Cruise control

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For the software build framework, see CruiseControl.

For the single by The Headless Chickens, see Cruise Control (song).

Cruise Control Controls on a 2000 Jeep Grand Cherokee Steering Wheel

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.

1 History
2 Theory of operation
3 Advantages and disadvantages
4 Autonomous cruise control system
5 Trivia
6 External links

[edit] 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 (also known as a speedostat) 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.

[edit] 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. Alternatively, 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 spokes or on the edge of the hub like those on Honda vehicles, on the turn signal stalk like in some General Motors vehicles or on a dedicated stalk like those found in Toyota and Mercedes-Benz vehicles. Early designs used a dial to set speed choice.

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, speed sensor (found on the wheels) 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.

Cruise controls currently being developed include the ability to automatically reduce speed when the speed limit decreases. This is an advantage for those driving in unfamiliar areas.

[edit] 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 unconsciously 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.

Driving over "rolling" terrain, with gentle up and down portions, can usually be done more economically (using less fuel) by a skilled driver viewing the approaching terrain, by maintaining a relatively constant throttle position and allowing the vehicle to accelerate on the downgrades and decelerate on upgrades, while reducing power when cresting a rise and adding a bit before an upgrade is reached. Cruise control will tend to overthrottle on the upgrades and retard on the downgrades, wasting the energy storage capabilities available from the inertia of the vehicle. The inefficiencies from cruise control can be even greater relative to skilled driving in hybrid vehicles such as the Prius.

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

[edit] Autonomous cruise control system

Main article: 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 keep pace with the car it is following, slow when closing in on the vehicle in front and accelerating again to the preset speed when traffic allows. Some systems also feature forward collision warning systems, which warns the driver if a vehicle in front - given the speed of both vehicles - gets too close (within the preset headway or braking distance).

[edit] Trivia

Most early cruise control units may also be set to provide back pressure upon the accelerator, to warn the driver against excessive speed. This was separate from holding a set speed.