Cruise control has become an indispensable feature in American cars, especially for long road trips.
Without it, driving over extended distances would be far more exhausting for drivers. Additionally, those prone to a heavy foot on the gas pedal might find themselves collecting a significant number of speeding tickets.
Cruise control is more prevalent in American cars than in European ones due to the differences in road infrastructure. American roads tend to be wider and straighter, with destinations often spaced further apart.
As traffic congestion continues to grow, traditional cruise control has begun to lose some of its practicality. However, instead of becoming outdated, cruise control systems are evolving.
Advanced versions, such as adaptive cruise control, are being developed. These systems will allow cars to maintain a safe distance from the vehicle ahead by dynamically adjusting their speed.
This article explores how conventional cruise control operates and delves into the adaptive cruise control systems currently in development.
What Cruise Control Does
Cruise control systems offer a range of functions beyond merely maintaining a set speed. For instance, many systems can incrementally increase or decrease the car’s speed by 1 mph with the press of a button.
Pressing the button five times raises the speed by 5 mph. Safety features are also built into these systems. For example, cruise control disengages as soon as the brake pedal is pressed and won’t activate at speeds below 25 mph (40 kph).
The system often includes five main buttons: On, Off, Set/Accel, Resume, and Coast, alongside a sixth control the brake pedal. For vehicles with a manual transmission, the clutch pedal also integrates with the cruise control.
- On/Off Buttons: These don’t directly affect the car’s speed. Pressing the “On” button merely indicates readiness for further input. The “Off” button disengages cruise control, even if it’s active. Some systems forgo these buttons entirely, instead relying on brake and set controls.
- Set/Accel Button: Pressing this button locks in the current speed. For example, pressing “Set” at 45 mph ensures the car maintains 45 mph. Holding it down causes the car to accelerate, while a single tap increases speed by 1 mph.
- Resume Button: After disengaging cruise control by pressing the brakes, this button restores the car to its previous speed.
- Coast Button: Holding it causes the car to decelerate, mimicking the effect of releasing the gas pedal. A single tap decreases speed by 1 mph.
- Brake and Clutch Pedals: These pedals come with switches that disengage cruise control upon pressing, allowing quick manual control.
Cruise Control Acceleration and Deceleration
Cruise control operates by adjusting the throttle position, just as a driver does manually.
Instead of pressing the accelerator, the system uses a cable connected to an actuator to control the throttle valve, which regulates the engine’s power and speed by managing air intake.
In many systems, two cables connect to the throttle mechanism: one from the accelerator pedal and another from the actuator.
When engaged, the actuator adjusts the throttle via its cable, simultaneously pulling on the accelerator pedal cable. This is why the gas pedal may move up and down while cruise control is active.
A common mechanism for throttle control is an electronically controlled vacuum actuator. This actuator uses a diaphragm and a regulated vacuum system, similar to the brake booster, to modulate the throttle position.
Controlling the Cruise Control System
At the core of a cruise control system is a small computer located under the hood or behind the dashboard. This computer interfaces with throttle controls and sensors, ensuring precise speed management.
Effective cruise control systems balance acceleration to reach the desired speed without overshooting and maintain that speed despite changes in terrain or vehicle load.
They rely on sensor inputs, primarily speed signals, to function correctly.
The system employs proportional-integral-derivative (PID) control to fine-tune throttle adjustments:
- Proportional Control: Adjusts the throttle based on the difference between actual and desired speeds. The greater the speed difference, the more the throttle opens. However, this alone may not be sufficient on steep inclines.
- Integral Control: Accounts for cumulative speed error over time, helping the system compensate for prolonged deviations, such as when climbing hills.
- Derivative Control: Reacts to changes in acceleration, allowing the system to preemptively adjust the throttle before significant speed fluctuations occur.
Adaptive Cruise Control
Adaptive cruise control (ACC) represents the next generation of this technology, incorporating features to automatically adjust a car’s speed to maintain safe following distances.
This system uses forward-looking radar, typically mounted behind the vehicle’s grille, to monitor the distance and speed of the car ahead.
While similar to conventional cruise control in maintaining a pre-set speed, ACC offers advanced functionality. It adjusts the vehicle’s speed in response to traffic, ensuring a safe gap between vehicles in the same lane.
If the leading car slows or an obstacle is detected, the system signals the engine or brakes to decelerate. Once the road clears, the system accelerates the vehicle back to its set speed.
Examples of ACC technology include the TRW 77-GHz Autocruise radar system and Delphi’s 76-GHz radar system.
Both offer detection ranges up to 492 feet (150 meters) and operate at speeds from as low as 18.6 mph (30 kph) to over 111 mph (180 kph).
Beyond speed adjustments, ongoing developments aim to integrate collision warning systems into ACC.
These enhancements will alert drivers with visual or auditory signals if braking or evasive action is necessary.