The multi body systems approach

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INTRODUCTION:

The purpose of suspension system is to reduce the vertical wheel load variations and isolation of road inputs from the body. The suspension geometry is the broad subject of how the unsprung mass of the vehicle is connected to the sprung mass. The angular relationship between the suspension, steering linkage and the wheels is known as Suspension Geometry. Suspension connections dictate the path of relative motion and control the forces that are transmitted between them. A particular geometry must be designed to meet the needs of particular vehicle for which it is to be applied. The research for this project is subjected to be fallen to areas of suspension geometry characteristics, the multi body simulation techniques and ADAMS program.

Evolution of suspension systems and their different types are well researched in order to gain a basic understanding for this project. Designing of suspension and mounting the suspension points on frame are critical to proper vehicle handling. The suspension characteristics such as camber angle, half track change, castor angle etc are thoroughly investigated to observe the influence of their settings for different applications of the vehicle. The behavior of the suspension linkages under cornering, braking and extreme load conditions has been studied from [1],[3] and [5] and these observations helps in design study of the suspension system to make changes to the geometric set up.

The usage of multi body dynamic package for the enhancement of vehicle dynamics particularly the design of suspension systems has given a better understanding from the published technical papers. The Multi body Dynamic Simulations and their development has given new opportunities in terms of simulations and analysis.

The ADAMS Program is used for modeling and analyzing the front and rear suspension systems. Advantages of the ADAMS tools encourage the suspension system to be modeled within different types of links, joints, primitives etc. by which the suspension characteristics are observed. From the graphical output and animations, a clear understanding of the suspension system under bump and rebound conditions can be analyzed. A research into the published papers where ADAMS used for the analysis of suspension systems helps in design study and optimization techniques of this package. For improving the suspension characteristics such as camber, castor, steer angle etc under bump and rebound effects, geometric changes to the model are made and validated.

DEFINITIONS:

  1. SPRUNG MASS: The mass supported by the suspension spring such as vehicle body, engine, space frame etc.
  2. UNSPRUNG MASS: The mass which is not supported by the suspension spring such as wheel, brakes, hub and bearings etc.
  3. WHEEL BASE: The distance between centre of front axle and centre of rear axle.
  4. TRACK WIDTH: The distance between right and left wheel centre lines.

LITERATURE REVIEW:

BACK GROUND:

Principle requirements of a suspension system are

  1. Good ride and handling performance - the suspension system should have vertical compliance providing chassis isolation and it should always ensure that the wheel follows the road profile with a little tire road fluctuations.
  2. Maintaining steering control during manoeuvring - the position of the wheels should be maintained in the proper positional attitude with respect to the road surface.
  3. Isolation from high frequency vibrations which arises from the tire excitations - the suspension joints should have appropriate isolation for preventing the transmission of road noise to the vehicle body.
  4. Favorable response of the vehicle for controlling the forces produced by the tires such as longitudinal braking accelerating forces lateral cornering forces, braking and accelerating torques. This can be achieved by designing the suspension geometry to resist squat, dive and roll of the vehicle body.

BASIC PARTS OF A SUSPENSION SYSTEM:

Springs makes a major role in a suspension system which provides a ride comfort. Struts and shock absorbers together contribute to control how fast the spring and suspension are allowed to move, by keeping tires in firm contact with the road surface.

  1. Springs
  2. Shock absorbers
  3. Struts
  4. tires

SPRINGS:

Springs are generally used in various applications. A good suspension system depends on springs used in it. When the vehicle comes over a bump, the tires which are in contact with the road reacts to the bump and they are forced to move in any direction (vertical, sideways). Then the spring takes that energy in the form of kinematic energy and stores it in its number of coils. Different types of springs have different capacities to store energy at the same stress levels. The performance characteristics and relative fatigue life depends on this capacity value. The spring energy is converted into heat and dissipated partly by the friction in the system and mostly by the shock absorbers.

Types of springs used in various suspension systems

  1. Coil springs
  2. Leaf springs
  3. Air springs
  4. Torsion bars

Coil Springs: A number of coils which are in uniform size serve a coil spring almost entirely made of round section wire. The diameter and length of the wire determine the strength of the spring. Increasing the diameter of the wire results for a strong spring and increasing the length results for a more flexible spring. For a given load, outside diameter and compressed length a coil spring has the minimum stress when the inner coil spaces minimal.

Leaf Springs are firstly used in horse drawn vehicles for avoiding the bumps and uneven surfaces on the road which serves as a suspension system. This kind of springs consists of several layers of metal called leaves; all these are put together in an order to act as a single unit. This type of springs is used in 1985 automobiles and also these can be seen in most trucks and heavy duty vehicles.

Torsion Bars are operated directly by one of the suspension arms whose sole purpose is to twist the torsion bar. One end of the bar is attached to frame of vehicle and the other end is fixed to the wish bone which is like a perpendicular to the torsion bar. When the vehicle hits any bumps the vertical force is transferred to the wishbone, through the levering action it reaches torsion bar. The torsion bar then twists about its own axis to provide spring force. Through 1950 -1960s this kind of system is used.

SHOCK ABSORBERS (DAMPERS):

The dampening exists in three forms: Friction, viscous and due to the presence of air. The shock absorber restraints the undesirable bounce characteristics of the sprung vehicle mass and also restraints the wheel assembly from losing its contact with the road surface by excitations at its natural vibration frequency. In the form of pistons working in a cylinder filled with hydraulic fluid, shock absorbers exert a force which is proportional to the square of the piston velocity.

If the vehicle is without shock absorbers then the drive will be like a boat (swinging). Shock absorbers make sure that the bouncing effect is not reached to the vehicle chassis and also they keep the full suspension at all the road conditions. Shock absorbers, as fast as they work (move) there is a better resistance for the movement of the vehicle.Types of shock absorbers used for suspension system:

  1. Oil filled
  2. Reservoir
  3. Gas charged

STRUTS:

Struts are generally preferred for wishbones because of their ability to spread the load inputs to the body effectively, eliminating the need in most cases for a heavy sub frame to achieve acceptable insulation from noise, vibration and harshness. Common forms of struts:

  1. Centre sleeve
  2. Spacer bushing
  3. Inner plane

TIRES:

Tires are most commonly known as air springs which support the total weight of the vehicle.

Size of the tire, construction, compound and inflation influences the ride quality of the vehicle.

Types of tires:

  • Radial ply, bias ply and bias belted

TYPES OF SUSPENSION SYSTEM:

  • DEPENDANT SUSPENSION SYSTEM: It normally has a simple beam axle which holds wheel parallel to each other and perpendicular to the axle. Dependent suspension systems are classified by the system of linkages used for locating them in transverse and longitudinal directions.

A typical solid axle suspension with coil springs

If the camber of one wheel changes, then the camber of the opposite wheel changes automatically. Most commonly used suspensions with straight line motion are watts suspension with pan hard arm, Robert suspension, De Dion Suspension and solid axle

INDEPENDENT SUSPENSION SYSTEM: It allows wheel to rise and fall on its own without affecting the opposite wheel. The main advantage of the independent suspension system is when the wheel undergoes any bump, only that wheel affected. All passenger cars and light truck uses independent front suspensions because of the advantages in providing room for the engine and there resistance to steering vibrations.

A typical Macpherson Independent suspension

Independent suspension system provides inherently high roll stiffness relative to the vehicle spring rate. Further Advantages: Easy control of the roll centre by choice of the geometry of the control arms, the ability to control the tread change with jounce and rebound, larger suspension deflections.

FRONT SUSPENSIONS:

Over the years many types of front suspensions have evolved in which beam type axles with steering via kingpin at each end of the axle, the parallel trailing arm type, the morgan sliding pillar type are included. In the recent years, the front suspension design has come down to two types.

  1. Macpherson Strut
  2. Short-Long Arm (SLA)

The basic principle of operation for these two types is same. As the strut merely gives motion equivalent to an arm of infinite radius whose centre lines lies on a line which is perpendicular to strut and starting from strut top anchorage pivot point.

FRONT SUSPENSION DESIGN ISSUES:

The following requirements establish a good Front Suspension Unit.

  • The suspension unit should allow the roll centre height to be arranged at a desired level.
  • It must allow anti-brake dive geometry to be incorporates if it is required
  • It should be possible to allow telescopic dampers, anti roll bar to be incorporated.
  • For each wheel knuckle, allowance for cross steering connections to be made which induce minimal variation of toe settings with vertical wheel movement
  • It should withstand all the forces induced on it by braking, accelerating or cornering with an ability of isolating the body structure from noise, vibration and harshness.
  • It should restrict and do not allow the inertia, gyroscopic or any other forces generated by the vertical movement of the tires.

MACPHERSON STRUTS:

It is named after a Ford suspension engineer called Earle S. Macpherson in 1940 from America who gave the idea of locating the lower end of an inclined strut system by means of the anti-roll bar link. It was introduced in 1950 English Ford and there after it has become one of predominate suspension systems in the world.

A Macpherson Strut is kinematically a slider mechanism equal to an A-arm which is infinitely long at right angles to the slider travel. It has the chassis as the ground link and the coupler as the wheel carrying link. The strut allows considerable design flexibility with a significant advantage that a front sub-frame is not usually required to ensure adequate close tolerance for the location points. The forces in the wheel introduce a bending moment in the shock absorber structure which is restricted by the reaction forces in the upper and lower mountings.

CONSTRUCTION: It is based on an outer tube which is fixed to the hub carrier at its lower end and welded to a seating cup for the suspension spring at its upper end. Inside the tube a telescopic damper with its piston road attached to a thrust bearing in the centre of a turret formed in the inner wheel arch area of the car body, which also carries as the upper spring seat. The location of the lower end of the strut is triangulated by a track control arm and a tie bar. The major compromise of the strut type suspension system is the long upper arm which yields a camber curve which loses rather than gains negative camber in a bump.

The advantages of Macpherson strut are its simple design with fewer components, widely spaced anchor points which reduced loads and efficient packaging.

The upper strut to body mounting point is a point about which the strut rotates in all the directions and is fixed from translating in any direction. For race cars, it is a spherical type mounting. Under light load conditions, the Macpherson strut suffers from the stickiness in the sliding motion of the strut because of the togetherness of cylinder rod bearing and damper piston.

There are two ways for reducing the friction between the inner and outer sliding members:

  1. Under normal straight ahead driving, eliminating the bending moment on the strut.
  2. By facing the bearing surfaces with impregnated poly tetra-fluorethytene which provides low coefficient of friction for the rubber pairs. This process is known as Stiction.

The disadvantage with Macpherson Strut is that the wheel movement and body roll leads to variations in camber angle and also it limits the designers to lower the hood height because of the high installed height, which is not desirable for sports cars' styling.

SLA Front Suspension:

This type of suspension system is suitable for front engine, rear wheel drive cars as the suspension provides package space for the engine oriented in the longitudinal direction. Double wishbone suspension system is the most common and reliable form of this type. The upper and lower arm (A-shaped arms) of unequal length can be used according to the type of the vehicle.

REAR SUSPENSION:

Basis categories of rear suspension are

  • Live axles with final drive and differential incorporated.
  • Dead axles
  • Independent rear suspension
  1. Trailing arms
  2. Macpherson Struts
  3. Short-Long Arms (SLA) etc.

LIVE AXLES:

For many decades the rear live axle was a universal design which proved cheap, robust and very efficient. The main disadvantage is the fairly considerable extra unsprung mass because of the final drive and differential and its enclosure. Also part of the propeller shaft taking the drive to the axle. When it is transmitting high torque, this unsprung mass compromised the ride quality and made the rear axle more prone to hop and tramp.

DEAD AXLES:

The dead axles are in form of either back end of a front driven car or as the embodiment of a de Dion axle with rear driven wheels and a frame mounted final drive and differential. The rear dead axle is simple light weight tubular assembly which locates undriven rear wheels with a constant track. As it has no complication of a drive system, the design and manufacturing is simple and cheaper than a rear live axle comparatively. Dead axle has instantaneous linkage centre which can completely avoid lifting if the vehicle back under braking by using a three or four link control system (also by a torque arm each side). The main types of sideways location are Panhard rod and Watt linkage.

The torque arm location each side ways can be used with a tubular axle beam which has a rotationally free joint somewhere along its length for avoiding the suspension being stiff in roll.

A beam of channel section which is flexible in torsion also extremely stiff in bending and compression can be used to produce a camber on both wheel in roll.

INDEPENDENT REAR SUSPENSION:

The simplest kind of independent rear suspension system is the swing axle.

TRAILING ARMS:

It a very simple and economic design hinge mechanism based suspension type. The wheel is attached to trailing end of an arm which pivots with relative to the sprung mass by using two bushings. The axis of these bushings is perpendicular to the centre line of the vehicle and also parallel to the ground by which it forms instant axis of the suspension. Cornering forces causes bushings and arm deflections, which produces toe-out known to be oversteer effect. Arm serves as the only link used in this suspension, so heavy structural requirement for the arm must be strong in bending in all directions to resist braking torque, camber torque and steer direction torques.

SEMI TRAILING ARM:

For several decades, semi trailing design successfully applied to a series of rear wheel drive vehicles. Semi trailing arm suspension is a compromise between the swing arm and trailing arm suspensions. The joint axis can have any angle; however an angle not too far from 45 deg is more applied. These can handle both lateral and longitudinal forces with an acceptable change in the camber angle.

In this type of suspension, the instant centre is fixed relative to the vehicle by which the camber change is constant with the wheel travel.

The camber change is a straight line and toe change is a curved line for this suspension, which is exactly the opposite in the case of good suspension.

Swing axle is a form of semi trailing arm suspension. It has a very high roll centre, large camber change and severe toe in with wheel travel.

This type of suspension has large amount of jacking forces resulting from its high roll centre. The cornering force raises the back of the vehicle. Because of the large camber change with the wheel travel, the outside loaded tire goes toward positive camber.

It was firstly improved by Mercedes with their low pivot swing axle design.

WISH BONE AND STRUT- LINK TYPE REAR SUSPENSION:

These suspensions are generally regarded for their flexibility in achieving desired overall geometric parameters with the least amount of compromise. Double independent wishbones and multi link locations suspension system can be regarded as the same fundamental type where they provide total flexibility of the static geometry and geometry changes with wheel travel. Also, the possibility of full squat and lift compensation and their unsprung mass is relatively low, especially when component economies (where the drive shafts provides location of the wheel)

A arm and Toe link Strut:

Two versions of this rear suspension are

  1. Almost like a typical front suspension but with a fixed toe link to a chassis grounded pivot. The design is very flexible with good control over the side view geometry with excellent toe control capability.
  2. The toe link attaching back to the control arm rather than the chassis. This design eliminates one attachment at the chassis. It is possible to obtain required toe control with this type of suspension and all the remaining geometry requirements are similar to the first version. Reason for this type of suspension to be used is that the ride steer curve is less sensitive to build variations than with the standard toe link attached to the chassis.

VEHICLE AXIS SYSTEM:

  • It is a right handed orthogonal system. The X- axis is horizontal and forward in the direction of motion when the vehicle is moving in a straight line.
  • The Y axis is point towards the right side of the vehicle. It is horizontal and it is 90o to the X axis. The Z axis is horizontal and positive downwards. It is exactly perpendicular to both X and Y axis. This axis system is followed throughout the suspension system design and analysis.

    SUSPENSION CHARACTERISTICS:

    The performance of the suspension system is highly dependent on its settings

    1. SLIP ANGLE: The angular deflection between the direction in which the tire is pointing and the direction in which the tire contact patch is travelling is known as Slip angle.
    2. CAMBER ANGLE: It is positive when the top of the wheel out in and negative when the top leans in. Under the geometry influences of wheel travel, the camber angle changes slightly. Camber angle affects the balance of cornering power, pressure distribution of the tire footprint on the road and handling characteristics.
    3. To achieve maximum traction and cornering power, vehicle with wide tires should run with low camber angles on their driving wheels. Excessive camber causes abnormal wear on the outer edge of the tire and excessive negative camber causes abnormal wear on the inner edge of the tire.

    4. STEERING ROLL RADIUS AND STEERING AXIS INCLINATION: The distance between the point of contact of the projected line drawn through the steering axis to the road surface and centre point of the tire contact area on to the road surface, is known as the steering offset. The distance between these two lines is called as the roll radius.
    5. If the steering axis line is outside of the tire centre line then a positive roll radius exists and if the steering axis line is outside of the tire centre line a negative roll radius exists.

      The stability during the braking is reduced when the steering roll radius is excessively positive. The directional stability is reduced when the steering roll radius is excessively negative. Improper tire and wheel combination influences the steering roll radius. The inward angle of the strut assembly with respect to a vertical line to the road surface is the Steering Axis Inclination.

      Bent strut and spindle assemblies are the most common causes of the incorrect steering axis inclination.

    6. TOE ANGLE: It is the angle between each wheel and the longitudinal axis of the vehicle. It is measured under static conditions by the difference in the distance between the front and rear edges of the left and right wheel rims at the centre line level.
    7. The amount of toe is expressed in degrees as the angle to which the wheels are out of parallel. Also as the difference between the track widths measured at the leading and trailing edges of tires. Tire wear, straight line stability and corner entry handling characteristics are the major areas affected by the Toe settings. Excessive toe in or toe out affects the tires to scrub as they are always turned relative to the direction of travel.

      The longitudinal and lateral compliance of the suspension and body often changes the toe setting. The amount of toe in or toe out given in a vehicle is dependent on the compliance of the suspension system and the desired handling characteristics.

    8. CASTOR ANGLE: The steered wheel is arranged to trail by a small angle by which the forward movement gives the stabilizing effect. This angle of trail is known as degree of castor. If the steering axis is tilted rearward it is known as Positive castor and the forward tilt is called as Negative castor. A positive castor increases stability at very high speeds and also causes increased steering effort even at low speeds.
    9. ROLL CENTRE: Under lateral cornering forces, the vehicle body rolls on its springs about centers at both ends of the vehicle. The line joining these two centers is known as Roll axis.
    10. ANTI DIVE: Under heavy braking and acceleration, for resisting front end (or rear end squat) dip, the suspension pivots are angled to provide upward reactions automatically in response to high wheel torque inputs.
    11. ANTI DIVE: The force that causes the front of the vehicle to drop down while breaking.
    12. INSTANT CENTRE: At a particular position of the linkage (instant), the projected imaginary point of that linkage at that instant is known as Instant Centre. It is a study of kinematics in two dimensions in a plane. For establishing motion relationship between two bodies, the instant centre is a convenient graphic aid.
    13. SCRUB RADIUS: The lateral distance between the point where the swivel axis of a steered wheel meets the ground and centre of the tire foot print is known as the offset. This offset is positive if the axis passes inside the footprint centre and it is negative if the axis passes outside the footprint centre.

    SUSPENSION KINEMATICS:

    The suspension kinematics is the study of motion without reference to mass and force. It describes the controlled orientation of wheels by the suspension links, by making assumptions of the rigid parts and also frictionless joints. By visualizing the attitude of the vehicle in a corner, the suspension design can be made to keep as much as the tire on the ground as possible,

    For a race car the kinematics, roll over, handling for the suspension design issues are discussed. The kinematic and dynamic analysis is performed by using the MBS and roll over, ride and handling are simulated and tuned on geometry, springs and dampers to achieve performance. The choice of camber gain, roll centre placement and scrub radius should be based on how the vehicle is expected to perform. By visualizing the attitude of the vehicle, the suspension design can be made to keep the tire as much as possible on to the road surface. This paper has concentrated on the design aspects and the test evaluation is agreed perfect with the simulation models. The computational tools have supplied the necessary support by which the sizing and design details occur in coherent form with engineering principles.

    [7]First stage of the suspension system design of any vehicle is to size the mechanism and ensuring that it is capable of fitting into the package envelope. If joint compliances are neglected, it can be simplified into pure kinematic problem and assumed to be 2 dimensional. By using graphical or computational methods a basic analysis can be performed.

    [2]The kinematic behavior of the suspension linkages is not obvious from its appearance and it is obvious far from it. A suspension system should incorporate a good kinematics design to keep the tire as perpendicular to the pavement as possible, optimal damping effect and spring rates to keep the tire to the road surface at all times. Also strong components which do not get deflected under the loads induced up on them.

    The amount of scrub must be kept small since it causes excessive cornering forces and it is desirable as it can provide feedback through the steering wheel for the driver. To reduce the scrub radius, King Pin Inclination can be incorporated into the suspension design only if the ball joint near the centre line of wheels is not feasible. With the positive castor the outside wheel in a corner will camber negatively which helps to offset the positive camber associated with KPI and body roll. Castor causes the wheel to rise or fall as it rotates about the steering axis where it transfers the weight diagonally across the chassis. It is more desirable to have the roll centre close to the round place in order to reduce the amount of chassis vertical movement due to the lateral forces. The roll centre is the instant centre which moves with the suspension travel, so the migration of the roll centre must be checked to ensure that the jacking forces overturning moments follow a relatively linear path for the predictable handling.

    [2] Presents an approach to suspension linkage design which avoids the geometry iteration process typically required to ensure specific kinematic behavior in the design condition. In [3] a methodology to calculate the suspension characteristics as the suspension moves between the bump and rebound positions are illustrated. This study based on the front double wishbone suspension of a passenger car where the suspension connections are considered as joints, linear or non linear bushes which establish the effects on suspension geometry changes during the vertical movement. The simulations results with measured suspension rig test data provided by the vehicle manufacturer are compared. The reaction forces at the bushes leads to distortions which produces the change in suspension geometry. This result confirms that the geometry changes are dependent on the position and orientation of the joints, and there will be little difference between the models using rigid joints, linear bushes and non linear bushes.

    [8] The suspension systems invariably exhibit asymmetric damping properties in compression and rebound. This study is conducted by using a kineto-dynamic quarter vehicle model consisting a double wishbone type suspension system.In [8] the influences of damper asymmetry together with the suspension kinematics and the tire lateral compliance on the dynamic responses of the vehicle are investigated analytically under bump and pothole excitations.

    SUSPENSOIN KINEMATICS THEORY:

    The wheel alignment to the vehicle is in complex manner, so in order to identify each and every element, a 3 dimensional approach makes it simpler by generating the simple kinematic equations. At the tire contact point all the external forces acts. These forces may include the influence of the wheel attitude. The co ordinates and angular positions of the wheel are so important in understanding the behavior of the wheel. Here the equations for calculating the suspension characteristics are briefly explained. The wheel centre is point M and the auxiliary fixed point H related to wheel carrier.

    USE OF MULTI BODY DYNAMICS SIMULATION:

    [3]Modern Multi Body Dynamics Analysis software allows describing the individual components of the mechanical systems and it will automatically calculate the contribution of them. The MBS is being an established tool for the virtual design of full vehicle behavior. The applications of MBS in an automotive industry are

    1. Calculation of suspension characteristics such as camber angle, steer angle and steer angle as a function of vertical movement of the suspension
    2. Full vehicle ride and handling simulations
    3. Prediction of joint and bush reaction forces for various loadcases at the tire to road surface contact patch.
    4. Advanced simulation of features such as Anti Lock Braking system,

    The MBS studies are valuable in providing guidance for suspension systems design and reduce product development cost and time. The calculations and assessment of the internal cross sectional forces of suspension components are enabled. The MBS techniques can be applied to the simulation of suspension kinematics and dynamics by offering the ability to model road loading and vehicle maneuvers with increasing accuracy.

    [7]The suspension system is a 3 dimensional mechanism and the analysis is complicated by the inclusion of many compliance bushes which results in links with variable links. The suspension system development is an iterative process, the parameters such as sprung and unsprung mass assumptions may change during the development process. The MDS models are useful for estimating the component specifications for any changes in the sprung mass assumptions. They also identify and optimize the important suspension component specification using DOE studies and decides the suspension component specifications for different value variants of the base vehicle.

    THE ADAMS PROGRAM:

    ADAMS (Automatic Dynamic Analysis of Mechanical Systems) is the most widely used multi body dynamics and motion analysis package which helps in understanding the dynamics of moving parts, distribution of loads and forces in the mechanical system, also to improve and optimize the performance of the system. ADAMS incorporates real physics by simultaneously solving the equations for kinematics, statics, quasi-static and dynamics. It enables to create and test virtual prototypes of mechanical systems in a fraction of time and cost required for physical build and test.

    There are four steps involved in ADAMS usage. In modeling, the decision for initiating the type of analysis and dividing the system in to different parts and type of joints can be done. Preprocessing is creating the input file from the data that is created in the modeling. In preprocessing, all the parts and points are to be clearly given according to the modeling data. Requesting different functions such as displacement between ant two points, measuring angle, etc can be associated. At analysis stage the system can be exposed to set of time and number of steps to be performed during analysis. In Post processing, crucial elements can be plotted and thoroughly checked by animating the system. Here, graphical data can be created by following the Objects, requests (given in preprocessor) and all results. The suspension characteristics such as camber, castor angle, half track change can be plotted against the bump movement.

    Every element and point of the system can be investigated for the changes that it is undergoing. This Post processing result is important and helps in making decision for any changes to the original system. Design study and optimization techniques are useful in modifying the position of the system members according to their limits by which it improves its response.

    [3]Suspension geometry analysis is one of the earliest applications of the MSC ADAMS program by the Automotive Industry in 1977. The output from this type of analysis is mainly geometric and allows results such as half track change, camber angle, roll centre position to be plotted graphically against the wheel vertical movement. ADAMS provides useful spline editing and plotting capabilities which considerably simplifies the modeling and inclusion of non linear elements such as bushes.

    The paper [9] explains the validation of the ADAMS suspension model results of the vehicle with benchmark K&C test. The difference is determined particularly between the elastic and rigid model in terms of road surface performance. It suggests that the kinematic quality of the vehicle axle is defined by the geometry of the suspension bearing points. Further modifications in the elastic elements can obtain improvements to the suspension unit on the road performance.

    In [5] the author describes studies of suspension component and system level analysis consisting of rigid or flexible parts which are connected by joints by the application of ADAMS Program. In the paper four case studies for suspension system performance optimization using MBD studies are presented. The important parameters to be finalized in the early stage of suspension design are the parameters that affect the vehicle ride comfort and handling like suspension spring rates, geometry, suspension travel, jounce rebound bumper, bushing compliance and stabilizer bar designs. Vehicle track, sprung mass centre of gravity, wheel base and weight distribution are the vehicle level parameters which affects the ride comfort and handing. The papers states that the large spring and geometric ratios are generally aimed to improve the suspension NVH. These reduce the loads on bushings, shock absorber damping force requirements by which improve the durability of the components.

    In the paper [11] for improving the ride safety and comfort of a multi link suspension system modeling and performing optimization design study has conducted with ADAMS program. From the analysis results it has been concluded that this method is high performance and can be used conveniently for designing multi link suspension. The paper states that a designer can acquire big design flexibility from the multi link layout form and can analyze kinematical and dynamical characteristics by adjusting the positioning of the connecting arms and bushing stiffness. While optimizing the mobility scale value of 10mm-10mm has been taken. The optimized camber angle drops from 1.30 to .50, the toe change is 0.30 which is in allowable range. The wheel track has been improved by the optimized variable which ranges from -2.73/9.66 mm to 1.76mm/8.40by which up to certain extent the abrasion of the tire can be reduced and increases the life of the tire.

    DESIGN SENSITIVITY ANALYSIS OF MACPHERSON STRUT SUSPENSION:

    In this paper an approach to optimize the suspension characteristics of the Macpherson strut is explained. Constraint equations for velocity, displacement and acceleration are generated by using the displacement matrix method and instantaneous screw theorem. Firstly, the suspension unit is modeled in three dimension co ordinate system. At the preprocessing stage the design equations are derived. At the analysis stage, the static design factor for the displacement, acceleration, moments and forces are performed. A 40 mm wheel travel of full bump and full rebound positions has been carried out.

    In the sensitivity analysis the most dominant variables which affecting the wheel alignment acted by forces and moments are specified. These variabels are subjected to change dimensoinally by the most priority design variables.

    From the sensitivity analysis the effects of design variables on the suspensoin characteristics can be found. From the changes made to the design variables, the camber and toe of the suspensoin system is improved which in turn increases the vehicle directional stabilty and handling on to the road surface. This study concludes that this type of analysis is effectively applicable for determing the suspension system lay out by estimating the changes in the suspensoin characetristics in the early design stages.

    BUMP AND REBOUND EFFECTS:

    The upward displacement of the wheel with respect to the vehicle body is known as bump and vice versa is known as rebound. The movement of suspension system should be limited to prevent metal to metal contact when the wheel is at maximum bump and rebound limit positions available. A better ride quality can be achieved by the greater movement that can be allowed.

    When the vehicle hits a bump, it influences the change in wheel camber and steer angles. Spring-damper forces are also influenced by the vertical force which is caused due to the effect of bump. When the vehicle is under cornering, the bump and droop occurs at the opposite wheels.

    EXPERIMENTAL PROCEDURES:

    Experimental procedures / Design concepts / Methodology / Analysis

    MODELLING AND ANALYSIS OF SUSPENSION SYSTEM

    Peugeot, Coventry University vehicle is chosen for analysis of the suspension system.

    The vehicle has Macpherson Strut as the front suspension and Torsion bar with a damper as the rear suspension system. By using FARO Arm the left front and rear suspension systems are measured. The trolley is ensured in such a position so that the arm can reach all the suspension points and it has been locked down for exact measurements.

    The suspension points such as upper, lower ball joints, tie rod end and spring damper seat position are for the front suspension unit are measured. In the same manner for the rear suspension unit suspension points are located.

    By using the CATIA V5 R18 Package, these points are observed. A reference axis system has been created at the wheel base point according to the standard format. For each point the co ordinates are taken from the reference axis system. For each suspension point, the co ordinates are given with point Ids.

    ADAMS ANALYSIS:

    An input deck is created by using the suspension point locations. Appropriate joints are assigned to the relevant points. A jack is prepared at the wheel base point for analyzing the behaviour of the suspension members. The jack is connected to the wheel base by using an in plane joint primitive. This will allow the wheel base to remain at the top of jack and it has no effect on wheel to move in any directions. A translational motion is applied at the end of jack for knowing the suspension characteristics

    DESIGN STUDY AND OPTIMIZATION:

    The suspension model can be refined by adding parametrics to the critical point locations. Design variables can add parametrics to the selected point. Firstly the design variables have created which represents the design points. These design variables can be reviewed for changing their range values. The parameterization gives information such as which design variables have the greatest effect by sensitivity analysis. Optimization in ADAMS determines which objective function to be minimized or maximized by choosing the design variables. It can also satisfy the specified constraints if there are any. Optimization is an iterative process in which each design variable has been changed according to the value range assigned to it. For every Iteration process, the change in value of function can be graphically plotted against the initial value of the function.

    For Macpherson Strut, a design study is conducted to investigate the critical point locations which are contributing in specific suspension characteristics.

    The camber angle mainly affects the directional stability of the vehicle. More negative camber influences the vehicle to turn quickly when cornering.

    From the research, if to limit the change in camber angle for the suspension undergoing bump and rebound positions, the upper mount and lower ball joint are the two main critical design location points.

    Also excessive castor angle increases the amount of camber for the wheel.

    REFERNCES:

    1. RACE CAR VEHICLE DYMANICS By WILLIAM F. MILLIKEN And DOUGLAS L. MILLIKEN
    2. KINEMATIC SUSPENSION LINKAGES - A MODEL FOR THEIR BEHAVIOUR AND A PROCEDURE FOR THEIR DESIGN By M.B.GERRARD
    3. THE MULTI BODY SYSTEMS APPROACH TO VEHICLE DYNAMICS By MIKE BLUNDELL AND DAMIAN HARTY
    4. Internet Resource www.mscsoftware.com
    5. SAE Technical Paper: Effective Use of Multi Body Dynamics Simulation in Vehicle Suspension System Development By Ramesh Edara and Shan Shih
    6. Journal Paper - The influence of suspension and tire modeling on vehicle handling simulation By Mike Blundell, Coventry Univerisity.
    7. Chapter.10 An Introduction to Modern vehicle Design
    8. Influence of Suspension Kinematics and Damper Asymmetry on the Dynamics Responses of a Vehicle under Bump and pothole Excitations.
    9. Suspension Kinematics and Compliance - Measuring and Simulations
    10. Introduction to modern vehicle design By Julian Happian - Smith.
    11. SAE Technical Paper- Analysis of Kinetic characteristic and Structural Parameter Optimization of Multi Link Suspension by Lei Li, Changgao Xia and Wei Qin, Jiangsu University.

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