CAD method used for improving the performances of lifting systems used for vehicles.

Spanu, Alina ; Stoenescu, Adrian ; Anghel, Florina 等

1. INTRODUCTION

The paper is focused on the study of the lifting assembly used for a great variety of automotive services in order to achieve a high positioning accuracy as well as high technical performances for the dynamic process. Such lifting systems are used for motocycles, cars, vans and trucks, so that we have to compute the optimal dimensions and actuating system in order to deliver a product which will meet the customer requirements. Much more, the range of products must be reliable and it must be built in compliance with regulations in force. The state of art takes mainly into account two kinds of lifting systems: the first one--a platform hydraulically actuated using a central hydraulic cylinder (Multi Ram, 2008); the second one--a scissor linkage hydraulically actuated too (Scissor Car Lift, 2008). We consider that the last one is more reliable due to its linkage and its safe system in case of cutting-out the hydraulic supplier system. Furthermore the system could be improved regarding the dynamic process by doing some research into the field of actuating system as a feed-back one.

2. DYNAMIC STUDY OF THE LINKAGE

The linkage system was designed as a scissor one (Fig.1) and we have been focused on two main aims: the study of the mechanical forces and the actuating system; the second one--the study of efforts and mechanical deformation during the loading process.

[FIGURE 1 OMITTED]

The kinematical study of motion for the assembly shown in Fig. 1, have been made using the scheme represented in Fig. 2 which are given below.

The kinematical study of motion has been made using the following nonlinear system of six equations:

JD * sln([phi]1) + DE * sln([phi]2) = 0 (1)

JD * cos([phi]1) l DE * cos([phi]2 = s1 (2)

DI * sln([phi]2 - [pi]) + s3 * sln([phi]4) = DG * sln([phi]1) (3)

DI * cos([phi]2 - [pi]) + s3 * cos([phi]4) = DG * cos([phi]1) (4)

s2 * sln([phi]3) = AD * sln([phi]1 + DC * sln([phi]2 - [pi]) (5)

s2 * cos([phi]3) = AD * cos([phi]1 + DC * cos([phi]2 - [pi]) (6)

where [[phi].sub.4] is the angular value between IG and JX axis.

We have computed it by using numerical method Newton-Raphson, so that we could determine the values for the six unknown variables: [[phi].sub.1], [[phi].sub.2], [[phi].sub.3], [[phi].sub.4] and [s.sub.1], [s.sub.2]. The independent variable is [s.sub.2] the displacement of the hydraulic piston of the cylinder for which we have given a constant increment. In Fig. 2 [P.sub.1] is the force acting on the platform during the process of lifting a vehicle as we have specified above.

Finally, we have written a twenty one linear equation system for computing the forces acting in each kinematical joint, in order to determine the deformation and the force acting on the hydraulic piston used as actuator. We have written for each kinematical element three equations, two equations for forces and one equation for the values of mechanical couple.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The final result for the force developed by the hydraulic system is given in Fig. 3. We may infer that the value for this force is absolutely great at the beginning of the motion, due to the influence of pressure angle established during the kinematical analysis. (Hong, 2002; Weisheng, 2002).

Based on the results of this study we have turned to the other aim of our work.

3. THE STUDY OF EFFORTS AND DEFORMATIONS FOR THE ENTIRE ASSEMBLY

Taking into account the value for the force acting on the platform, we have made the analyses for the entire assembly using CATIA V5 R16. First of all we have designed the assembly using the soft mentioned above. (Ghionea, 2007).

For the best result of such analyse we have to specify the kind of restraints for each joint as well as the type of connections.

We have considered for the computation the value of pressure force needed for hydraulically actuation, which was established during the above theoretical study.

The load on the platform may vary depending on the vehicle type--car, van, truck and so on. The load was considered distributed along a limited surface and following a percentage of the vehicle heavy: 40% for the front of the platform and 60% for the back of the platform.

As we may infer from the Fig. 4 and 5 the biggest values for efforts and linear displacement was achieved for the platform. Another critical zone was that of G and H joints (Fig. 2 and Fig. 4) due to their type especially regarding the use of this kind of ball bearings. The main idea was to find out a technical solution for increasing the rigidity of these two kinematic elements.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

Finally we have designed and we have analysed a new subassembly having the aim of improving the dynamic process. This subassembly could be attached to the sides of the platform. We have made the analyses again with these new parts and the results show us a considerable decreasing of efforts.

All the results of our research were applied by a company which produces such lifting systems and they have achieved expected functional parameters.

Future works will be focused on the improving the hydraulic supplier system especially regarding its dynamics.

4. CONCLUSION

The lifting linkage used for vehicles during their service activities has to be very reliable and compliant with regulations in force. A major problem is the computation of deformation and linear displacement of the entire linkage during the lifting process. First we have made a kinematic analyse which helped us to determine the values for speed and acceleration.

The second step has been regarding the computation of force acting on each kinematic element taking into account the dynamics for the hydraulic supplier system.

The final aspect was the 3D analyse using the 3D model of the entire assembly. We have studied the linear deformations taking into account the entire linkage, so that we could determine the direct influence between them. The critical zones were the platform as well as the upper side of the kinematic elements of the linkage used to sustain the platform.

Consequently, the future works would study technical solutions for the upper side elements and for the dynamics of hydraulic supplier system for a better lifting process using this kind of linkage.

5. REFERENCES

Ghionea, I. (2007). Proiectare asistata in CATIA V5. Elemente teoretice si aplicatii (Computer Aided Assisted in CATIA V5. Theory and applications), Editura Bren, ISBN 978973-648-654-8, Bucuresti, Romania.

Hong, S., Chiu, G., T. (2002). Motion Synchronization for Dual-Cylinder Electrohydraulic Lift Systems, Mechatronics IEEE/ASME Transaction, Volume 7, Issue 2, June 2002, Pg. 171-181.

MultiRam Lifting System, Available from: http://www.slift.de Accessed: 2008-03-21.

Scissor Car Lift Systems, Available from: http://www.cartuningcentral.com Accessed: 2008-03-21

Weisheng, Z. (2002). Automatic Control of the Hydraulic Lifting System, Proceedings ofthe Fifth (2002) ISOPE Pacific/Asia Offshore Mechanics Symposium, Daejeon, Korea, November 17-20, 2002.