Design and Analysis of Arc Springs used in Dual Mass Flywheel

Transcription

1 Volume-2, Issue-1, January-February, 2014, pp , IASTER Online: , Print: Design and Analysis of Arc Springs used in Dual Mass Flywheel ABSTRACT 1 Govinda, A, 2 Dr. Annamalai, K 1 M-Tech CAD-CAM, SMBS, VIT University, Chennai, India 2 Professor, SMBS, VIT University, Chennai, India Dual mass flywheel is a multi-clutch device which is used to dampen vibration that occurs due to the slight twist in the crankshaft during the power stroke. The torsional frequency is defined as the rate at which the torsional vibration occurs. When the torsional frequency of the crankshaft is equal to the transaxles torsional frequency an effect known as the torsional resonance occurs. When the operating speed of the engine is low, vibration occurs due to the torsional resonance and this can be avoided using dual mass flywheel. This work is carried out to study the effect of arc springs on the dual mass flywheel. The main aim is to increase durability of the arc spring and to elimination of gear rattle. A three dimensional model of a single arc spring, hard-soft spring combination and single mass with arc springs are optimized by modal analysis and fatigue analysis using ANSYS. Keywords: Dual Mass Flywheel, Arc Spring, Torsional Resonance and Torsional Frequency. 1. INTRODUCTION The recent development in the automotive sector is diminishing due to the demand by the automotive industry for saving cost during the increase in the research and development phase. This means very less experimental automotive vehicles are built and studied. In the development of Dual mass flywheel (DMF), the practical studies for vehicle testing are continuously decreasing, giving importance to simulation. Dual mass flywheel is a multi-clutch device which is used to dampen vibration that occurs due to the slight twist in the crankshaft during the power stroke. The torsional frequency is defined as the rate at which the torsional vibration occurs. When the torsional frequency of the crankshaft is equal to the transaxles torsional frequency an effect known as the torsional resonance occurs. The vibration caused by the torsional resonance when the operating speed of the engine is low can be avoided using dual mass flywheel. This work is carried out to study the effect of arc springs on the dual mass flywheel, a three dimensional model of a single arc spring, two arc springs with different stiffness and single mass with arc springs are optimized using ANSYS. The simulation of fatigue analysis is also performed using ANSYS. Dual mass flywheel has two important vibrational modes. The first mode which gets excited by a driver-induced load change, with natural frequency between 2 and 10 Hz. Hence by eliminating the gear rattle [1]. Six arc helix springs is designed in a dual mass flywheel and evaluated. It was observed that the resonance is avoided between the transmission and engine and the reduction in the vibration effect [2] Advantages of DMF are:- Reduced drivetrain noise Less synchronizer wear At low engine operating speeds fuel is saved Reduced emissions and Reduced shifting frequency 35

2 Evaluating a linear torque observer by considering both centrifugal force and redirectional force which acts radially on the arc spring used in dual mass flywheel, resulting in oscillation dampening at low engine speed [3]. The fatigue analysis of the spring materials are carried with four approaches and Soderberg s approach is found out to give better results for the analysis of life data for springs [4]. The fatigue strength of 60Si2MnA spring steel has been evaluated experimentally and tabulated. The durability for double stage springs is lower than for single stage ones. This must be caused by an increase in stress by a rise in tension or compression forces, while wear has not occurred [5]. Currently the DMF with single arc spring used in most of the vehicles was introduced by LUK, a Germany company, is most popular in the design technology of DMF. Determination of vibrational characteristics of a designed structure is a important process this is done by considering the modal analysis [6]. 2. METHODOLOGY 2.1 Materials and Properties The material used in this investigation is 60Si2MnA spring steel. Design parameters of 60Si2MnA spring steel used in this work are tabulated depending upon the type of engine and clutched installed table1. For hard spring the hardness is 57HRC and when subjected to a load of 1000N the strain was found to be less than zero. For soft spring the hardness is 45HRC and when subjected to same load as of hard spring the strain was found to be greater than zero. Table 1. Design Parameters Parameter Magnitude Spring length 155 Number of coils 15 spring mass 0.5kg Co-efficient of friction 0.1 Spring radius 0.15m Angular spring stiffness 6.5 (Nm/rad) The Material property of 60Si2MnA used for spring is tabulated in table2: 2.2 Modelling Table 2. Material Property Parameter Value Material selected-steel 60Si2MnA Young s modulus, E 210 GPa Poisson s Ratio Ultimate Tensile Strength 410 MPa-460 MPa Tensile strength Yield 250 MPa-300 MPa Density Kg/mm 3 Behaviour Isotropic Form the above given specification of the spring, a three dimensional model of the following arrangement was modelled using solid works: Single arc spring, Single mass with arc springs and Two arc springs with different stiffness. 36

3 The arc spring is mounted on the primary flywheel of the dual mass flywheel and the torque is applied by the secondary flywheel on one end of the spring. The other end of the spring is fixed. After modelling of the above given arrangement of springs with given specifications it is subjected to analysis. These models are then imported into Ansys 12 for conducting modal and fatigue analysis. The Analysis involves the following discretization called meshing, boundary conditions and loading. Fig. 1Single Arc Spring Fig. 2 Single Mass With Arc Springs HARD SPRING SOFT SPRING 2.3 Meshing of the Spring Model Fig.3Two Arc Springs With Different Stiffness Meshing is one of the most vital aspects of computer-aided engineering simulation process. Mesh generation involves division of the entire of model into small pieces called discretization. Meshing for the hard and soft spring is done (Fig4). It is convenient to select the free mesh because the spring has curves, so that shape of the object will not alter. Fine mesh is created with 8533 nodes and 1998 elements. After meshing is done the contacts and targets must be defined in between individual springs. 2.4 Boundary Conditions Fig.4 Meshing of Hard Spring and Soft Spring The arc spring is mounted on the primary flywheel of the dual mass flywheel and the torque of 150 Newton-meter (Nm) is applied by the secondary flywheel on one end of the spring by considering the co-efficient of friction to be 0.1 and the other end of the spring is fixed (Fig5). TR=FR*r Where TR is the torque and FR is the force applied by the secondary flywheel on the arc-spring with radius r. 37

4 Now with considering the co-efficient of friction: T (A, fric) = µ*fr*r Where T (A, fric) is the torque with considering the co-efficient of friction. Therefore the force to be applied becomes 1000 N. 2.5 Modal Analysis Fig.5 Boundary Condition Estimation of vibrational characteristics of a designed structure is an important process this is done by considering the modal analysis (Fig6). The main aim of a modal analysis is determining the natural frequencies and mode shapes. In this paper, the obtained harmonic analysis gives the natural frequencies and mode shapes for designed structurethe method to quantify the degree of importance of the attributes. 2.6 Fatigue Analysis Fig.6 The Typical Block Diagram for the Modal Analysis Fatigue analysis is done to know whether the spring model is susceptible to fatigue damage when subjected to cyclic loading and unloading. Many factors influence fatigue failure which is a complex and progressive form of local damage such as magnitude and frequency of the loads causing the fluctuating stress and environmental condition 3. RESULTS AND DISCUSSION The material considered for this investigation is 60Si2MnA spring steel. The modal analysis and fatigue analysis were conducted and tabulated 38

5 3.1 Modal Analysis Modal analysis was conducted on all the three spring arrangements by applying the load. The modal shapes and their respective natural frequency of the six harmonics is tabulated (table3). The modal shapes of the arrangement of hard spring and soft spring is shown below (fig7-fig12): Fig.7 1 st Mode Shape Fig.82 nd Mode Shape Fig.9 3 rd Mode Shape Fig.104 th Mode Shape Fig.115 th Mode Shape Fig.126 th Mode Shape Mode No. TABLE 3. Natural Frequencies For The Three Arrangements Single spring Natural frequency [Hz] Single mass with two arc springs Hard and soft spring

6 From the above table it is observed that the natural frequency of the first mode which gets excited by a driver-induced load change for the single spring and hard-soft spring combination is found to be Hz and Hz respectively. The above mentioned natural frequency of the first node is below the operating frequency (10 Hz). Hence the torsional resonance doesn t occur. The second mode, where the typical cause of the gear rattle is observed in the single spring and this occurs due to the natural frequency is Hz which lies between 40 Hz-80 Hz. Whereas in the hard-soft spring combination the natural frequency in second mode is Hz which is less than 40 Hz. The first mode of the spring mass system with natural frequency of Hz which is above the frequency of operating speed of the system. Hence torsional resonance occurs. 3.2 Fatigue Analysis Fatigue analysis is conducted for all the three arrangements namely Single arc spring (fig13), Single mass with arc springs (fig14) and the hard-soft spring combination (fig 15) using Soderberg s approach (fig16) and by applying a load of 1000N. It is observed that the durability of the single spring is less as the maximum value of the life 1*106 cycles which is represented in blue colour in life data figure is less. Whereas in spring mass system, red coloured region is greater. Hence it has a shorter life time compared to other arrangements. Fig.13 Life data of single springs with load of 1000N using Soderberg s approach Fig.14 Life data of mass-spring system with load of 1000N using Soderberg s approach Fig.15 Life data of hard-soft spring with load of 1000N using Soderberg s approach Fig.16 Soderberg s approach The durability of the hard-soft spring is more as the maximum value of the life 1*106 cycles which is represented in blue colour in life data figure is more 40

7 4. CONCLUSIONS Dual mass flywheel is a device which is used to dampen vibration that occurs at low speed. In this paper, a three dimensional model of a single arc spring, hard-soft spring combination and single mass with arc springs are optimized by modal analysis and fatigue analysis. From the modal analysis it was found that the torsional resonance doesn t occur in the single arc-spring and hard-soft spring combination. The overall conclusion of this study is that the high durability of the arc spring used in dual mass flywheel can be obtained and the elimination of gear rattle is achieved by using hardsoft spring combination. The effect of arc springs plays major role in the design of dual mass flywheel. 5. ACKNOWLEDGEMENT First author is thankful tomr A.S. Anantha Padmanabha, DGM, Mecon Limited for constant support and encouragementto publish this work. The first author is also thankful tomr. Kannan.S, Assistant Professor, SMBS, VIT Chennai for his constant help and encouragement to publish this work. REFERENCES [1] Dr.-lng. Albert Albers, Advanced Development of Dual Mass Flywheel (DMFW) Design - Noise Control for Today's Automobiles, LuK-Symposium. [2] Demin Chen, Yueyin Ma, Wei Sun, Xiaolin, Xaofei Shi, Research of Design and Vibration Reduction of Dual Mass Flywheel with Arc Helix Spring, International Conference on Electronic and Mechanical Engineering and Information Technology., vol. 11., 2011, [3] Ulf Schaper, Oliver Sawodny, Tobias Mahl and Uti Blessing, Modeling and Torque estimation of an automobile Dual Mass Flywheel, American Control Conference, vol. 09., Hyatt Regency Riverfront, St. Louis, MO, USA:, 2009, [4] Suprith.N,. Annamalai.K,Design and Analysis of Automotive Multi-Leaf springs using composite materials, Applied mechanics and materials, vol372, 2013, [5] Christophe De Metsenaere, Fracture Analysis of Dual Mass Flywheel Arc Springs, LuK GmbH & Co. de Metsenaere Christophe I EZV, vol. 78, 2002,1-42. [6] Oday I. Abdullah, Josef Schlattmann, Vibration Analysis of the Friction clutch Disc Using Finite Element Method, Advances in Mechanical Engineering and its Applications (AMEA), Vol. 1, No. 4 World Science Publisher, United States:, 2012,