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STEERING AND SUSPENSION SYSTEMS, , 2020, , UNIT 2, STEERING AND SUSPENSION SYSTEMS, SYLLABUS: Steering system; Principle of steering, Centre point steering, Steering, linkages, Steering geometry and wheel alignment, power steering., Suspension system: its need and types, Independent suspension, coil and leaf springs,, Suspension systems for multi-axle vehicles, troubleshooting and remedies., , Introduction of steering system:, Steering is the collection of components, linkages, etc. which allow a vessel (ship, boat) or, vehicle (car, motorcycle, and bicycle) to follow the desired course. An exception is the case, of rail transport by which rail tracks combined together with railroad switches (and also, known as 'points' in British English) provide the steering function., The most conventional steering arrangement is to turn the front wheels using a hand–operated, steering wheel which is positioned in front of the driver, via the steering column, which may, contain universal joints (which may also be part of the collapsible steering column design), to, allow it to deviate somewhat from a straight line. Other arrangements are sometimes found, on different types of vehicles, for example, a tiller or rear–wheel steering. Tracked vehicles, such as bulldozers and tanks usually employ differential steering— that is, the tracks are, made to move at different speeds or even in opposite directions, using clutches and brakes, to, bring about a change of course or direction., , Functions and Basic Principles:, The steering system, along with the suspension system, allows the driver to safely and easily, control the vehicle’s direction while driving. To accomplish these goals the steering system, works with components of the suspension to provide for the turning movement of the wheels., In addition to connecting the driver to the wheels, the steering system also provides feedback, to the driver from the front tires. This feedback, called road feel, is used by the driver to, determine how the vehicle is handling., , KECSP | Mr. S. S. Gaikwad, , 1

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STEERING AND SUSPENSION SYSTEMS, , 2020, , The Steering System:, The steering system consists of the components that allow the driver to turn the front wheels, of the vehicle, and for a few vehicles, provides for a limited amount of steering by the rear, wheels. The overall function of the steering system has not changed much since the earliest, days of the automobile., , Functions of the Steering System: The most basic function of the steering system is to, allow the driver to safely and precisely steer the vehicle. Beyond this, the steering system, also provides a way to reduce driver effort by making the act of steering the vehicle easier., The components of the steering system also absorb some of the road shock before it gets to, the driver. Very little has changed in the operation of the steering system or in some of the, components since the earliest automobiles. The things that have changed primarily have to do, with increased ease and effectiveness of operation and longer-lasting components that require, less maintenance.,  Primary function: to achieve angular motion of the front wheels to negotiate a turn. This, is achieved through linkages & steering gear which convert the rotary motion of the, steering wheel into angular motion of the front road wheels.,  Secondary functions are;, 1. Provide directional stability of the vehicle when going straight ahead., 2. Provide perfect steering condition. i.e. perfect rolling of all wheels at all times., 3. Facilitate straight ahead recovery after completing a turn., 4. To minimize tyre wear., 5. Absorb most of the road shocks going to the steering wheel., , Requirements of a good steering system:, 1. Steering system should be very accurate & easy to handle., 2. Effort required to steer should be minimal & must not be tiresome to the driver., 3. Steering mechanism should provide directional stability., 4. The vehicle should have a tendency to return to its straight ahead position after turning., 5. High rigidity., 6. Low friction resulting in high efficiency., , KECSP | Mr. S. S. Gaikwad, , 2

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STEERING AND SUSPENSION SYSTEMS, , KECSP | Mr. S. S. Gaikwad, , 2020, , 3

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STEERING AND SUSPENSION SYSTEMS, , 2020, , STEERING SYSTEMS:, 1. Manual steering system – relies solely on the driver to provide steering force, 2. Power assist (power steering) – uses hydraulic or electric power to help the driver apply, steering force., STEERING SYSTEM – COMPONENTS:, , KECSP | Mr. S. S. Gaikwad, , 4

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STEERING AND SUSPENSION SYSTEMS, , 2020, , •Steering wheel: used by the driver to rotate a steering shaft that passes through the steering, column., , •Steering shaft: Transfers turning motion from the steering wheel to the steering gear box., , •Steering Column: Supports the steering wheel & steering shaft, , Fig. Steering Geometry, KECSP | Mr. S. S. Gaikwad, , 5

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Steering Linkages:, •Connects the steering gear box to steering knuckles & wheels., •Steering linkage depends on the type of the vehicle, whether it’s a car which has independent, front suspension or a commercial vehicle having a rigid axle front suspension., 1. Steering linkage for vehicle with rigid axle suspension, 2. Steering linkage for vehicle with independent suspension., Front Axle:, •Till recently, all vehicles were steered by turning the front wheels in the desired directions,, with the rear wheels following., •Conventionally, the front axle was a dead axle, but these days, it’s true for heavy vehicles, only., •For 4WD vehicles & most of the cars, front axle is a live axle., •In case of a dead axle, the front axle beam is usually drop forged steel – 0.4% C or 1.3%, Nickel steel – no more used in modern cars., •Front axle has to take bending loads due to weight of the vehicle & torque loads due to, braking of the wheels. For this reason, front axle is made of I- section in the centre portion,, while the ends are made circular or elliptical., •A downward sweep is given to the centre portion to keep a low chassis height., , Main axle is connected to the stub axles by means of kingpins. The front wheels are mounted, on these stub axles., , Stub Axles:, , KECSP | Mr. S. S. Gaikwad, , 6

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Reversed Elliot type- most common. Stub axles; made of 3% Nickel steel & alloy steels, containing Chromium & Molybdenum, Steering Linkage for Vehicle with Rigid Axle Front Suspension:, Fig a and b shows such steering linkages. The drop arm (also called Pitman arm) is rigidly, connected to the cross-shaft of the steering gear at its upper end, while its lower end is, connected to the link rod through a ball joint. To the other end of the link rod connected the, link rod arm through a ball joint. Attached rigidly to the other end of the link rod arm is the, stub axle on which the road wheel is mounted. Each stub axle has a forged track rod arm, rigidly bolted to the wheel axis. The other ends of the track rod arms are connected to the, track rod by means of ball joints. The design of these ball joints is such that the expanding, springs compensates for wear or miss adjustments. An adjuster is also provided in the track, rod to change its length for adjusting wheel alignment., The steering gear provides mechanical advantage so that only a small effort is required at the, steering wheel to apply a much larger force to the steering linkage. Moreover it also provides, the desired velocity ratio so that much smaller movement of the stub axle is obtained with, large angular movement of the steering wheel. When the steering wheel is turned, the, swinging action of the drop arm imparts near linear movement to the link rod. This, movement is transmitted through the link rod arm to the stub axle so as to turn the later about, its pivot, which may be a king pin or ball joints. The other wheel is steered thorough the track, rod. Thus only one wheel is positively steered., , Fig. Steering Linkage for rigid axle suspension (line diagram), , KECSP | Mr. S. S. Gaikwad, , 7

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Fig. Steering Linkage for rigid axle suspension, Steering Linkage for Vehicle with Independent Front Suspension System:, In case of conventional rigid axle suspension, the main axle beam ensures the movement of, stub axle in the horizontal plane only. In this therefore, there is no vertical deflection of the, suspension and hence there is no change in effective track-rod length. However, in the case of, independent suspension, the two stub axles can move up or down independent of each other, due to which distance between ball-joint ends of the two track rod arms is continuously, varying. On account of this a single track rod as in conventional system described above,, cannot be used. Fig. depicts one linkage for independent suspension where the above, difficulty is avoided. Here three-piece track rod is used, the centre portion being called the, relay rod, which is connected at one end to an idler arm supported on body structure and to, the drop arm of the steering gear at the other end through ball joints. The relay rod is, restricted to move in horizontal plane only. Movement in vertical plane is provided by the, outer portions, viz, the tie rods about the end ball joints., , Fig. Steering linkage for vehicle with independent front suspension system, KECSP | Mr. S. S. Gaikwad, , 8

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STEERING AND SUSPENSION SYSTEMS, , 2020, , WHEEL ALIGNMENT:, Positioning the steered wheels in order to achieve the following is termed wheel alignment., 1. Directional stability during straight ahead position, 2. Perfect rolling condition on steering, 3. Recovery after completing the turn, Three different types of alignments can be done., 1. The front-end alignment – front axle’s angles are measured & adjusted., 2. Thrust angle alignment – confirms that the rear tyres are positioned directly behind, the front tyres., 3. Four-wheel alignment, Thus, an important design factor for the vehicle is the wheel alignment. Four parameters are, set by the designer, and these must be checked regularly to ensure they are within the original, vehicle specifications. The four parameters discussed here are as follows:, Automotive Engineering Fundamentals, 1. Camber, 2. Steering axis inclination (SAI), 3. Toe, 4. Caster, Factors of wheel alignment:, •The term ‘wheel alignment’ is used in connection with the stability & control of the vehicle, while in motion., •Wheel alignment means that while moving straight ahead, the wheels should be parallel., •If the wheels are pointing inward, they are said to be ‘toe-in’, •If the wheels are pointing outwards, they are said to be ‘toe-out’., •Both these situations are undesirable because in either case while rolling forward, each, wheel will be simultaneously slipping laterally due top which a continuous cross tread, scrubbing takes place., •Result of net toe-in & toe-out during running is excessive tread wear, heavy steering &, greater fuel consumption., •For good steering, handling & control, it’s also necessary that;, 1. There should not be any set back, which is the distance b/w the placing of the front tyres., Set back is a condition in which one wheel on an axle is in front or behind the other wheel in, relation to the chassis frame., 2. The thrust angle must be zero. Thrust angle is the angle made by the thrust line with the, longitudinal centre line of the vehicle. If the thrust angle is not zero, the vehicle will ‘dog, track’ & the steering will not be centered. When the thrust angle is zero, the rear wheels, follow the front wheels properly., 1. Camber:, Camber is the angle of the tire wheel with respect to the vertical as viewed from the front of, the vehicle, as shown in Fig. Camber angles usually are very small, on the order of 1 "; the, camber angles shown in Fig. are exaggerated. Positive camber is defined as the top of the, wheel being tilted away from the vehicle, whereas negative camber tilts the top of the wheel, KECSP | Mr. S. S. Gaikwad, , 9

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STEERING AND SUSPENSION SYSTEMS, , 2020, , toward the vehicle. Most vehicles use a small amount of positive camber, for reasons that will, be discussed in the next section. However, some off-road vehicles and race cars have zero or, slightly negative camber., , Fig. Positive & Negative camber (view from the front of the vehicle), STEERING AXIS INCLINATION (SAI):, Steering axis inclination (SAI) is the angle from the vertical defined by the centerline passing, through the upper and lower ball joints. Usually, the upper ball joint is closer to the vehicle, centerline than the lower, as shown in Fig., , Fig. Interaction of positive camber with steering axis inclination (SAI), Figure also shows the advantage of combining positive camber with an inclined steering axis., If a vertical steering axis is combined with zero camber (left side of Fig.), any steering input, requires the wheel to scrub in an arc around the steering axis. In addition to increasing driver, effort, it causes increased tire wear. The combination of SAI and positive camber reduces the, scrub radius (right side of Fig.). This reduces driver effort under low-speed turning conditions, and minimizes tire wear. An additional benefit of this system is that the wheel arc is no, longer parallel to the ground. Any turning of the wheel away from straight ahead causes it to, arc toward the ground. Because the ground is not movable, this causes the front of the vehicle, KECSP | Mr. S. S. Gaikwad, , 10

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STEERING AND SUSPENSION SYSTEMS, , 2020, , to be raised. This is not the minimum potential energy position for the vehicle; thus, the, weight of the vehicle tends to turn the wheel back to the straight ahead position. This, phenomenon is very evident on most vehicles-merely turning the steering wheel to full lock, while the vehicle is standing still will make the front end of the vehicle rise visibly. Although, the stationary the weight of the vehicle may not be sufficient to rotate the wheels back to the, straight-ahead position, as soon as the vehicle begins to move, the wheels will return to the, straight-ahead position without driver input. Caster angle also contributes to this self-aligning, torque. Note that the diagrams in the preceding figures have been simplified to facilitate, discussion. In practice, the wheel is dished so that the scrub radius is further reduced, as, illustrated in Fig., TOE:, Toe is defined as the difference of the distance between the leading edge of the wheels and, the distance between the trailing edge of the wheels when viewed from above. Toe-in means, the front of the wheels are closer than the rear; toe-out implies the opposite. Figure shows, both cases., , Cross-sectional view of a wheel and tire assembly Adapted from Automotive Engineering, (1 982)., , KECSP | Mr. S. S. Gaikwad, , 11

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Fig. Toe-in versus toe-out, For a rear-wheel-drive vehicle, the front wheels normally have a slight amount of toe-in., Figure shows why this is true. When the vehicle begins to roll, rolling resistance produces a, force through the tire contact patch perpendicular to the rolling axis. Due to the existence of, the scrub radius, this force produces a torque around the steering axis that tends to cause the, wheels to toe-out. The slight toe-in allows for this, and when rolling, the wheels align along, the axis of the vehicle. Conversely, front-wheel-drive vehicles require slight toe out. In this, case, the tractive force of the front wheels produces a moment about the steering axis that, tends to toe the wheels inward. In this case, proper toe-out absorbs this motion and allows the, wheels to parallel the direction of motion of the vehicle., CASTER:, Caster is the angle of the steering axis from the vertical as viewed from the side and is shown, in Fig. Positive caster is defined as the steering axis inclined toward the rear of the vehicle., , Figure Caster angle, , KECSP | Mr. S. S. Gaikwad, , 12

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STEERING AND SUSPENSION SYSTEMS, , 2020, , With positive caster, the tire contact patch is aft of the intersection of the steering axis and the, ground. This is a desirable feature for stability, as illustrated by Fig. When the wheel is, turned, the cornering force acts perpendicular to the wheel axis and through the contact patch., This creates a torque about the steering axis that acts to center the wheel. Obviously, negative, caster results in the opposite effect, and the wheel would tend to continue turning about the, steering axis. The most common example of positive caster is a shopping cart. The wheels are, free to turn around the steering axis, and when the cart is pushed straight ahead, the wheels, self-align to the straight-ahead position., , Fig. Self aligning generated by positive caster, , KECSP | Mr. S. S. Gaikwad, , 13

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STEERING AND SUSPENSION SYSTEMS, , 2020, , CENTRE POINT STEERING:, •If the centre line of the wheel meets the imaginary king pin axis at the road surface, this, condition is called Centre point steering., •With a standard axle, the point of intersection of the king pin axis with ground is different, from centre point steering., •This results in heavy steering & larger bending stress on the stub axles & king pin, •In order to avoid this, the wheel & the king pin are arranged to reduce the king pin offset –, Centre point Steering – reduces steering effort., , KECSP | Mr. S. S. Gaikwad, , 14

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Power Steering:, The power steering system is the system employed in automobiles to reduce the effort, required to operate the steering wheel. This feature adds to the comfort while driving, as less, effort is required to turn the steering by the driver., Need of Power Steering:, Drawbacks of Manual Steering, •More effort is needed at low speeds, in tight turns & while parking., •Doesn’t work well for large/heavy vehicles., •Can make a car more unsafe., Power Steering helps drivers to steer vehicles with less effort by providing steering comfort., Power steering (power assisted steering (PAS) ) helps drivers steer by augmenting steering, effort of the steering wheel., •Hydraulic or electric actuators add controlled energy to the steering mechanism, so the, driver can provide less effort to turn the steered wheels when driving at typical speeds, and, reduce considerably the physical effort necessary to turn the wheels when a vehicle is stopped, or moving slowly., •Usual power steering systems for cars augment steering effort via an actuator, a hydraulic, cylinder that is part of a servo system. These systems have a direct mechanical connection, between the steering wheel and the linkage that steers the wheels., •This means that power-steering system failure (to augment effort) still permits the vehicle to, be steered using manual effort alone., •Other power steering systems (such as those in the largest off-road construction vehicles), have no direct mechanical connection to the steering linkage; they require electrical power., , KECSP | Mr. S. S. Gaikwad, , 15

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STEERING AND SUSPENSION SYSTEMS, , 2020, , • Systems of this kind, with no mechanical connection, are sometimes called "drive by wire", or "steer by wire“. In this context, "wire" refers to electrical cables that carry power and data,, not thin-wire-rope mechanical control cables., •In other power steering systems, electric motors provide the assistance instead of hydraulic, systems. As with hydraulic types, power to the actuator (motor, in this case) is controlled by, the rest of the power-steering system., The following are the advantages and disadvantages of the power steering system., Advantages:, 1. The power steering system reduces the number of turns of steering wheel required to move, it from lock to lock (i.e. steering ratio on a vehicle having power steering us usually less)., 2. Easy steering while parking, at low speeds or tight turns., Disadvantages:, The components used in the power steering assembly are more costly than the ones used in, the normal steering. The most commonly power steering systems employed in automobiles, are, 1. Hydraulic power steering systems, and, 2. Electrically assisted, electronic power steering systems (or simply electronic power, steering systems)., Types of Power Steering:, There are two types of power steering system, ● Hydraulic Power Steering, ● Electronic Power Steering, Hydraulic Power Steering System: The hydraulic power steering, as discussed above, is the, system having a hydraulic booster that reduces the force required to operate the steering, wheel., Components, The hydraulic power steering system consists of the following major components, as shown, in fig., 1. Pump: It generates hydraulic pressure., 2. Control Valve: It switches the oil passage to the power cylinder according to the rotational, direction of the steering wheel., 3. Power Cylinder: It moves the piston in the cylinder to the right or left with hydraulic, force and thereby assists the steering wheel operation., 4. Fluid Reservoir: The power steering fluid reservoir stores fluid and cleans it using a built, in filter., , KECSP | Mr. S. S. Gaikwad, , 16

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Fig. Hydraulic Power Steering system, , Fig. Rack and Pinion Hydraulic Power Steering, KECSP | Mr. S. S. Gaikwad, , 17

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Working Principle, ● Neutral (Straight-Ahead) Position: Fluid from the pump is sent to the control valve., If the control valve is in the neutral position, the fluid will flow through the control valve into, the relief port and back to the pump. At this time hardly any pressure is created and because, the pressure on the cylinder piston equal on both sides, the piston will not move in either, direction., , Fig. Working Principle of Hydraulic Power Steering, ● While Turning: When the steering main shaft is turned is either direction, the control, valve also moves, closing one of the fluid passages. The other passage then opens wider,, causing a change in fluid flow volume and, at the same time, pressure is created., Consequently, a pressure difference occurs between both sides of the piston and the piston, moves in the direction of the lower pressure so that the fluid in the cylinder is forced back to, the pump through the control valve., Hydraulic Power Steering:, , KECSP | Mr. S. S. Gaikwad, , 18

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Hydraulic Power Steering System:, •Hydraulic power steering systems work by using a hydraulic system to multiply force, applied to the steering wheel inputs to the vehicle's steered (usually front) road wheels., •The hydraulic pressure typically comes from a rotary vane pump driven by the vehicle's, engine. A double-acting hydraulic cylinder applies a force to the steering gear, which in turn, steers the road wheels., • The steering wheel operates valves to control flow to the cylinder. The more torque the, driver applies to the steering wheel and column, the more fluid the valves allow through to, the cylinder, and so the more force is applied to steer the wheels., , Power Steering Fluid Reservoir & Pulley Driven Pump:, •Since the hydraulic pumps are positive-displacement type, the flow rate they deliver is, directly proportional to the speed of the engine., • This means that at high engine speeds, the steering would naturally operate faster than at, low engine speeds. Because this would be undesirable, a restricting orifice and flow-control, valve direct some of the pump's output back to the hydraulic reservoir at high engine speeds., •A steering booster is arranged so that should the booster fail, the steering will continue to, work (although the wheel will feel heavier)., •The working liquid, also called "hydraulic fluid" or "oil", is the medium by which pressure is, transmitted. Common working liquids are based on mineral oil., •Some modern systems also include an electronic control valve to reduce the hydraulic, supply pressure as the vehicle's speed increases; this is variable-assist power steering., Electro-Hydraulic Power Steering:, •Electro-hydraulic power steering systems, sometimes abbreviated EHPS, and also, sometimes called "hybrid" systems, use the same hydraulic assist technology as standard, systems, but the hydraulic pressure comes from a pump driven by an electric motor instead of, a drive belt at the engine., KECSP | Mr. S. S. Gaikwad, , 19

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STEERING AND SUSPENSION SYSTEMS, , 2020, , •This means that the power steering would still operate while the engine was stopped by the, computer to save fuel., • Electro-hydraulic systems can be found in some cars by Ford, Volkswagen, Audi, Peugeot,, Citroen, SEAT, Skoda, Suzuki, Opel, MINI, Toyota, Honda, and Mazda., Electronic Power Steering:, In electronic power steering, a magnet and a magnet torque sensor are mounted at the end of, the steering shaft. The torque sensor senses the amount and direction of turning moment the, driver is putting on the steering wheel. By the turning affect the magnet moves. The signal,, the strength of which depends on the amount of torque applied on the steering shaft, is sent to, an electronic control module (ECM). The ECM sends currents in varying magnitude to the, electric motor. The rotation of the motor forces the ball nut to move. This produces a force on, the rack. The steering effort is then supplied by the electric motor and the driver is relieved., , Electronic Power Steering:, •Electric power assisted steering (EPS/EPAS) uses an electric motor to assist the driver of a, vehicle. Sensors detect the position and torque of the steering column, and a computer, module applies assistive torque via the motor, which connects to either the steering gear or, steering column., •A mechanical linkage between the steering wheel and the steering gear is retained in EPAS., In the event of component failure or power failure that causes a failure to provide assistance,, the mechanical linkage serves as a back-up., •When EPAS fails, the driver encounters a situation where heavy effort is required to steer., This heavy effort is similar to that of an inoperative hydraulic steering assist system., •Electric systems have an advantage in fuel efficiency because there is no belt-driven, hydraulic pump constantly running, whether assistance is required or not, and this is a major, reason for their introduction., • Another major advantage is the elimination of a belt-driven engine accessory, and several, high-pressure hydraulic hoses between the hydraulic pump, mounted on the engine, and the, KECSP | Mr. S. S. Gaikwad, , 20

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STEERING AND SUSPENSION SYSTEMS, , 2020, , steering gear, mounted on the chassis. This greatly simplifies manufacturing and, maintenance., •The first electric power steering system appeared on the Suzuki Cervo in 1988. The system, has been applied by various automobile manufacturers, Limitations of Power Steering:, •Parasitic loss to the engine. (However, it is nearly negligible in most cases.), •Tends to be oversensitive (follows ruts in road, false inputs from harsh bumps), •Depending on suspension settings, power steering can make the car feel light, particularly at, high speeds., •Added weight and complexity., Trouble Shooting and Remedies:, , KECSP | Mr. S. S. Gaikwad, , 21

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STEERING AND SUSPENSION SYSTEMS, , 2020, , SUSPENSION SYSTEM, INTRODUCTION:, To isolate the vehicle body from the road shocks the automobile chassis is mounted on the, axle through some form of springs, shock absorber, etc. All the parts which perform the, function of isolating the automobile from the road shocks are collectively called a suspension, system., •The automobile chassis is mounted on the axles, not directly but through some form of, springs., •This is done to isolate the vehicle body from road shocks which may be in the form of pitch,, bounce, roll or sway., •These tendencies give rise to an uncomfortable ride & also cause additional stress in the, frame & body., •All the parts which perform the function of isolating the automobile from the road shocks –, Suspension System., NEED/OBJECTIVES OF SUSPENSION SYSTEM, 1. Protects the passengers from road shocks & provide a comfortable ride., 2. Prevents the vehicle body from tipping while traveling over rough ground or when turning., This helps to minimize the tendency of rolling, pitching, or vertical movement., 3. Provides cushioning effect. Thus, minimizes the effects of stress on vehicle components, and mechanisms., 4. Maintains the vehicle body at a perfect level while traveling over rough, uneven ground., This enables the up and down movement of the wheels relative to the body., 5. Insulates the vehicle structure from shocks and vibrations due to irregularities of the road, surface without affecting its stability., 6. Provides required height to the body structure as well as bears the torque and braking, reactions., •Suspension system maximizes the friction between road surface & the tyres during, acceleration, cruising & braking., Principle:, When a tire hits an obstruction, there is a reaction force. The size of this reaction force, depends on the unsprung mass at each wheel assembly., KECSP | Mr. S. S. Gaikwad, , 22

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STEERING AND SUSPENSION SYSTEMS, , 2020, , In general, the larger the ratio of sprung weight to unsprung weight, the less the body and, vehicle occupants are affected by bumps, dips, and other surface imperfections such as small, bridges. A large sprung weight to unsprung weight ratio can also impact vehicle control. No, road is perfectly flat i.e. without irregularities. Even a freshly paved highways have subtle, imperfections that can be interact with vehicle’s wheels. These are the imperfections that, apply forces on wheels., According to Newton‘s law of motion all forces have both magnitude and direction. A bump, in the road causes the wheel to move up and down perpendicular to the road surface. The, magnitude of course, depends on whether the wheel is striking a giant bump or a tiny speck., Thus, either the wheel experiences a vertical acceleration as it passes over an imperfection., The suspension of a car is actually part of the chassis, which comprises all of the important, systems located beneath the car's body. These systems include:, , The suspension system serves the following functions:, ● It connects the vehicle body and the wheels, and thus supports the weight of the vehicle., ● During running it acts together with the tyres to absorb and damp the various vibrations,, oscillations and shocks received by the vehicle due to irregularities of the road in order to, protect the passengers and cargo, and improve driving stability., ● It transmits the driving and braking forces, which are generated due to friction between the, road surface and the wheels, to the chassis and body., Requirements of a suspension system:, 1. Low initial cost., 2. Minimum weight., 3. Minimum tyre wear., 4. Minimum deflection consistent with required stability., Components of Suspension system:, There are three fundamental components of any suspension system.,  Springs, 1. Coil spring, 2. Leaf springs, 3. Air springs,  Dampers, 1. Shock Absorbers, 2. Struts:3. Anti-sway Bars,  Anti sway bars., , KECSP | Mr. S. S. Gaikwad, , 23

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STEERING AND SUSPENSION SYSTEMS, , 2020, , SUSPENSION GEOMETRY:, , SUSPENSION TERMINOLOGY:, •King pins (or) Swivel Joints: It’s the main part in the steering mechanism of a vehicle., •Pivot Centre: It’s the point where the king pin axis projects & intersects the ground., •Contact Patch: The flattened crown area of a tyre which contacts the ground., •Track: Distance b/w both steering wheel contact centres, Types of Suspension system:, , , , , , , , , , Conventional suspension system, Independent suspension system, Air suspension system, Hydro elastic suspension system, Non-independent suspension: - It has both right and left wheel attached to the same, solid axle. When one wheel hits a bump in the road, its upward movement causes a, slight tilt of the other wheel., Independent suspension:- Independent suspension is a broad term for, any automobile suspension system that allows each wheel on the same axle to move, vertically independently of each other, , KECSP | Mr. S. S. Gaikwad, , 24

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Types of Suspension System:, Before we go into the details of suspension we should understand that there are basically two, types of suspension front wheel suspension and rear wheel suspension. These two are, independent of each other except that they are both connected to the rigid structural frame of, the vehicle. Then again at the front wheels or the rear wheels there is scope for rigid, suspension and independent suspension, Rigid Suspension (Conventional suspension system):,  Two wheels are mounted on either side of the rigid axle,  When one wheel encounters the bump, both the wheel do not execute parallel up and, down motion,  So it gives rise to gyroscopic effect and wheel wobble,  Rear driving wheels mounted on live axle suspended by laminated leaf springs and, shock absorbers, An example of rigid suspension at the front wheels of a truck shown in the following figure,, for the convenience of the students. In this rigid suspension the front axle beam is connected, to the steering knuckles with the help of kingpins. On top of the front axle beam there are two, coil spring seats closer to the wheels for locating and supporting coil springs. The springs, support the frame. The disadvantage here is that the two wheels are not independent of each, other connected as they are by the rigid front axle. As a direct consequence the vehicle will, tilt when one of the front wheels passes over a bump or falls into a ditch or a pothole or when, the vehicle is running on an uneven surface or in rough terrain. Obviously, this causes lot of, discomfort to the driver in steering and to the other passengers., , KECSP | Mr. S. S. Gaikwad, , 25

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Fig. Rigid Axle Suspension System with coil springs and shock absorber, , Fig. Rigid Axle Suspension System with leaf springs and shock absorber, There cannot be any independent movement of the two stub axles in a rigid axle beam, suspension., , With a beam axle, the camber angle between the wheels is the same no matter where it is in, the travel of the suspension., KECSP | Mr. S. S. Gaikwad, , 26

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STEERING AND SUSPENSION SYSTEMS, , 2020, , ADVANTAGES:, •The principal advantage is its simplicity., •Very space-efficient and relatively cheap to manufacture., •Provide better vehicle articulation and durability in a high load environment, •They are universally used in buses and heavy-duty trucks., • Most light and medium duty pickup trucks, SUVs, and vans also use a beam axle, at least in, the rear., DISADVANTAGES, •It does not allow each wheel to move independently in response to bumps., •Mass of the beam is part of the unsprung weight of the vehicle, which can further reduce ride, quality., •Also the cornering ability is typically worse than other suspension designs., •Can cause a side-to-side oscillation of steering at certain speeds (typically 40-50 mph)., Independent Suspension:, The difficulty with the rigid suspension as explained above can be overcome by making the, two front wheels independent of each other. This arrangement is used passenger cars by, dispensing with the front axle beam. In the absence of the front axle beam the two front, wheels are made independent of each other and the vehicle does not tilt when one of the, wheels passes over a bump or falls into a pot hole on the road. Following figure shows the, principle of independent suspension system.,  Both the front and the rear wheel are utilized,  Design incorporated in the front wheels,  One wheel goes down ,the other wheel does not have much effect,  Basic classification of the design, 1. Macpherson Strut, 2. Double Wishbone, 3. Multi link, , KECSP | Mr. S. S. Gaikwad, , 27

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Fig. Independent Suspension System, At both ends of the steering knuckle there are ball joints for connecting the upper link and, lower link to the structural frame to ball joints. In this arrangement as compared to a rigid, axle the wheel is independent of the vehicle body. The spring between the two upper and, lower links is compressed and the ball joints accommodate all the three motions of the, vehicle – rolling, pitching and yawing, when the vehicle is running on an uneven surface., Note: The different variations of independent front wheel and rear wheel suspensions may be, of following categories;, ● With Coil Spring, ● With Leaf Spring, ● With Torsion Bar Spring, ● Shock Absorber with any of the above, Advantages:, 1. Comfort to passengers, 2. Good handling, 3. Shields the vehicle from damage, 4. Increases life of vehicle, 5. Keeps the tires pressed firmly to ground., Advantages (independent front):,  Bigger deflection of front wheels, no reaction on steering,  Greater distance for resisting rolling action,  Front axle (small-stub), improves road holding tendency of tyres.,  Minimum vibrations, Disadvantages:,  Better shock absorber required.,  Expensive,  Tyre wear increases due to transmission of torque., KECSP | Mr. S. S. Gaikwad, , 28

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Advantages (independent rear suspension):,  Lesser unsprung weight – improves ride, reduces tyre wear,  Increased passenger space,  Rear wheels remain stable, Disadvantages:,  Increased cost,  Complicated design,  Steering action is not proper, Components of a Suspension system:, It consists of the following principle components:, 1. Springs, which neutralize the shocks from the road surface?, 2. Shock absorbers (dampers), which act to improve riding comfort by limiting the free, oscillation of the springs., 3. Stabilizer (sway or anti roll bar), which prevents lateral swaying of the car., 4. A linkage system, which acts to hold the above components in place and to control the, longitudinal and lateral movements of the wheels., Suspension Spring:, The suspension springs are classified as follows:, , Leaf Spring:, Leaf springs are made of a number of curved bands of spring steel called “leaves”,, stacked together in order from shortest to longest. Stack of leaves is fastened together at the, centre with a centre bolt or a rivet. To keep the leaves from slipping out of place, they are, held at several places with clips. Both ends of the longest (main) leaf are bent to form spring, eyes, used to attack the spring to the frame or structural member of a body., Generally, the longer a leaf spring, the softer it will be. Also, the more leaves in a leaf, spring, the greater the load they will withstand. But on the other hand, the spring will become, firmer and riding comfort will suffer., , KECSP | Mr. S. S. Gaikwad, , 29

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Fig. Leaf Spring, Types of Leaf Springs:, a. Full elliptical leaf spring: This type of leaf spring refers to two semi-elliptical, springs connected at their ends, to form the shape of an ellipse as shown in Fig. (a)., b. Three quarter elliptical leaf spring: This type of leaf spring refers to one semielliptical spring connected over a quarter elliptical springs as shown in Fig. (b)., c. Semi-elliptical leaf spring: This type of leaf spring refers to forming the shape of, half ellipse as shown in Fig. (c). It is most commonly used in all types of heavy vehicles., d. Quarter elliptical leaf springs: This type of leaf spring refers to forming the shape, of half of semi-elliptical spring as shown in Fig. (d). this type of system is also called as, cantilever spring system, the thick end of which is bolted rigidly to the frame., e. Transverse leaf Spring: This type of leaf spring refers to a semi elliptical spring, mounted in a inverted manner, and has saddle at above forming a bow and is attached parallel, to the wheel axle as shown in Fig. (e)., , Fig. Different types of Leaf Springs, Helper Springs:, The helper springs are mounted directly on the main springs and are used in the, commercial vehicles such as trucks and buses to provide additional support for heavy loads,, at the rear end only. The helper springs are fixed on top of the rear main springs with the help, of a centre bolt and then clamped with U-bolts to the rear axle, whereas the ends are left, loose. When the vehicle is lightly loaded, only main springs are active. In case of heavy, KECSP | Mr. S. S. Gaikwad, , 30

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STEERING AND SUSPENSION SYSTEMS, , 2020, , loads, the helper springs rest against the brackets on the frame and then both the springs share, the load., , Fig. Helper Springs, ● Features of Leaf Springs, The curvature of each leaf is called “nip”. The overall curvature of the leaf spring is called, ‘‘camber’’. When a spring is flexed, nip causes the leaves in the spring to rub against, together and the friction created by this rubbing quickly damps the oscillations of the spring., This friction is called inter-leaf friction and is one of the greatest features of the leaf spring., However, this friction also causes a decrease in riding comfort, since it prevents the spring, from flexing easily. When the spring rebounds, nip prevents gaps from occurring between, each of the leaves, thus preventing dirt and sand, etc., from penetrating between the leaves, and causing wear., , Fig. Springs Nip and Camber, ● Techniques to reduce inter leaf friction, Since riding comfort deteriorates if the inter-leaf friction is great, measures are taken in actual, leaf springs to reduce this friction. Silencer pads are inserted between each of the leaves at, their ends to improve the sliding of the leaves against each other., , KECSP | Mr. S. S. Gaikwad, , 31

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Each of the leaves is also tapered at the ends so that they exert the proper amount of, pressure when they come in contact with each other., , Fig. Tapered at the ends of each Leaf, ● Characteristics of Leaf Springs:, 1. Since the springs themselves have adequate rigidity to hold the axle in the proper position,, it is not necessary to use linkages for this., 2. They control their own oscillation through inter-leaf friction., 3. They have sufficient durability for heavy-duty use., 4. Due to inter-leaf friction, it is difficult for them to absorb the minute vibrations from the, road surface. Therefore, leaf springs are generally used for large commercial vehicles which, carry heavy loads., Coil Springs:, The coil springs are extensively used in suspension system of automobiles. A standard coil, spring is made from a length of special spring steel, usually round in section. It is wound in, the shape of a coil. The ends of a coil spring are kept fl at so that they seat properly. The coil, spring is very elastic and compresses when a load is put on it. When a vehicle goes over a, bump or a pot hole, the spring compresses or expands to absorb the shock., , Fig. Coil Spring, KECSP | Mr. S. S. Gaikwad, , 32

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STEERING AND SUSPENSION SYSTEMS, , 2020, , Sometimes, instead of standard type of coil spring, progressive type coil springs are used in, automobiles. In progressive type coil springs, the wire is wound into coils of progressively, increased pitches. When the wheel hits a hole or bump, the larger pitch section absorbs, shocks or impacts with the smaller pitch section of the spring completely compressed. The, coil springs are mostly used in the independent suspension system. The advantage this type of, springs is that they can be assembled in compact space and are capable of storing twice the, energy than that of a leaf spring., ● Characteristics of Coil Springs, 1. The energy absorption rate per unit of weight is greater in comparison with leaf springs., 2. Soft springs can be made., 3. Since there is no inter-leaf friction, there is no control of oscillation by the spring itself. So, it is necessary to use shock absorbers along with them., 4. Since there is no resistance to lateral forces, linkage mechanisms to support the axle, (suspension arms, lateral control rod, etc.) are necessary., Suspension systems for multi-axle vehicles:, A multi-axle vehicle Suspension system comprising a first torsion axle mounted to a first, Suspension pivot member, the first Suspension pivot member pivotally coupled to a vehicle, frame, a second torsion axle mounted to a second Suspension pivot member, the second, Suspension pivot member pivotally coupled to the vehicle frame, a pivot member pivotally, Publication Classification coupled to the vehicle frame, the first Suspension pivot member, pivotally coupled to the pivot member, and the second Suspension pivot member pivotally, coupled to the pivot member., , The primary aspect of the invention is to provide a multi-axle vehicle Suspension system, having at least two torsion axles, each torsion axle coupled to a vehicle frame, and further, having a pivotal member pivotally coupled to the vehicle frame and pivotally coupled to each, torsion axle. Other aspects of the invention will be pointed out or made obvious by the, following description of the invention and the accompanying drawings., The invention comprises a multi-axle vehicle suspension system comprising a first torsion, axle mounted to a first Suspension pivot member, the first Suspension pivot member, pivotally coupled to a vehicle frame, a second torsion axle mounted to a second Suspension, KECSP | Mr. S. S. Gaikwad, , 33

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STEERING AND SUSPENSION SYSTEMS, , 2020, , pivot member, the second Suspension pivot member pivotally coupled to the vehicle frame, a, pivot member pivotally coupled to the vehicle frame, the first suspension pivot member, pivotally coupled to the pivot member, and the second Suspension pivot member pivotally, coupled to the pivot member., Trouble shooting Chart for Suspension System:, , KECSP | Mr. S. S. Gaikwad, , 34