1.8 Literature review Energy harvesting from vehicle suspension systems is a promising area of research, aiming to utilize wasted energy from vehicle vibrations.. In this journal, a scr
INTRODUCTION
The urgency of the topic
Fossil energy sources used for industry in general and automobiles in particular are gradually running out Besides, the energy from fuel used to propel the vehicle only accounts for less than 20% of the total energy input, it can be seen that the loss and energy loss is very large Recovering energy lost in vehicle like cars, and motobikes is a new research direction in the automotive field in the world as well as in the country Research directions on this issue are often associated with research subjects applied to electric vehicles, hybrid electric vehicles and vehicles using traditional internal combustion engines Many studies have shown that the suspension system creates a large amount of energy from vibrations and these vibrations occur continuously when the vehicle is operating However, most of them today use shock absorbers just to suppress vibrations to bring comfort to the user, especially when going through bumpy and rough roads This energy will be absorbed by hydraulic dampers and converted into an amount of heat released to the environment There have been many studies to recover this wasted energy, but in practice it has not been optimized Therefore, “HARVESTING ELECTRIC
ENERGY FROM SHOCK ABSORBER” is really necessary.
Topic’s objective
The purpose of this research is to explore, simulate, and define system performance based on input scenerios of energy regeneration system built in Mathlab/Simulink The proposed system would convert waste mechanical energy, produced during the normal function of a vehicle’s suspension, into usable electrical energy This transformation has the potential to create a more efficient energy system within the vehicle, contributing to lower fuel consumption rates, increased energy efficiency, and a reduced carbon footprint
The end objective is to not only understand the considerations and potential output of such a system but also to build a theoretical basis for future topics when starting to design and construct a model that can be tested and possible implemented in real-world scenarios This research holds the dual promise of contributing to environmental conservation efforts and reducing energy waste in vehicles, thus marking a step forward in the pursuit of sustainable and efficient energy systems.
Scientific and practical significance of the topic
Scientific significance of the topic: The topic researches, selects, simulate and try to build a prototype of an energy recovery model Applying theory to evaluate the ability to regenerate, from there draw conclusions about whether the energy recovery system meets the ability to regenerate good energy or not
Pratical significance of the topic: The thesis is aimed to contribute to the future of a green earth, minimizing vehicle emissions into the environment by reducing fuel consumption.
New points of the thesis
The vibrations from the suspension system caused by the road surface are employed to assist the electric energy regeneration unit in operating The linear structure of the energy regeneration system converts energy from the suspension system's forward motion into electricity, increasing fuel efficiency and reducing environmental emissions.
Research methods
Collect and study scientific literature, articles, and books on energy harvesting systems from motorcycle shock absorbers, and basics of electromagnet induction.
Research object
Energy harvesting system on motocycle rear shock absorber.
Research limitations of the topic
Within the research scope of the project, we only focus on studying the operation of the system, applying electromagnetic induction to generates electricity from the oscillating kinetic energy of the shock absorber combined with storing electricity logically Output power of the harvester Helps realize the ability to regenerate electricity from the vehicle's shock absorber.
Literature review
Energy harvesting from vehicle suspension systems is a promising area of research, aiming to utilize wasted energy from vehicle vibrations Various studies have explored different methods to capture this energy and convert it into electrical power One of the approach involves using Piezoelectric materials like PZT sensors to generate electricity from suspension system vibrations, “A NOVEL PIEZOELECTRIC ENERGY HARVESTER
OF NONCONTACT MAGNETIC FORCE FOR A VEHICLE SUSPENSION SYSTEM” with the authors Z.Zhao, B.Zhang, Y.Li, C.Bao, T.Wang published on December 15, 2022 in Energy Science & Engineering journal vol 11, pp 1133-1147 In this journal, a screw- nut mechanism was used for convert linear vibration between the vehicle body and the wheel into rotational motion is used as the motion conversion component and then the energy conversion component will convert the rotational energy into electrical energy through noncontact magnetic force and piezoelectric effect which is called PEH comonent Their result when driving on a random road, the maximum of the generated power of PEH is 24.28 W at 60km/h under laden state, and the PEH generate power of 3346 W at 30 km/h when driving on the pulse road under unladen state
“ENERGY HARVESTING FROM CAR SUSPENSION SYSTEM: MATHEMATICAL APPROACH FOR HALF CAR MODEL” published on Mar 08 2021 in vol 15, Iss 1, pp 7695-7714 of Journal of Mechanical Engineering and Sciences by T.Darabseh, D.Ai- Yafeai, Abdel-Hamid I.Mourad With the development a half car model with built-in piezoelectric stack to evaluate the potential of harvesting power from the car suspension system, regeneration system was constructed with two piezoelectric stacks installed in series with the front and rear suspension springs The system was tested in both time and frequency domain for the harvested voltage and power, in the end, it maximum generated voltage and power at the frequency of 1.46 Hz are 33.51 V and 56.25 mW, respectively
“ENERGY HARVESTING FROM SUSPENSION SYSTEMS USING REGENERATIVE FORCE ACTUATORS” conducted by F.Khoshnoud, D.B.Sundar, M.N.M.Badi, Y.Chen, R.K.Calay, C.W.Silva published on Aug 12 2013, International Journal of Vehicle Noise and Vibration in vol 9, pp.294 With an excitation signal in the frequency range of 0.5 Hz to 20 Hz, they applied to their vehicle and the harvested power is calculated As the results, the system give a maximum harvested power is 984.4 W at the highest frequency with the application of RFA – Regeneration Force Actuators is explored for harvesting the vibration energy and controlling vibration
CONSTRUCTION & OPERATING PRINCIPLES OF ENERGY
Introduction
The suspension system is an important part of a vehicle, it determines whether the vehicle’s driving feels smooth or bumpy, stable or unstable Simply put, this is the part that plays a role in the movement of the entire vehicle body, especially when the vehicle moves through rough roads
On motobike, there are only spring as a resilient part, single-shell damping as a damping part a Spring
Cylindrical Springs: These champions of consistency boast a constant outer diameter, ensuring a predictable compression response When encountering an imperfection, a cylindrical spring compresses proportionally, absorbing the impact energy effectively Their compact design shines in motorbikes, allowing for a lower center of gravity that enhances stability during high-speed maneuvering and cornering
Tapered or Coil Springs: Imagine a guardian with varying levels of strength That's the essence of a tapered spring Its wider base acts as a gentle giant, absorbing smaller bumps with ease As the terrain gets tougher, the stiffer midsection takes over, handling significant impacts without excessive compression This progressive spring rate allows the coil spring to adapt to changing road conditions, providing a comfortable and predictable ride
Spiral Springs (Helical Springs): Offering a balance between compactness and progressiveness, these coiled springs provide another avenue for motorbike suspension Their design might require slightly more installation space compared to cylindrical springs, but the trade-off can be worthwhile for specific applications
Springs have the following main characteristics:
Space-Saving Simplicity: The clean and uncluttered structure of springs, especially when nestled within the shock absorber, is a major advantage for motorbikes Every inch of space counts, and springs maximize space utilization without compromising performance
Lightweight Champion: Compared to heavier suspension components, springs boast a lower mass This translates to a lighter overall motorbike weight, leading to improved fuel efficiency and potentially sharper handling Every gram shed makes a difference, especially in performance-oriented bikes where agility and responsiveness are crucial
Durability Defined: Springs are renowned for their long lifespan, particularly when constructed from high-quality materials like high-carbon steel Their simple design minimizes potential wear and tear compared to more complex suspension components This translates to lower maintenance costs and a longer service life for your motorbike
Figure 2.1 Structure of some types of springs Disadvantages:
Limited Damping Control: Springs excel at absorbing impacts, but they lack the ability to control the rebound movement after a bump This is where additional components like damping rods come into play The lack of internal friction between the spring coils necessitates separate dampers for optimal performance Without proper damping, the motorbike can experience excessive bouncing after encountering a bump, compromising stability and control
Multitasking Challenges: Springs are masters of a single task: absorbing impacts
However, other crucial functions like guiding the wheel and transmitting traction or braking force require additional components in a suspension system using cylindrical springs This can lead to a slightly more complex structure compared to some suspension systems that integrate these functions within other components The need for a separate guide rod system adds to this complexity b Shock absorber
Taming the Bumps: Their primary function is to reduce and extinguish the shocks transmitted to the frame when the wheels encounter bumps and uneven surfaces By absorbing these impacts, they protect the motorbike's frame and other elastic parts from excessive wear and tear This translates to a longer lifespan for your motorbike and a more comfortable ride for you
Optimizing Tire Contact: Shock absorbers work to ensure the vibration of the unsprung parts (wheels, tires, and suspension components) is minimized This allows for consistent and optimal contact between the tires and the road surface Maintaining good tire contact is essential for safe maneuvering, effective braking, and proper acceleration
Enhanced Vehicle Dynamics: Properly functioning shock absorbers improve the overall handling and stability of the motorbike They help to control the vehicle's movements during acceleration and braking, contributing to a safer and more predictable riding experience
Damping the Jiggles: Shock absorbers act as dampers, converting unwanted vibrations from the road surface into heat energy This effectively reduces bouncing and excessive movement after encountering bumps, keeping the motorbike stable and composed
A shell damper has the following structure:
This is a detailed comparison of a motorcycle fork’s internal structure in two different states: normal and compressed Here’s a breakdown of the key components:
Fork Tube: The outer casing that houses the internal components
Spring: Located inside the fork tube, it compresses and expands to absorb shocks
Fork Seal: Ensures separation between the fork tube and slider, preventing fluid leaks Slider: Moves within the fork tube; it slides up when compressed
Damper Valve and Rod: Controls the damping force and connects to the slider
Fork Oil: Provides lubrication and damping; contained at the bottom Drain: Allows for the removal of fork oil
Damper Bolt: Secures the internal components at the bottom
When the piston moves down, it creates a pressure difference, leading to the opening of valve, the liquid flows to the top of the piston When the piston goes up to it open valve, the fluid flows into the cavity under the piston, the pressure in the shock absorber will not change much and fluctuate around the equilibrium position with the initial static pressure value, thereby avoiding The phenomenon of air bubbles is an unsafe state for the shock absorbers to work During work, due to oil pressure, the gas can only be compressed and the separating piston 4 moves to create a balance between liquid and gas so that the pressure does not drop below a dangerous value
This damper has high sensitivity even when the piston moves very small, avoiding the phenomenon of forced oil flow when temperature changes cause pressure changes
Shock absorber was known as a part of vehicle suspension which help driver and passengers received a comfort experience on driving and also travelling As the name, it absorb every shock or the vibration of the road profile to the vehicle for enhancing the smoothness, by that mean, this system will absorb the shock and dissipate it into the air as heat format while running Realise that the energy made from shock absorber is a waste and it might be a “game changer” while it can be a reliable system for improving the moving distance of EVs then regenerative shock absorber
Direct drive mode
Linear electromagnetic regenerative shock absorbers (LERA) offer a promising avenue for harvesting energy from a vehicle's suspension system Unlike rotary systems that require complex mechanisms to convert linear motion into rotational motion for electricity
9 generation, LERAs utilize a direct drive approach This eliminates the need for transmission components, reducing complexity and potential energy losses
The Power of Direct Drive
In an LERA system, the kinetic energy from the vehicle's vertical oscillations is directly converted into electrical power through electromagnetic induction The relative movement between magnets and coils within the LERA determines the generated voltage Here's the key takeaway:
Road Profile and Coil Speed: The roughness of the road surface directly impacts the relative speed of the magnets and coils This speed, also known as the reciprocating frequency, dictates the coil speed and consequently influences the generated voltage
Optimizing for Efficiency: Beyond Velocity Boosting
Unlike rotary systems that might require velocity boosting mechanisms to enhance power output, LERAs focus on optimizing the arrangement of magnets and coils for improved efficiency Here's where the exciting research comes in:
Magnet and Coil Configuration: Researchers are actively exploring various magnet and coil arrangements to maximize the LERA's efficiency One promising approach involves doubling the number of magnet layers This strategy aims to increase the magnetic flux, which is the density of magnetic field lines passing through the coil, ultimately leading to higher magnetic induction and potentially more electrical power generation
Figure 2.3: Design of the electromagnetic damper with two layers of magnets [9]
As shown in Figure 2.3, there are two layers of magnets coverage the coil stack between them It also have spacer in the design which has the same thickness with the magnet beside it
Table 2.1: Comparation in susceptibility of each material classes
After researches, there is a special of permanent magnet arrangement called Halbach Array
[10] This magnetic arrangement pattern concept is focus on produce a surface with higher magnetic flux than the other The magnetic flux this pattern made was high density compared with the other, this was studied by many researchers in all over the world By turning the polarity orientation of the magnets by 90 degree each, it formed a Halbach array In another hand, Halbach array can help to enhance the system stability with a control unit
Research by P.S Zhang [11] provides valuable insights through a comparative analysis of different magnet arrangements The study includes illustrations of magnetic flux lines for various configurations, including:
Axial Magnets with Spacers (a): This arrangement exhibits a significant presence of flux lines within the air gap
Radial Magnets with Spacers (b): Similar to arrangement (a), this configuration also shows a strong presence of flux lines in the air gap
Radial Magnets Only (c): This configuration demonstrates a weaker concentration of flux lines in the air gap compared to arrangements (a) and (b)
Halbach Array (d): This arrangement stands out with a clear advantage The majority of the flux lines are channeled through the air gap due to the guiding effect of the axial permanent magnets This results in fewer flux lines visible within the central rod, signifying a more efficient utilization of the magnetic field for power generation
Quantitative Evidence: Supporting the Advantage
Zhang's study further strengthens the case for the Halbach Array by analyzing the average flux density of different configurations The results showcase that arrangements (a) and (d) - axial with spacers and Halbach Array, respectively - possess the highest average flux density Notably, the Halbach Array (d) boasts an even higher density (0.8 Tesla) compared to arrangement (a) (0.4375 Tesla) when considering double-layered configurations
Figure 2.5: Magnetic flux density of each arrangement in single layer a) axial magnets with spacers, b) radial magnets with spacers, c) radial magnets only, d) axial and radial magnets [11]
Alongside a well-designed magnet arrangement, the coil profile emerges as a critical component for maximizing a system's overall electricity generation performance Understanding how coils function and the impact of their design choices is fundamental for engineers in this field
The Core Principle: Faraday's Law and Coil Operation
The process of electricity generation within a coil relies on Faraday's Law of electromagnetic induction In essence, when a magnet moves within a coil, it creates a constantly shifting and changing magnetic field This variation in the magnetic field has a profound effect on the electrons within the loops of wire that make up the coil As the magnetic field cuts through these loops, it induces a current to flow in the wire This phenomenon arises because the changing magnetic field exerts a force on the electrons, causing them to migrate in a specific direction within the conductor This directed flow of electrons constitutes the electric current
Optimizing Coil Performance: A Balancing Act
The design of the coil significantly impacts the efficiency of electricity generation Here, achieving an optimal balance between two key factors is crucial: the number of loops (N) within the coil and the overall coil geometry
Number of Loops (N): A higher number of loops within the coil translates to a greater interaction with the changing magnetic field This translates to a stronger induced current according to Faraday's Law
According to Ps.Zhang [11], the required length for one loop of wire can be calculated using the following equation:
Where: 𝐷 𝑎 is the average diameter of winding
𝑁 - the number of loops, can also be calculated as the equation below:
Where: Ac is the cross-sectional area of the coil; Aw is the cross-sectional area of the winding
R.Zhang [4], he shown the equations for find out the coil width as below:
Where: H is coil width; d is the diameter of wire of the coil.
Indirect drive mode
Regenerative shock absorbers offer a promising avenue for harvesting energy from the constant bumps and vibrations encountered by vehicles These systems convert the up-and- down motion of the suspension into electrical energy, potentially improving fuel efficiency or extending the range of electric vehicles Within the world of regenerative shock absorbers, two main design approaches exist: direct drive and indirect drive systems
Indirect Drive Systems: A Focus on Amplification
Indirect drive systems distinguish themselves by incorporating a conversion mechanism that transforms the linear motion of the shock absorber into rotational motion This approach offers several advantages compared to direct drive systems One key benefit lies in the ability to amplify the input excitation, the technical term for the vibration received from the road surface By increasing the coil speed (v) of the coil within the generator, indirect drive systems can potentially generate more electricity
Mechanisms for Amplification: A Toolbox of Options
Engineers have explored various conversion mechanisms to achieve the desired amplification in indirect drive systems Here are a few prominent examples:
Ball Screw Mechanism: This mechanism utilizes a threaded shaft and a nut to Beyond Amplification: Harnessing Piezoelectric Materials for Additional Energy Generation
In addition to the amplification capabilities of indirect drive systems, recent advancements explore the potential of piezoelectric materials These materials possess the unique ability to generate electricity when subjected to mechanical stress or vibration By incorporating piezoelectric elements strategically within the shock absorber design, the system can harvest energy directly from the vehicle's vibrations, further enhancing overall energy output
Delving into the Piezoelectric Effect
The piezoelectric effect, first observed by French mineralogist Pierre-Simon Curie and his brother Jacques in 1880, refers to the ability of certain materials to generate electricity when subjected to mechanical stress or vibration This phenomenon arises from the unique crystal structure of these materials, which allows for the separation of positive and negative charges when the material is deformed
The image depicts a basic setup to demonstrate the piezoelectric effect Here are the key components:
Piezoelectric crystal: This is the heart of the demonstration It's a specially designed crystal made of materials like quartz or ceramic that exhibit the piezoelectric effect
Metal plates: These conductive plates are positioned on opposite faces of the piezoelectric crystal They act as electrodes to collect the generated electrical charges
Weight or force: This represents an external mechanical stress or pressure applied to the piezoelectric crystal
The piezoelectric effect refers to the ability of certain materials to generate electricity when subjected to mechanical stress or vibration Here's how it works in this setup:
Applying Force: When a force (represented by the weight) is applied to the piezoelectric crystal, it compresses the crystal along one axis and stretches it along another axis This mechanical deformation disrupts the arrangement of positive and negative electrical charges within the crystal lattice
Charge Separation: Due to the deformation, the positive and negative charges get separated Positive charges accumulate on one electrode (metal plate), while negative charges accumulate on the opposite electrode This creates a voltage difference (potential difference) between the electrodes
Voltage Output: The voltage difference created by the separated charges represents the electrical output of the piezoelectric effect The magnitude of the voltage depends on the applied force and the properties of the piezoelectric material
The integration of piezoelectric materials into regenerative shock absorbers offers several compelling advantages:
Additional Energy Source: Piezoelectric elements provide an extra layer of energy generation, potentially increasing the overall efficiency of the system
Low-Speed Energy Harvesting: Piezoelectric materials are particularly effective at capturing energy from low-frequency vibrations, which are prevalent in vehicles
Compact and Lightweight: Piezoelectric elements are typically compact and lightweight, making them suitable for integration into shock absorber designs without compromising space or weight constraints
Combining Amplification and Piezoelectric Harvesting: A Synergistic Approach
By combining mechanical motion rectifiers (often used in indirect drive systems) with piezoelectric energy harvesting, a more comprehensive approach to energy recovery from vehicle vibrations can be achieved This combination has the potential to significantly enhance the efficiency and power output of regenerative shock absorbers, contributing to a more sustainable transportation future
Figure 2.8: Flow chart of the twin ball screws regenerative shock absorber design [14]
With ball screw mechanism, Z Zhang and his cooperators [14] was conducted a design of twin ball screws transmission This mechanism acting like a linkage between the suspension vibration input module and generator module which is presented in Figure 2.7, transmission module will be the main part that helps to convert reciprocating linear vibration between cylinders results in unidirectional rotation of the generator shaft
One of the promising of regenerative shock absorber is using hydraulic system to propel the hydraulic pump or motor to generate electricity It depends mainly on hyhdraulic fluid to transfer the up-down motion of shock absorber during operation to the rotation motion of electric generator module This system also need a motion rectifier as hydraulic check valves or gas accumulators to enhance the stability and damping performance
Figure 2.9: a) Hydraulic motion rectifier prototype, b) schematic diagram of the system
Indirect drive systems in regenerative shock absorbers offer a promising solution for harvesting energy from vehicle vibrations However, their design presents some challenges that need to be addressed
The Bidirectional Rotary Dilemma: Efficiency vs Wear and Tear
One approach within indirect drive systems utilizes a bidirectional rotary mechanism, often employing structures like rack and pinion sets or ball screws While this design aims to enhance damping coefficients, it faces certain drawbacks The irregular oscillation inherent in bidirectional motion can lead to:
Low mechanical reliability: The large impact forces generated during these oscillations can cause rapid wear and tear, particularly on components like rack teeth (as highlighted by G.P Dalwar and T.A Jadhav in [12]) This can lead to breakdowns and reduced system lifespan
AC voltage generation: The bidirectional oscillatory motion results in an irregular
AC voltage output However, for practical applications like battery charging, a DC voltage source is necessary
Introducing the Mechanical Motion Rectifier: A Solution for Smoother Operation
To address these challenges, engineers have introduced the concept of a mechanical motion rectifier This ingenious device functions similarly to a full-wave voltage rectifier used in electronics Just as a full-wave rectifier converts AC to DC electricity, a mechanical motion rectifier transforms the irregular reciprocating vibrations from the shock absorber into a regular unidirectional rotation
The working principle of a mechanical motion rectifier with two roller clutches can be compared to a full-wave rectifier using a center-tapped transformer and two diodes As described in [13], this mechanism, often used in conjunction with ball-screw or rack-pinion gears in conventional rotational regenerative shock absorbers, offers several advantages:
Smoother operation: By converting the bidirectional motion into unidirectional rotation, the mechanical motion rectifier eliminates the detrimental effects of irregular oscillations This leads to smoother operation and potentially reduces wear and tear on system components
DC output potential: The unidirectional rotation generated by the rectifier simplifies the conversion process to DC voltage, a more suitable form for battery charging or energy storage in supercapacitors
Benefits Beyond Conversion: Reduced Impact and Improved Reliability
Comparison direct drive mode with indirect drive mode
Regenerative shock absorbers have emerged as a promising technology for improving vehicle fuel efficiency and electric vehicle range by harvesting energy from road vibrations These systems employ various drive modes, with two primary categories being direct drive and indirect drive A comparative study by R Zhang [4] delved into the advantages and limitations of these approaches
Zhang's work highlights several benefits associated with indirect drive systems:
Enhanced Energy Harvesting and Vehicle Dynamics: Indirect drive designs are believed to offer superior capabilities in capturing vibration energy, potentially translating to improved vehicle dynamics through reduced suspension work This can be attributed to the decoupling of the energy conversion process from the shock absorber's primary function of vibration damping
Elimination of Strong Magnetic Fields: Indirect drive systems often utilize rotary generators, which can function with weaker magnetic fields compared to the linear generators typically employed in direct drive systems This simplification can lead to weight and cost reductions
Flexible System Layouts: The use of rotary generators in indirect drive affords greater design freedom in terms of system layout and packaging within the vehicle chassis This flexibility can be advantageous for accommodating space constraints and achieving optimal weight distribution
The study by Zhang also revealed a significant difference in electrical generation efficiency between the two modes During testing on a wooden beam, the indirect drive system achieved a remarkable 88.8W compared to the 7.4W generated by the direct drive system However, it's crucial to recognize that these results may not be universally applicable
Here's why a definitive conclusion about inherent efficiency superiority for indirect drive cannot be solely drawn from this comparison:
Generator Configuration Dependence: As Figure 2.10 illustrates, the specific generator configurations employed in each mode play a significant role in efficiency The inherent limitations of linear generators used in direct drive systems compared to the potentially higher efficiency of rotary generators in indirect drive can contribute to the observed discrepancy
Impact of Mechanical Motion Rectifier: Indirect drive systems typically necessitate a mechanical motion rectifier to convert the reciprocating motion of the shock absorber into rotary motion suitable for driving the DC generator shaft This additional mechanical component can introduce energy losses and potentially reduce overall system efficiency
Direct Drive: Simplicity and Potential
Direct drive systems offer an attractive alternative due to their inherent simplicity The absence of a mechanical motion rectifier translates to fewer moving parts and potentially lower manufacturing complexity While the efficiency results from the wooden beam test may suggest a disadvantage, further research and optimization efforts directed at linear generator design and material selection could improve their performance
Figure 2.13: a) Direct drive regeneration shock absorber system; b) Indirect drive regenerative shock absorber system [4]
Table 2.2 Comparision of two drive mode models
Direct drive mode Indirect drive mode
Feature Linear regeneration Rack and
Linear electromagnetic system converts movement of compression to electricity
Movement compresses fluid, pushing a rack that converts linear motion to rotary motion (via pinion gear) to drive a generator
Piezoelectric plates generate electricity when compressed by shock absorber movement
Similar to rack and pinion, but uses a ball screw for lower-friction rotary motion to drive a generator
Moderate (potentially higher than rack and pinion)
High (up to 70% conversion efficiency)
Potentially High (potentially higher than rack and pinion)
Ride comfort Tunable for comfort
May experience trade-off for efficiency
May be suitable for comfort- oriented vehicles
Potentially good due to lower friction
Complexity Low Moderate Low Moderate
Cost Potentially expensive Moderate Low May be more complex to manufacture
Based on the information collected and cited sources above along with the results from this comparison table, our team decided to choose to build an energy regeneration system according to direct drive mode or linear regeneration as the basis for the simulation and experimentation in the next chapter
MODELING, SIMULATION AND RESULTS ANALYSIST
Introducing the MATLAB/SIMULINK program
MATLAB is an application software developed by MathWorks (USA) This powerful mathematical processing software utilizes matrix (MAT - Matrix) operations programmed by mathematicians and computer experts through mathematical processing tool libraries (LAB - Laboratory)
The software offers various modules catering to specific fields and specializations
Target Users: MATLAB is designed for research, design, and programming personnel
Comparison with Traditional Programming Languages: Solving mechanical problems with ordinary programming languages
Advantage of MATLAB: In MATLAB, you don't need to worry extensively about using mathematical methods
MATLAB serves as a powerful calculation tool, enabling rapid computation of complex expressions and storage of their results in the computer's memory.
MATLAB provides tools for handling data arrays: vectors and matrices, allowing calculation of results from expressions with vector inputs
MATLAB offers functions for solving common engineering problems:
Polynomial operations (multiplication, division, finding roots (zeros) of a polynomial)
Processing measured signals using the fast Fourier transform
Various interpolation methods for data processing in tables
MATLAB provides programming tools for building application programs
Figure 3.2: A Fast Fourier Transform (FFT) visualization
Additionally, there are specialized application modules for in-depth research, such as:
Solving partial differential equations, used to address problems using the finite element method
Simulink for simulating mechanical systems
Stateflow for studying gas or fluid flow
Fuzzy logic for research on fuzzy logic
Figure 3.3: Stateflow for studying gas or fluid flow Starting Up and the MATLAB Interface
To launch MATLAB, double-click the MATLAB icon The MATLAB interface window will appear on your screen
The main interface window displays several toolbars, and smaller windows:
Toolbar (toolbar): Contains icons for performing common functions (Open, New, Save, Cut, Paste, etc.) and specific MATLAB functions (Simulink, Guide, Help, etc.)
Command window: This is the most crucial window, allowing you to directly execute commands, write programs, and connect with other MATLAB applications
The ">>" prompt appears on the main interface window, where you can type commands directly Press Enter to execute the command
If a command is long, use three dots " " before pressing Enter to continue on the next line Lines with a "%" symbol in front are comments, and MATLAB will not execute them
Upon successful execution of a valid command (without errors), MATLAB will display the result directly after the line if there's no semicolon (;) at the end The result will appear after the keyword ans line
How to Use MATLAB Software a Direct Calculations
There are two ways to perform direct calculations:
Type expressions or commands directly into the command window: The result will appear on the screen after pressing Enter
Place commands and expressions into a text file (script file) saved in ASCII format: This file should have the extension m (also known as an m-file) To perform calculations, simply call this file into MATLAB b Programming Applications
Save the program in an m-file: To run the program, call it into the MATLAB environment
To test each line of code: You can enter it directly into the MATLAB command window
To edit program files: You can use any text editor or the MATLAB-Editor program provided by MATLAB with programming support tools
Writing Expressions, Using Variables, and Function Keys a Calculating Numerical Expressions
Enter numerical expressions directly into the MATLAB command window: After pressing Enter, the result of the expression will appear on the screen
Operators: Addition (+), subtraction (-), multiplication (*), division (/), exponentiation (^), and parentheses for order of operations
Long lines of code: Can be split into multiple lines (by pressing Enter) However, a must be added at the end of each line (except the last line) b Using Functions, Constants, and Variables
Functions: abs, sqrt, sin, cos, tan, cot, exp, log, log10, asin, acos, atan, acot
Defined constants: realmax, eps, realmin, pi, inf
When writing expressions: The calculation result will be stored in a variable with the default name ans
To save the calculation result: Assign it to a variable using the following syntax:
= or = : Here: * The variable is named by the user, without spaces, and is case-sensitive * In syntax 1: The result of the expression will appear on the screen and be stored under the variable name *
In syntax 2: The result is not displayed on the screen
To check the current value of a variable: Simply type its name
In an expression: Instead of entering a specific value, you can type the variable name
To check the variables existing in the MATLAB environment: Type "who" or "whos," or use the menu option File > Show Workspace
To delete variables from the environment: Use the commands "clear" or "clear
Figure 3.5: Command window c Function Keys
To edit lines of code: Use the arrow keys or the cut-and-paste functions
Backspace, delete, End, Page Up, Page Down keys: For navigation
Other common keyboard shortcuts: Similar to those in Windows applications: Ctrl + C; Ctrl + V; Ctrl + N, Ctrl + O, Ctrl + X, etc d Controlling the Display of Numerical Results on Screen
The main modes and their meanings are:
FORMAT SHORT: Displays decimal notation with 5 digits after the decimal point
FORMAT LONG: Displays decimal notation with 15 digits after the decimal point
FORMAT SHORT E: Scientific notation with 5 decimal places
FORMAT LONG E: Scientific notation with 15 decimal places
FORMAT +: Uses "+" and "-" signs before numbers
Working with Files in MATLAB
MATLAB commonly uses a few main file types: a .m files (m.file)
This file type has multiple functionalities:
It can contain MATLAB expressions (script files) to be called into the MATLAB environment when needed
It can serve as an application program written in the MATLAB programming language
It can be a new user-defined MATLAB function M-files are saved in ASCII code b .mat files (with the extension mat)
Used to store variables from the MATLAB workspace These files are saved in binary code c Other File Types
Special file formats specific to MATLAB application modules (e.g., *.fig: MATLAB graphics; *.mdl: Simulink simulation file, etc.)
Commands for Handling mat Files a Save Command or File/Save Workspace As
"Save('filename')" saves variables from the MATLAB workspace to a file
"Save('filename', 'variable1', 'variable2', )" saves specific variables to a file
Using the menu command File/Save Workspace As
A dialog box named "Save as" will appear, allowing you to name the file and specify the directory where the file containing the variables from the MATLAB workspace will be saved b Load Command or File/Load Workspace
The command "Load('Filename')": Loads the variables stored in the file "" into the MATLAB workspace
A dialog box named "Open" will appear, allowing you to search for and open the file to load the stored variables into the MATLAB workspace
To work with files (saving or loading them): You usually need to specify the path to the file you want to work with
The MATLAB working environment has predefined paths to some MATLAB directories
If the files you specify don't have a path, MATLAB will search for them in these directories, called "default directories."
To work with MATLAB default directories: Use the commands "path," "addpath,"
"rmpath," or the menu option File/Set Path a path command
Syntax: "path" displays a list of paths to the default MATLAB directories b addpath command
Syntax: "addpath('path1', 'path2', )" adds permanent paths to the MATLAB environment c rmpath command
Syntax: "rmpath('path1', 'path2', )" removes specified paths from the MATLAB environment d Automatic Path Addition
When you run an m-file located in a directory that's not currently on your path, MATLAB will prompt you to add it to the current environment This reduces the need to manually add paths for frequently used folders
If you choose to add the path, it will be available during your current MATLAB session
While automatic addition works well for commonly used folders, you can still manually add paths if needed This path will persist across MATLAB sessions
There are two ways to achieve this:
In the MATLAB command window, type the addpath function followed by the path to the folder you want to add
For example: addpath('C:\Users\YourUsername\MyScripts') (replace with your actual path)
Using the "Set Path" button (if available):
Some versions of MATLAB might have a "Set Path" button within the interface (not through a menu) This button usually leads to a dialog for managing paths Consult your specific MATLAB documentation for details
Click the "New" icon on the toolbar or press Ctrl+N (Windows/Linux) or Command+N (Mac)
A new empty file will open in the MATLAB Editor
Type your m-file code in this editor
Click the "Open" icon on the toolbar or press Ctrl+O (Windows/Linux) or Command+O (Mac)
In the file browser window, select the m-file you want to open
The selected file will be displayed in the MATLAB Editor
Using an External Text Editor
If you prefer a different text editor, you can use one as long as it can save plain text files with the m extension However, you'll lose the benefits of the MATLAB Editor's features like syntax highlighting and debugging
Creating a New m-file: o Open your preferred text editor o Create a new file and type your m-file code o Save the file with a descriptive name and the m extension (e.g., my_script.m) o
Opening an Existing m-file: o Open your preferred text editor o Navigate to the location of the existing m-file o Open the file in your text editor
Saving and Running Your Code
Once you've written your code, save the file in the desired location The file extension should always be m
To run the code in the MATLAB workspace: o From the Editor: Click the "Run" button on the toolbar or press F5
(Windows/Linux) or Fn+Command+E (Mac) This will execute the code in the Editor window o From the Command Window: Navigate to the directory containing your m-file using the cd command (e.g., c'C:\Users\YourUsername\MyScripts') Then, type the name of the m-file (without the m extension) and press Enter This will also run the code.
Modelling linear harvester
Parameters of Sirius 2007 110cc: m = 120 kg (wet weight) c = 200 N.s/m (damping coefficient) k = 10000 N/m (spring stiffness)
Figure 3.6: Linear harvester simulation with Mathlab/Simulink
In Figure 3.6, it is the overall simulation construction of a linear harvester, which is mounted on a mass spring damper and generates power through the reciprocating motion of the damper
In this concept, the damper receive input signal from road profile block and its result in the changing of position Our harvester settled to be use the position signal from the damper block output to start processing and retrieve the EMF value as output voltage
In this project, we set out to evaluate the performance of an energy harvester designed for motorbikes To do this, we decided to utilize simulated scenarios that would allow us to analyze the harvester's response under controlled conditions
We implemented two distinct types of input signals sequentially to simulate different operating scenarios:
Step Signals: First, we used step signals These represent abrupt changes in the input, simulating the impact events encountered by a motorbike when traversing discrete obstacles like bumps or potholes
Harmonic Function Signals: Next, we used harmonic function signals These represent periodic oscillations in the input, mimicking the continuous vibrations experienced by a motorbike traveling on a typical road surface We planned to adjust the specific characteristics of these harmonic functions, such as frequency and amplitude, to represent various road conditions
Here, we focused on analyzing the harvester's response to discrete bumps on the road surface We defined the following key parameters within this step signal simulation:
Motorbike Velocities: The simulation considered two distinct motorbike velocities (6 m/s and 24 m/s) as it encountered the bumps This allowed us to evaluate the harvester's performance across a range of motorbike speeds
Bump Characteristics: The simulated bumps were each assigned a height of 5 cm We could have adjusted this value to represent different bump severities, but for this initial evaluation, we kept it consistent
Time Parameters: o Crossing Time: The motorbike was simulated to take 20 seconds to traverse each individual bump This duration could be modified to reflect the actual size and shape of the bumps encountered, but for this simulation, we kept it at 20 seconds o Rest Period: An 8-second period of rest was simulated between encountering the two bumps This allowed us to observe the harvester's behavior during both the impact event and the subsequent period of steady- state travel
Figure 3.8: Signal Editor window (step signal scenario)
Now, let's delve into how we set the value for the input signal in the step signal scenario The entire simulation lasted for 20 seconds To represent the motorbike encountering a bump, we decided to introduce a pulse within the signal
After the initial 4 seconds of simulation, we introduced a pulse with a magnitude of 5 This value directly corresponded to the height of the bump we wanted to simulate – in this case, 5 centimeters The pulse served as a clear indicator of the impact event It then dropped back down to zero at 6 seconds, signifying the end of the impact and the return to a flat road surface
Following this, I included an 8-second rest period This allowed me to observe the harvester's behavior during the post-impact phase, where it would be responding to the motorbike's steady-state travel on a flat surface Finally, at the 14-second mark, we reintroduced the same pulse to simulate the motorbike encountering another bump
Figure 3.9: Connection of gain block and input signal block to transfer the unit
Because the height of the bump is 5 centimeters, after the input signal block, we should convert it to meters for usage with 1
100 value of gain block and as we installed the harvester system at the rear shock absorber so we use the transport delay block for delay the input signal
(3.1) Where: L – Wheel base; V – Vehicle velocity
In this scenario, using the sinusoidal function, we wish to do simulations under each different condition in order to look more objectively at the harvester system, as we describe here: in reality, because shock absorber variations on a motorcycle with today's city road conditions are rather low, measuring about 1-5 mm, we will utilize an amplitude value of
5 mm or 0.005 m in our simulation In this case, we want to determine which frequency range the system will perform best in: [0:20] (Hz) when the input signal is a sinusoidal function with an amplitude of 5 (mm)
Using the switch block, we can add a sinusoidal input signal without altering the previously created bumps signal Depending on the value of the second input, the Switch block will pass through the first or third input signals The first and third inputs include data The second input is a control input When the second signal is larger than zero, it will give the same input signal as the first signal or a bumps signal, as we have done, and when the signal is less than zero, the block will output a signal The third signal is a sinusoidal signal, which will serve as the input signal for the entire system
Figure 3.11: Simulation input signals setup 3.2.2 Mass spring damper block
Figure 3.12: Mass spring damper block
Figure 3.13: Expansion of mass spring damper block
A complete mass spring damper (MSD) can be described as below:
(3.3) Where 𝑘 is the spring stiffness, 𝑥 is the position of mass 𝑚, 𝑐 is the damper coeficient
In use of the second law of motion to describe the relation between motion of an object with mass and the forces acting on it, its formular as below: Σ𝐹 = 𝑚𝑎 (3.4)
With 𝑦 is the input signal we were set in previous step After having a Free Body Diagram, we concluded that:
As the conversion in equation (3.5), we start simulate the road profile signal or the right side of equation We take 𝑦 from input signal then directly multiply it with 𝑘 and use for the derivative block because we need to have the 𝑦̇ to multiply with 𝑐, after that add all those value together with the add block in the end of the section
With the value of Road section, we add it to the MSD section as the equation (3.6) In the need of 𝑥 value, first we have to multiply both side of the equation with 1
𝑚 to remove 𝑚 from 𝑥̈ Then the flow will continue go to the gain block which is for multiply the road section value with 1
𝑚 as in equation (3.6) and also gain the 𝑥̈ after it The 𝑥̈ value will go to two more integrator for having 𝑥̇ and 𝑥, both of those value will multiply with 𝑐 and 𝑘
40 respectively Here we use close loop for get back the value from the previous calculation to the sum block at the beginning of MSD section
Moreover, the output value of this block is the position or the value of 𝑥 which is what we need for the next block called Energy harvester block
This is the part the topic mentioned, be inspired by the electric generator and all the researched documents about this topic, we start to modelling our energy harvester
The energy harvester block will receive the output of the MSD block which is position then transfer it into electricity The harvester will moving reciprocating along with the damper, based on the electromagnetic induction when the magnet moving in and out the coil winding, it will happens some changing in electron moving direction results in generate electricity
According to equation (2.1), (2.2), (2.3), (2.4) we can rewrite the equation as below:
𝐸𝑀𝐹 = 𝐵𝑙𝑣 = 𝜋 × 𝐷 𝑎 × 𝑁 × 𝐵 × 𝑣 (3.7) After we did some research about EMF, we found that there is the different in EMF with Voltage They all have the same unit is Volt (V), but their definition is not the same, EMF is the Electromotive Force it occurs whenever there is a energy transformation like the battery or a electric source, it transfer the chemical energy into electrical energy But voltage, it is potential difference of two point in a circuit and always has less magnitude than the EMF
Simulation and result analysist
After finishing the component arrangement according to the formulars, the system runs depending on the vibration of the suspension over time, while also generating electricity
After entering the parameters gathered above into the Mathlab/Simulink model, we get the following outcomes:
The image shows that when the vehicle passed the bumps, the MSD began to dampen the vibrations When the MSD receives a vibration, its position changes, or it moves up and down, and it tends to smooth out over time when no vibration happens In this simulation, we can see how the MSD reacts when it receives a vibration signal from the road or road profile
After running the simulation for a vehicle speed of 6 m/s, we obtained the results depicted in figure 3.15 As you can see, the simulation effectively captured the behavior of the system at this particular speed Here are some key observations:
Vibration Damping by the MSD: The image clearly demonstrates how the MSD comes into play when the vehicle encounters bumps on the road (represented by the increased vibration in the graph) The MSD actively dampens these vibrations, as indicated by the decrease in vibration amplitude following the initial bump encounters
MSD Response to Vibration Signal: The graph also reveals the MSD's response to the vibration signal received from the road profile When a vibration occurs, the MSD's position changes, signifying its internal movement to counteract the vibrations This movement is reflected in the graph's up-and-down pattern during periods of vibration
Smoothing Effect Over Time: Another important aspect to consider is the damping characteristic of the MSD The graph shows that after the initial impact from a bump, the vibration signal subsides, and the MSD's response gradually diminishes as well This highlights the effectiveness of the MSD in smoothing out residual vibrations over time
The previous section focused on the vibration damping capabilities of the MSD system at a vehicle speed of 6 m/s However, another key aspect of this system is its ability to generate electricity
Leveraging Linear Regenerator for Electricity Generation
The system incorporates a linear regenerator that plays a crucial role in the energy harvesting process Since the linear regenerator is positioned alongside the MSD, it experiences the same vibrations as the MSD during the vehicle's encounter with bumps This strategic placement allows the linear regenerator to convert the vibrations arising from the MSD's oscillation into electrical energy, essentially capturing the wasted energy from the damped vibrations
The specific parameters chosen for the system were crucial in maximizing its energy harvesting potential As detailed in table 3.1 (which you can reference for specifics), we configured the system to achieve optimal performance By leveraging these parameters, the linear regenerator reached its peak voltage output during the simulation
Peak Voltage Output at 14.358 Seconds
The results depicted in the figure below showcase the voltage output of the linear regenerator As you can see, it attained its highest value of 34.29 volts at approximately 14.358 seconds This corresponds to the time when the vehicle encounters the second bump, and the MSD's oscillations are most pronounced and we collect it as below figure:
Figure 3.17: Output voltage value at 6m/s
So, this time, we would like to know how much output voltage we will gain if we increased the velocity to 24 m/s and we are still utilizing the same scenario as in the first simulation, here are the results:
Figure 3.18: MSD behavior when vehicle at 24 m/s
In this scenario, because the velocity has increased, it also means that the collision between the wheel and the speed bump will become larger, or we may say that the displacement of the shock absorber will be larger at a speed At 6 m/s, it moves a maximum distance of 0.0844 m, while at 24 m/s, it moves a maximum distance of 0.0886 m in 4,372 seconds, as shown in the images below
Figure 3.19:MSD position value at 6m/s
Figure 3.20: MSD position value at 24 m/s
When the vehicle speed was changed, the system produced the greatest 39.38 volts at 14.211 seconds, whereas previously only 34.29 volts were collected at the peak
Figure 3.21: Output voltage when vehicle at 24 m/s
Figure 3.22: Output voltage value at 24 m/s
We determined the displacement distance or position of the MSD over time by adjusting the vehicle's speed and using step signal input The change in the voltage value generated by the regenerator is also unique in each case because it is dependent on the location of the MSD during operation
Now, let's look at the second simulation scenario, in which the input signal is a sinusoidal function As described above, in this simulation scenario, the goal is to find out with an amplitude of 5 mm, at what frequency will the linear regenerator produce the maximum performance We have collected max power data for each frequency level in the range of [0:20] Hz and shown in the chart below:
Figure 3.23: The correlation between linear regenerator’s power and stimulation frequency graph
As we can see, the most prominent part in the chart above belongs to the frequency range from 0 to 6 Hz, with a peak power level of 3.4 Watt at a frequency of 2 Hz With this chart, we can firmly conclude that when the amplitude of road surface vibrations increases, it means that the performance of the regenerator will also increase The above simulation result show that the optimal operating environment for the regenerator system is one with a large oscillation amplitude but not a high frequency
As the suspension system will have its own oscillation frequency, when the road surface excitation frequency coincides with the suspension system's oscillation frequency, the amplitude grows to infinity Because of the increasing amplitude, the displacement and displacement speed will both increase, damaging the suspension system Velocity is a property of our linear regenerator, which generates energy by changing the magnetic flux across the coil On cars and motorcycles, suspension systems are frequently designed with specific oscillation frequencies outside the resonance region, typically operating at frequencies as low as 1 Hz and as high as 2.5 Hz, as shown in figure 3.23 The system performs best at the frequency range designed for the vehicle and provides the highest performance, satisfying the smoothness of the vehicle's body and assisting the vehicle in remaining stable when operating with the system under study
CONCLUSION AND RECOMMENDATION
To meet our target, our group studied the structure and operating principles of the system, documented our findings, and successfully built a model of the energy recovery system MATLAB/Simulink provided an effective tool for modeling our motorbike suspension system By using the inherent vibration of the suspension system as the foundation for developing a simulation model of the linear energy recovery system, the team has opened up new avenues for research and study while also contributing to environmental conservation
The results of our simulation show that the system has the potential to recover a significant amount of electricity when applied in practice However, the model still has many flaws stemming from the structure of the linear energy converter and the scarcity of reference sources on the subject, which affects the magnetic parameters Consequently, it is impossible to avoid receiving some erroneous findings Furthermore, there are numerous limitations in the measurement process, including determining characteristics such as magnetism and the magnetic field density of magnets, as well as limitations in the measuring equipment Therefore, establishing those parameters requires significant time and effort
Due to economic constraints and a limited time frame, our team could only conduct calculations and develop models in the MATLAB/Simulink environment as a starting point This foundation will support future research, enabling more optimized and successful development of energy recovery equipment based on our research, eventually bringing it into real-world application
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