Bumper (car)
A bumper is a structure attached to or integrated with the front and rear ends of a motor vehicle, to absorb impact in a minor collision, ideally minimizing repair costs. Stiff metal bumpers appeared on automobiles as early as 1904 that had a mainly ornamental function. Numerous developments, improvements in materials and technologies, as well as greater focus on functionality for protecting vehicle components and improving safety have changed bumpers over the years. Bumpers ideally minimize height mismatches between vehicles and protect pedestrians from injury. Regulatory measures have been enacted to reduce vehicle repair costs and, more recently, impact on pedestrians.
History
Bumpers were, at first, just rigid metal bars. George Albert Lyon invented the earliest car bumper. The first bumper appeared on a vehicle in 1897, and Nesselsdorfer Wagenbau-Fabriksgesellschaft, an Austrian carmaker, installed it. The construction of these bumpers was unreliable as they featured only a cosmetic function. Early car owners had the front spring hanger bolt replaced with ones long enough to attach a metal bar. G.D. Fisher patented a bumper bracket to simplify the attachment of the accessory. The first bumper designed to absorb impacts appeared in 1901. It was made of rubber, and Frederick Simms gained a patent in 1905.File:1955 Cadillac Eldorado convertible.jpg|thumb|1955 Cadillac Eldorado with heavily chromed "Dagmar" or "bullet" bumper
Automakers added bumpers in the mid-1910s, but consisted of a strip of steel across the front and back. Often treated as an optional accessory, bumpers became more and more common in the 1920s as automobile designers made them more complex and substantial. Over the next decades, chrome-plated bumpers became heavy, elaborative, and increasingly decorative until the late 1950s when U.S. automakers began establishing new bumper trends and brand-specific designs. The 1960s saw the use of lighter chrome-plated blade-like bumpers with a painted metal valance filling the space below it. Multi-piece construction became the norm as automakers incorporated grilles, lighting, and even rear exhaust into the bumpers.
On the 1968 Pontiac GTO, General Motors incorporated an "Endura" body-colored plastic front bumper designed to absorb low-speed impact without permanent deformation. It was featured in a TV advertisement with John DeLorean hitting the bumper with a sledgehammer and no damage resulted. Similar elastomeric bumpers were available on the front and rear of the 1970-71 Plymouth Barracuda. In 1971, Renault introduced a plastic bumper on the Renault 5.
Current design practice is for the bumper structure on modern automobiles to consist of a plastic cover over a reinforcement bar made of steel, aluminum, fiberglass composite, or plastic. Bumpers of most modern automobiles have been made of a combination of polycarbonate and acrylonitrile butadiene styrene called PC/ABS.
Physics
Bumpers offer protection to other vehicle components by dissipating the kinetic energy generated by an impact. This energy is a function of vehicle mass and velocity squared. The kinetic energy is equal to 1/2 the product of the mass and the square of the speed. In formula form:A bumper that protects vehicle components from damage at 5 miles per hour must be four times as tough as a bumper that protects at 2.5 miles per hour, with the collision energy dissipation concentrated at the extreme front and rear of the vehicle. Small increases in bumper protection can lead to weight gain and loss of fuel efficiency.
Until 1959, rigidity was seen as beneficial to occupant safety among automotive engineers. Modern theories of vehicle crashworthiness point in the opposite direction, towards vehicles that crumple progressively. A completely rigid vehicle might have excellent bumper protection for vehicle components, but would offer poor occupant safety.
Pedestrian safety
Bumpers are increasingly being designed to mitigate injury to pedestrians struck by cars, such as through the use of bumper covers made of flexible materials. Front bumpers, especially, have been lowered and made of softer materials, such as foams and crushable plastics, to reduce the severity of impact on legs.Height mismatches
For passenger cars, the height and placement of bumpers are legally specified under both U.S. and EU regulations. Bumpers do not protect against moderate-speed collisions, because during emergency braking, suspension changes the pitch of each vehicle, so bumpers can bypass each other when the vehicles collide. Preventing override and underride can be accomplished by extremely tall bumper surfaces. Active suspension is another solution to keeping the vehicle level.Bumper height from the roadway surface is essential in engaging other protective systems. Airbag deployment sensors typically do not trigger until contact with an obstruction, and it is crucial that front bumpers be the first parts of a vehicle to make contact in the event of a frontal collision, to leave sufficient time to inflate the protective cushions.
Energy-absorbing crush zones are completely ineffective if they are physically bypassed; an extreme example of this occurs when the elevated platform of a tractor-trailer completely misses the front bumper of a passenger car, and the first contact is with the glass windshield of the passenger compartment.
Truck vs. car
s, in which a smaller vehicle such as a passenger sedan slides under a larger vehicle such as a tractor-trailer often result in severe injuries or fatalities. The platform bed of a typical tractor-trailer is at the head height of seated adults in a typical passenger car and thus can cause severe head trauma in even a moderate-speed collision. Around 500 people are killed this way in the United States annually.Following the June 1967 death of actress Jayne Mansfield in an auto/truck accident, the U.S. National Highway Traffic Safety Administration recommended requiring a rear underride guard, also known as a "Mansfield bar", an "ICC bar", or a "DOT bumper". These may not be more than from the road. The U.S. trucking industry has been slow to upgrade this safety feature, and there are no requirements to repair ICC bars damaged in service. However, in 1996 NHTSA upgraded the requirements for the rear underride prevention structure on truck trailers, and Transport Canada went further with an even more stringent requirement for energy-absorbing rear underride guards. In July 2015, NHTSA issued a proposal to upgrade the U.S. performance requirements for underride guards.
Many European nations have also required side underride guards to mitigate lethal collisions where the car impacts the truck from the side. A variety of different types of side underride guards of this nature are in use in Japan, the US, and Canada. However, they are not required in the United States.
UN Regulation 58 sets forth requirements for rear underrun protective devices and their installation, among which is that trucks and trailers of various types must have such devices with height above the ground not more than,, or.
SUV vs. car
Mismatches between SUV bumper heights and passenger car side impact beams have allowed serious injuries at relatively low speeds. In the United States, NHTSA is studying how to address this issue.Beyond lethal interactions, repair costs of passenger car/SUV collisions can also be significant due to the height mismatch. This mismatch can result in vehicles being so severely damaged that they are inoperable after low-speed collisions.
Regulation
In most jurisdictions, bumpers are legally required on all vehicles. Regulations for automobile bumpers have been implemented for two reasons – to allow the car to sustain a low-speed impact without damage to the vehicle's safety systems, and to protect pedestrians from injury. These requirements conflict: bumpers that withstand impact well and minimize repair costs tend to injure pedestrians more, while pedestrian-friendly bumpers tend to have higher repair costs.Although a vehicle's bumper systems are designed to absorb the energy of low-speed collisions and help protect the car's safety and other expensive nearby components, most bumpers are designed to meet only the minimum regulatory standards.