Designing of a Twin Tube Shock Absorber: A Study in Reverse Engineering

Introduction

With ever shortening lead times and the demand for accuracy of designs and manufacture, the path of least resistance for the redesign of a product is that of reverse engineering. As innocuous as it may seem, the term reverse engineering in itself encompasses multiple fields and specializations. It involves the reproduction of anything based on extracted information (Chikofsky & Cross, 1990; Eilam & Eldad, 2005). It has proved to be one of the best methods for data acquisition for the purpose of redesigning any product. It has come to be considered one of the technologies that have been able to provide business benefits by enabling a shorter product development cycle (Raja, 2008).

The demand for higher quality standards in the automotive industry has created the need for higher performance of shock absorbers. Noise reduction and vibration damping have become the thrust areas for designs.

Figures 1(a) and 1(b) show the designs of modern shock absorbers.

Figure 1.

(a) Mono tube shock absorber; (b) twin tube shock absorber

PartInfo.co.uk, n.d.

The function of the shock absorber is often misconstrued to be the absorption of vibrations in the system. However that job is done by the spring. The shock absorber provides the damping force necessary to dissipate the energy absorbed by the spring while neutralizing the original shock.

Brief Background

The design, manufacture, assembly and maintenance of products, systems or both, is the essence of the engineering process. In the pursuit of these goals, who paths are generally available to engineers: forward engineering and reverse engineering. The progression from high level abstractions and logical designs to the physical implementation of the system is termed as forward engineering. However, in certain scenarios, the physical product/system may be available readily, albeit without the accompanying technical details such as design specifications, drawings, etc. The reproduction of the part or system in such cases, in the absence of technical specifications is known as reverse engineering. The process of obtaining a geometric CAD model from 3-D points acquired by scanning or digitizing the extant system can also be called Reverse Engineering (RE).

Often defined by researchers according to their specific task, the process of digitally capturing the physical entities of a component is most commonly referred to as reverse engineering (Motavalli & Shamsaasef, 1996). RE has also been described as, “the basic concept of producing a part based on an original or physical model without the use of an engineering drawing” (Abella et al., 1994).

The mono-tube shock absorber presents a shorter stroke length due to the gas charge at the end. Hence it is most appropriate for surfaces which are relatively smooth. Motor sports such as Formula racing present such surfaces. Hence the mono-tube design finds widespread application in racing and associated motorsports. The twin tube design on the other hand provides greater stroke length. This enables the vehicle to accommodate larger bumps and allows the vehicle to navigate rougher surfaces. Therefore production cars and off-road vehicles use the twin-tube design.

Performance optimization of production cars has become a major thrust area for research and development. Despite the advances made in the field, the surface has barely been scratched. The potential for development in the field is still mostly untapped. With diminishing fossil fuel reserves and increasing global carbon footprint coupled with ever increasing quality of life and economic development, the need to improve the performance characteristics such as fuel efficiency is a persistent and major challenge, especially in the Indian Subcontinent given that the suspension system of a vehicle affects its fuel economy (United States Environmental Protection Agency, 1980; Gyenes & Mitchell, 1994). Hence optimization of performance characteristics of suspension elements is required.