Cruise Control

Dept. of Electronics & Communication RVCE, Bangalore Cruise Control System Cruise suppress is a new technological development which incorporates a agentive role of comfort in driving. Safety is only a sm both benefit of this administration. In short, travel ascendency can be said to be a frame which uses the principles of radar to determine the distances between two consecutive moving vehicles in which either one or both of them is incorporated with this system. Lalitha Chinmayee H M 1RV11EC052 Namratha H Mahesh 1RV11EC062 IntroductionEvery minute, on average, at least one person dies in a crash. activate bags and seat belts save tens of thousands of people a year. But the ultimate solution and the only thing that allow for save uttermost more lives, limbs and money is travel founder got system. Cruise tally was commercially posed in 1958 as an option on the Chrysler Imperial. Cruise mesh is an invaluable feature on American gondolas. Without travel swear, lon g road trips would be more tiring, for the driver at least, and those of us suffering from lead-foot syndrome would probably get a lot more velocity tickets.Cruise obtain is far more common on American cars than European cars, because the roads in America argon generally bigger and straighter, and destinations are farther apart. With dealing continually increasing, basic cruise go through is becoming less useful, but instead of becoming obsolete, cruise hold systems are adapting to this new reality soon, cars ordain be equipped with adaptive cruise control, which will allow your car to follow the car in front of it while continually adjusting speed to fend for a safe distance. What is Cruise Control System?Cruise control is a system, which mechanically controls the speed of an automobile. Most cruise control systems dont allow the use of cruise control below a certain speed. The purpose of the cruise control system is to maintain a eternal vehicle speed despite external dis turbances, such as changes in wind or road grade. This is accomplished by measuring the vehicle speed, comparing it to the in demand(p) or reference speed, and automatically adjusting the flatulence according to a control law. The cruise control system actually has a lot of functions other than imperative the speed of your car.It can accelerate or decelerate with the overwork of a exit. T present are also several important safety features the cruise control will disengage as soon as you hit the brake foot pedal, and it wont engage at speeds less than a particular value (usually around 25-30 mph). We all know that the things that control the speed of the car are the gas pedal and the brakes. And the brain that normally controls the speed of the car is the brain of the driver. The driver senses the speed by looking at the speedometer and then adjusting the pressure on the gas pedal or the brakes to compensate for variations in the desired speed.The cruise control system does t he same thing with one leave oution. It only controls the gas pedal it doesnt even know there are brakes in the car A Blind inventor and mechanical engineer called Ralph Teetor, invented cruise control in 1943. pic Modelling To understand the working of a cruise control system, we consider here a simple imitate of the vehicle dynamics, shown in the free-body diagram (FBD) below. The vehicle, of mass m, is acted on by a control force, u. The force u represents the force generated at the road/tire interface.For this simplified model we will assume that we can control this force directly and will neglect the dynamics of the functiontrain, tires, etc. , that go into generating the force. The resistive forces, bv, due to rolling resistance and wind drag, are assumed to vary linearly with the vehicle velocity, v, and act in the direction opposite the vehicles motion. pic skeletal frame 1 Summing forces in the x-direction and applying Newtons 2nd law, we arrive at the following system comparison (1)pic (1) Since we are interested in controlling the speed of the vehicle, the output equation is chosen as follows 2)pic (2) Taking Laplaces transform for equation (1), we get m sV(s) + b. V(s)=U(s) (3) We find the transfer function of the cruise control system to be pic pic framing 2 squeeze Diagram despotic the Cruise Control The brain of a cruise control system is a small electronic computer that is normally found under the hood or behind the dashboard. It connects to the hit man control as well as several detectors. The diagram below shows the input signals and outputs of a typical cruise control system. pic Figure 3 Cruise Control Working Block DiagramA 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 ofcontrol system theory. Si nce the cruise control system controls the speed of the car by adjusting the die position, 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.The most important input is the speed signal the cruise control system does a lot with this signal. The most basic control system is aproportional control. In a proportional control system, the cruise control adjusts the throttle proportional to the error, the error being the difference between the desired speed and the actual speed. So, if the cruise control is set at 60 mph and the car is way out 50 mph, the throttle position will be open quite far. When the car is going 55 mph, the throttle position opening will be only half of what it was before.The result is that the closer the car gets to the desired speed, the slower it accelerates. Also, if you were on a steep enough hill, the car might not accelerate at all. Most cruise co ntrol systems use a control scheme calledproportional-integral-derivative control (PIDcontrol). The integral of speed is distance. The derivative of speed is acceleration. A PID control system uses these three factors proportional, integral and derivative, calculating each individually and adding them to get the throttle position. Weve already discussed the proportional factor.Theintegralfactor is based on thetime integral of the vehicle speed error. Translation the difference between the distance your car actually travelled and the distance it would have travelled if it were going at the desired speed, calculated over a set period of time. This factor helps the car deal with hills, and also helps it settle into the correct speed and stay there. Lets say your car starts to go up a hill and slows down. The proportional control increases the throttle a little, but you may still slow down.After a little while, the integral control will start to increase the throttle, opening it more a nd more, because the longstanding the car maintains a speed slower than the desired speed, the larger the distance error gets. Now lets add in the final factor, thederivative. The derivative of speed is acceleration. This factor helps the cruise control respond quickly to changes, such as hills. If the car starts to slow down, the cruise control can see this acceleration (slowing down and speeding up are both acceleration) before the speed can actually change much, and respond by increasing the throttle position. pic Figure 4 Block Control of Cruise Control Model Setting of Cruise Control pic pic Figure 5 & 6 Setting of Cruise Control using buttons The system pictured above has five buttons On, Off, Set/Accel, Resume and Coast. It also has a sixth control the brake pedal, and if the car has a manual transmission the clutch bag pedal is also hooked up to the cruise control. The on and off buttons dont actually do much. Hitting the on button does not do anything except tell the c ar that you might be hitting another button soon.The off button turns the cruise control off even if it is engaged. Some cruise controls dont have these buttons instead, they turn off when the driver hits the brakes, and turn on when the driver hits the set button. The set/accel button tells the car to maintain the speed you are presently driving. If you hit the set button at 45 mph, the car will maintain your speed at 45 mph. retentivity down the set/accel button will make the car accelerate and on this car, tapping it one time will make the car go 1 mph faster. 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 gas. On this car, tapping the coast button once will cause the car to slow down by 1 mph. The brake pedal and clutch pedal each have a tack together 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.Adaptive Cruise Control System A more advanced cruise control is being developed that can automatically adjust a cars speed to maintain a safe following distance. Adaptive Cruise Control (ACC) is an automotive feature that allows a vehicles cruise control system to adapt the vehicles speed to the traffic environment. This new technology, called adaptive cruise control, uses forward-looking radar (or lidar light detecting and ranging. But lidar based ACCs are limited due to poor working in bad weather), installed behind the grill of a ehicle, to detect the speed and distance of the vehicle ahead of it. pic Figure 7 Adaptive Cruise Control System Adaptive cruise control is similar to schematic cruise control in that it maintains the vehicles pre-set speed. However, unlike conventional cruise control, this new system can a utomatically adjust speed in order to maintain a proper distance between vehicles in the same lane. This is achieved through a radar headway sensor, digital signal processor and longitudinal controller.If the lead vehicle slows down, or if another object is detected, the system sends a signal to the engine or braking system to decelerate. Then, when the road is clear, the system will re-accelerate the vehicle back to the set speed. The 77-GHz Autocruise radar system made by TRW has a forward-looking range of up to 492 feet (150 meters), and operates at vehicle speeds ranging from 18. 6 miles per hour (30 kph) to 111 mph (180 kph). Delphis 76-GHz system can also detect objects as far away as 492 feet, and operates at speeds as low as 20 mph (32 kph).These systems are being enhanced to include collision warning capabilities that will warn drivers through visual and/or audio signals that a collision is imminent and that braking or evasive steering is needed. In May 1998, Toyota became the first to introduce an ACC system on a production vehicle,luxury sedan. Main Parts & Working of ACCs The main components of a typical radar-based ACC system are 1. Fusion sensor 2. Headway control unit 3. Throttle 4. Brake 5. Dashboard display Fusion sensor It is a combination of sensors and processors.They are 1. Millimetre-wave radar 2. Stereo photographic camera 3. Image processor 4. Fusion processor pic Figure 8 Architecture of Radar Based ACC System Millimetre wave radar It is a sensor which uses millimetre wave for detecting the position and velocity of a distant object. Range is calculated using the formula C = 2*R/T Where, C is the velocity of light, R is the range, T is the time of flight of transmission. pic Figure 9 Millimetre Radar Unit Stereo camera The cameras function is detection of cars and other objects in the roadway.Image processor It processes the images from the stereo camera and the data fed into the fusion processor. Fusion processorThe function of fus ion processor is Data Fusion. Headway control unit It has control on the brakes and throttle and uses dashboard for immediate warnings. Canceling Cruise Control Operation Brake pedal is pressed Off button is pressed Vehicle Speed 25 mph An ACC system fault is detected pic Figure 10 A car model with advanced cruise control system First, the vehicle speed sensor might become flat. Normally the speedometer also fails so thats pretty easy to diagnose.Next, the power to the brain can be interrupted (Here brain is referred to the cruise control system as it works similar to brain). A blown fuse or a corroded connector can prevent the brain from working correctly or at all. Next, the brains can lose its ability to function. A faulty component can prevent the brain from doing its thing. The brain is a pretty sophisticated box that contains a lot of electronic components including a microprocessor. Normally when the brains fail you need to replace the box. The vacuum diaphragm can de velop a leak.If that happens then the cruise control might set and hold the speed for near time however if the leak is larger than the supply line and modulator can add vacuum to the system the system will slowly lose control and the vehicle will slow down. This can also happen if the vacuum line to the diaphragm is cracked or loose. Finally, the gene linkage that connects the diaphragm to the accelerator linkage can fail. Some aftermarket cruise control systems use a short length of what looks like fat key chain bead chain. I have seen several units fail when the chain simply breaks. ConclusionBut one drawback is that cruise control systems are dangerous in wet roads and slippery roads as they may cause some serious problems. Fully autonomous car is probably not viable in the foreseen future. Nearby vehicles would be in constant communication with each other and act co-operatively. It will probably take decades, but car accidents may eventually become almost as obsolete as plane crashes are now. References 1. www. howstuffworks. com 2. www. cars. com/features/adaptivecruisecontrol 3. www. autorepair. about. com 4. ctms. engin. umich. edu/CTMS/index. php? example=CruiseControl=SystemModeling