1

CONVERTIBLE AUTOMOBILE TOP Akmal B. Ismail Amirrudin B. Mat Ngu Ya May

Faculty of Mechanical Engineering Kolej Universiti Kejuruteraan & Teknologi Malaysia

ABSTRACT Convertible automobile top mechanism is a mechanism that can open the car roof. The mechanism of convertible automobile top is widely use in automotive fields nowadays. So, here the convertible automobile top and related will be discussed. INTRODUCTION Nowadays, a convertible automobile top is very popular among consumers. The reason is that they want to be part of the nature while driving and also a convertible automobile top is looks very stylish. So, this project is about to create a convertible automobile top mechanism using all the knowledge learned in Mechanism Design subject. The convertible automobile top consists of a lot of links that related to each others. In this project, the given convertible automobile top will be redesign according to its requirements. The original design of convertible automobile top cannot move smoothly and met problem during fold back due to the links position and its length. Also, all of the links needs to fit into the predefined space (1.36m x 0.44m) as mentioned. The specified requirements must be met while the employing the given number of links and kinematics pair. Finally, after the redesign process was finished, the model will be fabricated in scale dimension in order to show it is practically function. OBJECTIVES There are several objectives that need to be achieving in this project which are:

• to create the convertible automobile top mechanism

• to calculate the position, velocity, and acceleration of the point of interest from the driver link

• to design the top and rear panel, and all links be able to fold back and fit within the predefined space

METHODOLOGY In order to create the convertible automobile top mechanism, there are several methods that will lead into the fabrication. The methods are shown in the flowchart below:

Figure 1: Flowchart of Methodology

Kinematics Diagram

Start

Theoretical Calculation Method

Determination of Position and Length of Links/Elimination

Product

Simulation via Cosmos Motion

Fabrication of Kinematics Model

2

i. Kinematics Diagram

Figure 2: Kinematics diagram of convertible automobile top The Degree of Freedom (DoF) for this kinematics diagram is as below:

10=n as labeled 1- 10 ( )sliderpinsj p 112 += as labeled A-L 0=hj ( ) ( ) 01321103 −−−=∴F

2627 −= 1= ii. Theoretical Calculation Method Position Analysis Step 1: Firstly, calculation is started from piston

actuator which retraction length is a function of sinusoidal.

p = piston

The Piston with length Lp will retract and rotates clockwise. As given, the retraction,

s = sin (x) ; x = θp

= sin (θp - ∆θp ) , ∆θp =change in angle

Step 2: Calculation displacement for Link E which is attached to piston actuator.

hEf = hEi – s, hEf = final length of link E and hEi =

final length of link E

⎥⎥⎦

⎤

⎢⎢⎣

⎡= −

E

EE L

hf

f

1sinθ

⎥⎦

⎤⎢⎣

⎡= −

E

EE L

hi

i

1sinθ

fi EEE θθθ −=Δ

Step 3: Calculation angular displacement for Link

D which is attach to top panel

LR = Length of rear panel

Lp

θp D

θA

3

Rear linkage is assumed has the same amount of angular displacement as link E, then

EEDD ifθθθθ Δ=−=Δ

LR = Length of rear panel Rear linkage is assumed has the same amount of angular displacement as link E, then

EEDD ifθθθθ Δ=−=Δ

⎥⎦

⎤⎢⎣

⎡= −

ADR

AD L

L θθ sinsin 1

⎥⎦

⎤⎢⎣

⎡= −

DA

RAD L

L θθ sinsin 1

⎥⎦

⎤⎢⎣

⎡Δ=Δ − )(sinsin)( 1

DA

RAD L

L θθ

Finally, the position of top panel as the piston actuator retracted is:

DADA θθθ −−°=180 Velocity Analysis The velocity analysis here is conducted by using instant center method.

Total links, n = 10 Total number of instant center

= 452

)110(102

)1(=

−=

−nn

Possible Instant Center: 1 2 3 4 5 6 7 8 9 10

12 23 34 45 56 67 78 89 910

13 24 35 46 57 68 79 810

14 25 36 47 58 69 710

15 26 37 48 59 610

16 27 38 49 510

17 28 39 410

18 29 310

19 210

110

Acceleration Analysis There are two methods to be used in acceleration analysis which are determination of acceleration of general point on a floating point and coriolis acceleration. iii. Determination of Position and Length of

Links/Elimination In order to redesign the convertible automobile top, the position and also the length of the links that related should be determined. It is to easier the process of fabrication. The (sub) links position and dimension are adjusted through CAD software which is SolidWorks.

4

5

6

7 8

9

10

1

2 3

1

2 3

4

5

6

7 8

9

10

4

iv. Simulation via Cosmos Motion To make sure that all of the links that have been modified are reliable, the modified design, the modified design will be tested in Cosmos Motion to see whether the simulation is according to its requirements.

v. Fabrication of Kinematics Model Fabrication is the process after all of the links related are confirmed at the right position and at the right dimension. RESULT AND DISCUSSION Simulation Result for Convertible Automobile Top: Original Design:

Figure 3: Original Position - SolidWorks Assembly Cosmos Motion Output (Traced Path, Displacement, Velocity and Acceleration):

Figure 4: Displaced Position - Traced Path

Figure 5: Displacement within 10 seconds

Figure 6: Velocity within 10 seconds

Figure 7: Acceleration within 10 seconds

Modified Design:

Figure 8: Original Position - SolidWorks Assembly

0.00 0.36 0.71 1.07 1.43 1.79 2.14 2.50 2.86 3.21 3.57 3.93 4.29 4.64 5.00Time (sec)

-804

-674

-543

-413

-283

-153

-22

108

238

368

Acc

eler

atio

n (m

m/s

^2)

0.00 0.36 0.71 1.07 1.43 1.79 2.14 2.50 2.86 3.21 3.57 3.93 4.29 4.64 5.00Time (sec)

-813

-669

-525

-381

-237

-93

51

194

338

482

Vel

ocity

(mm

/s)

0.00 0.36 0.71 1.07 1.43 1.79 2.14 2.50 2.86 3.21 3.57 3.93 4.29 4.64 5.00Time (sec)

0

315

630

944

1259

1574

1889

2204

2519

Dis

plac

emen

t (m

m)

5

Cosmos Motion Output (Traced Path, Displacement, Velocity and Acceleration):

Figure 9: Original Position

Figure 10: Displaced Position - Traced Path

Figure 11: Displacement within 10 seconds

Figure 12: Velocity within 10 seconds

Figure 13: Acceleration within 10 seconds

Discussion:

Figure 14: Original Position Given Original Design of Convertible Automobile Top As seen from figure 4, there are two arrows (green and red color) which pointed to different direction. These are actually indicating the error during the simulation. Moreover, there is also fluctuation on the links which making the time cycle of the mechanism cannot be completed.

Meanwhile, the links especially link C and top panel also are not fitted within the predefined space – coordinate E (1.36, -0.44). Figure 5, 6, 7 is the displacement, velocity and acceleration graph.

0.00 0.91 1.82 2.73 3.64 4.55 5.45 6.36 7.27 8.18 9.09 10.00Time (sec)

-240

-137

-34

68

171

273

Acce

lera

tion

(mm

/s^2

)

0.00 0.91 1.82 2.73 3.64 4.55 5.45 6.36 7.27 8.18 9.09 10.00Time (sec)

-427.38

-274.66

-121.94

30.77

183.49

336.21

Vel

ocity

(m

m/s

ec)

0.00 0.91 1.82 2.73 3.64 4.55 5.45 6.36 7.27 8.18 9.09 10.00Time (sec)

398

802

1207

1612

2017

2422

Dis

plac

emen

t (m

m)

6

Modified Design of Convertible Automobile Top After several corrections have been done to the original design, those entire links finally can be fitted into predefined space without any error or fluctuation. The time cycle is assigned with 10s, and the mechanism is fully being performed within 10s also. Figure 11, 12, 13 is the displacement, velocity and acceleration graph. All of these graphs are illustrated its smoothness which mean no fluctuation.

Overall, modified design that has been getting through this simulation is the best design. Fabrication for convertible automobile top will be fabricated according to the modified design that performed from the simulation. CONCLUSION As the conclusion, the objectives of this project are achieved successfully where all the requirements were obtained. Hopefully, in the future, there is many more research about the convertible automobile top mechanism in order to improve its application. REFERENCES [1] Matthew Edward Doyle (1997). The

Foundation for CADSPAM: Computer Aided Design of SPAtial Mechanisms. Master Thesis of Faculty Mechanical Engineering, Virginia Polytechnic Institute and State University.

[2] Nilesh and G. K. Ananthasuresh (2002).

Contact Aided Compliant Mechanism: Concept and Preliminaries. Design Engineering Technical Conferences, Montreal, Quebec, Canada (DETC2002/MECH-34211)

[3] S. –J.Kwon, M.-W.Suh. Design Program for

the Kinematics and Dynamic Characteristic of the Bus Door Mechanism, Vol 6, NO.4 (2005) 403-411