TIPS ON SPEED CONTROL/CRUISE CONTROL
By Nnamdi Ikeh-Akabogu (FRSCN)
Cruise control (sometimes known as speed control or auto cruise, or tempomat in some countries) is a system that automatically controls the speed of a motor vehicle.
The system is a servomechanism that takes over the throttle of the car to maintain a steady speed as set by the driver.
Speed control was used in automobiles as early as 1900 in the Wilson-Pilcher and in the 1910s by Peerless.
Peerless advertised that their system would “maintain speed whether uphill or down”. The technology was adopted by James Watt and Matthew Boulton in 1788 to control steam engines, but the use of governors’ dates at least back to the 17th century.
On an engine the governor adjusts the throttle position as the speed of the engine changes with different loads, to maintain a near-constant speed.
Modern cruise control (also known as a speedostat or tempomat) was invented in 1948 by the inventor and mechanical engineer Ralph Teetor. His idea was borne 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 1958 Imperial (called “Auto-pilot”) using a speed dial on the dashboard.
This system calculated ground speed based on driveshaft rotations off the rotating speedometer-cable and used a bi-directional screw-drive electric motor to vary throttle position as needed.
A 1955 U.S. Patent for a “Constant Speed Regulator” was filed in 1950 by M-Sgt Frank J. Riley.
He installed his invention, which he conceived while driving on the Pennsylvania Turnpike, on his own car in 1948.
Despite this patent, the inventor, Riley, and the subsequent patent holders were not able to collect royalties for any of the inventions using cruise control.
In 1965, American Motors (AMC) introduced a low-priced automatic speed control for its large-sized cars with automatic transmissions.
The AMC “Cruise-Command” unit was engaged by a push-button once the desired speed was reached and then the throttle position was adjusted by a vacuum control directly from the speedometer cable rather than a separate dial on the dashboard.
Daniel Aaron Wisner invented “Automotive Electronic Cruise Control” in 1968 as an engineer for RCA’s Industrial and Automation Systems Division in Plymouth, Michigan.
His invention described in two patents filed that year (US 3570622 & US 3511329), with the second modifying his original design by debuting digital memory, was the first electronic device in controlling a car.
Two decades passed before an integrated circuit for his design was developed by Motorola as the MC14460 Automotive Speed Control Processor in CMOS.
The advantage of electronic speed control over its mechanical predecessor was that it could be integrated with electronic accident avoidance and engine management systems.
Following the 1973 oil crisis and rising fuel prices, the device became more popular in the U.S. “Cruise control can save gas by avoiding surges that expel fuel” while driving at steady speeds.
In 1974, AMC, GM, and Chrysler priced the option at $60 to $70, while Ford charged $103.
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, and 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 – typically around 25 mph (40 km/h). 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 from accelerating beyond the chosen speed, but will not apply the brakes in the event of overspeeding downhill.)
On vehicles with a manual transmission, cruise control is less flexible because the act of depressing the clutch pedal and shifting gears usually disengages the cruise control. The “resume” feature has to be used each time after selecting the new gear and releasing the clutch. Therefore, cruise control is of most benefit at motorway/highway speeds when top gear is used virtually all the time.
Some advantages of cruise control include:
- Its usefulness for long drives (reducing driver fatigue, improving comfort by allowing positioning changes more safely) across highways and sparsely populated roads.
- Some drivers use it to avoid subconsciously violating speed limits. A driver who otherwise tends to subconsciously increase speed over the course of a highway journey may avoid speeding.
Disadvantages: However, when used incorrectly cruise control can lead to accidents due to several factors, such as:
- Speeding around curves that require slowing down.
- Rough or loose terrain could negatively affect the cruise control controls.
- Rainy or wet weather could lose traction.
The traffic expert is DCC Nnamdi Ikeh-Akabogu, DCC Morning and Evaluation (M&E), Special Duties and External Relations (SEDER), FRCC HQ, Abuja.BEWARE All Rights Reserved. This material, and other digital content on this website, may not be reproduced, published, broadcast, rewritten or redistributed in whole or part without prior express written permission from Juliana Francis