Thursday, December 18, 2008
An intercooler, or charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged (forced induction) internal combustion engines to improve their volumetric efficiency by increasing intake air charge density through isochoric cooling. A decrease in air intake temperature provides a denser intake charge to the engine and allows more air and fuel to be combusted per engine cycle, increasing the output of the engine.
The inter prefix in the device name originates from historic compressor designs. In the past, aircraft engines were built with charge air coolers that were installed between multiple stages of supercharging, thus the designation of inter. Modern automobile designs are technically designated aftercoolers because of their placement at the end of supercharging chain. This term is now considered archaic in modern automobile terminology since most forced induction vehicles have single-stage superchargers or turbochargers. In a vehicle fitted with two-stage turbocharging, it is possible to have both an intercooler (between the two turbocharger units) and an aftercooler (between the second-stage turbo and the engine). The JCB Dieselmax land speed record-holding car is an example of such a system. In general, an intercooler or aftercooler is said to be a charge air cooler.
Intercoolers can vary dramatically in size, shape, and design, depending on the performance and space requirements of the entire supercharger system. Common spatial designs are front mounted intercoolers (FMIC), top mounted intercoolers (TMIC), hybrid mount intercoolers (HMIC). Each type can be cooled with an air-to-air system, air-to-liquid system, or a combination of both.
Many older turbo-charged cars, such as the Toyota Supra (JZA80 only), Nissan 300ZX Twin Turbo, Nissan 200SX (S13/14/14a/15), Mitsubishi 3000gt, Saab 900, Volkswagen, Audi TT, and Turbo Mitsubishi Eclipse use side-mounted air-to-air intercoolers (SMIC), which are mounted in the front corner of the bumper or in front of one of the wheels. Side-mounted intercoolers are generally smaller, mainly due to space constraints, and sometimes two are used to gain the performance of a larger, single intercooler. Cars such as the Subaru Impreza WRX, MINI Cooper S, Toyota Celica GT-Four, Nissan Pulsar GTI-R, MAZDASPEED3, MAZDASPEED6 and the PSA Peugeot Citroën turbo diesels, use air-to-air top mounted intercoolers (TMIC) located on top of the engine. Air is directed through the intercooler through the use of a hood scoop. In the case of the PSA cars the air intake is the grille above the front bumper, then flows through under-hood ducting. Top mounted intercoolers sometimes suffer from heat diffusion due to proximity with the engine, warming them and reducing their overall efficiency. Some World Rally Championship cars use a reverse-induction system design whereby air is forced through ducts in the front bumper to a horizontally-mounted intercooler.
Wednesday, December 10, 2008
The Global Positioning System (GPS) is a Global Navigation Satellite System (GNSS) developed by the United States Department of Defense. It is the only fully functional GNSS in the world. It uses a constellation of between 24 and 32 Medium Earth Orbit satellites that transmit precise microwave signals, which enable GPS receivers to determine their current location, the time, and their velocity. Its official name is NAVSTAR GPS. Although NAVSTAR is not an acronym, a few backronyms have been created for it. The GPS satellite constellation is managed by the United States Air Force 50th Space Wing. GPS is often used by civilians as a navigation system.
After Korean Air Lines Flight 007 was shot down in 1983 after straying into the USSR's prohibited airspace, President Ronald Reagan issued a directive making GPS freely available for civilian use as a common good. Since then, GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, scientific uses, and hobbies such as geocaching. Also, the precise time reference is used in many applications including the scientific study of earthquakes. GPS is also a required key synchronization resource of cellular networks, such as the Qualcomm CDMA air interface used by many wireless carriers in a multitude of countries.
The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. Using a constellation of five satellites, it could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology that GPS relies upon. In the 1970s, the ground-based Omega Navigation System, based on signal phase comparison, became the first worldwide radio navigation system. The design of GPS is based partly on similar ground-based radio navigation systems, such as LORAN and the Decca Navigator developed in the early 1940s, and used during World War II. Additional inspiration for the GPS came when the Soviet Union launched the first Sputnik in 1957. A team of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik's radio transmissions. They discovered that, because of the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them. They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion.
Tuesday, December 2, 2008
Prof Mitchell expects we will share cars that will be easier to drive in congested cities, will be pollution-free and can be customised at will.
The city car concept, with styling input by architect Frank Gehry, will be completed and delivered by MIT to General Motors early next year.
"Primarily we're interested in urban living," says Ryan Chin, an architect and engineer at MIT's media lab and a member of Prof Mitchell's research group. "Everything scales down from what we think the city of the future is."
The Smart Cities group focused on how cars could be better adapted to get round familiar problems of city life, namely congestion, pollution and parking. Motor companies are well aware of the issue. But the group felt the companies had missed the point, even with city cars such as the Smart, the iconic two-passenger cars introduced by Swatch and Mercedes in 1998.
"We have to think of city cars as not just small-footprint vehicles that can squeeze into tight spaces but ones that can work in unison and also be almost like a parasite that leeches on to mass-transit systems," says Mr Chin. While Smart changed the way people think about parking and size, the MIT engineers felt that, as it had not been widely adopted and congestion and pollution problems had got no better, its success had been limited.
So the MIT team started from scratch to come up with their own concept: a stackable, shareable, electric, two-passenger car. "Imagine a shopping cart - a vehicle that can stack - you can take the first vehicle out of a stack and off you go," says Mr Chin. "These stacks would be placed throughout the city. A good place would be outside a subway station or a bus line or an airport, places where there's a convergence of transportation lines and people."
The precedent for this type of shared personal transport is demonstrated with bicycle-sharing schemes in European towns and the ZipCar and FlexCar projects on the east and west coasts of the US respectively.
The MIT concept car is a complete re-think of vehicle technology. For a start, there is no engine, at least in the traditional sense. The power comes from devices called wheel robots. "These are self-contained wheel units that have electric motors inside," says Mr Chin. "The interesting thing is that the wheel can turn a full 360 degrees so you can have omni-directional wheel movements. You can rotate the car while you're moving, any direction can be front or back and you can do things like crabbing or translate sideways. It's almost like you imagine yourself driving a computer chair."
The wheel robots, complete with their own suspension, remove the need for a drive shaft and even the engine block, freeing up designers to make new use of the space in the car.
"Essentially the car will comprise four wheel-robots plus a customisable chassis," says Chin. "The frame can be built specifically for each customer."
Add wafer-thin, programmable displays that cover the interior and exterior of the car like a layer of paint, and you have a vehicle that can be customised at will. "You can imagine signalling being not just a static signal light but something more dynamic," says Mr Chin, who suggests the words "reversing" or "turning left" could roll across the car's body to declare the driver's intentions. "From a heating and cooling point of view, you might want your car to be darker or lighter depending on weather. On the interior, you can customise your dashboard for each person. If I'm an elderly person, I probably want a very large speedometer so I can see it; if I'm a race-car driver, maybe all I want is a tachometer."
The close proximity of cars in cities increases the risk of accidents, and the MIT car has a host of radical ideas to deal with this problem. Chief safety features include responsive seats that do away with the need for seat belts and air bags: these are based around a spine at the back of the seat with a number of "fingers" to embrace a passenger and hold them in place if the car detects that it is involved in an accident. And the cabin would absorb the impacts of crashes using new materials. "There is a new development in fluids that can be magnetised so that they move from liquid to solid state within a nanosecond. You can imagine using these fluids as a way of absorbing energy in an impact."
Over the next few months the MIT team will complete the final design and present their results to General Motors, which will build the first prototype. Beyond that, Mr Chin is already trying to arrange a public test in the Far East. "We might do this in Hong Kong or in Singapore," he says. "The interest in those places is that they are very dense, have mass transit and limited range. An island like Hong Kong would be a perfect place to test this because you have all those conditions."
Whether the city car concept appears on garage forecourts as designed by the Smart Cities group or whether the technologies are taken forward individually remains to be seen. Chin says the group would be happy with either outcome.