference observed in relation to the solution of the Volvo manufacturer is that a chassis runner is used. Conclusion The analysis of the guidelines of leading manufacturers for upgrades, transport vehicle chassis and their connections leads to the following conclusions: The connection with the basic superstructure frame is an extremely complex issue. It is necessary to consider many factors (type of connection, the connection location, size and shape of the assembly - extra frames, the types of upgrades, etc.) since its characteristics directly affect both the reliability and the payload mass. As shown in the guidelines for the implementation of certain kinds of connection upgrades, a type of interactions on the basic frame depends on the torsional stiffness of the superstructure. Truck superstructures must not move to limit the chassis and is thus important to properly choose the types of connections and chassis upgrades. The connection of the upgrade to the basic frame is taken as already given by the manufacturer, having in mind extensive research of the manufacturer in this field. Regardless the simplifications in the application of general recommendations, the comparative analysis shows that there is a proper connection of the base and mounting frame which eliminates the possibility of breakdown.