Cruise control



Cruise control (sometimes known as speed control or Autocruise) is a system to automatically control the speed of an automobile. The driver sets the speed and the system will take over the throttle of the car to maintain the same speed.

History
Speed control with a centrifugal governor was used in automobiles as early as the 1910s, notably by Peerless. Peerless advertised that their system would "maintain speed whether up hill or down". The technology was invented by James Watt and Matthew Boulton in 1788 for use in locomotives. It uses centrifugal force to adjust throttle position as the speed of the engine changes with different loads (e.g. when going up a hill).

Modern cruise control was invented in 1945 by the blind inventor and mechanical engineer Ralph Teetor. His idea was born out of the frustration of riding in a car driven by his lawyer, who kept speeding up and slowing down as he talked. The first car with Teetor's system was the Chrysler Corporation Imperial in 1958. This system calculated ground speed based on driveshaft rotations and used a solenoid to vary throttle position as needed.

Theory of operation
In modern designs, the cruise control may or may not need to be turned on before use — in some designs it is always "on" but not always enabled, others have a separate "on/off" switch, while still others just have an "on" switch that must be pressed after the vehicle has been started. Most designs have buttons for "set", "resume", "accelerate", and "coast" functions. Some also have a "cancel" button. Or simply tapping the brake on most cars equipped with cruise control will disable it. The system is operated with controls easily within the driver's reach, usually with two or more buttons on the steering wheel or on the turn signal stalk.

The driver must bring the car up to speed manually and use a button to set the cruise control to the current speed. The cruise control takes its speed signal from a rotating driveshaft, speedometer cable or from the engine's RPM. Most systems do not allow the use of the cruise control below a certain speed (normally 35 mph/55 km/h) to discourage use in city driving. The car will maintain that speed by pulling the throttle cable with a solenoid or a vacuum driven servomechanism. On the latest vehicles fitted with electronic throttle control, cruise control can be easily integrated into the vehicle's engine management system. Most systems can be turned off both explicitly and automatically, when the driver hits the brake or clutch. Cruise control often includes a memory feature to resume the set speed after braking and a coast feature to reset the speed lower without braking. When the cruise control is in effect, the throttle can still be used to accelerate the car, but once it is released the car will then slow down until it reaches the previously set speed.

Advantages and disadvantages
Cruise control has many advantages but also some serious vices.

Some of those advantages include:
 * Its usefulness for long drives across sparsely populated roads. This usually results in better fuel efficiency.
 * Some drivers use it to avoid unconciously violating speed limits. A driver who otherwise tends to unconsciously increase speed over the course of a highway journey may avoid a speeding ticket. Such drivers should note, however, that a cruise control may go over its setting on a downhill which is steep enough to accelerate with an idling engine.

However, cruise control can also lead to accidents due to several factors, such as:
 * The lack of need to maintain constant pedal pressure, which can help lead to accidents caused by highway hypnosis or incapacitated drivers; future systems may include a penalty switch to avoid this.
 * When used during inclement weather or while driving on wet or snow- and/or ice-covered roads, the vehicle could go into a skid. Stepping on the brake – such as to disengage the cruise control – often results in the driver losing control of the vehicle.

Many countries establish that it is illegal to drive within city limits with the cruise control feature activated.

Autonomous cruise control system
Some modern vehicles have autonomous cruise control (ACC) systems. These use either a radar or laser setup to allow the vehicle to slow when approaching another vehicle and accelerate again to the preset speed when traffic allows. Some systems also allow the driver to choose a preset headway or following distance. Mercedes-Benz was the first to offer such a system, under the Distronic name, but similar adaptive systems are now offered by other manufacturers. For 2006, Mercedes-Benz refined the Distronic system to completely halt the car if necessary (now called 'Distronic Plus'), a feature not offered by any other implementation.

Toyota's Lexus vehicles were second to market with "DLCC" (Dynamic Laser Cruise Control). Volkswagen will bring the technology to the mainstream with their 2006 Passat. Other vehicles with adaptive cruise control include the Acura RL, Audi A6, Audi A8, Audi Q7, BMW 3 Series (called Active Cruise Control), BMW 5 Series, BMW 7 Series, Cadillac STS, Cadillac XLR, Infiniti M, Infiniti Q45, Jaguar XK-R, Jaguar S, Lexus LS430/460, Lexus ES-350, Nissan Primera T-Spec Models (called Intelligent Cruise Control), Mercedes-Benz S-Class, E55 AMG, CLS, SL, CL, Toyota Sienna XLE (limited availability), and Volkswagen Phaeton.

General Motors Cadillac division now offers Adaptive Control on the DTS series of its luxury vehicles. This is most notable by sensors mounted on the front bumper of the DTS. One must look closely because they are seamlessly integrated into the front of the vehicle. The 2007 Volvo S80 will have such a system.