suspension_system.pptx

suspension_system.pptx

• 1.
  like the othersystems on cars and light trucks, the suspension system has become more advanced through the years. These advances have been made to provide better and safer handling and a better ride. Today, front and rear suspensions have many parts and can be quite complex (Figure 45–1). As a vehicle moves, the suspension and tires must react to the current driving conditions. Specifically, the suspension system: ■ Supports the weight of the vehicle ■ Keeps the tires in contact with the road ■ Controls the direction of the vehicle’s travel ■ Attempts to maintain the correct vehicle ride height ■ Maintains proper wheel alignment ■ Reduces the effect of shock forces as the vehicle travels on an irregular surface The suspension system for a late-model car. The front uses a strut setup, while the rear has a multilink system. Courtesy of BMW of North America, LLC
• 2.
  SUSPENSION SYSTEM COMPONENTS. Nearlyall automotive suspensions have the same basic components, and they operate similarly. The basic differences between the suspensions found on various vehicles are the construction and placement of the parts Springs A spring is the main of all suspension systems. Springs carry the weight of the vehicle and absorb shock forces while maintaining correct riding height. They are compressible links between the vehicle’s frame and body and the tires. Doing this, they dampen road shock and provide a comfortable ride. If a spring is worn or damaged, other suspension parts will change out of their proper positions and will experience increased wear. Various types of springs are used in suspension systems (Figure 45–2)—coil, torsion bar, leaf (both mono- and multi leaf types), and air springs.
• 3.
  Automotive springs aregenerally classified by the amount they compress under a specific load. This is referred to as the spring rate. When that force is removed, the spring returns to its original position if it is not overloaded. This is why a heavy vehicle needs rigid springs than a lightweight car. The springs take care of two fundamental vertical actions: jounce and rebound. Jounce, or compression, occurs when a wheel hits a bump and moves up (Figure 45–3A). When this happens, the suspension system acts to pull in the top of the wheel, maintaining an equal distance between the two wheels and preventing a sideways scrubbing action as the wheel moves up and down. Rebound, or extension, occurs when the wheel hits a dip or hole and moves downward (Figure 45–3B). In this case, the suspension system acts to move the wheel in at both the top and bottom equally, while maintaining an equal distance between the wheels. When the spring experiences compression or extension, it stores energy. This energy forces the spring to return to its normal shape. The spring oscillates between jounce and rebound until all energy has moved from the spring. Each oscillation becomes smaller until it stops. A shock absorber is added to each suspension to dampen and stop the motion of the spring after jounce.
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  Leaf Springs Although leafsprings were the first type of suspension spring used on automobiles, today they are generally found only on light- duty trucks, vans, and some passenger cars. There are three basic types of leaf springs: multiple leaf, mono leaf, and fiber combined. Multiple-Leaf Springs Multiple-leaf springs consist of a series of flat steel leafes that are bundled together and held with clips or by a bolt placed slightly ahead of the center of the bundle. One leaf, called the main leaf, runs the entire length of the spring. The next leaf is a little shorter and attaches to the main leaf. The next leaf is shorter yet and attaches to the second leaf, and so on. This system allows almost any number of leaves to be used to support the vehicle’s weight (Figure 45–5). leaf springs are typically mounted at right angles to the axle (Figure 45–6). In addition to absorbing road shock, leaf springs also serve as a mount for the drive axle. A centering pin is often used to keep the axle properly located on the springs . The front eye of the main leaf at either end of the axle is attached to a bracket on the frame of the vehicle with a bolt and bushing connection. The rear eye of the main leaf is secured to the frame with a shackle, which permits some fore and aft movement. Fiber Composite Springs While most leaf springs are still made of steel, fiber composite types are increasing in popularity (Figure 45–8). Some automotive people call them plastic springs . (Figure 45–7)
• 6.
  Air Springs Another typeof spring, an air spring, is used in an air-operated microprocessor-controlled system that replaces the conventional coil springs with air springs to provide a comfortable ride and automatic front and rear load leveling. uses four air springs to carry the vehicle’s weight. The air springs are located in the same positions where coil springs are usually found. Each spring consists of a reinforced rubber bag pressurized with air . s it is compressed, making it progressively stiffer. A vehicle equipped with an electronic air suspension system is able to provide a comfortable street ride, about a third softer than conventional coil springs . Torsion Bar Suspension System Torsion bars serve the same function as coil springs. In fact, they are often described as straightened-out coil springs. Instead of compressing like coil springs, a torsion bar twists and straightens out on the recoil. That is, as the bar twists, it resists up-and- down movement. One end of the bar—made of heat-treated alloy spring steel—is attached to the vehicle frame. The other end is attached to the lower control arm (Figure 45–10). When the wheel moves up and down, the lower control arm is raised and lowered. This twists the torsion bar, which causes it to absorb road shocks . Because the torsion bar is connected to the lower control arm, the lower ball joint is the load carrier. A shock absorber is connected between the lower control arm and the frame to damp the twisting motion of the torsion bar.
• 7.
  Shock Absorbers Shock absorbersdamp or control motion in a vehicle .If uncontrolled, springs continue expanding and contracting after a shock until all the energy is absorbed . it would also protect a great deal of wear on the suspension and steering systems. Shock absorbers prevent this. Regardless of their name, they actually dampen spring movement instead of absorbing shock. As a matter of fact, in England and almost everywhere else but the United States, shock absorbers are referred to as dampers . Today’s conventional shock absorber is a velocity . This allows it to automatically adjust to road conditions. A shock absorber works on the principle of fluid displacement on both its compression (jounce) and extension (rebound) cycles . Shock absorbers can be mounted either vertically or at an angle. Angle mounting of shock absorbers improves vehicle stability and dampens accelerating and braking torque. Sprung weigh ,Weight supported by car springs Powertrain, body, and frame Anything carried by the weight of springs Unsprang weight Reducing unsprang weight increases control Tires, wheels, brakes, bearings, axels, and differential.
• 8.
  Stabilizer Bars Nearly allsuspension systems have a sway bar, which is also known as the antisway bar or stabilizer. This bar, like the shock absorbers, provides directional stability by reducing body roll. It is a metal rod running between the opposite lower or upper control arms . (Figure 45–13). As the suspension at one wheel responds to the road surface, the sway bar transfers a similar movement to the suspension at the other wheel. For example, if the right wheel is drawn down by a dip in the road surface, the sway bar is drawn with it, creating a downward draw on the left wheel as well. In this way, a more level ride is produced. Sway or lean during cornering is also reduced. Depending on its thickness, the antisway bar can reduce vehicle roll or sway by up to 15%. The sway bar is typically a one-piece, U-shaped rod connected to the control arms with rubber bushings, or it can be attached to each control arm by a separate sway bar link (Figure 45–14). The arm is held to the links with nuts and rubber bushings and is also mounted to the frame in the center with rubber bushings. If it is too large, the sway bar causes the vehicle to wander. If it is too small, it has little effect on stability
• 10.
  Strut rods are usedon models that do not use the sway bar. Strut bars are attached to the lower control arm and frame with bushings, allowing the arm limited forward and backward movement. Strut rods are directly affected by braking forces and road shocks, and their failure can quickly lead to failure of the entire suspension system Some vehicles are equipped with round steel rods that are attached between the lower control arm at one end and the frame of the vehicle with rubber bushings, called strut rod bushings, at the other end. The purpose of these strut rods is to provide forward/backward support to the control arms. Strut rods are used on vehicles equipped with MacPherson struts and many short/long-arm-type suspensions. The bushings are very important in maintaining proper wheel alignment while providing the necessary up-and-down movement of the control arms during suspension travel. Strut rods prevent lower control arm movement back and forth during braking . Some vehicle manufacturers call the strut rod a drag rod because it is attached in front of the wheels, and therefore acts on the lower control arm as if to drag the wheels behind their attachment points
• 11.
  Bushings Bushings are usedat the stabilizer bars(Figure 45–15), control arms, and strut rods. They make good suspension system pivots, minimize the number of lubrication points, and allow for slight assembly misalignments. Bushings are able to absorb some of the road shock before the force is transferred to the vehicle’s frame, or body Suspension bushings are typically made of a rubber material, commonly an elastomer. Elastomers are capable of compressing in response to a force. When the force is removed, elastomers return to their original shape , They also allow movement or shifting of the parts they are between . The amount of movement depends on the design of the bushing For example, control arms are attached to the frame of the vehicle with rubber elastomeric bushings. The bushings become the pivoting point for the control arms. During suspension travel, the bushings twist as the control arm moves. The bushings, acting like a spring, attempt to untwist and push the control arm back into its original position . This twisting and untwisting of the bushings generate heat. Rough road conditions and/or bad shock absorbers will cause the suspension to move more than normal. This causes more heat to build up in the bushings, shortening their life. Excessive heat tends to harden the rubber and as the bushings become harder, they break, crack, or fall apart Worn suspension bushings may allow suspension parts to change positions. This can lead to vibrations, wheel alignment problems, tire wear, and poor ride and handling. Often, a clunking noise when traveling on a rough surface will be an indication of a worn bushing. Worn or damaged bushings should be replaced. Noise may also result from dry bushings and this may be corrected by lubricating them
• 12.
  STEERING KNUCKLES  Asteering knuckle is connected to control arms. In most cases, a steering knuckle and wheel spindle are forged to form a single piece A steering knuckle is hard to classify either as part of the suspension or as part of the wheel. A knuckle serves two purposes: To join the suspension to the wheel 1.Usually includes the spindle where the front wheel bearings are attached 2.To provide pivot points between the suspension and wheel. Knuckles are used with independent suspensions and at the wheels that steer the vehicle. The only knuckle that uses a kingpin is a steering knuckle on an I-beam or twin I-beam front suspension , A kingpin steering knuckle keeps the wheel rigid in relation to the I-beam during up-and-down wheel movement . but rotates around the steering axis to turn the wheels left and right. The steering axis is the vertical center of the kingpin
• 13.
  Control Arms movable leverthat fastens the steering knuckle to the vehicle’s body or frame A control arm holds the steering knuckle, bearing support or axle housing. The control arm is connected to the steering knuckle by a ball joint. The control arm is free to move up and down with the suspension. A control arm is a suspension link that connects a knuckle or wheel flange to the frame. One end of a control arm attaches to the knuckle or wheel flange, generally with either a ball joint or bushing. The opposite end of the arm, which attaches to a frame member, usually pivots on a bushing There are two types of control arms: the wishbone, or double-pivot, control arm and the single-pivot, or single-bushing, control arm
• 14.
  Ball Joints A balljoint (Figure 45–26) connects the steering knuckle to the control arm, allowing it to pivot on the control arm during steering. Ball joints also permit up-and-down movement of the control arm as the suspension reacts to road conditions. The ball joint stud protrudes from its socket through a rubber seal that keeps lubricating grease in the housing and keeps dirt out. Some ball joints require periodic lubrication, while most do not. These maintenance-free ball joints move in a pre-lubricated nylon bearing. Ball joints are either load carrying or are followers. A load-carrying ball joint supports the car’s weight and is generally in the control arm that holds or seats the spring . Follower ball joints are often called friction-loaded ball joints. A follower ball joint mounts on the control arm that does not provide a seat for the spring. The follower does not support vehicle weight and does not get the same stress as the load carrier If the coil spring is attached to the top of the upper control arm, then the upper ball joint is carrying the weight of the vehicle and is called the load-carrying ball joint. The lower ball joint is called the non-load-carrying, or follower, ball joint FIGURE 112–35. If the coil spring is attached to the lower control arm, then the lower ball joint is the load-carrying ball joint and the upper joint is the follower ball joint. SEE FIGURE 112–36.
• 16.
  MACPHERSON STRUT SUSPENSION TheMacPherson strut suspension is dramatically different in appearance from the traditional independent front suspension This is a very popular and efficient form of suspension. it has one control arm and a strut assembly. A coil spring and shock absorber will normally form parts of the strut assembly. Coil springs may be mounted on the control arm instead of being around the strut. On this type, the shock absorber connects the knuckle to the frame. This type of suspension strut is often also used on rear suspension systems. The top of the strut is bolted to a reinforced section of the frame structure. The lower end of the strut is attached to a steering knuckle. The control arm is also attached to the steering knuckle. The control arms are mounted on a cradle section of the frame. Advantages Disadvantages Camber does not change due to up & movement of wheels . Not suitable for Heavy motor vehicle Maximum Engine compartment available. Load caring capacity is less Maintenance cost is less. Initial cost is less. Ride comfort is more. Improve road safety. Light in weight.
• 19.
  Short-Long Arm Suspension Theunequal length control arm or short-long arm (SLA) suspension system has been common on domestic-made vehicles for many years (Figure 45–21). Each wheel is independently connected to the frame by a steering knuckle, ball joint assemblies, and short upper and longer lower control arms. Because the upper arm pivots in a shorter arc, the top of the wheel moves in and out slightly but the tire’s road contact remains constant (Figure 45–22) One design of an SLA uses a narrow lower control arm, shaped like an “I” (Figure 45–23). A strut rod is used to hold the control arm in place. The strut rod is attached to the control arm close to the steering knuckle and to the frame in front of the wheel assembly. Rubber bushings at the frame mounting allow the strut rod to move a little when the tire hits a bump. The bushing dampens the shock and prevents it from transmitting through the vehicle’s frame. The essential components of SLA systems are the wheel spindle assembly, control arms, ball joints, shock absorbers, and springs, among others.