Study on an Energy-Harvesting Magnetorheological Damper System in Parallel Conﬁguration for Lightweight Battery-Operated Automobiles

: Suspension dampers are extremely critical for modern automobiles for absorbing vibrational energy while in operation. For years now, the viscous passive damper has been dominant. However, there is a constant need to improve and revolutionize the damping technology to adapt to modern road conditions and for better performance. Controlled shock absorbers capable of adapting to uneven road proﬁles are required to meet this challenge and enhance the passenger comfort level. Among the many types of modern damping solutions, magnetorheological (MR) dampers have gained prominence, considering their damping force control capability, fast adjustable response, and low energy consumption. Advancements in energy-harvesting technologies allow for the regeneration of a portion of energy dissipated in automotive dampers. While the amount of regenerated energy is often insu ﬃ cient for regular automobiles, it could prove to be vital to support lightweight battery-operated vehicles. In battery-operated vehicles, this regenerated energy can be used for powering several secondary systems, including lighting, heating, air conditioning, and so on. This research focuses on developing a hybrid smart suspension system that combines the MR damping technology along with an electromagnetic induction (EMI)-based energy-harvesting system for applications in lightweight battery-operated vehicles. The research involves the extensive designing, numerical simulation, fabrication, and testing of the proposed smart suspension system. The development of the proposed damping system would help advance the harvesting of clean energy and enhance the performance and a ﬀ ordability of future battery-operated vehicles.


Introduction
Suspension dampers have played a significant role in the automobile industry for years and are a crucial part of the modern-day commute. For years now, the viscous passive damper has been dominant in the automobile industry [1]. However, with the improvement of vehicle performance and unpleasant road conditions, there is a constant need to improve and revolutionize the damping technology [2]. Controlled shock absorbers, capable of adapting to uneven road profiles, are required to meet this challenge and enhance the passenger comfort level [3]. Controlled shock absorbers can be classified into active and semi-active type suspension systems. The active suspension systems use an external power source to improve the controllability and responsiveness of the dampers to external disturbances [4]. The active systems add complexity, increase cost and weight, and often have reliability issues [5].
On the other hand, semi-active suspension systems use only a small source of power to moderate the damping and stiffness properties. The adjustable damping in the semi-active systems is achieved uses a predictive analytical model of the energy-harvesting system to predict the voltage generation. The research involves the extensive designing, numerical simulation, fabrication, and testing of the proposed smart suspension system.
An analytical model is developed using the fundamentals of vibrations to calculate the output energy of the energy-harvesting magnetorheological dampers. The free-body diagram of all the three dampers is constructed, and the damping forces acting on the systems are analyzed. This model is formulated using MATLAB/Simulink software to evaluate the equations used in the model. The design of the energy-harvesting magnetorheological dampers is developed using the CATIA V5 CAD tool. From this design, a prototype of the damper is fabricated. An in-house testing setup is built for testing this prototype. This prototype is tested for various parameters, such as damping force, velocity, and induced voltage. The prototype and the analytical model are validated.

Analytical Modeling of Energy-Harvesting Module
Induced voltage and magnetic flux can be found from the following equations [4]. The terms used in the equations are given in Table 1. Efficiency factor (η d ) is introduced to accommodate for the friction involved in the assembly while under oscillations. Friction ultimately causes a reduction in the displacement and speed of the damper during actuation. Due to this reduction, the movement of the magnet is decreased, which confines the power generation.

Term Symbol
Magnetic flux of air gap without considering the leakage φ g Flux density of the magnet B rem Magnet thickness τ m Relative magnetic permeability µ 0 Magnetic field intensity of the magnet H c Length of the air gap between piston rod and permanent magnet array g Surface area of cylindrical air gap A g Cross-sectional area of the magnet A m Diameter of the shaft s As the proposed damper is a downscaled version of the actual system, it is recommended to keep in mind the scaling laws. There are two types of scaling laws: (1) depends on the size of the physical objects and (2) involves both the size and material properties of the system. The project involves energy harvesting; therefore, the miniaturization of the EMI module needs to be considered. In a current-carrying wire in a magnetic field, for a given current density, the current i is proportional to the cross-sectional area of the wire [21]. Therefore, whenever a downscale is occurring, the cross-sectional area of the wire decreases in the order of square roots. So, to harvest more current from the magnetism, the length of the wire needs to be increased. To achieve that, a higher number of turns of inducing coil are required. Table 2 shows the values of various parameters of the energy-harvesting system used in this study.

MATLAB/Simulink Model
The MATLAB/Simulink model, based on the energy-harvesting equations, is attained as shown in Figure 1. The model starts with the equation of the cross-section area of the magnet. It requires the values of the diameter of the shaft and the width of the magnet. The second section is for finding the surface area of the cylindrical air gap, which requires the details of the length of the air gap between the piston rod and the permanent magnet array, magnet thickness, spacer thickness, the diameter of the shaft, and the width of the magnet. Furthermore, these findings are included in the equation of magnetic flux (φ g ). Based on the above values, the MATLAB/Simulink model can predict the induced voltage (E).

Energy-Harvesting Magneto-Rheological Suspension-Prototype Design
The CATIA V5 design modeling software program is used to model the proposed damper. Both the dampers on the side (energy harvesting module) consist of a copper generation coil and a neodymium N48 magnet inside. The schematic of the energy-harvesting module is shown in Figure 2a. Figure 2b shows the cross-sectional view of the MR damper. The energy-harvesting magnetorheological suspension prototype design in the parallel configuration is shown in Figure 3. The center damper has MR fluid inside it. Both the ends of MR damper and energy-harvesting modules are connected to the common beam. Therefore, any uneven profile coming from the bottom side can be equally distributed. The purpose of the MR damper is to damp the uneven vibrations. The EMI module generates energy, which can be further utilized for any other auxiliary systems.
Vibration 2020, 3 FOR PEER REVIEW 5 magnetorheological suspension prototype design in the parallel configuration is shown in Figure 3.

141
The center damper has MR fluid inside it. Both the ends of MR damper and energy-harvesting 142 modules are connected to the common beam. Therefore, any uneven profile coming from the bottom 143 side can be equally distributed. The purpose of the MR damper is to damp the uneven vibrations.

144
The EMI module generates energy, which can be further utilized for any other auxiliary systems.   Table 3.
153 Table 4 shows the design parameters of the MR damper. Vibration 2020, 3 FOR PEER REVIEW 5 magnetorheological suspension prototype design in the parallel configuration is shown in Figure 3.

141
The center damper has MR fluid inside it. Both the ends of MR damper and energy-harvesting 142 modules are connected to the common beam. Therefore, any uneven profile coming from the bottom 143 side can be equally distributed. The purpose of the MR damper is to damp the uneven vibrations.

144
The EMI module generates energy, which can be further utilized for any other auxiliary systems.   Table 3.
153 Table 4 shows the design parameters of the MR damper.   Table 3. Table 4 shows the design parameters of the MR damper.  in a base fluid. When exposed to a magnetic field, the rheology of MRF-132DG fluid instantaneously 160 changes from a free-flowing liquid to a semi-solid [22]. The properties of Lord MR Fluid-132DG are 161 shown in Table 5. The typical magnetic properties of the Lord MRF-132DG Fluid, as provided by the 162 manufacturer, are shown in Figure 5 [22]. Figure 6 shows the assembly of the proposed Energy-    The MR fluid used in the damper is MRF-132DG from Lord Corporation (Cary, NC, USA). Lord MR Fluid-132DG is a hydrocarbon-based MR fluid, which contains micron-sized particles in a base fluid. When exposed to a magnetic field, the rheology of MRF-132DG fluid instantaneously changes from a free-flowing liquid to a semi-solid [22]. The properties of Lord MR Fluid-132DG are shown in Table 5. The typical magnetic properties of the Lord MRF-132DG Fluid, as provided by the manufacturer, are shown in Figure 5 [22]. Figure 6 shows the assembly of the proposed Energy-Harvesting Magnetorheological (EHMR) damper in a parallel configuration.

185
An Adafruit digital ADXL345 is used as an accelerometer, as shown in Figure 8. The sensor has 186 three axes of measurements, X, Y, and Z, and pins that can be used as digital interfacing. The

187
sensitivity level needs to be given as ±2g, ±4g, ±8g, or ±16g. The lower range offers more resolution 188 for slow movements; the higher range is suitable for high-speed tracking. The ADXL345 is the latest 189 and greatest from Analog Devices, known for its exceptional quality micro-electro-mechanical   An Adafruit digital ADXL345 is used as an accelerometer, as shown in Figure 8. The sensor has three axes of measurements, X, Y, and Z, and pins that can be used as digital interfacing. The sensitivity level needs to be given as ±2 g, ±4 g, ±8 g, or ±16 g. The lower range offers more resolution for slow movements; the higher range is suitable for high-speed tracking. The ADXL345 is the latest and greatest from Analog Devices, known for its exceptional quality micro-electro-mechanical system (MEMS) devices. The voltage common collector (VCC) takes in up to 5 V and regulates it to 3.3 V with an output pin.

185
An Adafruit digital ADXL345 is used as an accelerometer, as shown in Figure 8. The sensor has 186 three axes of measurements, X, Y, and Z, and pins that can be used as digital interfacing. The 187 sensitivity level needs to be given as ±2g, ±4g, ±8g, or ±16g. The lower range offers more resolution 188 for slow movements; the higher range is suitable for high-speed tracking. The ADXL345 is the latest 189 and greatest from Analog Devices, known for its exceptional quality micro-electro-mechanical  A Qunqi L298N Motor Drive Controller Board Module Dual H Bridge DC Stepper (Qunqi, Guangzhou, China) is used for stepper control of the DC Motor. A Mini DC Motor-Type 130 is used to provide vibration inputs. The operative voltage for the motor is DC 1.5 V to 6.0 V. An Arduino Uno R3 Microcontroller A000066 is used to receive and deliver the data to and from the sensors. The microcontroller is connected to a computer with the use of USB 2.0 to supply the input voltage to the board itself. Arduino 1.8.5 software is used to collect the measured values of damping force and velocity. The full in-house built setup consists of a power supply for the MR damper, a computer with the Arduino software program, load cell, load sensor, accelerometer, stepper controller, DC motor, voltmeter, and the assembly of the energy-harvesting magnetorheological damper in the parallel configuration, as shown in Figure 9.

212
The damping force vs. velocity diagram decides the working ability of a damper. The force vs.

213
velocity diagram shown in Figure 11 represents the damping coefficient value. Ideally, this graph 214 should be on a linear slope. However, no system in the world is ideal or perfect. Therefore, any force 215 Figure 9. In-house built energy-harvesting MR damper test setup.

212
The damping force vs. velocity diagram decides the working ability of a damper. The force vs.

213
velocity diagram shown in Figure 11 represents the damping coefficient value. Ideally, this graph The damping force vs. velocity diagram decides the working ability of a damper. The force vs. velocity diagram shown in Figure 11 represents the damping coefficient value. Ideally, this graph should be on a linear slope. However, no system in the world is ideal or perfect. Therefore, any force vs. velocity diagram of the actual damper does not have a linear straight line curve. In the compression stroke, the velocity of the damper increases, which also causes an increment in the damping force. Meanwhile, during rebound, the stroke velocity and damping force decreases. The curve of the compression and rebound stroke does not follow the same path, and a loop is created. This loop is called a hysteresis loop. It can be seen from the graph that under various input currents, the loop curve changes. These data show that with the increase in current, the damping force increased as the fluid thickened. The highest force observed was 31 N for 2 A current.     Figure 12 shows the calculated (theoretical) and measured (experimental) values of the induced voltage with respect to time. The amount of harvested energy is almost around that of the generated energy. The percentage of error is very low. The major reason for this error could be friction in the elements of the design and test setups.

231
In this study, an energy-harvesting magnetorheological damper system, in parallel 232 configuration for application in lightweight battery-operated automobiles, is designed, fabricated,

Conclusions
In this study, an energy-harvesting magnetorheological damper system, in parallel configuration for application in lightweight battery-operated automobiles, is designed, fabricated, and tested. An analytical model is developed to predict the induced voltage through an energy-harvesting module, and a further parametric study is conducted through experimentation to understand the system performance. Furthermore, the analytical model is validated through experimentation. The major conclusions of the study are as below: • In this study, an EHMR suspension system consisting of an MR damper and an energy-harvesting module in the parallel configuration is successfully designed and fabricated.

•
The parametric study suggested that the parallel configuration of the energy-harvesting module with an MRD does not adversely affect the MR system performance. • The analytical model is validated, and the model can predict the induced voltage from the energy-harvesting module within an accuracy of 3.5% error.

•
The energy-harvesting capability of the proposed system can be further improved by providing additional sets of magnets and increased coil windings.