International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008Certified Journal, Volume 4, Issue 4, April 2014)

Design of Electro-Hydraulic Active Suspension System for Four Wheel Vehicles Bhuwaneshwar Chandekar1, Hemant D. Lagdive2 1,2

Mechanical Engg Dept., N.B. Navale Sinhgad College Of Engg., Solapur

Abstract - Suspension systems have been widely applied to vehicles, from the horse-drawn carriage with flexible leaf springs fixed in the four corners, to the modern automobile with complex control algorithms. The suspension of a road vehicle is usually designed with two objectives; to isolate the vehicle body from road irregularities and to maintain contact of the wheels with the roadway. Active or adaptive suspension is an automotive technology that controls the vertical movement of the wheels with an onboard system rather than the movement being determined entirely by the road surface. This paper deals with design of electrohydraulic combined active suspension system for four wheel vehicles.

Passive suspension systems are subject to various tradeoffs when they are excited across a large frequency bandwidth. Compared with passive control, active control can improve the performance over a wide range of frequencies. However, active vibration control has the disadvantages of complexity and high-energy consumption. Active suspensions can be generally divided into two main classes: pure active suspensions and semi-active suspensions. Semi-active control has shown many advantages in vehicle suspension systems due to its low energy consumption with similar vibration control performance to the active control methods. [14] Active or adaptive suspension is an automotive technology that controls the vertical movement of the wheels with an onboard system rather than the movement being determined entirely by the road surface. The system virtually eliminates body roll and pitch variation in many driving situations including cornering, accelerating, and braking. This technology allows car manufacturers to achieve a greater degree of ride quality and car handling by keeping the tires perpendicular to the road in corners, allowing better traction and control. Active suspensions, the first to be introduced, use separate actuators which can exert an independent force on the suspension to improve the riding characteristics. The drawbacks of this design (at least today) are high cost, added complication/mass of the apparatus, and the need for rather frequent maintenance on some implementations.[15] Maintenance can be problematic, since only a factory-authorized dealer will have the tools and mechanics with knowledge of the system, and some problems can be difficult to diagnose. Michelin's Active Wheel incorporates an in-wheel electrical suspension motor that controls torque distribution, traction, turning maneuvers, pitch, roll and suspension damping for that wheel, in addition to an in-wheel electric traction motor.[12] Hydraulically actuated suspensions are controlled with the use of hydraulic servomechanisms. The hydraulic pressure to the servos is supplied by a high pressure radial piston hydraulic pump. Sensors continually monitor body movement and vehicle ride level, constantly supplying the computer with new data. As the computer receives and processes data, it operates the hydraulic servos, mounted beside each wheel.

Keywords- hydraulic, suspension, active, electro.

I. INTRODUCTION Suspension systems have been widely applied to vehicles, from the horse-drawn carriage with flexible leaf springs fixed in the four corners, to the modern automobile with complex control algorithms. The suspension of a road vehicle is usually designed with two objectives; to isolate the vehicle body from road irregularities and to maintain contact of the wheels with the roadway. Isolation is achieved by the use of springs and dampers and by rubber mountings at the connections of the individual suspension components. From a system design point of view, there are two main categories of disturbances on a vehicle, namely road and load disturbances. Road disturbances have the characteristics of large magnitude in low frequency (such as hills) and small magnitude in high frequency (such as road roughness)[1]. Load disturbances include the variation of loads induced by accelerating, braking and cornering. Therefore, a good suspension design is concerned with disturbance rejection from these disturbances to the outputs. Roughly speaking, a conventional suspension needs to be “soft” to insulate against road disturbances and “hard” to insulate against load disturbances. An automobile suspension system isolates to some degree the tires and wheels of the automobile from the occupant carrying body of the automobile. Mainly suspension system is divided into two system- active and passive suspension system. Passive suspension system consists of an energy dissipating element, which is the damper, and an energy-storing element, which is the spring. Since these two elements cannot add energy to the system this kind of suspension systems are called passive. 885

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008Certified Journal, Volume 4, Issue 4, April 2014) Helmut Kammel, Damme and et al [5], gives the working of an upper Macpherson strut step bearing for wheel suspensions in a motor vehicle. The Macpherson strut step bearing includes a metallic housing that is potshaped in the vertical section, a rubber buffer arranged in the housing, and a support piece, which can be connected to a shock absorber and protrudes with radially extending projections into the rubber buffer that is rigidly connected to it. A radially directed housing flange forms an abutment for an annular spring buffer made of an elastomeric material, against which the top end of a coil spring of the MacPherson strut, which coil spring surrounds the shock absorber, is supported. Recesses, which influence the axial damping characteristic of the MacPherson strut step bearing, are provided in the spring buffer. The metallic housing is connected to a cover plate, which passes over at the outer wall into a jacket ring, which is directed downward and projects beyond the spring buffer. M.S.P. Leegwater in their papers gives the working of a mechanically operated active suspension system. During the design of a suspension system, a number of conflicting requirements has to be met. The suspension setup has to ensure a comfortable ride and good cornering characteristics at the same time. Also, optimal contact between wheels and road surface is needed in various driving conditions in order to maximize safety. Instead of a passive suspension, present in most of today’s cars, an active suspension can be used in order to better resolve the trade-off between these conflicts. However, this is generally accompanied by considerable energy consumption. In this report an active suspension is investigated which is capable of leveling the car during cornering theoretically without consuming energy. Simulations using a full-car model show that this maximizes the car’s cornering velocity. As extreme cornering may be required to remain on the road or to avoid an obstacle, implementing the active suspension system improves safety. As the active part of the suspension takes care of realizing good cornering behavior and of static load variations, the primary suspension springs can be tuned purely for optimizing comfort and road holding. Simulations show that the required energy for leveling the car during cornering is negligible, so it can be concluded that the active suspension system is able to economically level the car. Furthermore, the active suspension’s potential for improving comfort is examined using a quarter-car model in combination with the skyhook damping principle. Performing simulations with an unrestricted actuator shows that comfort can slightly be improved with little actuator action and without deteriorating road holding and suspension travel.

Almost instantly, the servo-regulated suspension generates counter forces to body lean, dive, and squat during driving maneuvers. In practice, the system has always incorporated the desirable self-leveling suspension and height adjustable suspension features, with the latter now tied to vehicle speed for improved aerodynamic performance, as the vehicle lowers itself at high speed. II. LITERATURE REVIEW Y.G.Srinivasa and et.al [1], in their paper studies the ride dynamic performance of a high-speed tracked vehicle with active suspensions, and to compare it with that of a tracked vehicle having passive suspensions. To achieve the above mentioned purpose, a non-linear, inplane ride dynamic model which evaluates the driver’s seat acceleration, ride height and hull angular acceleration of a typical high-speed tracked vehicle has been developed, and its motion has been simulated. The ride dynamic behavior of a typical high-speed tracked vehicle negotiating a round bump is studied using a nonlinear, in-plane ride dynamics simulation model. The dynamic track load and track-terrain interaction is taken into account in the simulation. The wheel/track-terrain interaction is modeled with an equivalent damper and continuous radial spring. The dynamic track load is modeled considering the track belt stretching and the initial track tension. The influence of each of the parameters initial track tension, stiffness of torsion bar, longitudinal stiffness of track belt and damping rate of the suspension unit on the ride dynamics of the vehicle is studied through the computer simulation. Yunjun Li and et.al[3] in their paper gives the method of operating the active suspension system for a vehicle. The active suspension system receives information from one or more input sources; including both internal and external vehicle inputs, and uses that information to actively control the vehicle height. By doing so, the active suspension system can reduce aerodynamic drag on vehicle and improve the vehicles fuel economy ride comfort, handling and other aspects of operation. Some examples of external vehicle inputs that may be used include; short range road and vehicle information as well as long range traffic, road and route information. The active suspension may comprise of suspension control module electronically coupled to one or more internal vehicle input and one or external vehicle input; an actuator controlled by the suspension control module; a sprung mass mechanically coupled to the actuator. The suspension control module uses information from the internal and external vehicle input to drive the actuator and control a vehicle height.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008Certified Journal, Volume 4, Issue 4, April 2014) Further improving the comfort level requires more actuator action and results in considerable degradation of road holding and suspension travel. Performing simulations including actuator dynamics and force limitation shows that comfort can be improvement with only 5 [%] with this active suspension. However, improving comfort with the active suspension does not require but actually produces a small amount of energy as it functions as a skyhook damper. The ground hook damping principle in combination with a quarter-car model is used to investigate the possibilities of improving road holding with the active suspension. Performing simulations with an unrestricted actuator on a deterministic road surface shows that variations in force between tire and road are reduced considerably at the expense of deteriorating comfort. However, while performing simulations including actuator dynamics and force limitation show that the active suspension is hardly able to improve road holding because of the large required forces to be produced by the actuator. Moreover, because the enormous peaks in power require extremely powerful electric actuators it is not very interesting to apply the presented active suspension system in combination with the ground hook damping principle. Furthermore, the improvement when driving over a stochastic road surface is marginal and accompanied by an unacceptable deterioration in comfort. James D. Bennett [6] focuses on imaging techniques to identify the road condition like potholes, debris on road to vary the parameters of the Active suspension system. An active suspension system senses roadway defects and adjusts an active and controllable suspension system of the vehicle before tires come in contact with the defect. The active suspension system identifies a type of defect or debris, e.g., pothole, bump, object, etc., along with the size, width, depth, and/or height information of the defect to more accurately control operation of the suspension system to prepare for, or avoid contact with the roadway defects and obstacles. Imaging techniques are employed to identify the defect or debris. Operation of a serviced cruise control system is controlled to enhance passenger safety and comfort. T. Ram Mohan Rao and et. al [7] ,describes in their paper the modeling, and testing of skyhook and other semi active suspension control strategies. The control performance of a three-degree-of-freedom quarter car semi active suspension systems is investigated using Matlab/Simulink, model. The objective of this paper is to present a comprehensive analysis of novel hybrid semiactive control algorithms and to compare the semi-active and passive systems in terms of human body vibrational displacements and accelerations.

A theoretical model of the human seated model is developed in order to simulate the vertical motion of the Passenger in an omnibus when the vehicle passing over a speed bump. The mathematical model of these systems is presented. Ride comfort of off-road vehicles can be estimated by replacing the normal passive dampers in the vehicle suspension system with controllable, two-state, semi-active dampers. Abdolvahab Agharkakli and et. al [8], studies the passive and active suspension system using the mathematical model for quarter car model system. Current automobile suspension systems using passive components only by utilizing spring and damping coefficient with fixed rates. Vehicle suspensions systems typically rated by its ability to provide good road handling and improve passenger comfort. Passive suspensions only offer compromise between these two conflicting criteria. Active suspension poses the ability to reduce the traditional design as a compromise between handling and comfort by directly controlling the suspensions force actuators. In this study, the Linear Quadratic Control (LQR) technique implemented to the active suspensions system for a quarter car model. Comparison between passive and active suspensions system are performed by using different types of road profiles. The performance of the controller is compared with the LQR controller and the passive suspension system. Mohd Asqalani Bin Naharudin[10] studies the design and simulation of a semi-active suspension system for a quarter car model by controlling two input, spring stiffness, ks, and damper rate, bs. The performance of this system will be compared with the passive suspension system. There are two parameters to be observed in this study namely, the sprung mass acceleration and the suspension distortion. The performance of this system will be determined by performing computer simulations using the Matlab and Simulink toolbox. Duygu Guler[4] in their thesis studied the dynamic analysis of Double wishbone suspension system. In this thesis the natural frequencies, body displacements, velocities, and accelerations of a quarter-car with double wishbone suspension are examined by considering the proportionally damped system. Two models of quartercar suspension system are idealized employing two different assumptions due to the suspension links to describe the dynamic behavior of vehicles running on base excitation. In the first model, the links of the suspension are assumed to be rigid and the stiffness and mass matrices of the model are obtained by using the analytical method. In the second model, the links of the suspension are assumed to be flexible and the elastic stiffness, mass, and geometric stiffness matrices are obtained by using Finite Element Method. 887

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008Certified Journal, Volume 4, Issue 4, April 2014) III. WORKING PRINCIPLE Figure 1 shows the MacPherson strut suspension combines a coil spring and a shock absorber into a single unit. This provides a more compact and lighter suspension system that can be used in front wheel drive vehicles. [5] They provide a dampening function of shock absorbing and provide structural support to the vehicle suspension.

Fig 2 Concept Diagram of Electro Hydraulic Active Suspension System

The free length adjustment is done using a precision linear actuator in the form of a DC motor, coupled to recirculating ball screw arrangement with precise displacement and accuracy of motion. The inputs given \to the motor will be from electronically control module which have the traffic, road conditions and vehicle information .The motor drive the re-circulating screw and thereby the nut displaces to adjust the free length of spring and also adjust the displacement of the piston of the hydraulic damper arrangement. The second part of the hybrid system that is the hydraulic damper part, is coupled to the screw arrangement and it adapts itself as per the motion of the screw and nut arrangement, thereby adjusting the damping coefficient. Geared motor is used to drive the pinion which will move the rack either up or down, this used to change  Deflection of the spring to change the spring rate as per condition of the road.ie, for large bumps spring length will be maximum and for short bumps but in series the spring length will be short. The rack moves upward thereby deflecting the spring to reduce the length of spring, similarly rack moves downward to deflect the spring to increase the length of spring.

Fig 1 MacPherson Strut Suspension [11]

The set-up shown in figure 2 is an innovation over the conventional Mc-pherson strut arrangement. The spring used in a helical compression spring with both end ground, the free length of the spring is adjustable. The Free length adjustment will adjust the ground clearance of the vehicle and at the same time make the suspension light thereby increasing the displacement ability of the shock absorber.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008Certified Journal, Volume 4, Issue 4, April 2014)  To change the damping coefficient of the system by changing the damper hole size using the variable pitch disk. The downward motion of the rack makes the cam to open the holes of damper thereby allowing oil to easily pass through system disks thus enable a smooth descent of the suspension in large bump where as the upward motion of the rack makes helical cam to close holes of the damper to allow reduced oil flow to provide better damping in case of short but series of bumps. In this study the new concept EHAS will be implemented in the Double wishbone suspension system as center member with two wishbones control arms on both sides. Many suspension designers choose double wishbone, as double wishbones are the ideal suspension. It can be used on front and rear wheels, it is independent and most importantly, it has near perfect camber control. For over 40 years and even today, this is the first choice for racing cars, sports cars and High end Saloons. Double wishbone suspension always maintains the wheel perpendicular to the road surface; irrespective of the wheel's movement as it have more control over the camber angle of the wheel. This helps to ensure good handling.

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IV. OBJECTIVE OF THE WORK The aim of this paper is to design an active Electro Hydraulic suspension which will give a good road handling or driving safety and passenger comfort than passive suspensions.

[10]

[11]

V. SCOPE OF THE WORK

[12]

 The study will focus on comparison of the existing performance of passive suspension system with the electro-hydraulic active suspension system.  Analytical performance will be calculated for each element of the suspension system.  Experimental performance will be evaluated using the excitation conditions depicting the road conditions. Parameters such as amplitude, displacement ability, excitation frequency and damping coefficient etc. will be measured for their behavior.

[13]

[14]

[15]

VI. CONCLUSION From the above concept it can be concluded that the hybrid active suspension comprising electrical and hydraulic system can give better results to achieve a greater degree of ride quality and car handling by varying the height of the vehicle and provide better suspension and damping on different road conditions.

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