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In pursuit of offering the best driving comfort, heavy/ light commercial vehicle producers usually need to make serious optimizations on the design of leaf springs and natural frequency calculations in order to decrease the vibration and noise that have negative effects on the human body - especially severe on long road trips. Leaf spring design parameters and natural frequency calculations provide a different approach to minimizing such negative effects on the driver. In this study, design of the leaf spring, boundary conditions of which depend on vehicle, is examined virtually within the triangle of driving comfort by natural frequency, durability and stiffness. Besides the driving comfort, optimization work aimed at decreasing the vibration and noise factors are also determined through finite element methods. Prototypes of leaf springs are produced and their natural frequency measurements, stress levels under maximum load through strain gauges as well as life tests are completed.

Besides the innovative work in the commercial vehicles sector, where there is an ever growing competition, lighter, more comfortable, safer, and more robust products are also being developed through optimization of design parameters of currently available systems. This study explains the possible effects of changing the design parameters of leaf springs on a vehicle's driving dynamics, which has a significant effect on the total weight of the vehicle. These effects include the vehicle's suspension specifications and the suspension system's interaction with the steering system. A virtual vehicle model is analyzed under the loads gathered in road tests, to measure the stress levels on the spring layers and the movement of the leaf spring depending on the limits determined by the vehicle manufacturer. Furthermore, the conformity of the movement of the front axles in connection with the leaf spring with the steering system is also analyzed.

Leaf springs are used as the suspension elements for the front and rear axles of light and heavy commercial vehicles in the automotive key industry. While the vehicle is running empty or with a load under on-road or off-road conditions, it catches the loads transmitted from the wheels i.e., the loads from the ground to the hub axle, and working together with the damper it helps absorption of such loads and prevents them from being transmitted to the chassis. As a result, vehicle comfort is achieved. In addition to this function, leaf springs act as a safety part that continuously hold the chassis and axle together under static and dynamic loads. While the vehicle is runs under rough road conditions, the impact loads from the road not only cause negative impacts on the vehicle but also damage the drivetrain. Such impact loads substantially disturb both the vehicle and the passengers.

Decarburization occurs on heat treated components. At leaf spring manufacturers, the occurrence of decarburization, which has a negative impact on fatigue, starts at hot rolled leaf spring steel raw materials' production process. The decarburization rate of the raw material, which is taken through a heat treatment, increases during the leaf spring manufacturing process. Through metallographic analyses and experimental tests, this study manifests how leaf spring's resistance to fatigue is affected by the correlation of ferrite structure occurred by decarburization on heat treated leaf springs, the surface hardness, and the permanent surface tension to be occurred during the shot peening process. This study conveys the techniques that can be applied to obtain low decarburization in leaf spring manufacturing, and the improvements achieved through optimization of high temperature treatment times of materials through use of thermographic survey at heat treatment furnaces.

The leaf spring manufacturer must supply high quality raw material at required strength for ensuring endurance rig tests. It's very important to maintain both inside and surface cleanliness of raw material. This study presents micro crack effects on material surface by evaluating residual stress values. Residual stress values on leaf springs are measured with X-ray diffractometer and different residual stress values are classified on the same raw material batch which have also the same material failures. Finally, micro cracks are measured in metrics. Micro crack standardization is performed considering the residual stress values and rig tests. The outputs in metrics which correlated with endurance rig tests can be taken as reference by the manufacturers of leaf spring and original equipment manufacturers.

In addition to providing a wide product range and meeting individual requirements of the customers to make the companies able to orient themselves to the competitive conditions in the automotive industry, properly structuring a capacity-productivity calculation algorithm is of a great importance in obtaining a competitive price advantage. In cases product diversity is too wide, and finished products cannot be measured with a single unit, measuring the production efficiency gets complicated. In addition, the ability to analyze all the inputs and outputs of the production with a single unit based on the same value for enterprises instead of analysis of combined units carried out based on a single perspective when calculating the production efficiency of the enterprises underlies continuous improvement and being able to set goals for the processes.

The main reason for the definition of leaf springs as safety parts is that even the smallest mistake in its functioning can cause severe accidents. It is imperative to ensure the endurance of leaf springs under high deformation and stress. In this reference study, we examine deviations resulting from production and design variations known as” noise factor” which can affect the fatigue life of a parabolic leaf spring. It will be a mistake to evaluate the design roughly with the stress levels on the layer. It has been described in this study with relevant examples that the leaf spring with 1550 N/mm2 tensile strength may be broken under much lower stress levels if it is exposed to dynamic loads.

Parabolic leaf springs are used as safety parts in heavy/ light commercial vehicles. When designing leaf springs, one must complete the evaluation from the perspectives of fatigue life and durability in order to ensure optimization of the design. After the initial design, rather than trying to establish optimization by producing prototypes by trial and error method, using the virtual prototype process to achieve design optimization, thereby reducing the costs will offer competitive advantage for both suppliers and original equipment manufacturers in the global market. In a reference study carried out in a partnership with Ford Otosan, the finite element methodology was used to verify the design of a 4- layered parabolic leaf spring and a multi-parabolic spring designed as its alternative. The stress distribution on layers during vertical, loaded and windup moment was examined.

It has been a significant challenge to reduce weights of the vehicles to satisfy the regulations that require development of environmentally-safe vehicles with low CO2 emissions. The conventional leaf springs, designed for the optimized performance together with safety factors, are made of steel. However, it is considered that the steel leaf springs are replaced by lighter ones in order to fulfill the specified requirements. Fiber reinforced composite materials with polymer based matrix offer a great potential for manufacturing leaf springs with lightweight, high mechanical and fatigue performance. Therefore, leaf spring manufacturers have great interest in those materials to replace steel parts with the composite ones and an increasing number of studies have been published in the literature in recent years. In this study, fiber reinforced composite compared with steel leaf springs based on endurance rig tests will be presented.

Leaf springs are mainly used for absorbing energy associated with road outputs and they release energy coming from the road. If the complete leaf stiffness and each leaf stress distribution can be calculated carefully, while ensuring safety, required ride comfort will also be maintained. The desired vehicle ride height (attitude) under load must be taken into consideration during calculations of leaf spring design. In addition to providing the loads coming from the vehicle, leaf springs are significantly controllers of windup effects. Braking windup causes rotation at the lateral axis. When vertical F jounce load and braking moment are applied to the leaf spring simultaneously, von misses stress value on leafs will increase to a higher level which is very close to and sometimes higher than the tensile strength. The designers must ensure safety and endurance for any case during working conditions. The most critical point is front axle windup stopper position.

Parabolic leaf springs are safety components on the suspension system. They provide ride comfort due to calculated stiffness characteristics and they absorb and release energy associated with the road outputs of a fully loaded vehicle. Leaf springs determine the desired vehicle ride height from the ground. As a critical safety part, leaf spring endurance must be ensured. Conventional leaf springs, multi-parabolic leaf springs and parabolic leaf springs are the general types in use. The most commonly used type of leaf spring is the parabolic leaf spring. The main advantages of parabolic leaf springs are that they are lighter, cheaper, with fatigue advantages, and they isolate more noise. Classical leaf spring design and prototype process methodology consists of fatigue tests repeated for each case considering different geometry alternatives, leaf layer additions, material and suspension hard points improvements. This methodology takes a long time and requires a significant budget.

The parabolic leaf spring plays a vital role in suspension systems, since it has an effect on ride comfort and vehicle dynamics. Primarily, leaf spring endurance must be ensured. Presently, there are two approaches to designing a leaf spring. In the traditional method, fatigue tests should be repeated for each case, considering different material, geometry and suspension hard points. However, it takes a long time and requires a heavy budget to get the optimized solution. In the contemporary method, a numerical approach is used to obtain the fatigue life and the leaf geometry against the environmental condition on the basis of material properties. This paper presents a more precise method based on non-linear finite element solutions by evaluating the effects of the production parameters, the geometrical tolerances and the variations in the characteristics of the material.