Motoring corner : “The Cruise Control System”

The cruise control is an invaluable feature on most American motor vehicles. Without cruise control, long road trips would be more tiring for many drivers; and those with “lead-foot syndrome” (heavy accelerating foot) would most likely find themselves with lots of speeding tickets. Cruise control is far more common on American cars than European cars, because the roads in America are generally bigger and straighter, and destinations are farther apart. With traffic continually increasing, basic cruise control is becoming less useful, but instead of becoming obsolete, cruise control systems are adapting to this new reality, soon, cars will be equipped with adaptive cruise control, which will allow your car to follow the car in front of it while continually adjusting speed to maintain a safe distance. The cruise control system actually has a number of functions other than controlling the speed of the car; for instance, the cruise control can accelerate or decelerate the car by 2 kph with the tap of a button. Hit the button five times to go 10 kph faster. There are also several important safety features the cruise control will disengage as soon as you hit the brake pedal, and it won’t engage at speeds less than 40 kph. If you recently disengaged the cruise control by hitting the brake pedal, hitting the resume button will command the car to accelerate back to the most recent speed setting. Holding down the coast button will cause the car to decelerate, just as if you took your foot completely off the accelerator. On this car, tapping the coast button once will cause the car to slow down by 2 kph. The brake pedal and clutch pedal each have a switch that disengages the cruise control as soon as the pedal is pressed, so you can shut off the cruise control with a light tap on the brake or clutch. The cruise control system controls the speed of your car the same way you do; by adjusting the throttle position. But cruise control actuates the throttle valve by a cable connected to an actuator, instead of by pressing a pedal. The throttle valve controls the power and speed of the engine by limiting how much air the engine takes in. One cable comes from the accelerator pedal, and one from the actuator. When the cruise control is engaged, the actuator moves the cable connected to the pivot, which adjusts the throttle; but it also pulls on the cable that is connected to the accelerator pedal; this is why your pedal moves up and down when the cruise control is engaged. The intelligence of a cruise control system comes from a small computer that is normally found under the hood or behind the dashboard. It connects to the throttle control, as well as several sensors. A good cruise control system accelerates aggressively to the desired speed without overshooting, and then maintains that speed with little deviation no matter how much weight is in the car, or how steep the hill you drive up. Controlling the speed of a car is a classic application of control system theory. The cruise control system controls the speed of the car by adjusting the throttle position, so it needs sensors to tell it the speed and throttle position. It also needs to monitor the controls so it can tell what the desired speed is and when to disengage. (To be Cont’d) motoringcorner@live.co.uk

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Motoring corner : “The Cruise Control System”