A LOW COST INTELLIGENT ELECTRONIC

CRUISE CONTROL SYSTEM

A LOW COST INTELLIGENT ELECTRONIC

CRUISE CONTROL SYSTEMV. Srinivas Meher, Department of Electrical Engineering, M. Bharath Kumar, Department of Electrical Engineering,Siddharth Institute of Science and Technology, Puttur, Siddharth Institute of Science and Technology, Puttur, Andhra Pradesh, India. Andhra Pradesh, India.Email ID: vyas.sri@gmail.com Email ID: iambalkris@gmail.com

Abstract − Cruise or speed control systems are designed to allow driver to maintain a constant speed without having to apply continual foot pressure on the accelerator pedal. Cruise control can be effectively realized using electronic components rather than mechanical components.

In the present paper cruise control in vehicles is realized with the help of a Miniature Communication System that operates the cruise control module to manipulate the position of throttle with the help of an actuator, in order to limit the speed of the vehicle. The design is of vital importance in two aspects – a) To control the speed of the vehicle in accident prone regions, high traffic zones and congested areas in cities. The system should be capable of reducing the vehicle speeds in those regions although the driver doesn’t pay attention, b) To avoid the skidding of vehicles while negotiating a curved path. Keywords − Cruise control, Miniature Communication System, Banking Angle

I. INTRODUCTION

An electronic system frequently fitted to modern vehicles is a cruise control system, or vehicle speed control system, which keeps a vehicle's speed constant on long runs and therefore may help prevent driver fatigue. However, cruise control is not suitable for all road conditions and drivers are warned not to use it at low speeds, or in heavy traffic, on winding roads or in foggy or icy conditions. There are built-in logical interlocks intended  to prevent its use in certain gears, below certain speeds etc. and switches that disconnect the cruise control if, for example, the brakes are applied.

If the driver hands over speed control to a cruise control system, then the capability of the system to control speed to the set value is just as critical to safety as is the capability of the driver to control speed manually. Yet, strangely, although the capability of the driver is regarded as a critical safety factor - e.g. the slogan "Don't drink and drive" - not so cruise control systems which are currently classified as non-safety-critical.

II. CRUISE CONTROL

A. Principles of operation and implementation

An automobile cruise control system is an outer speed control loop that ”takes over" control of the throttle - normally exercised by the driver through the accelerator pedal - and holds the vehicle speed steady at a set value.  The driver controls the state of the cruise or speed control system (typically: ON, OFF, RESUME, SET/ACCEL, COAST) by means of a set of switches usually mounted in the centre of the steering wheel. 

B. Vehicle Speed Control – Block Diagram

The block diagram below shows the main elements of a typical cruise control system (vehicle speed control system. A signal proportional to road speed is fed back and compared with a set speed reference to give a speed error signal that is used to control throttle position, and hence engine power, so as to change the speed to reduce the speed error signal to zero. In some systems, the speed reference voltage is held in a sample and hold amplifier that uses a low loss capacitor.

Figure 1. Block Diagram of Vehicle Speed Control System

Most cruise control systems are functionally very similar and appear to be of the "proportional + integral" type of closed loop control system. Cruise control systems are likely to exhibit similar failure modes and have the same potential for exhibiting suboptimal performance as other industrial and domestic PI control systems.

C. Methods of Throttle actuation

The throttle actuation can be done with: (a) Electro pneumatic servo valve actuation (engine vacuum used to provide the force via bellows), (b) Electronically controlled DC motor with a worm drive, (c)Stepper motor with electronic control

D. Type of Electronic Control

The Electronic control can be implemented using: (a) Analogue + hard wired logic, (b)Digital, using a discrete cruise controller, (c) Digital cruise control function incorporated in the engine control module, (d) Digital cruise control function incorporated in the engine control module with electronic systems multiplexed together via typically one or more CAN-Bus systems

III. ELECTRONIC CRUISE CONTROL

There will be a transmitter installed near the region where speed is to be controlled. It transmits the information of speed which is set by the user and the receiver installed in the vehicle will respond to that signals and control the speed. The speed is controlled by manipulating the throttle position with the help of electronic controller.

A. Transmitter

It has a range of up to 1/4-mile (400 meters) or more, depending on the line-of-sight, obstructions by large buildings, etc. L1 is 8 to 10 turns of 22 gauge hookup wire close wound around a non-conductive 1/4-inch diameter form, such as a pencil. C4 is a small, screw-adjustable, trimmer capacitor. Its range is 50-90 MHz. The LC forms a tank circuit and the capacitance value is changed to adjust the frequency.

B. Receiver

50MHz Receiver based on MC3372

The figure shows a 50MHz Receiver based on MC3372, which is a very narrow band FM receiver, and the receiver frequency can be set with a LC tank or with a crystal. The sensitivity can be increased by the help of an antenna preamplifier (dual gate input FET amp).

C. Digital to Analog Converter (DAC)

An 8 bit digital to analog converter can be used to convert the set value of speed in kmph and is sent to the transmitter module. By suitably taking the reference voltage of DAC we can transmit a voltage of 0-5V range corresponding to the value of speed set.By suitable signal conditioning circuits using voltage divider at the out-put stage of DAC we can obtain the desired voltage range of signal to be transmitted. The required range of signal to be transmitted can be easily set by changing reference value Vref. The digital input to the DAC corresponds to the value of speed to be set in Kmph

D. Comparator

A typical sample and hold circuit feeding the speed error amplifier, as used in an analog cruise control circuit. Voltage holding capability depends upon the storage capacitor not losing or gaining charge via a

leakage path. This may be difficult to guarantee under all circumstances in an automobile environment. In order to keep down the leakage current from the capacitor, Rs must be kept very high.

IV. BLOCK DIAGRAMS

A. The Communication System - Transmitter Section

The Transmitter will be installed at the place where vehicle speed is to be controlled.

Figure 2. Block Diagram of the Transmitter Section

B. The Receiver Section

The receiver section will be a part of the vehicle.

Figure 3.The Block diagram of the Receiver Section

C. The Transmitter Module

Figure 4. Block Diagram of the Transmitter Section

D. The Receiver Module

Figure 5. Block Diagram of the Receiver Section Module

The E. Comparator

Figure 6. Block Diagram of the Electronic Comparator Section

V. WORKING PRINCIPLE

The speed limit (kmph) in a particular region is fed to the transmitter module as digital input through a keyboard (set by the traffic authority). Then the digital value of the speed limit ( kmph) is converted into a voltage range of 0-5V with the help of a Digital-Analog converter(DAC). And it is the transmitted with the help of frequency modulation (FM) covering a range of 30 meters.

The transmitted signal is received by the receiver and converted into to the voltage range of 0-5V by suitable signal conditioning circuits and fed to a comparator circuit. This value is compared with the output of a speed sensor fitted in the vehicle whose indication is scaled to the voltage range of 0-5V.

The comparator output signal is given to the cruise controller that controls the position of the throttle, which in turn limits the speed of the vehicle. a) If the speed of the vehicle is less than the speed

limit, then the comparator output will be low and does not trigger the controller and hence no control action on the throttle position .

b). If the speed of the vehicle is greater than the speed limit , then the comparator output will be high and controller will take control action on the throttle position and hence the speed is limited.

In the present proposal ,operational amplifier based comparator circuitry is the Electronic control module whose action is based on the error(difference) between the set value of speed (from the transmitter) and the vehicle speed output from speedometer and controls the servo unit. The servo unit is used to control the vacuum, which in turn controls the throttle.

The vehicle speed sensor (VSS) buffer amplifier monitor the vehicle speed. The signal created is sent to electronic controller. A clutch switch is used with manual transmission to disengage the cruise control when the clutch is depressed.

VI. TO AVOID OVERSPEED IN RESTRICTED AREAS

The speed limit is fed to the transmitter module and hence by electronic controller module we can effectively control the speed of the vehicle in the restricted and accident prone regions.

The servo is controlled by the controller, which in turn controls the amount of vacuum sent to the inside of the servo. Depending upon the vacuum, the servo will be either engaged or disengaged.

Figure 7 .Electronic cruise control uses an controller to operate a servo that controls the position of the throttle

Figure 8. A cruise control circuit with vacuum and electrical system

(Courtesy of General Motors Corporation)

VII. TO AVIOD SKIDDING OF

VEHICLE ON CURVED ROADS

If a car is on a level (unbanked) surface, the forces acting on the car are its weight, mg, pulling the car downward, and the normal force, N, due to the road, which pushes the car upward. Both of these forces act in the vertical direction and have no horizontal component. If there is no friction, there is no force that can supply the centripetal force required to make the car move in a circular path - there is no way that the car can turn.

On the other hand, if the car is on a banked turn, the normal force (which is always

perpendicular to the road's surface) is no longer vertical. The normal force now has a horizontal component, and this component can act as the centripetal force on the car!

The car will have to move with just the right speed so that it needs a centripetal force equal to this available force, but it could be done. Given just the right speed, a car could safely negotiate a banked curve even if the road is covered with perfectly smooth ice!

A. Conceptual Diagram

Figure 9. Position of Vehicle on curved roads

A Car on a Level Surface

All forces on the car are vertical, so no

horizontal force can be generated.

A Car on a Banked Turn

The normal force on the car due to the road is no longer vertical, so a component of the normal

force acts in the horizontal direction.

The Centripetal Force

The horizontal component of the normal force is shown in blue in the diagram above.

This force can supply a centripetal force to turn the

car.

B. Mathematical Derivation

Figure 10. A free-body diagram for

the car on the banked turn is shown.

The banking angle between the road and the

horizontal is (theta).

The normal force, N, has been resolved into horizontal and vertical components.

In the vertical direction there is no acceleration:

(1)

(2)

In the horizontal direction:

since

(3)

(4)

Solving for v gives:

C. Friction of the banked road

Friction provides additional safety to skidding. Looking at the figure, it may appear

as if friction should work away from the center of curvature.

cos

mgN

( ) sin tancosnet centripetal

mgF F NSin mg

net centripetalF F

tanv rg

Following points about the condition as put on the speed of the car:

There is a limiting or maximum speed of car to ensure that the car moves along curved path without skidding.

If the limiting condition with regard to

velocity is not met then the car will skid.

The limiting condition is independent of the mass of the car.

If friction between tires and the road is more, then we can negotiate a curved path with higher speed and vice-versa. This explains why we drive slowly on slippery road.

Smaller the radius of curvature, smaller is the limiting speed. This explains why sharper turn (smaller radius of curvature) is negotiated with smaller speed.

D. Banking of roads

Figure 11. The horizontal component of normal force meets the requirement of centripetal force.

VIII. HOW TO AVOID SKIDDING

The best way to avoid skidding of vehicle while negotiating a curve is to maintain the speed

well below the velocity .

Hence a suitable design is necessary that automatically control the speed below the limiting or maximum speed. From the radius of curvature, banking angle and gravity for a particular place, it is possible to estimate the value of the limiting speed. Now the transmitter module is installed near the curved lanes and the speed is set, in order to control the vehicle speed and hence we can effectively control speed of the vehicle.

IX. LIMITATIONS OF THE DESIGN

The automobile engine compartment is a particularly unfavorable environment in which to expect sensitive electronics to operate reliably

i) It is hot, dirty, humid and vibration levels are high;

ii) Radio Frequency Interference (RFI) levels can be high;

1) Sensors, switches, connectors and wiring:

i) Presence or absence of extreme cold/ heat, moisture, pollution, road salt etc. may play a significant role here, a speed sensor or its wiring may fail;

2) The Cruise Control Module :

i) electronic components may fail;

ii) moisture and surface contamination  may cause electrical tracking across insulating surfaces, in turn causing :

iii) the speed reference signal to drift,

tanv rg

tanv rg

iv) a high gain amplifier or integrator, or digital equivalent, to drift into saturation; v) logic may be affected by transient signals/noise;

3) The throttle actuator i) There are various different kinds of actuator used (electro-pneumatic and electro-mechanical) but they are all essentially power amplifiers, converting a small control signal into throttle movement. The result of an input signal, whatever its source, will be movement of the throttle. Spurious control signals may derive from many sources including : ii) RF noise at the input; iii) false signals from a malfunctioning cruise control module;

X FUTURE DEVELOPMENTS

The Cruise control system can be completely automated with the help of advancements in CAN (Controller Area Networks) thereby providing fast, accurate and reliable control of the vehicle. These features are being incorporated in the modern hybrid vehicles

XI CONCLUSION

In spite of its limitations, the cruise control system with the above electronic design can efficiently work to control the speeds in traffic zones, avoids skidding of vehicle and will be a effective control measure for long distance journey by safeguarding driver as well as outsiders.

The design considered can be implemented with a low cost communication system. Hence the overall system cost is reduced. The FM modulation used does not depend on line-of-sight and geographical structures (unlike IR-communication), hence we can able to bring down the velocity of vehicle well beyond the set value before reaching the area of interest.

XI REFERENCES

1. A Handbook of “Automotive Technology” by

Jack Ejjavec

2. Society of Automotive Engineers, INC,

Www. Sae.org