In the automobile industry, weight transfer customarily refers to the change in load borne by different wheels during acceleration. This article uses this latter pair of definitions, in wheeled vehicles, load transfer is the measurable change of load borne by different wheels during acceleration. No motion of the center of mass relative to the wheels is necessary, load transfer is a crucial concept in understanding vehicle dynamics. The same is true in bikes, though only longitudinally, the major forces that accelerate a vehicle occur at the tires contact patches. It is these moments that cause variation in the load distributed between the tires, often this is interpreted by the casual observer as a pitching or rolling motion of the vehicles body. A perfectly rigid vehicle without suspension that would not exhibit pitching or rolling of the body still undergoes load transfer. e, contact patch displacement relative to wheel. Lowering the CoM towards the ground is one method of reducing load transfer, as a result load transfer is reduced in both the longitudinal and lateral directions.
Another method of reducing load transfer is by increasing the wheel spacings, increasing the vehicles wheelbase reduces longitudinal load transfer while increasing the vehicles track reduces lateral load transfer. Most high performance automobiles are designed to sit as low as possible and usually have an extended wheelbase, weight transfer occurs as the vehicles CoM shifts during automotive maneuvers. Acceleration causes the mass to rotate about a geometric axis resulting in relocation of the CoM. Liquids, such as fuel, readily flow within their containers, as fuel is consumed, not only does the position of the CoM change, but the total weight of the vehicle is reduced. By way of example, when a vehicle accelerates, a weight transfer toward the wheels can occur. An outside observer might witness this as the vehicle visibly leans to the back, under braking, weight transfer toward the front of the car can occur. Under hard braking it might be visible even from inside the vehicle as the nose dives toward the ground.
Similarly, during changes in direction, weight transfer to the outside of the direction of the turn can occur, weight transfer is generally of far less practical importance than load transfer, for cars and SUVs at least. Total available grip will drop by around 6% as a result of load transfer. 01%. Load transfer causes the available traction at all four wheels to vary as the car brakes and this bias to one pair of tires doing more work than the other pair results in a net loss of total available traction. The net loss can be attributed to the known as tire load sensitivity
A torsion spring is a spring that works by torsion or twisting, that is, a flexible elastic object that stores mechanical energy when it is twisted. When it is twisted, it exerts a force in the opposite direction, a torsion bar is a straight bar of metal or rubber that is subjected to twisting about its axis by torque applied at its ends. A more delicate form used in instruments, called a torsion fiber consists of a fiber of silk, glass, or quartz under tension. This terminology can be confusing because in a torsion spring the forces acting on the wire are actually bending stresses. It is analogous to the constant of a linear spring. The negative sign indicates that the direction of the torque is opposite to the direction of twist. Other uses are in the large, coiled torsion springs used to counterbalance the weight of doors. Small, coiled torsion springs are used to operate pop-up doors found on small consumer goods like digital cameras. It absorbs road shocks as the wheel goes over bumps and rough road surfaces, torsion-bar suspensions are used in many modern cars and trucks, as well as military vehicles.
The sway bar used in vehicle suspension systems uses the torsion spring principle. The torsion pendulum used in pendulum clocks is a wheel-shaped weight suspended from its center by a wire torsion spring. The weight rotates about the axis of the spring, twisting it, the force of the spring reverses the direction of rotation, so the wheel oscillates back and forth, driven at the top by the clocks gears. The balance spring or hairspring in mechanical watches is a fine, spiral-shaped torsion spring that pushes the wheel back toward its center position as it rotates back. The balance wheel and spring function similarly to the torsion pendulum above in keeping time for the watch, the DArsonval movement used in mechanical pointer-type meters to measure electric current is a type of torsion balance. A coil of wire attached to the twists in a magnetic field against the resistance of a torsion spring. Hookes law ensures that the angle of the pointer is proportional to the current, a DMD or digital micromirror device chip is at the heart of many video projectors.
It uses hundreds of thousands of mirrors on tiny torsion springs fabricated on a silicon surface to reflect light onto the screen. The torsion balance consists of a bar suspended from its middle by a thin fiber, the fiber acts as a very weak torsion spring
Center of mass
The distribution of mass is balanced around the center of mass and the average of the weighted position coordinates of the distributed mass defines its coordinates. Calculations in mechanics are simplified when formulated with respect to the center of mass. It is a point where entire mass of an object may be assumed to be concentrated to visualise its motion. In other words, the center of mass is the equivalent of a given object for application of Newtons laws of motion. In the case of a rigid body, the center of mass is fixed in relation to the body. The center of mass may be located outside the body, as is sometimes the case for hollow or open-shaped objects. In the case of a distribution of separate bodies, such as the planets of the Solar System, in orbital mechanics, the equations of motion of planets are formulated as point masses located at the centers of mass. The center of mass frame is a frame in which the center of mass of a system is at rest with respect to the origin of the coordinate system.
The concept of center of mass in the form of the center of gravity was first introduced by the ancient Greek physicist and engineer Archimedes of Syracuse. He worked with simplified assumptions about gravity that amount to a uniform field, in work on floating bodies he demonstrated that the orientation of a floating object is the one that makes its center of mass as low as possible. He developed mathematical techniques for finding the centers of mass of objects of uniform density of various well-defined shapes, Newtons second law is reformulated with respect to the center of mass in Eulers first law. The center of mass is the point at the center of a distribution of mass in space that has the property that the weighted position vectors relative to this point sum to zero. In analogy to statistics, the center of mass is the location of a distribution of mass in space. Solving this equation for R yields the formula R =1 M ∑ i =1 n m i r i, solve this equation for the coordinates R to obtain R =1 M ∭ Q ρ r d V, where M is the total mass in the volume.
If a continuous mass distribution has density, which means ρ is constant. The center of mass is not generally the point at which a plane separates the distribution of mass into two equal halves, in analogy with statistics, the median is not the same as the mean. The coordinates R of the center of mass of a system, P1 and P2, with masses m1. The percentages of mass at each point can be viewed as projective coordinates of the point R on this line, another way of interpreting the process here is the mechanical balancing of moments about an arbitrary point
An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating them, or fixed to the vehicle. In the former case, bearings or bushings are provided at the points where the axle is supported. In the latter case, a bearing or bushing sits inside a hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes, especially on bicycles, the latter type axle is referred to as a spindle, on cars and trucks, several senses of the word axle occur in casual usage, referring to the shaft itself, its housing, or simply any transverse pair of wheels. Strictly speaking, a shaft which rotates with the wheel, being either bolted or splined in fixed relation to it, is called an axle or axle shaft, however, in looser usage an entire assembly including the surrounding axle housing is called an axle. An even broader sense of the word refers to every pair of wheels on opposite sides of the vehicle, regardless of their mechanical connection to each other.
Thus, transverse pairs of wheels in an independent suspension may be called an axle in some contexts, axles are an integral component of most practical wheeled vehicles. In a live-axle suspension system, the serve to transmit driving torque to the wheel, as well as to maintain the position of the wheels relative to each other. The axles in this system must bear the weight of the vehicle plus any cargo. A non-driving axle, such as the front beam axle in heavy duty trucks and some 2-wheel drive light trucks and vans, will have no shaft, many front wheel drive cars have a solid rear beam axle. In other types of systems, the axles serve only to transmit driving torque to the wheels. This is typical of the independent suspension found on most newer cars and SUVs and these systems still have a differential, but it will not have attached axle housing tubes. It may be attached to the frame or body, or integral in a transaxle. The axle shafts transmit driving torque to the wheels, like a full floating axle system, the drive shafts in a front wheel drive independent suspension system do not support any vehicle weight. A straight axle is a rigid shaft connecting a wheel on the left side of the vehicle to a wheel on the right side.
The axis of rotation fixed by the axle is common to both wheels, such a design can keep the wheel positions steady under heavy stress, and can therefore support heavy loads. Straight axles are used on trains, for the axles of commercial trucks
A spring is an elastic object used to store mechanical energy. Springs are usually out of spring steel. There are a number of spring designs, in everyday usage the term often refers to coil springs. When a spring is compressed or stretched from its resting position, the rate or spring constant of a spring is the change in the force it exerts, divided by the change in deflection of the spring. That is, it is the gradient of the force versus deflection curve, an extension or compression springs rate is expressed in units of force divided by distance, for example lbf/in or N/m. A torsion spring is a spring that works by twisting, when it is twisted about its axis by an angle, a torsion springs rate is in units of torque divided by angle, such as N·m/rad or ft·lbf/degree. The inverse of spring rate is compliance, that is, if a spring has a rate of 10 N/mm, the stiffness of springs in parallel is additive, as is the compliance of springs in series. Springs are made from a variety of materials, the most common being spring steel.
Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel, some non-ferrous metals are used including phosphor bronze and titanium for parts requiring corrosion resistance and beryllium copper for springs carrying electrical current. Simple non-coiled springs were used throughout history, e. g. the bow. In the Bronze Age more sophisticated spring devices were used, as shown by the spread of tweezers in many cultures, coiled springs appeared early in the 15th century, in door locks. The first spring powered-clocks appeared in that century and evolved into the first large watches by the 16th century, in 1676 British physicist Robert Hooke discovered Hookes law which states that the force a spring exerts is proportional to its extension. Compression spring – is designed to operate with a compression load, flat spring – this type is made of a flat spring steel. Machined spring – this type of spring is manufactured by machining bar stock with a lathe and/or milling operation rather than a coiling operation, since it is machined, the spring may incorporate features in addition to the elastic element.
Machined springs can be made in the load cases of compression/extension, torsion. Serpentine spring - a zig-zag of thick wire - often used in modern upholstery/furniture, the most common types of spring are, Cantilever spring – a spring which is fixed only at one end. Coil spring or helical spring – a spring is of two types, Tension or extension springs are designed to become longer under load and their turns are normally touching in the unloaded position, and they have a hook, eye or some other means of attachment at each end. Compression springs are designed to become shorter when loaded and their turns are not touching in the unloaded position, and they need no attachment points
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
Twist-beam rear suspension
The twist-beam rear suspension is a type of automobile suspension based on a large H or C shaped member. The front of the H attaches to the body via rubber bushings, the cross beam of the H holds the two trailing arms together, and provides the roll stiffness of the suspension, by twisting as the two trailing arms move vertically, relative to each other. The coil springs usually bear on a pad alongside the stub-axle, often the shock is colinear with the spring, to form a coilover. This location gives them a high motion ratio compared with most suspensions, which improves their performance. The longitudinal location of the cross beam controls important parameters of the behaviour, such as the roll steer curve and toe. The closer the cross beam to the axle stubs the more the camber, a key difference between the camber and toe changes of a twist beam vs independent suspension is the change in camber and toe is dependent on the position of the other wheel, not the cars chassis. In a traditional independent suspension the camber and toe are based on the position of the relative to the body.
If both wheels compress together their camber and toe will not change, thus if both wheels started perpendicular to the road and car compressed together they will stay perpendicular to the road. The camber and toe changes are the result of one wheel being compressed relative to the other and this suspension is commonly used on a wide variety of front wheel drive cars, and was almost ubiquitous on European superminis. It was popularised by Volkswagen when they changed from rear engined RR layout cars in the 1970s and this can mildly compromise the handling and ride quality of the vehicle. For this reason, some manufacturers have changed to different linkage designs, general Motors in Europe Vauxhall/Opel have continued to use twist- or torsion- beam suspension. This is at a cost saving of €100 per car compared to multi-link rear suspension and their latest version as used in the 2009-on Opel Astra uses a Watts linkage at a cost of €20 to address the drawbacks and provide a competitive and cost effective rear suspension.
The Renault Megane and Citroen C4 have stayed with the twist beam, toyota switched from torsion beam to multilink with the 2007 Auris E150. Alignment geometry is factory-set and not generally adjustable, any deviation from factory specifications/tolerances could mean a bent axle or compromised mounting points. Trailing arm and Semi-trailing arm suspension, a picture of a twist beam
A tire or tyre is a ring-shaped vehicle component that covers the wheels rim to protect it and enable better vehicle performance. Most tires, such as those for automobiles and bicycles, provide traction between the vehicle and the road providing a flexible cushion that absorbs shock. The materials of modern tires are synthetic rubber, natural rubber and wire, along with carbon black. They consist of a tread and a body, the tread provides traction while the body provides containment for a quantity of compressed air. Before rubber was developed, the first versions of tires were bands of metal fitted around wooden wheels to prevent wear and tear. Pneumatic tires are used on many types of vehicles, including cars, motorcycles, trucks, heavy equipment, and aircraft. Metal tires are used on locomotives and railcars, and solid rubber tires are still used in various non-automotive applications, such as some casters, lawnmowers. The etymology of tire is that the word is a form of attire. The spelling tyre does not appear until the 1840s when the English began shrink fitting railway car wheels with malleable iron, traditional publishers continued using tire.
The Times newspaper in Britain was still using tire as late as 1905, the spelling tyre began to be commonly used in the 19th century for pneumatic tires in the UK. However, over the course of the 20th century, tyre became established as the standard British spelling, the earliest tires were bands of leather, placed on wooden wheels, used on carts and wagons. The tire would be heated in a fire, placed over the wheel and quenched, causing the metal to contract. A skilled worker, known as a wheelwright, carried out this work, the outer ring served to tie the wheel segments together for use, providing a wear-resistant surface to the perimeter of the wheel. The word tire thus emerged as a variant spelling to refer to the bands used to tie wheels. The first patent for what appears to be a standard pneumatic tire appeared in 1847 lodged by the Scottish inventor Robert William Thomson, this never went into production. The first practical pneumatic tire was made in 1888 on May Street, Belfast, by Scots-born John Boyd Dunlop and it was an effort to prevent the headaches of his 10-year-old son Johnnie, while riding his tricycle on rough pavements.
His doctor, Sir John Fagan, had prescribed cycling as an exercise for the boy, Fagan participated in designing the first pneumatic tires. In Dunlops tire patent specification dated 31 October 1888, his interest is only in its use in cycles, in September 1890, he was made aware of an earlier development but the company kept the information to itself
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
Jaguar independent rear suspension
The two generations overlap in time due to their being used in both full size and sports models that were updated at different times. The X-Type has two versions of IRS based on the Ford Mondeo estate system, depending on whether front or 4-wheel drive. When first introduced, it was rare for British cars to have independently sprung rear wheels. The reduction in transfer of vertical undulations in road surface to the body provides a smoother ride. Jaguars first IRS system took five years to develop, a Mark 2 saloon fitted with a prototype IRS demonstrated a reduction in unsprung weight of 190 lb compared with a live axle. Its first production application was in the E-Type from its launch in 1961, the assembly was manufactured in three different sizes with differing track widths to suit different models. The first generation Jaguar IRS continued to be updated and used until production of the XJS ended in 1996, the IRS is built around a fabricated steel crossbeam that allows it to be relatively easily removed from the vehicle as a complete assembly.
This feature has made it suitable for adaptation as a component on other vehicles. The complete rear suspension assembly is carried in a steel crossbeam, the rear wheels are located transversely by top links and wheel carriers and lower links. The top link is the driving half-shaft with a joint at each end. The lower link pivots adjacent to the casing at its inboard end. The pivot bearings at each end of the link are widely spaced so as to provide maximum longitudinal rigidity. Suspension is provided by two coil spring and damper units on each side of the casing, the spring and damper units attaching to the crossbeam at the top. The crossbeam is located by two radius arms each of which runs forward from the link to a point on the vehicle body and is pivoted at each end via rubber bushings. The only other points of contact with the body are by means of metal sleeved rubber bushes. The fabricated steel crossbeam carries the differential and inboard brakes, the differential is a Salisbury 4HU unit with a hypoid spiral bevel gear.
It provides final drive reduction ratios ranging from 2.88,1 to 3.54,1, a limited slip differential was standard on some models and optional on others. The first generation IRS always had the disc brakes mounted inboard, the top link is a fixed-length half-shaft universally jointed at each end
A leaf spring is a simple form of spring commonly used for the suspension in wheeled vehicles. Originally called a laminated or carriage spring, and sometimes referred to as a spring or cart spring. A leaf spring takes the form of a slender arc-shaped length of spring steel of rectangular cross-section, in the most common configuration, the center of the arc provides location for the axle, while tie holes are provided at either end for attaching to the vehicle body. For very heavy vehicles, a spring can be made from several leaves stacked on top of each other in several layers. Leaf springs can serve locating and to some extent damping as well as springing functions, while the interleaf friction provides a damping action, it is not well controlled and results in stiction in the motion of the suspension. For this reason some manufacturers have used mono-leaf springs, a leaf spring can either be attached directly to the frame at both ends or attached directly at one end, usually the front, with the other end attached through a shackle, a short swinging arm.
The shackle takes up the tendency of the spring to elongate when compressed. Some springs terminated in an end, called a spoon end. There were a variety of springs, usually employing the word elliptical. Elliptical or full elliptical leaf springs referred to two circular arcs linked at their tips and this was joined to the frame at the top center of the upper arc, the bottom center was joined to the live suspension components, such as a solid front axle. Additional suspension components, such as trailing arms, would usually be needed for this design and that employed the lower arc, hence its name. As an example of leaf springs, the Ford Model T had multiple leaf springs over its differential that were curved in the shape of a yoke. As a substitute for dampers, some manufacturers laid non-metallic sheets in between the leaves, such as wood. Today leaf springs are used in heavy commercial vehicles such as vans and trucks, SUVs. For heavy vehicles, they have the advantage of spreading the load more widely over the vehicles chassis, whereas coil springs transfer it to a single point.
Unlike coil springs, leaf springs locate the axle, eliminating the need for trailing arms. A further advantage of a leaf spring over a spring is that the end of the leaf spring may be guided along a definite path. A more modern implementation is the leaf spring