03-01-2011, 11:16 AM
CRUISE CONTROL.docx (Size: 434.27 KB / Downloads: 62)
DONE BY:
K.Raghunath
CRUISE CONTROL
Abstract— The cruise control system in a vehicle is studied in details. First, control concepts in cruise control system are investigated. Second, simplified cruise control models are developed and simulated. Third, an introduction to adaptive cruise control system is presented. Fourth, modeling of adaptive cruise control system in a traffic simulation is carried. Finally, the future development of the advanced adaptive cruise control system is presented.
INTRODUCTION
Cruise control system has become a common feature in automobiles nowadays. Instead of having the driver frequently checking the speedometer and adjusting pressure on the gas pedal or the brake, cruise control system control the speed of the car by maintaining the constant speed set by the driver. Therefore, cruise control system can help reduce driver’s fatigue in driving a long road trip. This paper presents the control system behind the cruise control.
BACKGROUND
Before getting into to the control system concepts of cruise control, the components and the basic mechanism of the cruise control system in a vehicle are summarized.
A. Components of Cruise Control
Cruise control system can be divided in to three main parts, which are the input, the processor, and the output. The input of the system includes the setting buttons on the steering wheel, gas pedal, brake, clutch and the feedback signal of the cruise control. The processor of the system is to control the speed of the car by utilizing the control system theory. The output is the throttle position, which is corresponding to the actual speed of the car.
1) Input of Cruise Control
There are usually three to five setting buttons on the steering wheels for the input to the cruise control system. The buttons are on/off, set/accel, resume, and coast. The on button turns on the cruise control function. The off button turns off the cruise control function. The set/accel button is to set the speed of the car to the current speed that the car is driving at. Also, by tapping the set/accel button once can increase the speed of the car by 1mph and so forth. The resume button is to set the speed of the car back to the last maintained speed, which is he speed right before the cruise control is disengaged. The coast button is to decrease the speed of the car.
The brake and the clutch are the other inputs to the cruise control system. When the pedal is pressed, the cruise control system is disengaged, so the speed control of the car is taken over by the driver in adjusting the gas pedal and the brake.
Furthermore, the speed for the cruise control can be set by pressing the gas pedal to accelerate the car to the desired speed, and then hitting the set button. Also, when the cruise control is engaged, the gas pedal overrides the set speed from the cruise control, so the car accelerates as long as the gas pedal is pressed.
Finally, the feedback signal from the measured speed of the car is taken into account of the input of the curse control system. This input is closely related to the control system of the cruise control. The detailed of the feedback input is presented under the control system of cruise control later.
2) Processor of Cruise Control
The processor of a cruise control is a control system designed to obtain the speed set by the driver. It plays an important role in the cruise control system. The processor is integrated with electronic components to a system transfer function, which is discussed under the control system of cruise control in detail.
3) Output of Cruise Control
The output of the cruise control is the throttle position. The actual speed of the car varies corresponding to different throttle position, as the throttle valve limiting how much air the engines takes in. A different air-to-fuel ratio in the combustion process affects the power and the speed of the engine, and this eventually leads to the change of the car speed.
B. Mechanism of Cruise Control
An overview of the relationship between different components of cruise control system is shown in Fig. 1. The processor of the cruise control system is shown as the Cruise Control Computer in the figure.
The process of the cruise control system in a vehicle is: First, the driver sets the desired speed of the car by turning on the cruise control at the desired speed that the car is traveling at and hit the set button. An alternate way to set the desired speed of the car is by tapping the set/accel button to increase the speed of the car or by tapping the coast button to decrease the speed of the car. Second, the processor of the system gets the input signal, and then sends the output signal to the actuator. Third, the actuator adjusts the throttle position. Finally, the changes in the throttle position would leads to the changes in the speed of the car traveling. Also, the actual speed of the car is measured by a sensor and sent to the processor. The process of sending the current speed of the car continues for the processor to maintain the desired speed, as long as the cruise control is engaged [1]. This process is explained in details in terms of control system concepts later.