16-01-2013, 03:19 PM
MiniBaja Vehicle Front Suspension Design
1MiniBaja Vehicle.pdf (Size: 3.77 MB / Downloads: 509)
DEFINITION
Suspension is the term given to the system of shock absorbers and linkages that connects a vehicle to its wheels. The job of a suspension system is to contribute to the car’s handling and braking for a better safety driving, and to keep the driver as isolated possible from bumps, vibrations, etc. It is important for the suspension to keep the wheel in contact with the road surface as much as possible, since all the forces acting on the vehicle do so through the tires. The suspension also has the important task to protect the vehicle itself and any cargo from damage. In this report the design of the front suspension for the miniBaja vehicle will be improved.
PROBLEM IDENTIFICATION
Analyzing the current suspension there are several points that could be improved in order to optimize the functionality of the suspension. The first issue with the current suspension being used on the UTEP MiniBaja vehicle is that there is no recorded analysis for stresses nor forces; it was fabricated without previous examination nor calculations of the components used. The lack of study of these components results in the failure to provide the required information to whether the components will fail under the circumstances to which the suspension will be submitted. That means there is no reference point to know at what point they could fail. It may be noted too that the material used in the current suspension is unknown.
The two A arms that constitute the suspension are another point to discuss. Even when this design is frequently used in different types of suspension the use of space and appearance could be improved. The upper A arm is not adjustable therefore the vehicle cannot take advantage of the different tracks that it might experience.
SOLUTION IDEAS
After taking into account all the missing data and realizing the points that could be improved, we started the optimization of the components of the suspension. We analyzed each component separately with their respective forces and stresses and calculated the required information to perform a stress analysis to see if they would fail and if so at which point.
DESIGN TOOLS
Various tools were used in the development of our design. The NX6 software is used for tasks such as the three dimensional solid modeling of each component. The use of solid modeling techniques allows us the computerization of many difficult engineering calculations that are carried out as a part of the design process. Simulation, planning, and verification of processes such as machining and assembly of the components of the suspension are some of the tasks that will be performed in NX6. Also this software will be used to perform an engineering analysis of the stresses acting on each component to reveal the state of stress and failure on the device.
The use of NX6 is very important, but the use of other tools is also necessary. These will be the knowledge acquired in engineering mechanisms and design from our current and prior classes such as mechanical design, mechanics of material, dynamics, etc.
DESIGN INTRODUCTION
OVERLOOK
The suspension designed for the MiniBaja cart consists of two single control arms that are attached to the upright and the hub that is mounted on the spindle, as shown in Figure 3.1. The frame of the existing cart will have to be modified in order to hold the top arm, the bottom arm, and the shock absorber. The following paragraphs will go more in detail in the description of each individual part.
PARTS
The top arm will be connected by a ball joint to the upright, and will be pinned to the frame, and was designed to have an adjustable length. The top arm will consist of one solid shaft that will have a nut fixed in the center and it will be threaded on both sides. The solid shaft will fit into the two shafts that will have a hole at the ends. Both shafts will have an inner thread and the ends will be secured by two additional nuts, one on each side. The top arm was designed adjustable in length to take advantage of the track and the environment in which the cart will be placed. For example, if the track only requires the cart to take right turns the length of the arm can be adjusted to change the angle of the tire which will minimize over steer. The range of the length of the upper arm can be adjusted between the lengths of 420 millimeters and 480 millimeters. The ball joint that will have to be placed at one ends of the arm will have to be placed into the arm by force. The following image shows the finished arm.
CONCLUSION
After an in depth analysis of each individual part of our suspension unit design we have come to the conclusion that if we optimize our design it will be a good choice for SAE Mini –Baja requirements. Some of the optimizations we have in mind include further analyzing the upper control arm and possibly increasing its diameter; and also considering finding a more appropriate ball joint for this part. In the optimization section of this report it was mentioned that because of the increase in height of the bottom arm, we will need to find a more adequate ball joint for this component that will adapt more to the modified dimensions and increase its performance. After further review of our analysis we took notice that our spindle and upright did not fail in any of the presented scenarios. This implies that the two parts that we designed do not need additional modifications to improve their performance. Putting aside the analysis of our design, we can say that each of our group members have become more familiar with the useful tools that were applied during the design process. This includes the NX6 software, knowledge acquired during lectures, as well as applying basic concepts of design. Furthermore we had to use knowledge acquired from prior classes not just our current ones.