Mechanics

Cruise Control

This article explains how an automotive cruise control works. This information pertains to all vehicles except electric.


Cruise Control (appearance will vary)

The cruise control system is used to control and maintain a consistent vehicle speed with the help of an electronic throttle or vacuum actuator which is connected to the engine throttle. The electronic throttle control is controlled by the main computer which has recorded the desired setting from the driver. These controls include; set, disengage and resume. Using data feedback from the vehicle speed sensor VSS the computer can increase or decrease engine speed. When the brake or clutch pedal is used the cruise control is released allowing the driver to slow the vehicle. Using the resume button will cause the vehicle will speed up to the last recorded set speed (MPH.)

A laser or radar control system is known as an autonomous cruise control, or active cruise control which sets the distance between cars. When the distance setting is compromised the vehicle speed is automatically decreased, then holds an alternative speed until the distance increases. A warning light is illumiated on the dash to alert the driver and is used to avoid vehicle collisions.

History

The cruise control system is also known by alternative names such as auto-cruise and speed control. A mechanical engineer by the name of Ralph Teetor in 1945, invented the Speedostat, which is a version of the modern cruise control system. The idea was conceptualized when Ralph observed a rotating driveshaft. Having knowledge of electronics he devised a counter and throttle actuator which was connected to the engine. Throttle position was varied by the actuator using a controller which sensed the rotations. The cruise control system is by default turned off, but can be activated by the user. Other than the on switch, there are switches for set, accelerate, resume, cancel and coast features. These first cruise control systems consisted of a control unit, driveshaft, control switch, brake cutoff switch, vacuum servo, wiring harness and vacuum lines.

Common Problems

  • Brake pedal cutoff switch become maladjusted causing the cruise control not to engage.
 

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-20)