PROPOSAL TUGAS AKHIRPRA ELEMENTARY STUDY RIDE SEMAR-T MODEL

by:IPNU CANDRAI0408039

MECHANICAL ENGINEERING DEPARTEMENTFACULTY OF ENGINEERINGSEBELAS MARET UNIVERSITYSURAKARTA2012A. TITLE : Pra Elementary Study Ride Semar-T Model.B. BACKGROUNDThe ride and handling characteristics of an automobile is center on the characteristics of the tires. Tires are the vehicle's reaction point with the roadway. Tire manages the input of forces and disturbances from the road, and the final link in the driver's chain of output commands. Tire characteristics are therefore a key factor in the effect the road has on the vehicle, and in the effectiveness of the output forces that control vehicle stability ang cornering characteristics. The tire's basic characteristics are managed by the system of springs, dampers, and linkages that control the way in which tires move and react to disturbances and control inputswheels provide for a variety of simultaneous needs. The bounce and steering movements provide steering input for directional control, conpensate for body roll to improve cornering ability, and move vertically in response to roadway irregularities in order to smooth out the ride and maintain adhesion. Wheels are connected to the sprung mass throught linkages and are therefore affected by the rolling and pitching movements that occur about the suspensions system's reaction enter. The mechanical requirements for directional contrl, cornering forces, and ride comfort are continuously changing according to roadway and driving conditions. The suspensions and steering linkages are designed to allow the wheels to move as needed to meet the dynamic requirements of various combinations of events. However, the designer is normally constrained by mehanichal conflics between structural members, the engine and drive train, and other components that also must fit into the vehicle. Consequently, errors in geometry are common, and the actual suspension system often falls short of the ideal in a variety of ways.Road condition can show real performance of vehicle ride just like ride over bump. The center of gravity height, relative to the track, determines load transfer, also called weight transfer, from side to side and causes body lean. Centrifugal force acts at the center of gravity to lean the car toward the outside of the curve, increasing downward force on the outside tires. The center of gravity height, relative to the wheelbase, determines load transfer between front and rear. The car's momentum acts at is center of gravity to twist the car forward or backward, respectively during braking and acceleration. Since it is only downward force that changes and not the location of the center of gravity, the effect on over/under steer is opposite to that of an actual change in the center of gravity. When a car is braking, the downroad load on the front tires increases and that on the rear decreases, with corresponding change in their ability to take sideways load, causing oversteer.The quality referred to as ride comfort is affected by a variety of factors, including high frequency vibrations, body booming, body roll and pitch, as well as the vertical spring action normaly associated with a smooth ride. If the vehicle is noisy, if t rolls excesively in turns, or lurches and pitchs during accelerations and braking, or if the body produces a booming resonance, occupants will experience uncomfortable ride.The ride quality normally associated with the vehicle's response to bumps is a factor of the relatively low frequency bounce and rebound movements of the suspension system. Following a bump, the un-damped suspension of a vehicle will experience a series of ascillations that will cycle accoeding to the natural frequency of the system.According to newton's first law, a moving body will continue moving a straight line until it is acted upon by a disturbing force. Newton's second law refers to the balance that exists between the disturbing force and the reaction of the moving body. In the case of the automobile, whether the distrubinhg force in the form of a wind-gust, an incline in the roadway, or the cornering forces produced by tires, the force causing the turn and the force resisting the turn will always be in balance.Vehicle handling characteristics have to do with the way in which the vehicle's inertial forces and the cornering forces of the tires act against each other. The magnitude and vector of the inertial forces are establihed by the vehicle's weight and balance. In a turn, angular acceleration results in a force that is centered at the vehicle center of gravity and acts in a direction away from the turn center. The ability to overcome these forces and produce a controlled, stable turn depends upon the combined characteristics of the suspension and tires. The job of the suspension system is to support, turn, tilt and otherwise manage the tires and their relationship to the vehicle and the ground in a way that will maximize their capabilities.

C. PROBLEM DESCRIPTONWhen any wheel lose contact with the road there is a change in handling, so the suspension should keep all four wheels on the road in spite of hard cornering, swerving and bumps in the road. It is very important for handling, as well as other reason, not to turn out of suspension travel and bottom or drop.It is usually most desirable to have the car adjusted for neutral steer, so that it responds predictably to a turn of the steering wheel and the rear wheels have the same slip angle as the front wheels. However this may not be achievable for all loading, road and weather conditions, speed ranges, or while turning under acceleration or braking. ideally, a car should carry passangers and baggage near its center of grafity and have similiar tire loading, camber angle and roll stiffness in front and back to minimize the variation in handling characteristics. a driver can learn to deal with oversteer or understeer, but not if it varies greatly.

The most important common handling failure is:1. Understeer is the front wheels tend to crawl slightly or even slip and drift towards the outside of the turn. The driver can compensate by turning a little more tightly, but road-holding is reduced, the car's behavior is less predictable and the tires are liable to wear more quickly.2. Oversteer is the rear wheels tend to crawl or slip towards the outside of the turn more than the front. The driver must correct by steering away from the corner, otherwise the car isliable to spin, if pushed to its limit. Oversteer is sometimes useful, to assist in steering, especially if it occurs only when the driver chooses it by applying power.3. Bump steer is the result of the kinematics motion of the suspension rising or falling, causing tow-in or toe-out at the loaded wheel, ultimately affecting the yaw angle of the car. this will always happen under some conditions but depends on suspension, sreering linkage, unsprung weight, angular inertia, differential type, fame rigidity, tires and tire pressure. Bump steer is commonly seen sa the results of undulations in the road but it also plays an important role in vehicle behavior after steering input. As the vehicle rolls into a turn, the outer suspension compresses. if this compression cause's toe-in at the front wheels, the car will steer more. conversely if toe-out is the result, then the car will steer less. It is the opposite at the rear. In extreme cases, bump steer may require a steering correction by the driver. If suspension travel is exhausted the whel either bottoms or loses contact with the road. As with hard turning on flat roads, it is better if the wheel picks up by the spring reaching its neutral shape, rather than by suddenly contacting a limiting structure of the suspension.4. Body roll is the car leans towards the outside of the curve. This interferes with the driver's control, because he must wait for the car to finish learning before he can fully judge the effect of his steering change. it also adds to the delay before the car moves in the desired direction.

D. SCOPE OF PROJECTThe scopes of this project are:1. Create full vehicle model by using MATLAB-Simulink.2. Get a suitable parameter for the vehicle model.3. Verification model via ADAMS software.

E. RESEARCH OBJECTIVESThe objectives of the research are:1. To study effect of steering, throttle (disturbance) and road profile on vehicle ride performance.2. To find suitable parameter of the vehicle to achieve ride performance.

F. BENEFITS OF RESEARCHThe results obtained are expected to provide the following benefits:1. Determine the effect of the road profile to the ride performance.2. Determine the effect of the strength of springs and dampers to the ride performance.

G. WRITING SYSTEMATICSThe systematics of writing this final project are:Chapter I:Introduction, describes the background of the problem, formulation of the problem, limit the problem, objectives and benefits of research and writing systematic.Chapter II:Basic theory, contains a review of the literature relating to the modeling and simulation of vehicle ride and handling performance, the basic theory of the vehicle model, road profiles, ride performance, and handling performance.Chapter III:Research methodology, describes the tools and materials research, research steps, and the flow chart of the research.Chapter IV:Data and analysis, explaining the research data and analysis results of the calculations.Chapter V:Closing, contains the conclusions and suggestions.

H. PREVIOUS RESEARCHOliever Durieux (2009) conducted a study on semi-active suspension system simulation using simulink. Results from studies using the Matlab-Simulink showed that the quality referred to as ride comfort is affected by a variety of factors, including high frequency vibrations, body booming, body roll and pitch, as well as the vertical spring action normally associated with a smooth ride. if the vehicle is noisy, if it rolls excessively in turns, or pitches during acceleration and braking, or if the body produces a booming resonance, passangers will experience an uncomfortable ride.The ride quality, normally associated with the vehicle's response to bumps, is a factor of therelatively low frequency bounce and rebound movements of the suspension systems. following a bump, the undamped suspension (without shocks) of a vehicle will experience a series of oscillations that will cycle according to the natural frequency of the system. ride is perceived most comfortable when the natural frequency is inthe range of 60 to 90 cycles per minute (CPM), or about 1 Hz to 1,5 Hz. when the frequency approaches 120 CPM (2 Hz), passangers perceive the ride as harsh.Ride comfort deteriorates when the road roughness coefficient it increased (ISO classification of road roughness). the reason for this is the rolling resistance coefficient, which is not a constant but varies with the road roughness coefficients and the vehicle speed. hence, when the road roughness coefficient is increased, the rolling resistance force induced by road roughness increases too.Measuring and quantifying ride comfort can help development teams in meeting the necessary standards and regulations, but moreover gives the required insight to troubleshoot, understand and improve the noise and vibration comfort of the vehicle.In order to give a quantitative evaluation of the ride comfort performances achieved by the considered control strategy, the RMS value of the sprung mass acceleration (), normalized with respect to the gravity acceleration (g) can be considered:

Neda Nickmehr (2011) conducted a study on ride quality and drivability of a typical passenger car subject to engine/driveline and road non-uniformities excitations. Results from this studies showed that approprite figures in order to evaluate ride comfort of a typical passenger car at a certain frequency interval by using the sprung mass responses and the ISO criteria which are shown in the previous section.Measured vertical RMS acceleration of the vehicle body, with 80 km/h traveling speed on the average road roughness, is shown again in figure 1 but together with ISO fatigue-decreased boundaries to investigate the level of comfort for this specific passenger car.

Figure 1. Vehicle body vertical acceleration due to road excitation in comparison with ISO ride comfort boundaries.Regarding Figure 1, it can be concluded that for this type of passenger car and passive suspension system properties, in the situation of average road roughness, it is desired to have exposure time less than 2.5 hours, however in the vibration duration is more than 2.5 hours, the vertical RMS acceleration is beyond the limitations, specifically around the modal frequencies or in the other words low frequency region, consequently the ride quality level is low. One good suggestion is moving th second modal frequency to the outside of the critical region for human sensitivity (4-8 Hz), thus it will exist wider band to the allowed boundaries.Now, the longitudinal RMS acceleration of the vehicle body due to engine excitations is compared to ISO proposed boundaries to evaluate the ride comfort in lateral direction. To achieve this goal first, it is necessary to differentiate the velocity data and obtain time history for longitudinal acceleration using MATLAB command gradient, secondly, we have to determine acceleration power spectral density in order to calcuate RMS value, one-third octave band rule is again utulized for each frequency in the interval of 1-80 Hz, Figure 2 illustrates the corresponding longitudinal RMS acceleration of the vehicle body.

Figure 2. Measured longitudinal acceleration of a passenger car body due to engine excitation torques.As it was already explained, for high frequency force input, suspension system has good vibration isolation, and since the engine excitation frequencies are high in comparison with natural frequency of the sprung mass (in longitudinal direction), the acceleration amplitude is too low in Figure 2.

I. BASIC OF THEORY1. Vehicle ModelsThere exist many possibilities arraying for decribing the car suspension behaviour (quarter-car model, half-car model and full-car model). There is an extensive amount of literature relating to these model (Coizet and Gatignol, 2002). The full-car model is presented in the following section.The full-vehicle suspension system is represented as a linear seven degree of freedom (DOF) system. It consist of a single sprung mass (car body) connected tofour unsprung masses (front-left, front-right, rear-left, rear-right wheels) at each corner. The sprung mass is free to bounce, pitch and oll while the unsprung masses are free only to bounce vertically with respect to the sprung mass. All other motions are neglected for this model. Hence this system has seven degrees of freedom and allows simulation of tyre load forces in all four tyres, body acceleration and vertical body displacement as well as roll and pitch motion of the car body. The suspensions between the sprung mass and unsprung masses are modeled as linear viscous dampers and linear spring elements, while the tyres are modelled as simple linear springs without damping. For simplicity, all pitch and roll angles are assumed to be small.

The model of a full-car suspension system is shown in Figure 3. The full vehicle suspension model is represented as a linear seven degree of fredom system. The lateral dynamics of the vehice are ignored. It consist of a single sprung mass (car body) connected to four unsprung masses , , , and (front-left, front-right, rear-left, and rear-right wheels) at each corner. The suspensions between the sprung mass and unsprung masses are modelled as linear viscous dampers and spring elements, while the tyres are modelled as simple linear springs without damping components (exactly in a same way as with quarter-car and half-car models). The actuator system between the sprung body and the wheels provide forces determined by the displacement of the actuators. The damper between the body and the wheels represent sources of conventional damping such as friction between the mechanical elements. For the vehicle modelling full-car will be used as a good approximation of the entire car. The equations of motion for this system are:

(2)

(3)

(4)

(5)

(6)

(7)

(8)

Where,

Figure 3. Full-car model

2. Ride modelRide model is used to study behavior of body movement, roll and pitch of the vehicle. The output the model is body displacement, body velocity, body acceleration, roll angle, roll velocity, pitch angle, pitch velocity, and pitch acceleration. The second law of Newton state that force is created when the body is moving. The equation of this second law is:

Where,

= force created

= body mass

= body acceleration (m/s2)From equation above, it can be stated that and every moving body will have displacement, velocity and acceleration.

Figure 41. Vehicle model

Figure 5 show the full car model that consist 7 degree of freedom (DOF). It consist body acceleration, pitch acceleration. The factor affects the body, pitch, and roll acceleration is , and . this factor can be described in figure 6 . the forces acting at suspension system is and . is force at tire and acting as spring. These forces are worked to minimize unwanted movement of body, roll and pitch that created by road prfile. The four remaining degree of freedom is at all the tire. The equation of motion for body motion is:

Where,

= force acting at vehicle body

= vehicle mass

= body accleration of the vehicle (m/s2)Hence, the sum of force acting at vehicle body is derived. The force acting at the vehicle body is:

Where,

= front left spring force

= front left damper force

= front right spring force

= front right damper force

= rear left spring force

= rear left damper force

= rear right spring force

= rear right damper force

= vehicle body mass

= body accleration of the vehicle (m/s2)

Figure 5. Vehicle free body diagramWhen vehicle is moving, there will be have a pitch motion on the vehicle. It can be simply describe when driver give a brake input, the vehicle is tend to pitch. The sum of pitch moment acting at center of gravity of vehicle is,

Where,

= sum of pitch moment

= pitch inertia

= pitch angular acceleration

From equation is the distance between center of front to the center of rear tire or it also called as wheelbase. When a driver give steering input, it can simply describe that the vehicle has a tendency to roll.

Figure 6. Free body diagram of roll motion

3. Road3.1 Modeling aspects

Sophisticated road models provide the roa height and the local friction coefficient at each point , . (Figure 7).

Figure 7. Sophisticated road model

The tire model is than responsible to calculate the local road inclination. By separating the horizontal course decription from thevertical layout and the surface properties of the roadway almost arbitary road layouts are possible.Besides single obstacles or track grooves the irregularities of a road are of stochastic nature. A vehicle driving over a random road profile mainly performs hub, pitch and roll motions. The local inclination of the road profile also induces longitudinal and lateral motions as well as yaw motions. On normal roads the latter motions have less influence on ride comfort and ride safety. To limit the effort of the stochastic description usually simpler road models are used.

If the vehicle drives along a given path its momentary position can be described by the path variable . Hence, a fully two-dimensional road model canbe reduced to a parallel track model (Figure 8).

Figure 8. Parallel track road model

Now, the road heights on the left and right track are provided by two one-dimensional functions and . Within the parallel track model no information about the local lateral road inclination is available. If this information is not provided by additional functions the impact a local lateral road inclination to vehicle motions is not taken into account.

For basic studies the irregularities at the left and the right track can considered to be approximately the same, . Then, a single track road model with can be used. Now, the roll excitation of the vehicle is neglected too.

3.2 Deterministic profiles3.2.1 Bumps and potholesBumps and potholes on the road are single obstacles of nearly arbitary shpe. Already with simple rectangular cleats the dynamic reaction of a vehicle or a single tire to a sudden impact can be investigated if the shape of the obstacle is approximated by a smooth function, like a cosine wave, then, discontinuities will be avoided. Usually the obstacles are described in local reference frames (Figure 9).Then, the rectangular cleat is simply defined by,

Figure 9. Rectangular cleat and cosine-shaped bump

and the cosine-shaped bump is given by,

where , and denote height, widht and lngth of the obstacle. Potholes are obtained if negative values for the height are used.In a similar way track grooves can be modeled too. By appropriate coordinate tranformations the obstacles can the be integrated into the global road description.3.2.2 Sine wavesUsing the parallel track road model, a periodic excitation can be realized by,

Where,

= path variable

= amplitude

= wave number

= phase lag between the left and the right track

The special cases and represent the in-phase excitation with and the out of phase excitation with .

If the vehicle runs with constant velocity , the mmentary position of the vehicle is given by , where the initial position at was assumed.By introducing the wavelength,

The term can be written as,

Hence, in the time domain the excitation frequency is given by .

For most of the vehicles the rigid body vibrations are in between 0.5 to 15. This range is covered by waves which satisfy the conditions and .

For a given wave length, letss say , the rigid body vibration of a vehicle are excited if the velocity of the vehicle will be varied from to . Hence, to achieve an excitation in the whole frequency range with moderate vehicle velocities profiles with different varying wavelengths are needed.

J. RESEARCH METHODOLOGY1. Equipments and materials researchThe equipments and materials used in this study are as follows:a. Computer

Figure 10. Computer

b. MATLAB-Simulink software

Figure 11. MATLAB-Simulink software

c. Semar-T electric car

Figure 12. Semar-T electric car

d. Mistar

Figure 13. Mistar

2. Implementation of research2.1. Dimensional measurements of Semar-T electric cars. The results of the measurements are shown as follows: Table 1. Semar-T parameters.SymbolDescriptionUnits

Sprung masskg

Pitch moment of inertiakgm2

Roll moment of inertiakgm2

Front-left unsprung masskg

Rear-left unsprung masskg

Rear-right unsprung mass kg

Front-right unsprung mass kg

Front-left suspension stiffness coefficient N/m

Rear-left suspension stiffness coefficient N/m

Rear-right suspension stiffness coefficient N/m

Front-right suspension stiffness coefficient N/m

Front-left suspension damping coefficient N s/m

Rear-left suspension damping coefficient N s/m

Rear-right suspension damping coefficient N s/m

Front-right suspension damping coefficient N s/m

Front-left tyre stiffness coefficient N/m

Rear-left tyre stiffness coefficient N/m

Rear-right tyre stiffness coefficient N/m

Front-right tyre stiffness coefficient N/m

Side distance from CG to the front axle M

Side distance from CG to the rear axle M

Frontal distance from CG to the frontal-left axle M

Frontal distance from CG to the rear-left axle M

Frontal distance from CG to the rear-right axle M

Frontal distance from CG to the frontal-right axle M

2.2. Create free body diagram of Semar-T.Free-body diagrams are diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation.

Figure 14. Free body diagram of Semar-T.Figure descriptions are as follows:Table 2. States and input description.SymbolDescriptionUnits

Sprung mass heavy displacementm

Sprung mass pitch angular displacementrad

Sprung mass roll angular displacementrad

Front-left unsprung mass displacementm

Rear-left unsprung mass displacementm

Rear-right unsprung mass displacementm

Front-right unsprung mass displacementm

Front-left displacement inputm

Rear-left displacement inputm

Rear-right displacement inputm

Front-right displacement inputm

2.3. Create full Semar-T model by using MATLAB-Simulink.

Figure 15. Full Semar-T model

2.4. Enter Semar-T parameters in to model simulation.

Figure 16. Full Semar-T block diagram2.5. Discussion.a. Analyzing the effect of steering, throttle (disturbance) and road profile on vehicle ride performance.b. Summing up the results of data analysis.

3. Validation Validation model via ADAMS software.

K. FLOW CHART OF THE RESEARCH

Figure 17. Flow chart of the researchL. SCHEDULE OF THE RESEARCHTable 3. Schedule of the researchTYPE OF WORKSMONTH

IIIIIIIVVVI

123412341234123412341234

Study literature

Make a proposal research and tool prepared

Researching

Data research analysis

Result and conclusion of research

Report

REFERENCES

[1]Nickmehr N. 2011. Ride Quality and Drivability of a Typical Passenger Car Subject to Engine/Driveline and Road Non-uniformities Excitations. Linkoping: Linkoping University.[2]Prof. Rill G. 2009. Vehicle Dynamics. Regensbury: Regensburg University of Applied Sciences(RUAS).[3]Durieux. O. 2009. Semi-Active Suspension System Simulation Using SIMULINK. Wrexham: Glyndwr University.[4]Fazree M.A. 2007. Modeling Simulation of Vehicle Ride and Handling Performance. Melaka: Technical Malaysia Melaka University.[5]Ihsan S.I. 2007. Dynamics and Control Policies Analysis of Semi-Active Suspension System Using A Full-Car Model. Kuala Lumpur: International Islamic University Malaysia (IIUM).