A scientific control is an experiment or observation designed to minimize the effects of variables other than the independent variable. This increases the reliability of the results, often through a comparison between control measurements and the other measurements, scientific controls are a part of the scientific method. Controls eliminate alternate explanations of experimental results, especially experimental errors, the selection and use of proper controls to ensure that experimental results are valid can be very difficult. Other variables, which may not be obvious, may interfere with the experimental design. For instance, the artificial sweetener might be mixed with a dilutant, to control for the effect of the dilutant, another treatment is added which is the dilutant alone. Now the experiment is controlled for the dilutant and the experimenter can distinguish between sweetener and non-treatment, controls are most often necessary where a confounding factor cannot easily be separated from the primary treatments.
For example, it may be necessary to use a tractor to spread fertilizer where there is no practicable way to spread fertilizer. The simplest solution is to have a treatment where a tractor is driven over plots without spreading fertilizer, the simplest types of control are negative and positive controls, and both are found in many different types of experiments. Negative controls are groups where no phenomenon is expected and they ensure that there is no effect when there should be no effect. To continue with the example of drug testing, a control is a group that has not been administered the drug of interest. This group receives either no preparation at all or a sham preparation and we would say that the control group should show a negative or null effect. In other examples, outcomes might be measured as lengths, percentages, in the drug testing example, we could measure the percentage of patients cured. In this case, the treatment is inferred to have no effect when the treatment group, some improvement is expected in the placebo group due to the placebo effect, and this result sets the baseline which the treatment must improve upon.
Even if the treatment group shows improvement, it needs to be compared to the placebo group, if the groups show the same effect, the treatment was not responsible for the improvement. The treatment is effective if the treatment group shows more improvement than the placebo group. Positive controls are groups where a phenomenon is expected and that is, they ensure that there is an effect when there should be an effect, by using an experimental treatment that is already known to produce that effect. Positive controls are used to assess test validity. For example, to assess a new ability to detect a disease
A shock absorber is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the energy of the shock into another form of energy which is dissipated. Most shock absorbers are a form of dashpot and hydraulic shock absorbers are used in conjunction with cushions and springs. An automobile shock absorber contains spring-loaded check valves and orifices to control the flow of oil through an internal piston, one design consideration, when designing or choosing a shock absorber, is where that energy will go. In most shock absorbers, energy is converted to heat inside the viscous fluid, in hydraulic cylinders, the hydraulic fluid heats up, while in air cylinders, the hot air is usually exhausted to the atmosphere. In other types of shock absorbers, such as electromagnetic types, in general terms, shock absorbers help cushion vehicles on uneven roads. In a vehicle, shock absorbers reduce the effect of traveling over rough ground, leading to improved ride quality, while shock absorbers serve the purpose of limiting excessive suspension movement, their intended sole purpose is to damp spring oscillations.
Shock absorbers use valving of oil and gasses to absorb energy from the springs. Spring rates are chosen by the based on the weight of the vehicle. Some people use shocks to modify spring rates but this is not the correct use, along with hysteresis in the tire itself, they damp the energy stored in the motion of the unsprung weight up and down. Effective wheel bounce damping may require tuning shocks to an optimal resistance, spring-based shock absorbers commonly use coil springs or leaf springs, though torsion bars are used in torsional shocks as well. Ideal springs alone, are not shock absorbers, as only store. Vehicles typically employ both hydraulic shock absorbers and springs or torsion bars, in this combination, shock absorber refers specifically to the hydraulic piston that absorbs and dissipates vibration. Now, composite suspension system are used mainly in 2 wheelers, in common with carriages and railway locomotives, most early motor vehicles used leaf springs. However the amount of damping provided by leaf spring friction was limited and variable according to the conditions of the springs and it operated in both directions.
Motorcycle front suspension adopted coil sprung Druid forks from about 1906, and similar designs added rotary friction dampers and these friction disk shock absorbers were fitted to many cars. One of the problems with motor cars was the variation in sprung weight between lightly loaded and fully loaded, especially for the rear springs. What was called for was damping that operated on the rebound, horock came up with a design in 1901 that had hydraulic damping, it worked in one direction only
Independent suspension is a broad term for any automobile suspension system that allows each wheel on the same axle to move vertically independently of the others. This is contrasted with an axle or deDion axle system in which the wheels are linked – movement on one side affects the wheel on the other side. Independent refers to the motion or path of movement of the wheels or suspension and it is common for the left and right sides of the suspension to be connected with anti-roll bars or other such mechanisms. The anti-roll bar ties the left and right suspension spring rates together, most modern vehicles have independent front suspension. Many vehicles have an independent rear suspension, IRS, as the name implies, has the rear wheels independently sprung. A fully independent suspension has an independent suspension on all wheels, some early independent systems used swing axles, but modern systems use Chapman or MacPherson struts, trailing arms, multilink, or wishbones. Independent suspension requires additional engineering effort and expense in development versus a beam or live axle arrangement, a very complex IRS solution can result in higher manufacturing costs.
The key reason for lower unsprung weight relative to a live axle design is that, for driven wheels, instead it is either bolted directly to the vehicles chassis or more commonly to a subframe. Suspension is the component that separates the driver and/or passenger from the ground. The suspension in a vehicle helps absorb harshness in the road, there are many systems and designs that do this, such as independent suspension. This system provides many advantages over other suspension systems, for example, in solid axle suspension systems, when one wheel hits a bump, it affects both wheels. This will compromise traction, smoothness of the ride, and could cause a dangerous wheel shimmy when moving at high speeds. According to Car Suspension Bible with independent suspension systems, the bump only affects the contacted wheel and this offers many advantages such as greater ride comfort, better traction, and safer, more stable vehicles on and off the road. Double wishbone suspension Multi-link suspension This is the most common, widely used front suspension system in cars of European and Japanese origin.
It is a simple and effective design that uses a strut-type spring. This system has used in the BMW E21 series, which are the first generation 3 series from 1976-1983. People can often confuse this with a CV joint knock, several independent suspension designs have featured transverse leaf springs. Most applications used multi-leaf steel springs though more recent designs have used fiber reinforced plastic springs, in addition to spring type, a distinction can be drawn between systems where the spring acts as a locating link and those where the spring only acts as a spring member
An anti-roll bar is a part of many automobile suspensions that helps reduce the body roll of a vehicle during fast cornering or over road irregularities. It connects opposite wheels together through short lever arms linked by a torsion spring, a sway bar increases the suspensions roll stiffness—its resistance to roll in turns, independent of its spring rate in the vertical direction. The first stabilizer bar patent was awarded to Canadian inventor Stephen Coleman of Fredericton, anti-roll bars were unusual on pre-war cars due to the generally much stiffer suspension and acceptance of body roll. From the 1950s, production cars were commonly fitted with anti-roll bars. With the bar removed, a vehicles wheels can tilt away by much larger distances. Although there are variations in design, a common function is to force the opposite wheels shock absorber, spring or suspension rod to lower, or rise. In a fast turn, a vehicle tends to drop closer onto the wheels. As a result, the vehicle tends to hug the road closer in a fast turn, where all wheels are closer to the body.
After the fast turn, the pressure is reduced. A vehicle that runs over several potholes scattered in the road tends to rock side-to-side, or waddle, a sway bar is usually a torsion spring that resists body roll motions. It is usually constructed out of a steel bar, formed into a U shape. If the left and right wheels move together, the bar rotates about its mounting points, if the wheels move relative to each other, the bar is subjected to torsion and forced to twist. Each end of the bar is connected to an end link through a flexible joint, the sway bar end link connects in turn to a spot near a wheel or axle, transferring forces from a heavily-loaded axle to the opposite side. The bar resists the torsion through its stiffness, the stiffness of an anti-roll bar is proportional to the stiffness of the material, the fourth power of its radius, and the inverse of the length of the lever arms. Stiffness is related to the geometry of the mounting points, the stiffer the bar, the more force required to move the left and right wheels relative to each other.
This increases the amount of required to make the body roll. In a turn the sprung mass of the body produces a lateral force at the centre of gravity. Because the CG is usually not on the axis, the lateral force creates a moment about the roll axis that tends to roll the body
Torsion bar suspension
A torsion bar suspension, known as a torsion spring suspension, is a general term for any vehicle suspension that uses a torsion bar as its main weight bearing spring. Vertical motion of the causes the bar to twist around its axis and is resisted by the bars torsion resistance. The effective spring rate of the bar is determined by its length, cross section, material, manufacturers change the torsion bar or key to adjust the ride height, usually to compensate for heavier or lighter engines. Over-rotating the torsion bars can cause the suspension to hit the bump-stop prematurely. Aftermarket forged-metal torsion key kits use relocked adjuster keys to prevent over-rotation, the main advantages of a torsion bar suspension are durability, easy adjustability of ride height, and small profile along the width of the vehicle. It takes up less of the interior volume than coil springs. Torsion bars reached the height of their popularity on mass-production road cars in the middle of the 20th century at the time that unitary construction was being adopted.
Using MacPherson struts to achieve independent front suspension with coil springs meant providing strong turrets in the structure of the car. A disadvantage is that torsion bars, unlike coil springs, usually provide a progressive spring rate. In most torsion bar systems, ride height may be changed by simply adjusting bolts that connect the torsion bars to the steering knuckles, in most cars with this type of suspension, swapping torsion bars for a different spring rate is usually an easy task. Some vehicles use torsion bars to provide automatic levelling, using a motor to pre-stress the bars to provide resistance to load and, in some cases. Height adjustable suspension has been used to implement a wheel-change mode where the vehicle is raised on three wheels so that the wheel is lifted off the ground without the aid of a jack. Before World War II, the front wheel drive Citroen Traction Avant had independent front torsion bar suspension, the flexibility of the axle beam provided wheel location features like a twist beam axle.
The Czechoslovakian Tatra cars designed by Professor Hans Ledwinka in the mid-1930s used all round independent torsion bar suspension, in the 1930s, prototypes of the first Volkswagen Beetle incorporated torsion bars—especially its transverse mounting style. The system first saw use in the Swedish Stridsvagn L-60 tank of 1934. It was used extensively in European cars Renault, Citroën and Volkswagen, the Packard used torsion bars at both front and rear, and interconnected the front and rear systems to improve ride quality. Morris Minor and Oxford from the late 1940s onwards used a front torsion bar system very similar to the Citroen, the single torsion bar was mounted through the frame sides behind the rear axle and attached by arms and links to the front side of the spring U-bolt plates. Axle Flex was discontinued for the 1936 model year, the designer of these cars, Alec Issigonis was inspired by the Traction Avants suspension although the Morris cars were rear-wheel drive and used conventional leaf springs for their rear axles
This article is primarily about four-wheeled vehicle suspension. For information on two-wheeled vehicles suspensions see the motorcycle suspension, motorcycle fork, bicycle suspension, Suspension is the system of tires, tire air, 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. The suspension protects the vehicle itself and any cargo or luggage from damage, the design of front and rear suspension of a car may be different. An early form of suspension on ox-drawn carts had the 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, no modern automobiles use the strap suspension system. Automobiles were initially developed as self-propelled versions of horse-drawn vehicles, 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, 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 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 springs in catapults was refined and made to work years later. Springs were not only made of metal, a tree branch could be used as a spring. Horse-drawn carriages and the Ford Model T used this system, and it is used today in larger vehicles. This was the first modern system and, along with advances in the construction of roads. In 1901 Mors of Paris first fitted an automobile with shock absorbers, with the advantage of a damped suspension system on his Mors Machine, Henri Fournier won the prestigious Paris-to-Berlin race on 20 June 1901.
Fourniers superior time was 11 hrs 46 min 10 sec, while the best competitor was Léonce Girardot in a Panhard with a time of 12 hrs 15 min 40 sec. Coil springs first appeared on a vehicle in 1906 in the Brush Runabout made by the Brush Motor Company. Today, coil springs are used in most cars, in 1920, Leyland Motors used torsion bars in a suspension system
Double wishbone suspension
In automobiles, a double wishbone suspension is an independent suspension design using two wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle, the shock absorber and coil spring mount to the wishbones to control vertical movement. The double-wishbone suspension can be referred to as double A-arms, though the arms themselves can be A-shaped, L-shaped, a single wishbone or A-arm can be used in various other suspension types, such as variations of the MacPherson strut. The upper arm is shorter to induce negative camber as the suspension jounces. When the vehicle is in a turn, body roll results in positive camber gain on the lightly loaded inside wheel, between the outboard end of the arms is a knuckle. The knuckle contains a kingpin for horizontal radial movement in older designs, in newer designs, a ball joint at each end allow for all movement. Attached to the knuckle at its center is a hub, or in many older designs.
To resist fore-aft loads such as acceleration and braking, the arms require two bushings or ball joints at the body. At the knuckle end, single ball joints are used, in which case the steering loads have to be taken via a steering arm. An L-shaped arm is generally preferred on passenger vehicles because it allows a better compromise of handling and comfort to be tuned in. The bushing in line with the wheel can be kept relatively stiff to effectively handle cornering loads while the joint can be softer to allow the wheel to recess under fore-aft impact loads. For a rear suspension, a pair of joints can be used at both ends of the arm, making them more H-shaped in plan view. Alternatively, a fixed-length driveshaft can perform the function of a wishbone as long as the shape of the other wishbone provides control of the upright and this arrangement has been successfully used in the Jaguar IRS. In elevation view, the suspension is a 4-bar link, and it is easy to work out the camber gain, the various bushings or ball joints do not have to be on horizontal axes, parallel to the vehicle centre line.
If they are set at an angle, anti-dive and anti-squat geometry can be dialled in, in many racing cars, the springs and dampers are relocated inside the bodywork. The suspension uses a bellcrank to transfer the forces at the end of the suspension to the internal spring. This is known as a rod if bump travel pushes on the rod. As the wheel rises, the push rod compresses the spring via a pivot or pivoting system
A chassis consists of an internal vehicle frame that supports an artificial object in its construction and use, can provide protection for some internal parts. An example of a chassis is the underpart of a motor vehicle, if the running gear such as wheels and transmission, and sometimes even the drivers seat, are included, the assembly is described as a rolling chassis. In the case of vehicles, the rolling chassis means the frame plus the running gear like engine, drive shaft, differential. An under body, which is not necessary for integrity of the structure, is built on the chassis to complete the vehicle. For commercial vehicles, a rolling chassis consists of an assembly of all the parts of a truck to be ready for operation on the road. The design of a car chassis will be different than one for commercial vehicles because of the heavier loads. Commercial vehicle manufacturers sell chassis only and chassis, as well as chassis cab versions that can be outfitted with specialized bodies and these include motor homes, fire engines, box trucks, etc.
In particular applications, such as buses, a government agency like National Highway Traffic Safety Administration in the U. S. defines the design standards of chassis. An armoured fighting vehicles hull serves as the chassis and comprises the part of the AFV that includes the tracks, drivers seat. This describes the hull, although common usage might include the upper hull to mean the AFV without the turret. The hull serves as a basis for platforms on tanks, armoured carriers, combat engineering vehicles. In an electronic device, the chassis consists of a frame or other supporting structure on which the circuit boards. In the absence of a frame, the chassis refers to the circuit boards and components themselves. The combination of chassis and outer covering is called an enclosure. Vietnam Studies, Department of the Army, Washington, D. C.1978