cruise control

Cruise control mounted on a 2000 Jeep Grand Cherokee Steering Wheel

Cruise control (sometimes known as speed control or autocruise) is a system that automatically controls the speed of a motor vehicle. The system takes over the throttle of the car to maintain a steady speed as set by the driver.

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 to control steam engines. The governor adjusts the throttle position as the speed of the engine changes with different loads.

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 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 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 or clutch pedal will disable the system so the driver can change the speed without resistance from the system. 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, wheel speed sensor 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.

All systems must 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 the accelerator is released the car will then slow down until it reaches the previously set speed.

On the latest vehicles fitted with electronic throttle control, cruise control can be easily integrated into the vehicle's engine management system. Cruise controls currently being developed include the ability to automatically reduce speed when the distance to a car in front, or the speed limit decreases. This is an advantage for those driving in unfamiliar areas.

Advantages and disadvantages

Some of those advantages include:

• Its usefulness for long drives across Interstate highways and 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 dead man's 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 (although this may be somewhat mitigated by cars equipped with Electronic Stability Control). 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.

Many countries establish that it is illegal to drive within city limits with the cruise control feature activated.^{[citation needed]}

Adaptive cruise control

Some modern vehicles have adaptive cruise control (ACC) systems, which is a general term meaning improved cruise control. These improvements can be automatic braking or dynamic set-speed type controls.

Automatic Braking Type: The automatic braking type 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).

Dynamic Set Speed Type: The dynamic set speed uses the GPS position of speed limit signs, from a database. Some are modifiable by the driver.

References

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2008)

External links

• Overview of intelligent vehicle safety systems
• Intelligent Transport Systems
• Preventive safety applications and technologies
• Cruise [Un]Control: Driver sets the cruise control on his vehicle, then slips into the backseat for a nap at Snopes.com