Designing a Formula SAE Wheel Lifting System - Term Paper Example

Designing a formula SAE wheel lifting system Institution of Affiliation: Student’s Name: Course: Date: INTRODUCTION A jack is a device that can be used in rising of vehicles off the ground for maintenance and service operations. The jacks are readily available in the market however some of the designs available require a lot of energy making it difficult for the women or weaker men to be able to use them effectively. This has led to the modification of the current jack systems to come up with a design considering all the human aspects regarding reliability comfort when using as well as the degree of easiness in their application. The use of car jack systems has made it easier to raise or lift vehicles o more saw during emergencies where tires have to be replaced. There are two main types of jacks for automotive. The hydraulic type of jacks using hydraulic fluid to lift the load. Secondly, the screw driven jack to uses the screwing mechanism to raise a heavier load by application of a small force at the handle that generates an amplified force lifting the required load (Blodgett et al. 2008). Types of jack systems Hydraulic jack systems Two types of hydraulic jacks currently exist. They include the bottle and floor jacks. The bottle jacks are designed in such a way that they have a main shaft supporting the weight holding platform. The platform directly carries the weight of the vehicle in our case The floor jack is the other type of hydraulic jack. The difference in this design is that the shaft is along the horizontal axis. The shafts apply force to the lifting pad this movement allows the weight to lift horizontally (Blodgett et al. 2008). Working principle of a hydraulic jack When the handle is pressed it results in reciprocating motion of the plunger, in the process oil is sucked into the plunger cylinder during the upstroke and conveyed through the delivery valve to the ram cylinder during the downstroke. After the required load lifting has been accomplished the pressure at the ram cylinder is gently released with the help of a screw that is loosened. The oil in the cylinder flow back to the reservoir awaiting the next up stoke where it will flow through the suction valve to the plunger cylinder. The design has a plunger cylinder and a ram cylinder on the other side. The cylinders are mounted on a mild steel material basement which provides the required strength to overcome the stresses involved in the whole operation. The plunger is essential in generating pressure that acts of the incompressible liquid which is oil in this case. Its cylinder has two valves the suction and the delivery responsible for intake and release of the oil respectively. The ram in the ram cylinder lifts the required load. The lowering screw is a valve that releases pressure in the cylinder allowing the ram to be lowered as desired (Blodgett et al. 2008). Screw jacks They incorporate a machined screw that is responsible for transforming the rotational energy into linear energy. When the worm screw rotates on the lead screw, it transforms the rotator energy into linear energy at the end of the lead screw. In the machined screw design, the warm screw acts directly onto the lead screw leading to energy direction transformation. However, for the ball screw design, the ball nut is used to actuate the movement of the lead screw after the movement of the warm screw. The second type of design has a better efficiency when it comes to converting the input into useful output. As a result, it is commonly used as compared to the first type. The other advantage of the ball screw design is that it has less friction alongside being a durable type of jacking system for vehicles. The other design, however, provides a self-locking mechanism which the second type lacks. The load screw has different designs to handle different applications according to the user needs. They can either take the form of Acme lead screw used in imperial designs or rather take the form of the square based screws. When designing the ball screws, one has to obtain the threads of the lead screw to ensure that the balls can effectively travel in the threads of the lead screw. The Gothic arch profile in the ball screws helps in even distribution of the load minimizing the chances of wearing out of the jack (Blodgett et al. 2008). Types of screw jacks The translating screw jack where the rotation of the warm gear directly acts to the lead screw which transforms the motion linearly. There is high friction between the screw and the threads caused by the rotation of the lead screw. Fig 1: Translating type of screw jack The second type is the translating keyed jack system. In this design, the idea of friction is minimized as the lead screwed held in position by a key which restricts unnecessary movements. It is commonly used in applications where the load screw does not need to be fixed to the load (Blodgett et al. 2008). Fig 2: translated screwed jack system with a key. In the rotating type, the warm gear is fixed to the lead screw. This joint allows the lead screw to move whenever the worm moves thereby transforming the rotary motion to the linear one. The paper looks at the design of a screwed Jack with all the design considerations put in place (Blodgett et al. 2008). DISCUSSION Calculations Relation between the force applied and the weight being lifted For the screw jack, the calculations involved are more or less similar to that of an inclined plane when it comes to determining the required force for lifting a certain load. In this case, the applied force is considered to be horizontal. The load being lifted has an equal opposing friction force F acting downwards. This is expressed as F = µR Where µ = coefficient of friction F = force of friction, R = normal reaction generated at the point of contact of the interacting surfaces. The forces are resolved in the horizontal plane resulting to: P cos α = W sin α + µR………(i) Perpendicular forces are also resolved to give: R = P sin α + W cos α The value of R is substituted in the first equation resulting to the following: P cos α = W sin α + µR = W sin α + µ(P sin α + W cos α) = W sin α + µP sin α + µW cos α Or P cos α – µP sin α = W sin α + µW cos α Or P(cos α – µ sin α) = W(sin α + µ cos α) Or P = W × (sin α + µ cos α) / (cos α – µ sin α) Replacing the value of µ = tan φ, P = W × (sin α + tan φ cos α) / (cos α – tan φ sin α) Numerator and the denominator are multiplied by a common factor cos φ, we get P = W × (sin α + cos φ + sin φ cos α) / (cos α cos φ – sin α sin φ), = W × sin (α + φ) / cos (α + φ), Finally, we write, P = W tan (α + φ) The equation shows the relationship between the forces P to be lifted alongside the effort that is needed. Power calculations The formal for the relationship between the power and speed is given as Where Pin= Input power (kW) Sin = Worm shaft input speed (RPM) Tin = Input torque (Nm) The speed of the input worm shaft is given by the equation Where Sr = Travelling rate (mm/rev) St = Linear travelling speed (mm/min) Determination of the input torque for the lifter was given by the following formulae Where Tin = Input torque which was specified by the dynamic load (Nm) Tc = Input torque for nominal Capacity (Nm) Ln = Nominal capacity of the lifter (kN) Ld = Dynamic load applied to the lifter (kN) Sizing considerations During the design of the vehicle lifter system, the following were put into consideration for effectiveness in the design. The loading capacity was very essential as we had to work with the heaviest vehicle of the sporting design the lifter was meant to raise. This provided the perfect consideration for all other lighter SAE vehicles. After determining our loading weight, we were able to reach to the required ball screw as well as finding out its life time when in operation. The other consideration was our column guidance which had to take into consideration the weights the lifter will be raising. As a result, we used mild steel tubes to provide the required strength and reliability of the whole design (Blodgett et al. 2008). Loading capacity The loading capacity of our design was determined the bearings, driving sleeves strength as well as the strength of the lift shaft which was able to raise the load. All the static and dynamic loads were taken into considerations ensuring the design had minimum chances of failure during its application. A safety factor of 1.5 was found the most appropriate in calculating the impact of the shock loads that were essential in considering the shock loads. To take into consideration of the accidental loads that may occur during operation ten percent of the dynamic loads as well as thirty percent of static loads was used in the calculations (Blodgett et al. 2008). Total loads The total loads in our design were a combination of the dynamic, static loads as well as the inertia loads caused by deceleration and acceleration of the wheel lifter. The effect of gravity, as well as the stiffness of the lifter alongside the load distributions, was considered when determining the total loads acting on the lifter (Blodgett et al. 2008). Advantages of the wheel lifters using the screw mechanism The first advantage is that it is a self-locking in nature which allows the lifted wheel to remain in the position it is left until when the handle will be moved. This eases the work of the operator. Having the self-locking mechanism makes this design safer when compared to the use of hydraulic lifters. It has a higher mechanical advantage which refers to the force applied to the lifter for it to raise a given load (Blodgett et al. 2008). Disadvantages However, the design has also its limitations because it is not effective in lifting very heavy loads. This is attributed to the high friction rates between the screw threads. The design if constantly used is prone to faster wear that makes use of hydraulic lifters a better option (Blodgett et al. 2008). Maintenance operation To have the lifter working at its best condition regular preventive and corrective maintenance will be required. Preventive maintenance is essential in reducing the frequency of breakdown of the wheel lifting system. Regular checking of the worn out parts such as bearings and replacement with the correct type will help a lot in avoiding unexpected failure when in operation. Oiling and greasing of the moving parts especially the worm and the lead screws will help a lot in minimizing friction thereby increasing the lifespan of the design. Finally, the wheel lifter should only be exposed to loads below it's threshing hold limits to avoid unexpected failures due to the excess loads that it was not designed to accommodate (Blodgett et al. 2008). CONCLUSION At the end of the study, we were able to come up with our wheel lifter for the Formula SAE vehicles. This helped ease the process of lifting the vehicles usually at a low level. The efficiency of the design allowed the process to use minimum efforts raised the vehicle up to the required height. It special locking mechanism ensures that the vehicle remains in the position it is meant until when the handle will be unwound by the operator. However, our design has some limitations, for instance, it is not suitable for lifting hefty machinery due to the strength limitations. Developing of the wheel lifter has made it easier to raise the formula vehicle in case of maintenance operations.However, the lifter will give the best performance under correct maintenance routine which will reduce the frequency of failure or wear out of screw threads. More improvements can be made in the design to ensure that it is more efficient compared to initial design. REFERENCE Blodgett Jr, R. W., & Fletes, B. J. (2008). U.S. Patent No. 7,377,362. Washington, DC: U.S. Patent and Trademark Office. Read More