Modelling and Design of an Auto Street Light Generation Speed Breaker Mechanism

O.A. Olugboji, M.S. Abolarin, I.E. Ohiemi, K.C. Ajani

American Journal of Mechanical Engineering OPEN ACCESSPEER-REVIEWED

Modelling and Design of an Auto Street Light Generation Speed Breaker Mechanism

O.A. Olugboji1, M.S. Abolarin1, I.E. Ohiemi1, K.C. Ajani1,

1Department of Mechanical Engineering, School of Engineering and Engineering Technology, Federal University of Technology, Minna, Nigeria

Abstract

Energy usage is inevitable to Man’s daily living. For any task to be achieved in life energy must be converted from one form to another. This method of power generation is one of the most recent forms of energy generation concepts. The mechanism converts the kinetic energy of vehicles at speed bump into electric energy. A preliminary modelling of the speed breaker system was developed. The component members were designed and modelled on SolidWorks software based on the properties of the selected materials. A static and fatigue analysis of the spring using SolidWorks reveals a yield stress of 172.3 Mpa. The computational fluid dynamics of the air reveals an average total pressure and velocity of 29.74 bar and 1.018 m/srespectively.The conceptual design was carried out and resulted to the selection of materials needed for each component of the design. A prototype of the speed breaker mechanism was constructed and tested. The mechanism generated 6V D.C which validates the principle. The light sensor automatically opens the valve to on the light when it is dark and closes it to off the light at dawn.

Cite this article:

  • O.A. Olugboji, M.S. Abolarin, I.E. Ohiemi, K.C. Ajani. Modelling and Design of an Auto Street Light Generation Speed Breaker Mechanism. American Journal of Mechanical Engineering. Vol. 3, No. 3, 2015, pp 84-92. http://pubs.sciepub.com/ajme/3/3/3
  • Olugboji, O.A., et al. "Modelling and Design of an Auto Street Light Generation Speed Breaker Mechanism." American Journal of Mechanical Engineering 3.3 (2015): 84-92.
  • Olugboji, O. , Abolarin, M. , Ohiemi, I. , & Ajani, K. (2015). Modelling and Design of an Auto Street Light Generation Speed Breaker Mechanism. American Journal of Mechanical Engineering, 3(3), 84-92.
  • Olugboji, O.A., M.S. Abolarin, I.E. Ohiemi, and K.C. Ajani. "Modelling and Design of an Auto Street Light Generation Speed Breaker Mechanism." American Journal of Mechanical Engineering 3, no. 3 (2015): 84-92.

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At a glance: Figures

1. Introduction

A speed breaker or speed bump is a traffic calming device that uses vertical deflection to slow otor-vehicle traffic in order to improve safety conditions on roads. The use of vertical deflection devices is widespread around the world and they are most commonly found where vehicle speeds are statutorily mandated to be low so as to guarantee safety to road users.A speed breaker mechanism is a device that converts the impulse energy produced by the passage of the vehicle over a speed bump into the kinetic energy needed to rotate the rotor of an alternator to generate electrical Energy.

There has been a wide attention of researchers in design and development of renewable energy conversion systems. Electrical energy is normally generated through thermal Energy, Mechanical Energy nuclear Energy and chemical Energy. Researchers over the years have devised a new method that involves mechanical vibrations. There are three categories of devices that generate electricity by vibration. These are piezoelectric generation device, electrostatic generation device [1] and the Work function energy devices.

Piezoelectricity is the electric charge that accumulates in certain solid materials in response to applied mechanical stress [2]. Piezoelectric energy generation still remains an emerging technology, though several investigation has been carried out on it since the late 1990s [3, 4, 5, 6]. Elementary principles of vibration theory, reveals that the resonance of a system can be tuned by changing the stiffness or mass [7, 8, 9, 10, 11].

Different from previous research on generating energy from translational base excitation, Gu and Livermore [12] focused on rotational motion. As identified by Aswathaman [12], three different mechanisms are currently being used in power generation via speed breakers. These are: Roller type mechanism [14, 15], the Rack- Pinion mechanism [12, 16], Crank-shaft mechanism [17]. When vehicles move on the road, the piezoelectric materials under the road are vibrated due to vehicle suspension in the tires that force the road and produces electricity in large amount [18]. The energy of water in the hosepipe is used to drive the turbine. As the water rushes through the pipe it turns the blades of the small turbine to generate electricity [19].

Epileptic power supply is a common problem prevalent in developing countries. Anytime there is power failure especially at night, the streets are turned into darkness which in turns affects the social economic life. It is against this backdrop that this research was conceived.

The work aims to develop a speed breaker mechanism for generating electrical energy by compression method with auto light sensing system. The speed breaker mechanism will be developedusing a static analysis of the spring and computational fluid dynamics (CFD) analysis of the air flow using SolidWorks software. A prototype of a speed breaker mechanism is also developed.

2. Materials and Method

2.1. Materials and Equipment.

The conceptual design of the speed breaker system include essential component such as: The speed breaker where the force is applied, Helical spring to return the breaker to its original position when the load is removed, Air pump /compressor, Receiver tank, Mini turbine, the automatic light sensor system which include transistor TIP31, Light emitting diodes, resistors, relays, wires, gears, 12v battery, vero board, capacitors, 7808 regulator, toggle switches and white junction box. The operations were performed using the following instruments: measuring tape, scriber, hack saw and the electric arc welding machine.

2.2. Methods
2.2.1. Speed Breaker

The speed breaker is required to have adequate mechanical strength to withstand continuous loading and unloading. Therefore, Mild steel was selected because of its cost and its good machinability. The speed breaker was cut and machined and welded based on the specification.


2.2.2. Spring Selection

The primary function of the spring in this application is to withstand twist and pull resulting from the applied force. Based on the strength, functional requirements and the properties of the candidate materials as earlier stated, Stainless steel was selected as the most suitable material for its excellent ability to withstand high stress, good fatigue resistance and long endurance for shock and impact loads. The spring stiffness and spring deflection for the chosen spring are 17500 N/m and 0.01M.


2.2.3. Cylinder and Piston Assembly

The Cylinder Piston Assembly serves as a unit that compresses air into the receiver tank. The reciprocating compressor is selected since its application requires the compression of air at a very high pressure.


2.2.4. Receiver Tank

Receiver tanks are used as air storage facility for mechanical units powered by compressed air. Mild steel is selected, as the ideal material due to its cost and its ability to be turned into different shape and form. The receiver tank was equally fabricated to specification.


2.2.5. Alternator Selection

Electric generator or Alternator is a device that converts mechanical energy to electrical energy. Direct current (D.C) alternator of different ratings and Alternating Current (AC) alternator of different ratings were used. A 6V DC alternator was used to power at least three LED bulbs of 1.8 Volts each.


2.2.6. Mini Turbine

The Turbine unit and its components were installed on the machine by drilling and fastening of screws, bolts and nuts using the drilling machine, screw driver and spanner respectively. All the components fabricated were assembled on the supporting frame of the speed breaker mechanism by welding, filing, drilling and fastening operations. The air compressor is installed between the speed bump and a DC alternator. The weight of the vehicle on the speed breaker pushes the speed breaker downward. The movement of the speed breaker pushes the piston through the barrel thereby compressing the air into an air receiver tank. The stored air is then released by the help of a valve to rotate a coil through an electromagnetic field to generate electric current.


2.2.7. Supporting Frame Work, Accessories and Assembly

The supporting frame was made from a square mile steel pipe (30 mm x 30 mm 0.5 mm).The operation was carried out by measurement, marking out, cutting and welding. The cylinder liners was made from a steel pipe with an inner bore diameter of 55 mm and outer diameter of 70 mm the sleeve was made smooth by turning the bore size to 60 mm using a lathe machine. The resulting cylinder was welded on a 3 mm mild steel sheet to form a dead end. The metal sheet was drilled using a power drilling machine to provide an orifice for the air that will be compressed out of the cylinder. The piston rod was welded to a circular connector where the piston can be joined to the piston rod. The piston rings were mounted on it and using the piston pins, the piston was connected to the piston rod. The air receiver tank was installed on the supporting frame by placing it on the seat provided for it at its base and by welding the cylinder holder at the top to the body of the supporting frame. The speed breaker was constructed from a 3 mm thick mild steel sheet. The road surface was made from plywood.


2.2.8. Automatic Light Sensor Unit

In the circuit as shown in Figure 1 below, SW2 and SW3 are switches connected to the battery to form a series and parallel connection. When the two 6Vbatteries are connected in series they yield 12V at the discharging mode which is connected to the entire circuit. While when connected in parallel, the total emf of the 6V batteries at the charging mode is connected to the incoming 6V from the turbine connected to D5.The SW2 is connected to the positive side of the B2and SW3 is connected to GND of B1. The diode D5 allows voltage coming in from the turbine to charge the battery thereby preventing back emf coming from the battery and over charging. The SW1 prevents excessive flow of current from the D7 to D13 by changing the value of resistors connected in series with the light emitting diodes D7 to D13. The LDR (light dependent resistor sensor R2) in series with the variable resistor (VR2) controls the base of Q1 to switch RL1 (relay switch) during the day and night. R1is controlled by RL1 (day and night switching) to bias D2 or D1 to switch the bases of Q2 or Q3 depending on the intensity of light or darkness on the LDR. Q2 and Q3 are connected to forward and reverse polarity of the motor MT1 which in turn closes or opens the release valve to stop or start the turbine.


2.2.9. Computational Fluid Dynamics (CFD) of the Air Flow Using Solid Works

Several steps were taken in order to perfectly execute the fluid flow analysis. A project file in SolidWorks Flow Simulation containing all the settings, results of a problem and each project that is associated with a SolidWorks configuration was created. The analysis was then Ran and the Vectors, Contours, Isolines, Cut Plots, Surface, Flow Trajectories, Isosurfaces were plotted. The Results for XY Plots, Goals was presented using Microsoft Excel, while Surface Parameters Point Parameters was Reported using Microsoft Word.

Figure 1. Schematic circuit diagram showing the light sensing unit

2.2.10. Testing of the Speed Breaker Mechanism

The speed bump was subjected to a continuous loading and unloading force for a period of five minutes. Air was compressed continuously into the receiver tank by the to and fro movement of the piston in the cylinder liners. The air outlet valve was then opened to release the compressed air from the receiver tank into the blade of the mini-turbine. The turbine was turned for a period of two second and 3 volt was generated as read from the connected voltmeter. The above procedure was repeated for a period of 10, 15, 20, 25, 30 and 35 minutes. The results is as shown in Table 1.

3. Design Analysis and Calculations

3.1. Theoretical Analysis
3.1.1. Solid Simulation (Static and Fatigue) Analysis of the Spring Using Solid Work.

Finite-element analysis (FEA) is used to predict the response of the speed breaker mechanism model to the influence of forces and torques. FEA analyzes large or complicated models where analytical solutions are impossible. FEA software breaks the model into thousands of small tetrahedral elements and solves for them numerically.


3.1.2. Static Analysis

Static analysis computes the effects of static loading on the model. It is the determination of stress, strain, displacement, and the factor of safety at each segment of a model. In Simulating the model, the location and magnitude of each load is specified, as well as where and how the model is supported. Identification of the areas with high and low stress quickly shows where the model can be improved on either by the addition of supports or by the removal of excess material. The part model used for this simulation is the spring and must be specified.

To specify the material, the Feature Manager Design tree on the left-side panel was selected. An icon named “Material <not specified>” as shown in Figure 2 was Right-clicked and “Edit material” was selected on the Materials window. Furthermore, the material was selected by clicking on the folder named SolidWork materials and Steel Alloy on the dropdown menu selected. Finally, Stainless Steel alloy was selected from the array of steel alloy.

3.2. Design calculation
3.2.1. Speed Bump Design

The Speed bump is meant to bear the load of the input force. The material for this component is mild steel. The Tensile Strength of mild steel is 407 MPa

Yield Stress of Mild Steel,

Allowable Stress,

(1)

[20]

Factor of safety, F.O.S = 1.5

But,

(2)

Designing for a cross sectional Area of 200 mm 60 mm, therefore, the Allowable Maximum Load that can be bored by the cross section

(3)

Therefore the speed bump should not be loaded beyond 168 KN force. The Bump is supported at both ends by spring, which results to reactions FA and FB, due to the application of load, F as shown in Figure 3.

Sum of all vertical forces,

(4)

Sum of moment about Support A, (Clockwise Positive)

(5)

From equation 4 above, making FA, subject of the formulae

The shear force at A is equal to RA = 0.5 F, where x = 0 and continues on a straight line to the mid-point of the beam where x = L/2; beyond which it continues to decrease uniformly to -0.5 Fl at C where it remained constant till point B where x = L.Also the bending moment is zero at A and B (when x = 0, x = L) and increase in a triangular form to a point C. The Bending Moment is maximum where shear force is zero. Taking Moment about C,

(6)

Let b= Length of the bump, d=Thickness of the bump

Also, considering a rectangular section cut from the speed bump ABCD as shown in Figure 4 as a segment of the bump

Considering a strip PQ of thickness dy parallel to X-X’ axis and at a distance y.

(7)

Moment of inertia of strip about X-X’ axis

(8)

Moment of inertia of the whole section is the integration equation 8 from

(9)

[18]

(10)

From bending moment equation,

(11)

Also from Figure 4,

Substituting for y and in equation 11

(12)

Minimum Thickness of the bump material


3.2.2. Spring Design

Consider a helical spring shown in Figure 5 below under a load, F

Consider a helical spring under a load, F, Where, D = Diameter of coil; d = diameter of the coil wire; R = Radius of Coil; = Deflection of the coil under load; C = Modulus of Rigidity of the Spring Material; n = Number of coils or turns , Length of wire, .

From Hooke’s Law,

(13)

Calculating for a minimum deflection of 0.01 m and applying force FA as calculated from equation 2 above

(14)

Also Allowable Stress for mild steel

Force acting on spring,

Cross sectional area of spring,

(15)

Minimum spring wire diameter,

(16)

Also the minimum deflection as a result of 175 N load

(17)

[20]

Making the minimum mean radius subject of the formula from equation 17

(18)

But mean diameter of spring, D

(19)

The Length of the wire

(20)

3.2.3. Cylinder and Piston Assembly Design
3.2.3.1. Load Bearing Capacity of Piston Rod

The application of load on one face of the piston leads to pressure, since pressure is a function of Surface area. The other face of the piston moves to and fro a fixed wall. Failure or breakage of piston rod will only occur due to excessive compressive stress developed in the piston rod.

(21)

Where,

r = radius of the piston rod, σ = stress, A = cross section area of the piston rod.

The compressive yield stress of mild steel (σ) = 152 N/mm2

Applying a factor of Safety of 1.5,

The allowable Compressive stress

(22)

Therefore the maximum Load the piston can bear is 7957.5 Newton. The load of 8 kN on the buckling chart for cylinder corresponds to a piston rod diameter of 12 mm, the cylinder bore size diameter is 60 mm, Length of the piston and piston rod assembly is 300 mm, the set pressure of 24.93 bars by interpolating between 7 kN and 10 kN


3.2.3.2. The Maximum inside Pressure of Barrel

The maximum inside pressure in the barrel will be due to the effect of the maximum Load 7957.5 N

(23)

Force on the piston =7957.5 N

Radius of Piston = 30 mm (determined from buckling chart for cylinders in appendix B)

Cross sectional area of piston = 2828.57 mm2

This means that pressure of 2.8133 MPa acts on the walls of the cylinder barrel when the air cylinder is loaded with 7957.5 N force.


3.2.3.3. Thickness of the Barrel

The internal diameter of the barrel is 60 mm. The outer diameter of the barrel will be calculated for as follows.

Inner radius, r1

(24)

The maximum tensile yield strength for mild steel is 250 MPa. Applying a factor of safety of 1.5, the working tensile stress becomes 166.7 MPa

The circumferential stress at the inner radius is 166.7 MPa,

(25)

Also, since pressure at the inner surface of the cylinder is calculated as 2.257 MPa, it implies that radial stress at inner radius is 2.8133 N/mm2, Equation 17 becomes

(26)

Adding equation 26 and 27 we get,

Therefore, from equation 26, replacing ‘b’ results to [20]

Therefore, Lamen's equation for this case become

(27)
(28)

Now the air cylinder barrel must be strong enough to absolve all the stress such that the stress at the outer surface of the barrel must be zero. That is, the radial stress at outside radius

Therefore, equation 28 becomes

Barrel Minimum wall thickness (t) = Outer radius - Inner radius

(29)

3.2.4. Receiver Tank Sizing

Receiver tanks are found in most modern compressed air systems. Hence, one of the most common design tasks in sizing of a compressor system is the sizing of receiver tanks. To size the receiver tanks appropriately, we need to identify the key function of the receiver tank. In this design, the receiver tank is serving as a buffer. Therefore, the Volume of the tank, taking into consideration the free air delivery from the air compression unit, is given by equation below. The height of the tank is 350 mm which is 0.35 m.

Therefore, Volume of Receiver Tank

(30)

The radius of the Tank (r) is given by

(31)

4. Results

Table 1. Speed beaker prototype test Results

Table 3 below gives a summary of the results obtained from the analysis of the fluid flow simulation. The solid work fatique analysis of the spring is as presented in Figure 6 with the various colors showing the probable regions of fatique.

Figure 7 shows a graph of the global goal average pressure against the total pressure obtained from the CFD analysis. The total pressure increases as the goal average pressure increases. The graph shows the adequacy of the air pressure for effective performance of the mechanism.

Figure 8. Fluid flow simulations showing the velocity of air flow

5. Discussions

Table 1 reveals the results of the testing of the speed breaker mechanism. A peak voltage of 6V was generated with a 10 seconds time taken to power the turbine. Table 2 presents the capacity of the air receiver tank. The minimum Volume of the air receiver tank was evaluated as 0.01447 m3. Also a minimum wall thickness of 0.0023 m was obtained. The results of the solid simulation of the spring were presented in Figure 6. This involves the results obtained from the static and fatique analysis of the spring. The solid simulation was carried out by subjecting the system to repeated loading and unloading. This action weakens the affected part over time even when the induced stresses are considerably less than the allowable stress limits. This phenomenon is known as fatigue. Each cycle of stress fluctuation in the system, weakens the mechanism to some extent. After a number of cycles, the object becomes so weak that it fails. Figure 8 shows the fluid flow simulation on solid work for the velocity of the air flow. This reveals that the air speed decreases with time.

6. Conclusion

The existing sources of energy such as oil, coal just to mention a few, may not be adequate to meet the ever increasing energy demands. Development of renewable energy sources has emerged in recent times as a vital component of the power industrial revolution. A large amount of energy is unutilized at speed breakers through friction, every time a vehicle passes over the speed breaker. Based on the results obtained in this work, the following conclusions were drawn. The speed breaker mechanism is a source of electricity generation. Thus it is concluded that stakeholders in the power sector should embrace the use of a speed breaker mechanism as an alternative power source for lighting street lights. This source of energy is pollution free and can be used to power street lights and traffic indicators on roads. The results obtained from the development design, modelling and simulation were used to construct a prototype of the Speed breaker mechanism and the test results revealed that the mechanism generated an average of 6 volts D.C. The result obtained from the constructed prototype is an indication that the speed breaker mechanism is a viable source of renewable energy and will function efficiently on a mega scale. The automatic light sensing system will also enhance an effective energy utilization.

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