Autodes kasutatavad pneuma-ja hüdrosüsteemid (3)

Viljandi Ühendatud Kutsekeskkool.
Autommaaler.

Marius Lepik
Autodes kasutatavad pneuma -ja hüdrosüsteemid
Referaat



Juhendaja :
Jaanus Kaido

Viljandi 2009

Compressed Air Brake System

A "Compressed Air Brake System" is a different air brake used for trucks, consisting of a standard disc or drum brake arrangement using compressed air in place of hydraulic fluid. Most types of truck air brakes are drum units, though there is an increasing trend towards the use of disc brakes in this application . The compressed air brakes system works by drawing filtered air from the atmosphere, compressing it, and holding it in high- pressure reservoirs at around 120 PSI. When needed for braking, this high pressure air is routed to the operating cylinders on the brakes, which actuate the braking hardware and slow the vehicle . Air brakes use compressed air to maximise braking forces.

Design and Function

A compressed air brake system is divided into a supply system and a control system. The supply system compresses, stores and supplies high-pressure air to the control system as well as to additional air operated auxiliary truck systems (gearbox shift control, clutch pedal air assistance servo, etc.).

How airbags work

The design is conceptually simple ; a central " Airbag control unit "[14] (ACU) (a specific type of ECU) monitors a number of related sensors within the vehicle, including accelerometers, impact sensors, side ( door ) pressure sensors[15], wheel speed sensors, gyroscopes, brake pressure sensors, and seat occupancy sensors. When the requisite 'threshold' has been reached or exceeded , the airbag control unit will trigger the ignition of a gas generator propellant to rapidly inflate a nylon fabric bag. As the vehicle occupant collides with and squeezes the bag, the gas escapes in a controlled manner through small vent holes . The airbag's volume and the size of the vents in the bag are tailored to each vehicle type, to spread out the deceleration of (and thus force experienced by) the occupant over time and over the occupant's body , compared to a seat belt alone.
The signals from the various sensors are fed into the Airbag control unit, which determines from them the angle of impact, the severity, or force of the crash, along with other variables. Depending on the result of these calculations, the ACU may also deploy various additional restraint devices , such as seat belt pre-tensioners, and/or airbags (including frontal bags for driver and front passenger, along with seat-mounted side bags, and " curtain " airbags which cover the side glass). Each restraint device is typically activated with one or more pyrotechnic devices, commonly called an initiator or electric match. The electric match, which consists of an electrical conductor wrapped in a combustible material , activates with a current pulse between 1 to 3 amperes in less than 2 milliseconds. When the conductor becomes hot enough, it ignites the combustible material, which initiates the gas generator. In a seat belt pre-tensioner, this hot gas is used to drive a piston that pulls the slack out of the seat belt. In an airbag, the initiator is used to ignite solid propellant inside the airbag inflater. The burning propellant generates inert gas which rapidly inflates the airbag in approximately 20 to 30 milliseconds. An airbag must inflate quickly in order to be fully inflated by the time the forward -traveling occupant reaches its outer surface. Typically, the decision to deploy an airbag in a frontal crash is made within 15 to 30 milliseconds after the onset of the crash, and both the driver and passenger airbags are fully inflated within approximately 60-80 milliseconds after the first moment of vehicle contact. If an airbag deploys too late or too slowly, the risk of occupant injury from contact with the inflating airbag may increase . Since more distance typically exists between the passenger and the instrument panel, the passenger airbag is larger and requires more gas to fill it.
Front airbags normally do not protect the occupants during side, rear, or rollover accidents. [16] Since airbags deploy only once and deflate quickly after the initial impact, they will not be beneficial during a subsequent collision. Safety belts help reduce the risk of injury in many types of crashes. They help to properly position occupants to maximize the airbag's benefits and they help restrain occupants during the initial and any following collisions.
In vehicles equipped with a rollover sensing system, accelerometers and gyroscopes are used to sense the onset of a rollover event. If a rollover event is determined to be imminent , side-curtain airbags are deployed to help protect the occupant from contact with the side of the vehicle interior, and also to help prevent occupant ejection as the vehicle rolls over.

Hydropneumatic is a type of automotive suspension system, invented by Citroën, and fitted to Citroën cars, as well as being adapted by other car manufacturers, notably Rolls-Royce, Mercedes - Benz and Peugeot . It was also used on Berliet trucks. Similar systems are also used on some military vehicles.
The purpose of this system is to provide a soft , comfortable, yet well-controlled ride quality . Its nitrogen springing medium is approximately six times more flexible than conventional steel , so self-leveling is incorporated to allow the vehicle to cope with the extraordinary suppleness provided . France was noted for poor road quality in the post-war years , so the only way to maintain relatively high speed in a vehicle was if it could easily absorb road irregularities.
While the system has inherent advantages over steel springs , generally recognized in the auto industry, it also has an element of complexity , so automakers like Mercedes-Benz, British Leyland (Hydrolastic, Hydragas), and Lincoln have sought to create simpler variants.
This system uses a belt or camshaft driven pump from the engine to pressurise a special hydraulic fluid, which then powers the brakes, suspension and power steering. It can also power any number of features such as the clutch, turning headlamps and even power windows . The suspension system usually features driver-variable ride height, to provide extra clearance in rough terrain.
The suspension setup is referred to as 'oléopneumatique' in early literature, pointing to oil and air as its main components.
There have been many improvements to this system over the years, including variable ride firmness (Hydractive) and active control of body roll (Citroën Activa). The latest incarnation features a simplified single pump-accumulator sphere combination.
The system had one key negative impact on the inventor , Citroën - only specialist garages were qualified to work on the cars - making them seem radically different from ordinary cars with common mechanicals.
Auto manufacturers are still trying to catch up with the combination of features offered by this 1955 suspension system, typically by adding layers of complexity to an ordinary steel spring mechanical system
Air Suspension.

Air suspension is a type of vehicle suspension powered by an engine driven or electric air pump or compressor. This pump pressurizes the air, using compressed air as a spring. Air suspension replaces conventional steel springs. If the engine is left off for an extended period, the car will settle to the ground . The purpose of air suspension is to provide a smooth ride quality and in some cases self-leveling.
While not using high pressure mineral oil, the system aims to achieve a result similar to the hydropneumatic suspension arrangement introduced in 1954 by Citroën.
With a "leg up" on other companies, GM used its experience with commercial busses' air suspension to introduce systems for its car lines, beginning with the 1958 model year . Air bags at each wheel replaced the standard coil springs, and had sensors to keep the car level under load and in turns. It was too slow to react in sudden maneuvers, however .
Period reviews rated the air suspension somewhat superior in ride quality, but not dramatically. Some reliability issues plagued these systems, as well. Thus, as an option, air suspension was short lived in that era.
Vehicles that use air suspension today include models from Maybach, Rolls-Royce, Lexus , Mercedes-Benz, Land Rover /Range Rover, SsangYong, Audi , Subaru , Volkswagen , and Lincoln, among others .
The air suspension designs from Land Rover, SsangYong, Subaru and some Audi, VW, and Lexus models, feature height adjustable suspension controlled by the driver, suitable for clearing rough terrain. The Lincoln Continental and Mark VIII also featured an air suspension system in which the driver could choose how sporty or comfortable they wanted the suspension to feel. These suspension settings were also linked to the memory seat system, meaning that the car would automatically adjust the suspension to the individual driver. The control system in the Mark VIII also lowered the suspension by about 25 mm (1 inch ) at speeds exceeding about 100 km/h (60 mph) [1] for improved aerodynamic performance . Unfortunately, however, these systems turned out to be unreliable and in many cases ended up being retrofitted with aftermarket replacements [2] or conventional steel coil springs. [3]
In addition to passenger cars, air suspension is broadly used on semi trailers and buses , which are both transportation sectors that helped pioneer the use and design of air suspension. An unusual application was on EMD's experimental Aerotrain.