How Does Cruise Control Work?
We invented cars as means of transportation, to go faster and to go further. But the evolution of cars didn’t stop there. Comfort has become a necessity, leading to the invention of features purely for driver convenience—features such as cruise control.
Cruise control lets you take your foot off the gas pedal without your car losing speed. With cruise control, you enter the speed, and then the car keeps cruising at that speed.
It’s bliss for driving long distances on highways, but how does cruise control actually work?
What Is Cruise Control?
Cruise control is a driving assist that maintains a constant driving speed without your foot on the gas pedal. Cruise control has been around for a long time, but only in the past few years has it become more common in economy cars.
There are various types of cruise control mechanisms, and these usually work according to the type of throttle system in your car. However, some manufacturers take this feature to the next level with adaptive cruise control, automatically altering cruise speed.
How Does Cruise Control Work?
Cruise control has evolved many times since it was first used in automobiles. As mentioned before, cruise control’s working mechanism revolves around the throttle system. Right now, there are mostly two types of throttle systems in the cars you see out in the streets: the older cable throttle and the newer drive-by-wire throttle.
Cruise Control in Older Cars with Cable Throttle
Cable throttle systems use mechanical connections, and thus, the cruise control on these cars works mechanically as well.
In cars with cable throttle systems, the cruise control actuator is connected to the throttle body through a cable on one side. On the other side, the actuator is connected to a pump.
Most cruise control actuators in cable throttle bodies use a set of springs and rely on vacuum pressure. The pump connected to the actuator creates a vacuum that tightens the springs in the actuator and this, in turn, puts tension on the cable. This cable is connected to the throttle body, and when the actuator puts tension on the cable, the throttle body opens in response. This ultimately gives your car gas without the gas pedal being used.
Now remains the question of how a specific speed is set for the actuator. This all goes through the car’s electronic control unit or ECU. You press a button in your car to activate cruise control, and the ECU powers the pump in just the right amount to put the right tension on the cable. Lo and behold your car drives without your foot on the gas pedal!
The ECU also takes info from the speed sensor to see if the current speed and the target speed match. If your car is going faster than it should, then the ECU will release some tension on the cable, and if it’s going slower, it will increase the tension.
Some cars use valves instead of pumps to create the vacuum in the cruise control actuator. In that case, the ECU is responsible for opening and closing that valve.
Keep in mind that there are various types of cruise control actuators, and not all use springs, though most do.
Cruise Control in Newer Cars with Drive-By-Wire Throttle
The cruise control system in newer cars with drive-by-wire throttle bodies is entirely electronic. Since there are no mechanical parts involved, the ECU gets the current speed and decreases or increases it to reach the target speed.
In these cars, the ECU talks directly to the electronic control module (ECM). The ECM is responsible for controlling the throttle body to accelerate or decelerate. Once you set your preferred speed, the ECU grabs that and sorts it out with the ECM and just like that, your car drives at your preferred speed.
How Does Adaptive Cruise Control Work?
Adaptive cruise control (ACC) is an advanced form of cruise control that takes in information from sensors other than the speed sensor to determine the ideal speed in real-time.
ACC talks to proximity sensors such as radar and lidar, speed sensors, and a combination of cameras to take in the other vehicles on the road and the road itself. Once the signals are received and processed, ACC determines the safe distance and speed.
This system then alters the speed accordingly, reducing your car’s speed if you’re getting too close to another car in front or if you’re nearing a turn. Once the road is clear, ACC accelerates the car to the target speed you have set.
In some cars, ACC can even trigger the brake systems to decelerate the car quickly in case the car in front suddenly brakes or a hazard appears.
Cruise Control in Motorcycles
Unlike cars, motorcycles don’t have gas pedals. They have gas handles instead. Unfortunately, holding a gas handle for a long duration is much more frustrating than holding a gas pedal. This nuisance has called for a technology similar to cruise control in function but different in design: throttle lock.
Throttle lock functions similarly to cruise control in cable throttle cars, except it skips the actuator and the ECU and directly deals with the throttle body.
Throttle lock works by locking the throttle cable and maintaining a constant amount of tension on the cable. This keeps the motorcycle cruising at a steady speed.
The simplicity of the throttle lock has a catch. Throttle lock doesn’t check in with the speed sensors to see if it’s going any faster or slower than the target speed, so it only works well on flat roads.
When to Use (and Not to Use!) Cruise Control
Use cruise control on straight roads with little traffic. As a safety measure, braking will disengage cruise control, and on a road with lots of vehicles, you’ll need to brake often.
Cars naturally decelerate when you take your foot off the gas pedal, but that won’t be the case when you have cruise control activated. It might be too late by the time you hit the brakes when you use cruise control on a crowded road.
This also goes for roads with lots of turns and twists. Entering a sharp turn with high speed is often dangerous. Put the turns behind you and once you have a straight road, engage the cruise control.
Though the point of cruise control is to make your ride more comfortable, it’s prone to make you a bit too comfortable. Falling asleep behind the wheels with cruise control engaged is likelier to happen. Albeit this time, the car won’t decelerate and will keep going.
Adaptive cruise control solves most of the limitations that come with ordinary cruise control systems, but it still isn’t flawless. Adaptive cruise control relies on your car’s sensors to decide the appropriate speed, and these sensors can get blocked in bad weather. Snow, mud, rain, and other natural hazards can get in the way of your car’s sensors and make the adaptive cruise control less reliable.
Adaptive cruise control has limited access to the braking system, and it won’t be able to stop a head-on collision. Use the brakes yourself and remember that cruise control is only a driver assist feature, not an autopiloting system.
With this in mind, please take full control of your vehicle in bad weather and tricky roads. Don’t trust the cruise control, be it normal or adaptive.
Cruising with Control
The cruise control system was first strictly found on high-end luxury cars, but now even economy cars are often equipped with this feature. This system makes driving long trips much easier, as you don’t have to keep your foot on the gas pedal for hours.
Though cruise control makes things easier, it doesn’t mean that you should use cruise control all the time. There are times where you need to take things into your own hands.
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