DESIGN OPTIMIZATION OF CLUTCH DISC

Abstract

Clutch disc is an essential component of approximately all the mechanical system. It is majorly used in automotive vehicles. The automotive industry has share of 5.6% in GDP and producing about Rs. 8 billion as tax. Original Equipment Manufacturer (OEM) includes Toyota, Honda, Suzuki and Nissan use about 50% local components of a vehicle which are later on assembled in Pakistan. This usage was 70% but due to deletion policy, it is reduced to 50%. The main flaw in the components is lack of functionality and non-optimized design. The clutch system is consist of axial cushion which is sandwiched between friction linings and is present between flywheel (driving end) and pressure plate (driven end). The torque produced by the engine (flywheel) is transmitted to wheels (pressure plate) through clutch disc, hence this component plays a vital role is deciding the efficiency of an automotive vehicle. The objective of the research is to optimize a clutch disc under certain constraint to maximize the efficiency and life of a friction lining of clutch disc by varying design parameters like inner radius, outer radius and thickness of friction lining as well as by using more suitable friction lining materials like S2 glass fibre, carbon – carbon composite and aluminium metal matrix composite. The research is carried out by making benchmark material as asbestos which is mostly used in under developed countries but is about to ban in developed countries due to its hazardous effects on health. Hence, it is a necessity to search for alternate materials for friction lining. The design parameters are standardized on the basis of research paper of O. I. Abdullah and J. Schlattmann namely "Contact Analysis of a Dry Friction Clutch System". The problem is formulated mathematically and analyzed numerically in commercial finite element package. Since the friction linings slip against flywheel and pressure plate which - 4 - generates heat energy during the engagement/disengagement that rises the temperature at the friction lining and flywheel/pressure plate interaction. This causes thermal stress, thermal cracking and wear and tear of friction. The life and efficiency of clutch disc vastly depends upon this heat generation and dissipation. On the other side, pressure is applied on pressure plate to make it stick with flywheel that also results in stress and penetration. To analyze above mentioned effects, the clutch system is designed including flywheel and pressure plate and is analyzed numerically in commercial finite element package ANSYS. The transient thermal analysis is carried out to evaluate heat dissipation and temperature rise on the interface of contacting surfaces followed by transient structural analysis to view the deformations and stresses. The structural analysis is further extended to determine the contacting parameters like frictional pressure, penetration (wear), stress and sliding distance. To ensure the life of the clutch disc, fatigue analysis is performed. These analyses are executed for each alternate friction lining material. After simulating the clutch system thermally and structurally, the next task is to optimize the clutch system. To fulfill optimization, three design variables inner radius, outer radius and thickness of friction lining are considered and Design of Experiment (DoE) is carried out to get design points using standard Central Composite Design technique. The DoE table consists of 15 design points with all the input and output parameters is observed. The behavior of output parameters as varying the input parameters is obtained by Response Surface Methodology which gives response on the basis on DoE. The objective function is made as to minimize all the output parameters subject to changing in the input parameters under the specified limits and the candidate points are selected. The best candidate point after Response Surface Optimization is selected as optimized design point.