Cruise Control System

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4/4/2005

BNCE PUSAD

CRUISE CONTROL SYSTEM

Ritesh Bhusari

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ABSTRACT Now a day Cruise Control is an invaluable feature on luxury cars. Without cruise control, long 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 speeding tickets. Cruise control is far more common in American cars, because the roads in America are generally bigger and straighter, and destinations are farther apart. But now in India too thanks to the construction of Express Highway & The Golden Quadrilateral underway Cruise Control sees a bright future. With traffic continually increasing, basic cruise control is becoming less useful, but instead of becoming obsolete, cruise control systems are adapting to this new reality. Soon, cars will be equipped with adaptive cruise control, which will allow your car to follow the car in front of it while continually adjusting speed to maintain a safe distance.

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INTRODUCTION Necessity of Cruise Control System A 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 of Cruise control system. Every minute, on average, at least one person dies in a crash. If you read this article from start to finish, 30 or more deaths will have occurred across the globe by the time you are done. Auto accidents will also injure at least 10 million people this year, two or three million of them seriously. On the other hand, if we think about, the hospital bills, damaged property, and other costs will add up to 1-3 percent of the world's gross domestic product, according to the Paris-based Organization for Economic Cooperation and Development. For the United States alone, the tally will amount to roughly US $200 billion. And, of course, the losses that matter most are not even captured by these statistics, because there's no way to put a dollar value on them. So we need such a system that will provide the safe way of driving and will probably be reduced the chances of accident. If cruise control system will give faith to do so, then it is sure that the maximum chances of accident might have been reduced.

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BASIC FEATURES OF CRUISE CONTROL SYSTEM

FIG. 1 SHOWING THE FEATURES OF THE CRUISE CONTROL SYSTEM ON THE STEERING

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FIG. 2 – A CLOSURE VIEW SHOWING THE FEATURES OF THE CRUISE CONTROL SYSTEM The cruise control system actually has a lot of functions other than controlling the speed of your car. For instance, the cruise control as shown in fig.1 and fig. 2 can accelerate or decelerate the car by 1 mph with the tap of a button. Hit the button five times to go 5 mph faster. There are several important safety features -- the cruise control will disengage as soon as you hit the brake pedal, and it won't engage at speeds less than 25 mph (40 kmph). The system as shown in fig.1 and fig. 2 has five buttons: On, Off, Set/Accel, Resume and Coast. It also has a sixth control -- the brake pedal, and if your car has a manual transmission the clutch pedal is also hooked up to the cruise control.

The basic features provided by this system are, The ON and OFF buttons don't actually do much. Hitting the on button does not do anything except tell the car that you might be hitting another button soon. The off button turns the cruise control off even if it is engaged. Some cruise controls don't 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 currently driving. If you hit the set button at 45 mph, the car will maintain your speed at 45 mph. Holding down the SET /ACCEL button will make the car accelerate; and on this car, tapping it once will make the car go 1 mph faster.

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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 acceleration pedal. 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 switch 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.

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BLOCK DIAGRAM OF CRUISE CONTROL SYSTEM

FIG. 3 – BLOCK DIAGRAM OF CRUISE CONTROL SYSTEM

A cruise-control system exists to maintain the speed of a car, even over varying terrain, when turned on by the driver. When the brake is applied, the system must relinquish speed control until told to resume. The system must also steadily increase or decrease speed to reach a new maintenance speed when directed to do so by the driver. It is very simple to understand the working of Cruise Control System with the help of the block diagram as shown in the fig. 3 For such a system, there are several inputs: ·

System on/off: If on, denotes that the cruise-control system should maintain the car speed.

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·

Engine on/off: If on, denotes that the car engine is turned on; the cruise-control system is only active if the engine is on.

·

Pulses from wheel: A pulse is sent for every revolution of the wheel.

·

Accelerator: Indication of how far the accelerator has been pressed.

·

Brake: On when the brake is pressed; the cruise-control system temporarily reverts to manual control if the brake is pressed.

·

Increase/Decrease Speed: Increase or decrease the maintained speed; only applicable if the cruise-control system is on.

·

Resume: Resume the last maintained speed; only applicable if the cruisecontrol system is on.

·

Clock: Timing pulse every millisecond. There is one output from the system:

·

Throttle: Digital value for the engineer throttle setting

CONSTRUCTIONAL DETAILS OF VARIOUS PARTS OF CRUISE CONTROL SYSTEM 1. Servo The two solenoids are for Vacuum and Vent. One side of each solenoid is connected to battery positive with the key on. To activate a solenoid, the Amp grounds out the other side of it. When the Amp wants to open the throttle, it activates the Vent solenoid, which blocks it off. It then pulses the ground on the Vacuum

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solenoid to apply vacuum to the diaphragm. The diaphragm pulls the throttle open a little more each time the Vacuum solenoid is pulsed. The Amp keeps activating the Vacuum solenoid until the desired throttle opening is reached. The Amp also uses the feedback potentiometer to determine how much the throttle is moving and bases its adjustments on that. Even if the Vacuum solenoid stops applying vacuum, the diaphragm will hold its position. It won't release the vacuum until the vent solenoid ground is released. Then the vacuum gets dumped to the atmosphere. If the Amp just wants to let the throttle reduce by a small amount (if it is going too fast for example) it will momentarily ground the Vent solenoid to dump a small amount of vacuum.

FIG. SHOWING SERVO

2.

Vehicle speed sensors (VSS) The VSS is connected to the speedometer cable. Most of the later models had the Speedo cable plugged INTO the speed sensor. On this type, the gear on the end of the sensor is driven by the output shaft in the transmission, and the sensor in turn drives the Speedo cable.

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The sensor acts as a little generator. A magnet spins in a coil of wire to generate an AC voltage. 3.

Switches The system switches are built into the steering wheel cover, which are already discussed in chapter 3.

4.

Brake Light Switch The Cruise Control Computer has a wire coming from the brake lights. It senses the brake light voltage when the operator steps on the brakes and disengages the cruise control. If both brake light bulbs are burned out, the cruise won't work.

5.

Clutch Switch Vehicles with manual transmissions also have a switch that opens when the clutch is pushed in. This keeps the engine from revving up. The clutch switch is wired in with the brake light switch so that it breaks the circuit to the brake light bulbs. Due to the safety feature mentioned with the brake lights above, the systems disengages.

6.

Vacuum Dump Valve Later systems have a vacuum dump valve on the brake pedal. A vacuum line is connected from the valve to the Servo diaphragm. When the brake pedal is pushed, vacuum in the Servo is released (dumped). This is another safety feature. In the earlier models without this valve, when the brake light switch went bad and you were using the cruise, the more you tried to stop the car the more the Amp tried to accelerate.

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WORKING OF CONVENTIONAL CRUISE CONTROL SYSTEM

FIG. 4 – SHOWING THE WORKING OF CRUISE CONTROL SYSTEM Cruise control systems are comprised of electronic and mechanical subsystems. 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 the same thing.

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The vehicle's speed sensor which is mounted on the output shaft of the transmission (the thing that drives the wheels) sends electrical pulses to the computer, pulses which are generated by a magnet spinning past a sensor coil. When the speed of the vehicle increases, the frequency of the pulse increases. For any given speed of the vehicle there is a corresponding pulse frequency. It is this pulse frequency, which the cruise control tries to maintain as a constant. You think of it as the vehicle's speed. The brain of the control box of the cruise control has three functions: 1. It stores the speed of the vehicle when you press the "set" button while traveling at the desired speed. It keeps this value in its memory until you turn the ignition off. 2. It receives the pulses from the transmission sensor and compares the frequency of those pulses to the frequency value stored in its memory - the set point. 3. It sends pulses to a vacuum controlled diaphragm connected to the accelerator linkage. The pulses it sends regulates the amount of vacuum the diaphragm receives. The more pulses, the more vacuum and the more vacuum the more force on the accelerator linkage. The system continues to add vacuum force until the set point speed is reached. At that point the system modulates the amount of vacuum the diaphragm receives in an effort to maintain the number of pulses coming from the speed sensor as close to the stored value as possible.

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MOUNTING OF CRUISE CONTROL SYSTEM The cruise control system controls the speed of your car the same way you do -by adjusting the throttle position. But cruise control actuates the throttle valve by a cable connected to an actuator, instead of by pressing a pedal. The throttle valve controls the power and speed of the engine by limiting how much air the engine takes in. In the Fig. 8 , you can see two cables connected to a pivot that moves the throttle valve. One cable comes from the accelerator pedal, and one from the actuator. When the cruise control is engaged, the actuator moves the cable connected to the pivot, which adjusts the throttle; but it also pulls on the cable that is connected to the gas pedal -- this is why your pedal moves up and down when the cruise control is engaged. Many cars use actuators powered by engine vacuum to open and close the throttle, Fig. 9. These systems use a small, electronically-controlled valve to regulate the vacuum in a diaphragm. This works in a similar way to the brake booster, which provides power to your brake system.

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FIG. 8 ONE OF THE CABLES IS CONNECTED TO THE GAS PEDAL, OTHER TO THE VACUUM ACTUATOR.

FIG. 9 ELECTRONICALLY CONTROLLED VACUUM ACTUATOR.

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WORKING OF THE NEXT GENERATION CRUISE CONTROL SYSTEM (ADAPTIVE C.C.S.) Adaptive cruise control is similar to conventional cruise control in that it maintains the vehicle's pre-set speed. However, unlike conventional cruise control, this new system can automatically 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. A prototype "fusion processor" from Fujitsu Ten Ltd. depends on optical and radar sensors to move a car automatically at the varying speeds of traffic. A camera and radar report on the width, distance, and speed of objects ahead, and the processor combines the data, feeding it to a unit that controls the car, as shown in the fig. 5

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FIG. 5 – ADAPTIVE CRUISE CONTROL SYSTEM

Moreover the Adaptive Cruise Control (The Fujitsu Ten) system keeps a safe distance behind cars in its lane [reaction zone] by combining radar data on distance with stereo-camera data on the size of objects. The camera derives the width of cars by detecting their edges [black dots, and white square boxes in the photo]. Objects

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that are too wide, like a bridge abutment, are ignored. The system's wide field of view allows it to continue tracking vehicles around curves, as shown in the fig. 6 & fig. 7

FIG. 6 – TRACKING OF THE VEHICLES AROUND

FIG. 7 – STEREO CAMERA VIEW

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ADVANTAGES OF CRUISE CONTROL SYSTEM 1. Provides the safest way of driving by sensing the proper distance between the rear and front vehicle and control the vehicle by providing the same to the control unit. 2. Provides less fatigue to the driver as the system can be operated simply by switches on the steering column without using the foot pedal. 3. Useful for those suffering from lead foot syndrome. 4. If battery failure occurs, this system is automatically sets to the manual control and hence no chances of getting into dangerous situation. 5. 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.

DISADVANTAGES OF CRUISE CONTROL SYSTEM 1. System may fail if the above mentioned components are not maintained properly. 2. The driver should have a complete knowledge about working of the system. 3. In the adaptive cruise control , the system will activate if anything is almost anywhere in front of you. This causes some false slowing or braking in multiple lane situations. Thus the system fails on more crowded

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multilane roadways, with vehicles cutting into that safe margin between you and the vehicle in front and with smaller objects such as motorcycles and bicycles. 4. Most current systems shut off below 30 km/h or so.

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CONCLUSION Since now a day, vehicle owners are curious about the speed of the vehicle but at the same time they also think about the safety. But a little consideration shows that as the speed increases, the same result in decrease in the safety, but if we think about the Cruise Control System it makes the provision for both, i.e. it can cruise the vehicle whenever required and also controls the speed if it exceed the required one. Also the new version has more add on features, so if this system will faith for better speed of the vehicle with proper safety it will become popular soon in the future through out the world.

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