Basic Function of the Suspension System

Active Suspension System-- A Mechatronic System Chetan Bokare Arindam Sengupta Mechanical Engineering Y.C.C.E. Nagpur Maharashtra. INTRODUCTION: Air suspension was offered as an option years ago by some car manufactures. However, it was not widely accepted for use in passenger cars. In recent years, some heavy duty trucks and buses have used in air-suspension. Now, with electronic air suspension, air springs are making a comeback. In air-suspension systems, the four steel springs are replaced by four rubber cylinder, or air springs. Each rubber cylinder is filled with compressed air, with supports the car weight. When a wheel encounters a bump in the road, the air is further compressed & absorbs the shock. The electronic air-suspension system is shown in fig. It includes an electric air compressor, a microcomputer control module (MCM), four air springs with built-in solenoid valves, three height sensors (two front and one rear), and the air-distribution system at lines and fittings. The height sensors monitor the riding height, or vehicle trim height. They signal the contract module of any change. If the height is too high, the control module opens the solenoid valves in the spring with too much air. This allows some at the air to escape, towering the car. It height is too low, the control module turns on the air compressor. Then the control module opens the solenoid valves in the spring until proper trim height is restored. The control and operation of system are very similar to that of automatic-level control system. However air-suspension systems provides springing for all four wheels, instead at only two rear wheels as with automatic level control. ROLLING, BRAKE DIP, BOUNCING AND PITCHING :- Centre of gravity of a vehicle is at a height but retarding and cornering forces are applied of necessity at road levels. During cornering, a turning couple about the longitudinal axis of the vehicle is produced due to the centrifugal force acting at e.g. and the forces at tyre-road contact patch. This results in a motion called rolling. The left hand side suspensions move out of phase with right hand side. Braking causes a tendency for the nose of the vehicle to dip. This phenomenon is called brake dip. Other types of sprung mass motion are shown in fig. Pitching is defined as the rotating motion about a transverse line through the vehicle parallel to ground, the front suspension moves out at phase with the rear. Bounce is defined as the vertical motion of the center at gravity. The bounce can be front end bound or rear and bounce. Diagonal pitch is combination of pitch and roll. Softness of springing is limited by relation of wheel base and track to c.g. height and the permissible values of dip and roll. Smaller vehicles usually have relatively stiffer springs because c.g. height can be reduced that much. Suspension pitching and rolling axes should be arranged to pass through the c.g. of the vehicle so that the nose dip and the roll are confined to those due to tyre deflections only. However, such axis positions are difficult to obtain in practice. Road Irregularities and human susceptibility:- Some indication of the magnitudes of the disturbances caused by road irregularities can be gained from surface irregularity of Roads, DSIR Road Research Board Report, and 1936-7. It appears that surface undulations on medium – quality roads have amplitudes of 0.005m are characteristics of very good roads. The average pitch of these undulations is under 4m while most road vehicle wheels roll forwards at about 2m / rev. In Additional to the conventional tarmac roads, there are pave and washboard surface, the letter occurring largely on unsurfaced roads and tracks. Representative replies of these two types of surface are described in the MIRA proving ground, by A. Fogg, Proc. A.D. Inst. Mech. Engrs 1955-56. Obviously the diameter of the tyre, size of contact patch between tyre and road, the rate of the tyre acting as a spring, and weight of wheel and axle assembly affect the magnitude of the shock transmitted to the axle, while the amplitude of wheel motion is influenced by all these factors plus the rate of the suspension springs, damping effect of the shock absorbers, and the weights of the unsprung and sprung masses. The unsprung mass can be loosely defined as that between the road and the main suspension springs, while the sprung mass is that supported on these suspension springs, through both may also include the weights of ports of the springs and linkages. Two entirely different types of shock are applied to the wheel; that due to the wheel’s striking a bump, and that caused by the wheel’s falling into a pot-hole. The formed will be influenced to a major extent by the geometry of the bump and the speed of vehicle, while the major influence on the latter, apart from the geometry of the hole, is the unsprung masses and spring rates, speed being an incidental influenced factor. Human sensitivity to these disturbances is very complex, and a more detailed discussion can be found in Car Suspension and Handling by Donald Bastow, Pentech Press, London, 1980. It is widely held that vertical frequencies associated with walking speeds between 2.5 and 4 mph that is, 1.5 to 2.3 Hz – are comfortable, and that fore-and-aft or lateral frequencies of the head should be less than 1.5 Hz Dizziness and sickness is liable to be experienced if the inner ear is subjected to frequencies between 0.5 and about 0.75 Hz. Serious discomfort may be felt in other important organs at frequencies between 5 and 7 Hz. SPRINGING OF THE CAR :- If the front, and rear wheel axles were allowed to run in bearings fixed rigidly to the frame, the result would be extremely uncomfortable, the maximum speed of the car would be very limited, and the engine and transmission, as well as the bodywork, would be subjected to severe stresses, which in time would no doubt result in the fracture or breakdown of one or other of the working parts. It has become recognized, as a result of the long experience, that all types of vehicles used for locomotion, including railway trains, motor vehicle horse-drawn vehicles, pedal cycles and even children’s prams, must be provided with some means of insulating the wheels and axles from the rest of the vehicle, so that the road or rail shocks received by the wheels when traveling over uneven ground will not be transmitted appreciably to the other parts. The axles at railway carriages run in gunmetal axles boxes which can slide vertically is guides (known as ‘horn plates’) in the carriage frames, stiff spring bear down on the tops of these boxes and absorb most of the rail shocks; i.e., spring-insulate the carriage frames from the wheels and axles. The familiar leaf springs of horse-drawn vehicles serve also for the same purpose. Similarly, the pneumatic tyres and the spring saddles of pedal cycles afford a fair degree of insulation from road shocks. The object of the springing, or as it is terms, the suspension system, then is : 1) To protect the occupants from road shocks. 2) To reduce the stresses due to road shocks on the mechanism of the car , and 3) To maintain the body on an even keel when traveling over rough ground, or when turning so that any rolling, pitching or vertical movement tendency is minimized. The ideal suspension system would be that which allowed the road wheels to travels over rough uneven ground at any speed, whilst maintaining the body perfectly level; all the wheels would therefore move up and down relatively to the body. The Principles of Motor Springing:- Before outlining the usual methods of springing cars it should be mentioned that in the earlier days of motor-cars, members of the engine and transmission, and in some cases the frame themselves, were opt the fracture through ‘fatigue’ of the metal under rapidly alternating stresses caused by road shocks, so that the importance at protecting these parts will appreciated. The important principles underlying the satisfactory springing of motor vehicles are firstly, the reduction, to a minimum, of weight of the wheels and others parts receiving the road shocks this is usually termed ‘reduction of unsprung weight’. Secondly, the reduction of rolling or pitching of the body, to a minimum, by suitable design and attachment of the springs. It is usual to mount the body frame on the springing system at four points – generally at the corners of the rectangle formed by the framed members. Thirdly, it has become recognized that it is not yet possible to absorb satisfactorily the larger and also the smaller road impacts with one springing device, so that auxiliary attachments, or subsidiary members of the main springs are provided to look after the minor shocks; these are termed shock absorbers. BASIC FUNCTION OF THE SUSPENSION SYSTEM:- 1) To Provide Suitable Riding and Cushioning Properties – The frame should have a high degree of isolation from the axle so that the effect of road and tyre irregularities and wheel out of balance forces are not transmitted to the vehicle frame. 2) To Provide Good Road Holding – Since the basic functions of driving, cornering and braking are obtained by virtue of the road tyre contact area, the suspension system should always maintain the wheels in contact with road to obtain these functions which would otherwise be lost. In addition to these basic functions the vehicle suspension system must perform a No. of Complex functions which may conflict with each other. These functions are summarized below. These are general considerations which are applicable to passenger cars as well as heavy duty commercial vehicles as the case may be. 3) The suspension system must support the vertical load imposed by the weight of the vehicle, plus the body and payload weight. 4) It must Provide Adequate Stability and Resistance to Sideways and Roll Over – This is especially important for commercial trucks where substantial variations in the vertical center of gravity location can occur and also, in certain operations. Swaying, shifting and surging loads may be encountered cornering causes a tendency for the vehicle to roll. 5) It must Transfer Driving and Braking Forces between Frame and Axles – The suspension system must provide means to transfer the longitudinal forces generated during acceleration or deceleration. 6) It must resist Drive and Brake Torque Wind-up – When the driving and braking torques are applied to the ground through the tyre-road contact areas. The front suspension springs have a tendency to ‘wind-up’. Due to the spring wind-up, any point on the unsprung components other than the center of rotation is displaced. This will cause steering wheel rotation or change the angular position of the road wheel. Spring wind- up also displaces the tie-rod towards the engine and may affect the clearance between tie- road and engine exhaust system, and other components. 7) It must Resist the Cornering Effects – When negotiating a Curve or a Turn. Normally a vehicle has a tendency to continue in straight line and when the front wheels are turned forces are generated that cause the vehicle to turn. The cornering forces cause a weight shift which results in compression on one spring and release of another which may result in a rotation of axle in the plan view. This is called axle role steer. Another effect such load transfer can cause is the displacement of the steering arm ball from its normal load position and may result in what is called compliance steer. 8) It must maintain proper positioning of the castor on steering axle so that proper steering geometry is maintained. It should also maintain axles in alignment parallel to each other and perpendicular to the front. 9) In case of drive axles, the suspension system must provide for limited movement of drive shaft slip splines and in case of tandem axles the load transfer between the axles should be minimum. CLASSIFICATION OF SUSPENSION SYSTEM:- According to elements used for suspensions. a. Laminated or leaf springs. b. Coil Springs. c. Torsion bars. d. Air Springs. e. Rubber Springs. f. Hydro-elastic Springs. According to point of application. a. Front axel Suspension. b. Rear Axel Suspension. DESIRABLE CHARACTERISTICS OF A SUSPENSION SYSTEM:- The following are the desirable characteristics of a vehicle suspension below: 1) Maximum Deflection Consistent with Required Stability – In order to provide good cushioning ability together with better riding qualities, the suspension system must provide maximum deflection. However, it should be consistent with the vehicle stability requirements. 2) Compatibility with other Vehicle Components – Suspension system alone cannot completely determine the actual ride provided in a vehicle tyres, frame stiffness, wheelbase. Steering linkage all affect vehicle ride and hence the suspension system must be compatible with these components. 3) Minimize Wheel Hop – For the purpose of suspension analysis the vehicle weight is divided into sprung weight and unsprung weight. Spring weight is the weight of the vehicle that is supported on springs; rest is called unsprung weight. Frame and components attached to it come into the definition of sprung weight while wheels and wheel axles comes into unsprung weight. The resonance frequency. This wheel top frequency should be minimum wheel hop frequency and its amplitude greatly affect the road holding and hence, the cornering and braking obtainable because cornering and braking forces are at necessity applied at the road level. 4) It must provide sprung mass frequency that is relatively constant between laden and unloaded conditions. Furthermore, this natural frequency must not be in resonance with tyre rpm or with pavement expansion strips. Typical values of sprung mass frequency for passenger cars varies from 0.75 C/S to 2.5 C/S. Alternative to this is provision of a variable rate spring which will be effective on a wide range of loading and under varying conditions 5) It must have low maintenance and operating costs. It’s initial cost should also be low. 6) The total weight of the suspension system should be minimum. 7) It should minimise tyre wear. STRUCTURE OF ACTIVE SUSPENSION SYSTEM:- Fig. shows the active suspension system for Toyota Soarer and Fig. shows the hydraulic circuit for the system of Fig. The active suspension system for Soarer has four functions – ride comfort control, vehicle attitude control, height control and stability (Maneuverability) control. These functions are carried out by controlling hydraulic cylinder which have gas springs support each wheel. In the relatively low frequency band of less than 2 Hz, the pressure control valve receives pressure supply and discharge signals from the electric sensors, such as a G-sensor and controls the system. In the intermediate frequency band of 2 – 6 Hz, a spool valve in the pressure control valve senses the pressure changes and mechanically (Mechanical servo function ) operates to keep the line pressure constant, thereby preventing the transmission of vibrations to the vehicle body. As shown in Fig, oil pressure generated in the oil pump is temporarily accumulated in the accumulator via an attenuator which reduces pressure pulsation. A pressure control valve in the integrated valve unit control high pressure to necessary levels and supplies pressure to each hydro-pneumatic cylinder or returns the oil in the hydraulic cylinders. Generally, line pressure from the oil pump is changes according to the oil consumed by the pressure control valve. In this system, there is a PC valve in the pump. The PC valve balance the discharged flow rate and oil consumption properly, so that the line pressure is kept constant. AIR SPRINGS :- A volume of air, enclosed either in a cylinder fitted with a piston or in a flexible bellows, can be used as a spring, as shown in fig. Under the static load, the air is compressed to a predetermined pressure, and subsequent motion of the piston either increases or decreases the pressure and consequently increases or decreases the force acting on the piston. If this force is plotted against the piston travel, a curve similar to the compression curve of an engine indicator card will be obtained, so obviously the rate at which the force varies with the piston travel becomes greater as the air pressure increases. It follows that, whereas with a metal spring, equal increments of force result in equal increments of deflection the rate of an air spring is not constant. This varying rate is an advantage in that a low rate can be obtained for small deflections from the mean riding position while keeping the total rise and fall of the axles within reasonable limits. Air springs are fairly widely employed on vehicles whose laden and unladen weights differ greatly. This includes principally tractors for semi-trailers, the semi-trailers themselves and large drawbar trailers. They are also used to some extent on coaches, more especially in continental Europe and the USA, because of the very high quality ride obtainable with them, particularly if used with independent suspension. The disadvantages are high cost, complexity of compressed air ancillary system, and therefore risk of breakdown, more maintenance than other types of springing and freezing of moisture in the air in cold weather, which can cause malfunction of valves. Air suspension systems of this sort are, in general, too bulky and too complex for cars, though Citroen cars for instance have their hydro- pneumatic system, as shown in fig. In double-wishbone type suspensions a rubber bellows, circular in section and having two convolutions, is generally used and simply replaces the coiled spring of the conventional design. Rubber bellows type springs are used also in the Dunlop Stabilair suspension, as shown in fig. Alternatively a metal air-container in the form of an inverted drum is fixed to the frame and a piston, or plunger, is attached to the lower wishbone. Since the piston is considerably smaller than the drum, sealing is affected by a flexible diaphragm secured to its periphery and the lip of the drum. This construction enables the load deflection characteristics of an air spring to be varied considerably by using profiled guides, such as E and F in fig, to control the form assumed by the diaphragm, and thus it’s effective area, as the inner member moves relative to the other one. Elongated convoluted bellows such as are indicated in fig, have been used in trucks and coaches, with radius rods to deal with the driving and breaking torques and thrusts, and a panhard rod for lateral location. DEVELOPMENT OF VARIABLE DISPLACEMENT OIL PUMP FOR ACTIVE AIR SUSPENSION :- Introduction – The subject of this report is to outline our development of a variable displacement pump for automobiles. The pump has reduced the pressure pulsation to realize a quiet system. This was accomplished by simulation analyses. Experiments were conducted on a pressure sensing control valve ( hereinafter, PC valve ) having stable controllability in a board area if revolutions from 600 r.p.m. to 6000 r.p.m. and off supply from 5 lit / min. to 23 lit / min. It has been our desire to realize compatibility between stability and ride comfort in an automobile. Recently, due to the increased advances of electronics technology and integration with hydraulic technology, active control has been adapted to the classis system. Active suspension gives the driver soft ride comfort running on rough roads and stability which the driver expects. In order to actively and instantly restrain or control undesired movements generated by the vehicle vibrations and inclinations, it is necessary for the vehicle itself to provide a power source which can always supply energies necessary for controlling. On the other hand, running on a smooth road such as a highway, the vibrations or attitude changes of vehicle do not occur so often and not much energy is needed. Therefore, it is necessary developed hydraulic system with an efficient energy supply. Active suspension was first introduced on a commercial basis in the 1989 model vehicles ( TOYOTA CELICA AND NISSAN INFINITY ). The active suspension wad further installed in the 1991 model ( TOYOTA SOARER ) which abolish metal springs for supporting the vehicle body in order to improve attitude control during critical turning of the vehicle. The suspension system without metal springs, known as the Full Hydro-Pneumatic System, requires twice as much as energy as the previous active suspension system installed in the CELICA. Thus, focus was placed on the swash plate type variable displacement pump to efficiently supply energy. Design of variable Displacement Pump :- It is necessary for the pump to determine the proper values on response for oil consumption changes and maximum discharged flow rate in order to instantly and accurately control the automobile for ride comfort and vehicle attitude. Discarded Flow Rate – The oil consumption conditions were preliminarily tested under various running modes, from relatively constant running conditions at high speed cruising to running on rough roads. It was found from the test that the all consumption wad changeable from 5  / min during high speed cruising to 18 lit / min on rough road running. Based on these results and considering more severe conditions, the maximum oil is set at 23 lit / min ( 2000 r.p.m. ). It was further set to 7 lit / min ( 600 r.p.m. ) for the height control under the engine idling conditions. These two levers were targeted. ( as shown in fig. ) Response of Variable Displacement – A change at high speed will create a delay of about 0.2 sec. from the actual operation of steering wheel to the initiation of vehicle inclination. If such lane changes are repeatedly made, rolling control is made by using oil in the accumulator. During this time, compensation for this oil consumption is balanced by increasing the discharge flow rate. ( as shown in fig. ) In addition to these specifications, the following two points were considered for automobile use : Synthetic oil of low viscosity was used to keep the viscosity stable under the environmental temperature between –30 0C and 120 0C. Secondly, the pump pulsation was reduced ( which is the original cause of the vibration ) to reduce the noises in the passenger compartment for comfortable driving. Structure of the Variable Displacement Oil Pump and Operation Thereof : In order to make the pump compact, the active suspension and power steering pumps are placed in tandem and separated by oil seals. The pumps are driven by the engine. As shown in fig, the active suspension pump is of axial piston type having 9 cylinders and also comprised of a PC valve for swash plate angle control and swash plate. The pump is always kept the pressure at 11.7 MPa pressure. In order to reduce the pressure pulsation, the shape of the pump outlet portion is modified and an attenuator is mounted on the pump to absorb the pulsation immediately after the discharging. This attenuator includes metal bellows to prevent gas from pressure nitrogen gas introduced to make a seal. Operation : 1) When the oil supply in the suspension system is reduced or the number of pump revolutions is increased, the pump pressure increases. 2) Then, the PC valve is moved upward ( as shown in fig. ) to increase the pressure in the swash plate control cylinders which moves the actuator piston to the left to reduce the swash plate angle. 3) Thus, the oil flow from the pump is reduced to keep the line pressure constant. As above, if the pump pressure decreases, the line pressure is also kept constant. As explained, when high discharge flow rate is unnecessary, the flow rate is reduced, thereby reducing the horse power and heat loss. CONTROL SYSTEM FOR ACTIVE AIR SUSPENSION SYSTEMS :- Suspension control entails more than just regulation of the vertical movement of the wheels. The many factors that have to be taken into account include comfort of the occupants, roll, both longitudinal and lateral weight transfer, and the maintenance of contact pressure between the wheels and the ground consistent with good stability and handling. In a fully-active system there is a pump and hydraulic fluid reservoir and generally, one hydraulic actuator and one control valve for each wheel or pair of wheels. There may also be one or more hydraulic accumulators, to supplement the rate of flow from the pump to cater for sudden deflections of the suspension. The control valves may be all in one unit. They execute commands from an on- board computer which is served with information by sensors. The computer may be programmed to make instantaneous responses to changes inroad surface or equilibrium ( speed, roll, bake dive, or acceleration squat ) as indicated by the sensors or, in a simpler control arrangement, it may issue its commands periodically, to adjust the system to suit average conditions over periods of seconds or even minutes, depending on the precision of control required. Correction can be made also to under or oversteer, by adjustment of the front: rear roll stiffness ratio, even automatically while the car is being driven. Ideally, perhaps, sensors would defect the rise and fall of the ground in front of each wheel, so that the suspension could be made to deflect a precisely equal amount and thus keep the vehicle riding at a constant height above the ground. A speed sensor would be necessary, too, so that the computer could synchronise the movements of the suspension with the passage of the measured surface profile under the wheels. A further refinement might be a transducer to measure the actual response of the wheel so that, by taking into account hardness or softness of the surface, the dynamic loading on the tyres could be limited. Such a system, however, is impracticable at the current state of the art, and it is simpler to use a pressure transducer in each hydraulic actuator to signal to the computer any increase or decrease in the load applied by the ground to the wheel. Responding virtually instantaneously to this signal, the control system can direct fluid to flow either into or out of the actuator as necessary. The sensors actually used may include one transducer on each axle to measure the variations in height of the sprung mass above it under varying loads, a speed sensor, a yaw detection gyroscope or steering motion transducer, or a lateral accelerometer for measuring tendency to roll, a longitudinal accelerometer to detect braking and acceleration forces, and an accelerometer or strain gauge on each hub for assessing the quality of the road surface. In some instances a degree of simplification has been obtained by using for the rear axle only one height sensor and one actuator, the motions of two rear wheels being made interdependent through a hydraulic interconnection. Alternatives to some of the above-mentioned sensors might be transducers sensing the displacements of the throttle, brake pedal, steering gear and axle. A typical fully active suspension system and a semi-active system as shown in fig, neither, however, is a standard option in a quantity-produced vehicle. Since if studied in relation to the basic principles already outlined, are self explanatory, it is not proposed to describe then in detail here, however, some comments are necessary regarding Figs. Fig. shows a single suspension unit in the AP system. An increase in the static load on the right in the illustration, to be deflected upwards about its pivot. This of course is provided the relative movement between suspension arm and body is slow, so that the coil spring and damper in the linkage between the suspension arm and the lever are not compressed. The consequent upward deflection of the lever pulls the spool valve to the left, causing it to direct hydraulic fluid the hydraulically damped gas spring, thus extending it until the ride-height returns to what it was before. Rapid upward movement of the lever, on the other hand, are opposed by the inertia of the offset mass, so the coil spring and damper are compressed and there is little or no movement of the spool valve. In these circumstances the gas spring performs as in a conventional suspension system and, since little or no fluid motion is involved, the energy consumption by the engine driven pump is correspondingly small. To obtain this effect, the coil spring and damper have to be turned so that the force exerted on the offset pendulous mass gives it the same vertical acceleration as that imparted to the body of the vehicle by its gas spring and integral damper. This system has two major advantages. First, the body does not sink down on its suspension when it is switched off. Secondly, it does not need an electronic control. The AP system can be turned to take into account not only the lateral weight transfer but also the vertical deflection of the tyres during cornering. In some instance, however, especially for heavy vehicles, it may react too slowly. This cam be overcome by arranging for a steering input, as shown in Fig. 35.32. A double-acting ram, actuated by the steering mechanism, transfers hydraulic fluid from one side to the other of the vehicle through the dampers in the links between the suspension arms and the levers actuating the spool valve.. it does this in a direction such as to lift the lever on the outer and lower that on the inner side of the turn. Further information on active suspension in general, including design calculation, can be obtained from two papers, by Sharp and Hassan, Proc. I. Mech. E., Vols. 200 D3, 1986, and 201 D2, 1987. ** General Description of the Control Systems :- Figure shows the system configuration of the Active Suspension and the Active 4WS. Basic Control Strategy :- Fig shows the control block diagram of the Slow Active Suspension system various sensors are installed to get information on the vehicle, the longitudinal, lateral and vertical acceleration of the body, the relative strokes between sprung and unsprung mass, steering angle, and vehicle speeds etc. The basic control strategy is based on three functions shown below. 1) PID feed-back control of the height’s deflection – PID (Proportional, Integral, Differential) feed-back control is executed to reduce the deflection between the height target given by Selector Switch etc. and present height by relative stroke sensors. The objective of this control is to adjust static height corresponding to height target and to compensate feed-forward errors. 2) PI feed back control of vertical acceleration – Proportional value of vertical acceleration to compensate the lag of servo response and integrate that equivalent to vertical velocity are used for food-back control in order to realize Sky-hook damping. This damping is effective for improving ride comfort as shown in Fig, and it can also compensate feed-forward errors. 3) PD feed-forward control of longitudinal and lateral acceleration – The movements of sprung turning i.e. the pitch and roll, can be estimated from the longitudinal and lateral acceleration. Inertial moments are cancelled by this feed-forward control, and then equivalent pitch and roll stiffness of the suspension can be raised up to keep the vehicle’s attitude flat as shown in fig. Effect of Integrated Control :- The effects of integrated control are shown in fig, Plotted are the magnitudes of acceleration, deceleration by braking and lateral acceleration when the vehicles turns different radius of curves on a test course. The outermost solid line shows the limits of tire traction. The inner area enclosed by solid lines shown the distribution of acceleration and deceleration of a vehicle that has no integrated control system. The outer solid line shows the distribution of acceleration and deceleration of a vehicle that has an integrated control system. As shown in this diagram the vehicle with an integrated control system provides higher acceleration and deceleration than the vehicle without integrated control. It is clearly seen that the control vehicle has improved performance with higher stability and control. The overall ECU configuration involving the Active Suspension, Active 4WS, ABS and TRC is shown in fig, integrated control is accomplished through exchanging several bits of information within this electronic control unit. The effects of the integrated control systems are shown bellow. The Importance of Feed-Forward Control – Fig. shows the conceptional structure of the vehicle’s attitude control. The fluctuation of the vehicle attitude  is determined by the equivalent disturbance force to the vehicle  Fd and the robustness of the vehicle system H(s) which depends on the feed-back characteristics. That is  =  Fd / H(s) Generally an order to reduce the change in the vehicle’s attitude, it is necessary to make a more robust system or to decrease the equivalent disturbance force using more correct feed-forward canceling. However, comparing to a Full Active Suspension system with robust feed-back control, a Slow Active Suspension system cannot have enough robust feed-back control due to the lack of response, so feed-forward control becomes more important in order to attain good performance of vehicle’s attitude control. Therefore for a suitable control of vehicle’s attitude in the Slow Active Suspension system, a more precise estimation of the disturbance force and a more accurate compensation of the rag are necessary. Hence we developed new feed-forward control algorithms described hereinafter for the Slow Active Suspension to improve the vehicle’s attitude control. Effects of the Active Suspension :- Balance of Frequency Response between Yaw and Roll – From wheel steering angle proportional control combined with yaw rate feedback controlled by the Active 4WS, significantly improves the steering response and convergence of yawing after a lane change. However, it tends to generate a lateral acceleration at high frequency causing an ordinary vehicle to develop a fast transient roll (initial roll from sharp steering and rollback) resulting in an uncomfortable feeling to the driver. With the attitude control of the Active Suspension, there is a positive feeling of stability with a high level of dynamic balance in the yaw and roll direction. Stability & controllability in Lower and Higher Ranges of Lateral Acceleration:- The use of the tires relative to slip angle and load is very important for the integrated control by the two systems. The important characteristic of the Active Suspension is that it does not only control the attitude of the vehicle when turning, but also improves critical controllability by roll stiffness distribution control. Figure shows the effects of the rear steering control and roll stiffness distribution control on controllability and stability. As shown, the Active 4WS produces a large control effect in the range of less than 0.5G, while the Active Suspension produces a large control on roll rigidly distribution in higher G range. The new SOAERE provides sharp and stable steering performance in the range of les than 0.5G by implementing the Active 4WS. Improved performance by additional steering in a turn by the Active suspension’s roll rigidly distribution control is obtained in higher G range. Emergency Lane Change Performance :- Emergency lane change performance is one of the characteristics that best demonstrate the effect of integrated control of the Active Suspension and Active 4WS. Speedy response and convergence of yaw and lateral acceleration are essential. Controllability in the non-linear range is also momentarily required. Figure shows a comparison of performance in terms of approach speed, steering angle and yaw rate change in an emergency avoidance situation. The quick response to steering by the integrated control of the Active 4WS and Active Suspension enable the vehicle to change lanes smoothly with good stability and without excess yaw ADJUSTABLE AND SELF-ADJUSTING SUSPENSION :- When steel torsion-bar springs are used, some method of adjusting the standing height at the suspension is needed. This is because, owing to the multiplying effect of the lever arm connected to the active end of the torsion bar, even a small tolerance on the angular relationship between the fittings at its ends can make a significant difference to the attitude of the vehicle. Moreover, it is generally difficult to maintain tight tolerance on the angular relationship between the ends, especially when the bar has been overstressed, or scragged, to increase its fatigue resistance. The adjustment device is generally a screw stop against which a short lever on the static end of the bar bears. There are also variants of this principle, in which a warm-and-wheel drive is used, the wheel being on the Static end at the torsion bar and the worm on a spindle that can be rotated by the driver whilst sealed in the vehicle. Whereas the screw type adjustment is for the initial setting on the production line and only rarely used when the vehicle is being serviced, the worm and wheel or other mechanism – sometimes actuated by a small electric motor – is employed also for adjusting the fore-and-aft trim of the vehicle to cater for variations in the load distribution – for example, when heavy luggage is carried in the boot. While provision for such manual adjustment system is uncommon, automatic adjustment is the norm for air-suspension. There are two distinctly different types of automatic adjustment system for air suspension. One is the Citroen arrangement as shown in fig, in which on engine-driven hydraulic pump supplies fluid under pressure to an accumulator and thence through leveling valves to combined are spring and strut – damaged units. This is the constant mass system, in which the mass of the air, or an inert gas, enclosed in the spring is constant. The principle is illustrated diagrammatically, but greatly simplified, in fig, where the hydraulic accumulator is omitted and a floating piston P is depicted instead of the flexible diaphragm of the Citroen system, and the hydraulic damping system is omitted from the chamber O. The constant mass at gas A is compressed above the floating piston. Space O, between the floating piston P and the piston b attached to the axle, is filled with oil O, which moves up and down with the piston b and P, the air being correspondingly compressed or expanded. If the load in increased so that the assembly C, which is fixed to the body B, moves downwards, the valve V opens port D, so oil from the pump E passes into the space O. The piston P and assembly C, together with the body, therefore move upwards, and this continues until the port D closes again. Similarly, if the load decreases, the port F is opened and oil escapes from the space O until the port F closers again. Similarly, if the load decreases, the port F is opened and oil escapes from the space O until the port F closes again. This the basic ride height of the suspension can be kept constant. This self-adjusting action is damped so that the motions between the body and axle due to irregularities of the road do not influence the basic setting of the ride height. ADVANTAGES OF THE ACTIVE SUSPENSION: - Figure shows a circuit diagram of the Hydraulic system. In Figure, a block diagram of the control system is shown. The features of the system are as follows. 1) The normal coil spring is not used in this suspension, thus eliminating its vibration. This improves riding comfort at how frequencies. The spring function has been replaced by the Hydro-pneumatic Suspension system. The pressure control range has been widened to maintain a flat vehicle position even while turning. 2) The variable displacement piston pump is used to reduce energy consumption during non turning maneuvers, but still have sufficient flow in the turn ( as shown in fig. ). It features nine pistons to reduce pressure pulsation. 3) Vertical G sensors are used for skyhook damping. 4) Active Suspension has four control functions as follows. a. Riding comfort control to absorb road surface irregularities. b. Vehicle attitude control to maintain a constant vehicle attitude at all times. c. Stability and controllability control to ensure stability in turning and straight driving. d. Vehicle height control to maintain a constant height regardless of the load. These functions operate mutually for overall control.