24-04-2012, 02:02 PM
Cruise Control technology
What Is Cruise Control technology?
The purpose of a cruise control system is to accurately maintain the driver's desired set speed, without intervention from the driver, by actuating the throttle-accelerator pedal linkage. A modern automotive cruise control is a control loop that takes over control of the throttle, which is normally controlled by the driver with the gas pedal, and holds the vehicle speed at a set value...
The driver can set the cruise control with the cruise switches, usually ON, OFF, RESUME, SET/ACCEL and COAST, that are located in the steering wheel or on the windshield wiper or turn signal stalk. On most cars the cruise control can accelerate or decelerate the car by 1 mph with the tap of the SET/ACCEL button.
How Does Cruise Control System Work?
We do not intend to go very technical over here and will keep the explanation of its working, simple. The modern systems constitute of a computer control system, several inputs signals, vacuum actuator and throttle position sensor. The main computers takes the input from the starring wheel controls, vehicle speed signals etc. and sends these to a vacuum actuator through a vacuum valve. The actuator in turn is connected to the throttle valve by a cable and the throttle valve has a position sensor mounted on it. The sensor directs the signals back to the main computer, so it forms a loop.
Signals are sent from the computer to the actuator which further positions the throttle through a cable. The position of the throttle is sensed and the signals are sent back to the computer thereby ensuring that the correct position for the set speed has been reached and if it is not there, the computer again positions the throttle.
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 (not very common), 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, depressing 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 many older General Motors vehicles or on a dedicated stalk like those found in, particularly, Toyota and Lexus. Earlier designs used a dial to set speed choice.
The driver must bring the vehicle 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 from the engine's RPM, or from internal speed pulses produced electronically by the vehicle. Most systems do not allow the use of the cruise control below a certain speed (normally around 25 mph). The vehicle will maintain the desired speed by pulling the throttle cable with a solenoid, a vacuum driven servomechanism, or by using the electronic systems built into the vehicle (fully electronic) if it uses a 'drive-by-wire' system.
All cruise control systems must be capable of being turned off both explicitly and automatically when the driver depresses the brake and often also the clutch. Cruise control often includes a memory feature to resume the set speed after braking and a coast feature to reduce the set speed without braking. When the cruise control is engaged, the throttle can still be used to accelerate the car, but once the pedal 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. Modern "adaptive" systems (see below) 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.
The cruise control systems of some vehicles incorporate a "speed limiter" function, which will not allow the vehicle to accelerate beyond a pre-set maximum; this can usually be overridden by fully depressing the accelerator pedal. (Most systems will prevent the vehicle accelerating beyond the chosen speed, but will not apply the brakes in the event of over speeding downhill.)
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 uphill 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.
Advantages:
• Its usefulness for long drives (reducing driver fatigue, improving comfort by allowing positioning changes more safely) across 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. Note however, that in many jurisdictions, officers cannot write a ticket for a violation of a speed limit due to a steep hill.
Disadvantages:
• The lack of need to maintain constant pedal pressure, which can help lead to accidents caused by highway hypnosis or incapacitated drivers.
• 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.