Active suspension

Active suspension is a type of automotive suspension that controls the vertical movement of the wheels relative to the chassis or vehicle body with an onboard system, rather than in passive suspension where the movement is being determined entirely by the road surface. Active suspensions can be generally divided into two classes: pure active suspensions, and adaptive/semi-active suspensions. While adaptive suspensions only vary shock absorber firmness to match changing road or dynamic conditions, active suspensions use some type of actuator to raise and lower the chassis independently at each wheel. These technologies allow car manufacturers to achieve a greater degree of ride quality and car handling by keeping the tires perpendicular to the road in corners, allowing better traction (engineering) and control. An onboard computer detects body movement from sensors throughout the vehicle and, using data calculated by opportune control techniques, controls the action of the active and semi-active suspensions. The system virtually eliminates body roll and pitch variation in many driving situations including cornering, accelerating, and braking. Principle Figure 1 Figure 2 Figure 3 Skyhook theory is that the ideal suspension would let the vehicle maintain a stable posture as if suspended by an imaginary hook in the sky, unaffected by road conditions. Since an actual skyhook is impractical, real active suspension systems are based on actuator operations. The imaginary line (of zero vertical acceleration) is calculated based on the value provided by an acceleration sensor installed on the body of the vehicle (see Figure 3). Since the dynamic elements are only made up of the linear spring and the linear damper, no complicated calculations are necessary. A vehicle contacts the ground through the spring and damper in a normal spring damper suspension, as in Figure 1. To achieve the same level of stability as the Skyhook theory, the vehicle must contact the ground through the spring, and the imaginary line with the damper, as in Figure 2. Theoretically, in a case where the coefficient of the damper reaches an infinite value, the vehicle will be in a state where it is completely fixed to the imaginary line, thus the vehicle will not shake. Active Active suspensions, the first to be introduced, use separate actuators which can exert an independent force on the suspension to improve the riding characteristics. The drawbacks of this design are high cost, added complication and mass of the apparatus, and the need for frequent maintenance on some implementations. Maintenance can require specialised tools, and some problems can be difficult to diagnose. Hydraulic actuation Hydraulically actuated suspensions are controlled with the use of hydraulics. The first example appeared in 1954, with the Hydropneumatic suspensiondeveloped by Paul Magès at Citroën....

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Suspension (vehicle)

Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support both roadholding/handling and ride quality, which are at odds with each other. The tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different. The front suspension components of a Ford Model T. The rear suspension on a truck: a leaf spring. Part of car front suspension and steeringmechanism: tie rod, steering arm, king pin axis (using ball joints). Van Diemen RF01 Racing Car Suspension. History Strap suspension 1605 Strap suspension 2008 note the transverse limiting straps An early form of suspension on ox-drawn carts had the platform swing on iron chains attached to the wheeled frame of the carriage. This system remained the basis for all suspension systems until the turn of the 19th century, although the iron chains were replaced with the use of leather straps by the 17th century. No modern automobiles use the 'strap suspension' system. Automobiles were initially developed as self-propelled versions of horse-drawn vehicles. However, horse-drawn vehicles had been designed for relatively slow speeds, and their suspension was not well suited to the higher speeds permitted by the internal combustion engine. The first workable spring-suspension required advanced metallurgical knowledge and skill, and only became possible with the advent of industrialisation. Obadiah Elliott registered the first patent for a spring-suspension vehicle; - each wheel had two durable steel leaf springs on each side and the body of the carriage was fixed directly to the springs which were attached to the axles. Within a decade, most British horse carriages were equipped with springs; wooden springs in the case of light one-horse vehicles to avoid taxation, and steel springs in larger vehicles. These were often made of low-carbon steel and usually took the form of multiple layer leaf springs. Leaf springs have been around since the early Egyptians. Ancient military engineers used leaf springs in the form of bows to power their siege engines, with little success at first. The use of leaf springs in catapults was later refined and made to work years later. Springs were not only made of metal, a sturdy tree branch could be used...

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