An Experimental Feasibility Study on Regenerative Semi-Active Suspension Systems Mohammad Mehdi Naserimojarad1, Ali Tadayoninejad2, Mehrdad Moallem3 and Mohammad Eghtesad4 1

School of Electrical and Computer Engineering, Shiraz University, Shiraz, Iran, [email protected] School of Mechanical Engineering, Shiraz University, Shiraz, Iran, [email protected] 3 Professor, Mechatronic Systems Engineering, Simon Fraser University, BC, Canada, [email protected] 4 Professor, School of Mechanical Engineering, Shiraz University, Shiraz, Iran, [email protected] 2

This paper presents results of an experimental study on a regenerative semi-active suspension system. In this paper, a novel design of a suspension fork, equipped with an MR damper on one side and an electric generator on the other side, will be proposed. In this research the rotary electric generator is attached to a gearbox which converts the linear displacement to unidirectional rotation. First, the system will be tested in order to find an optimal input resistance of power converter attached to the regenerative damper for generating maximum power. The generated power is studied in each condition. Finally the effect of the MR damper on the vibrations of the system is studied.

Keywords Control.

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Semi-Active Regenerative suspension system; Energy Harvesting ; Vibration

Introduction

In the recent few years auto makers have shown interest in using regenerative systems in vehicles, especially in hybrid and electric vehicles in order to improve efficiency, reduce fuel consumption and also satisfy customers’ demands. In addition to energy which is dissipated as heat during brake, there are other sources of undesirable energy dissipation in a vehicle. All of consumed energy in a vehicle is not used for propulsion but also some of the energy is dissipated because of vibrations, aerodynamic drag and tires friction. Therefore producers and researchers are trying to eliminate these dissipations and turn them to beneficial energy which can be used for propulsion or accessories. Primarily re-generative brakes were introduced to regenerate the dissipated energy by braking and then regenerative suspensions were introduced to convert the dissipated energy in suspension systems to applicable energy. There are many methods for generating electric energy from vibrations in different applications including low power and high power. In low power applications where the acquired power is less than a few watts many researches have been done using piezoelectric transducers and electromagnetic generators [1][2][3]. In high power applications such as automotive and civil applications the feasibility of regenerative suspension systems has been studied in many works [4][5][6][7]. There are many methods for harvesting energy in high power regenerative suspensions using elec-

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2nd International Conference on Acoustics & Vibration (ISAV2012), Tehran, Iran, 26-27 Dec. 2012 tromagnetic generators. Many generators have been designed for energy harvesting applications including linear generators and rotary generators [8][9]. There are three major types of commercial suspension systems in vehicles, including passive suspension system, semi-active suspension system and active suspension system. A vast research has been done on these systems in the past few decades and many advances has took place in the performance and efficiency [10][11][12][13]. Semi-active suspension systems because of low power consumption, reliability, reasonable cost and good performance has been considered as a good solution for vibration control and handling improvement in vehicles. Many control strategies have been developed for these systems [14][15][16] and they can be controlled quick and easily using power converters. Semi-active suspension systems are based on smart fluids such as ElectroRheological Fluid (ERF) and MagnetoRheological Fluid (MRF). MRF is more commonly being used in comparison to ERF because of higher shear rate and acquiring low voltages [17]. In order to combine the benefits of regenerative suspension systems and semi-active suspension systems many studies has been done [18][19]. The main aim in designing Regenerative Semiactive Suspension System (RSSS) is harvesting the required energy for the semi-active part from the regenerative part so that there would be no need to external power source for driving the suspension system. The aforementioned works have studied different aspects of regenerative suspension systems in many applications but none of them has studied the regenerative suspension systems in addition to a semi-active damper on a suspension fork. In this paper we have introduced a semi-active regenerative suspension system based on a rotational DC generator and an MR damper.

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Modelling Regenerative Semi-active suspension systems

RSSSs are a combination of semi-active suspension systems and regenerative suspension systems. In a suspension system there are three major parts; mass, spring and damper. The quarter model of a 1-DOF suspension system is depicted in Fig.1.

Figure 1. Quarter model of a 1-DOF suspension system

. In a regenerative suspension system the electric generator can be modeled as a damper which relates the force to velocity [20][21] .Regenerative dampers can provide adaptive damping force, similar to active and semi-active dampers, based on the current which is drawn from them. Many studies have been done for modeling MR dampers like [22] and [ 23] . The behaviour of MR dampers is a hysteresis like behaviour. For example a force- velocity curve of MR dampers is shown in Fig. 2.

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2nd International Conference on Acoustics & Vibration (ISAV2012), Tehran, Iran, 26-27 Dec. 2012

Figure 2. Force-Velocity behaviour of an MR damper [23]

Modeling this behaviour have been an interesting topic in the past decade[22][23]. Between all of these models, [23] have been more successful in computational efficiency and accuracy. Considering the aforementioned topics about modeling RSSSs a model can be developed for the system. The schematic of the is depicted in Fig.3 .

Figure 3. Model of an RSSS

In this model The MR damper is modeled as current dependent damper and the electric generator is modeled as a resistance dependent damper. As it is mentioned in [24] the maximum power can be drawn when the input impedance of power converter is totally resistive. The value of the virtual resistor of a power converter can be selected based on the needed damping force or the needed electrical energy. The equations of this system can be written as below:

m s x s = - k s (x s - x u ) - c(i)(x s - x u ) - c(R)(x s - x u ) m u x u = - k s (x s - x u ) - c(i)(x s - x u ) - c(R)(x s - x u ) - k t (x u - x 0 )

(1) (2)

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2nd International Conference on Acoustics & Vibration (ISAV2012), Tehran, Iran, 26-27 Dec. 2012

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Experimental setup and results

In this research a RSSSs for a mountain bike was designed and fabricated. The designed system was based on a suspension fork. The suspension fork was equipped with an MR damper on one side and a rotary electric generator on the other side. A gearbox converts the linear displacements to unidirectional rotation for the electric generator. The MR damper was filled with PRSD MRF-710 from Pars Robin Smart Devices. The figure of the designed system is depicted in Fig. 4.

Figure 4. The fabricated suspension fork

In order to check the feasibility of the designed system it was tested under vibrations with an amplitude of about 4 cm. The system was tested with different resistors and the generated power was measured while the input impedance of the power converter was 1K , 100 ,10 and 5 . The results is shown in Table.1. Table 1. Generated power by the regenerative damper Resistance

Average generated voltage(Volts)

Average generated power(mW)

1k 100

2.03 1.19

4.12 14.16

10

1.07

115.9

5

0.67

89

Also a study was done in order to study the effect of MR damper on the vibrations of the system. The vibration results are shown in Fig.5.

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2nd International Conference on Acoustics & Vibration (ISAV2012), Tehran, Iran, 26-27 Dec. 2012

Figure 5. Vibration acceleration of the sprung mass while the MR damper is turned off(RED) and while the MR damper is activated(BLUE)

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Discussion

As it was shown in the last section the generated power when the generator is attached to a power converter with internal impedance of 10 is considerable and it can be used in practice. The generated power increases by decreasing the resistance at the beginning but starts to decrease with resistance under 10 . The reason is that by decreasing the resistance, the current increases so that the voltage loss in the generator’s windings increases. Also in the second experiment it is evident that the MR damper is able to reduce the acceleration of vibrations remarkably even while no control strategy is implemented on the system and the MR damper is only turned on.

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Conclusion

In this research a regenerative semi-active suspension fork was designed and fabricated. The designed system was tested in different conditions including different input impedance of power converter connected to the regenerative damper and different currents applied to the MR damper. An optimal input resistance was considered for the system for maximum power generation. The generated power was calculated in order to study the feasibility of the regenerative suspension system. Finally the system was tested under vibrations the acceleration of sprung mass was measured while the MR damper was activated and while it was turned off in order to test the performance of the MR damper..

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