The Hindu Business Line : How cruise control takes control

Cruise control systems offer unique levels of comfort by eliminating the need for the driver to have the throttle pedal constantly floored when the car is travelling at high speeds.

With new highways coming up in the last few years, more Indian are taking to the roads. But they will have missed one interesting feature in their cars, either completely unaware of its existence or knowing fully well about it but accepting with a sense of resignation that it is available only in high-end cars or through imports.

This feature, offered as standard fitment in cars sold in the US and Germany, is Cruise Control. As yet, it is a super premium feature that carmakers in India don't deem it fit to offer. This is not without reason. After all, even the best Indian highways still don't seem to be able to offer users unhindered passage. But cruise control can be particularly useful during long drives on some of the less crowded expressways, where maintaining the car at a constant speed for long stretches is actually possible.

Look mom, no throttle!

Cruise control has been around for more than a decade now in the US and Europe.

This system obviates the need for the driver to hold the throttle pedal on the floor when the car is cruising at high speeds.

Cars with the system have a speed sensor, usually located near the transmission's (manual or automatic) output shank, which constantly sends electrical signals, generated by a magnet and sensor coil combo, to the onboard computer. The car's computer or ECU is fed with data regarding the frequency of the incoming electrical signal at any given speed. The speed is itself monitored by the speed sensor based on the spinning of the output shank.

The cruise control system, which combines specialised hardware and electronics, tries to keep this electrical signal frequency constant, which in turn ensures that the vehicle's speed is also maintained at the level set by the driver.

So, the system coordinates and maintains the frequency of electrical signals required to sustain the car's speed at the set level.

But to achieve that the car's acceleration also has to be sustained without physical inputs from the driver. For this purpose, a part of the hardware also involves the car's throttle connectors being fitted with a vacuum-controlled diaphragm that applies force to the connectors so as to increase or decrease gradually the speed.

Based on the electrical impulses or signals that the cruise control's command box sends to the vacuum diaphragm, an increase or decrease in the vacuum force to the throttle connectors is applied to either accelerate or decelerate the car automatically up to the cruise control's preset level.

The force on the accelerator's connectors is maintained until the cruise control's preset level is cut off by the driver applying the brakes or when he depresses the clutch (in a manual transmission car). Switches located in the brake and clutch pedals deactivate the cruise control preset.

Cruise control systems usually feature set up and control buttons on the steering wheel (or on the dash in earlier generation vehicles) and may differ from being a simple pair of on/off switches to a more sophisticated layout that includes controls for progressive acceleration and/or deceleration from the preset speed.

Some recent advancements include automatic resetting of speed after deceleration or stoppage, separate buttons for progressive increase or decrease in the preset speed, and the new adaptive cruise control systems which incorporate a radar system at the front of the vehicle to automatically adjust the car's speed based on the speed of the vehicle in front.

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