PREVENTIVE SAFETY AND INTELLIGENT SPEED GOVERNORS full report
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PREVENTIVE SAFETY AND INTELLIGENT SPEED GOVERNORS
Conventional speed governors are designed only to limit the maximum speed attainable by a vehicle. We are trying to implement Preventive Safety Systems using advanced Mechatronics and Active Safety Methods. This system can provide necessary warning and aid to the driver when required.
Keywords: Intelligent speed governor, Preventive safety, Predictive braking.
Nowadays speed governor is a common term of which almost everyone is familiar with. Speed governor is just a device that alerts the driver and decrease the speed of the vehicle when the vehicle speed exceeds the reference value entered in the speed governor. This thought i.e. whether this speed governor which merely controls the speed of a vehicle is worth in a fast moving society of ours ended up in an alternative for speed governor that can take decisions according to varying environmental and driver behavior.
Active safety systems are gradually becoming practical with advance in environment sensing and vehicle control technologies. On the other hand analyses of driver mistakes retrieved to as human errors, in road accidents has shown that driver continues to make mistakes in the cognition of their external world and judging the safe or not safe. A total 60% of all rear and almost 30% of head-on collision could have been avoided if the driver reacted mere a half a second early. So in this paper we are focusing on driver aids which combines both environment senses and driver monitoring system.
The development of driver supporting system that address the mistakes made by drivers requires Environmental sensors, driver monitoring system and a brake assist system to ordinate vehicle control.
The environmental sensor system consists of equipments that make the vehicle aware of its surroundings. In general it consists of radars, infrared night vision systems, high resolution digital video for medium distance observation, and ultra sonic systems for ultra short monitoring. In our system we are using a radar system and a laser based tracking system as environmental sensors.
It enables the vehicle to acquire data using radar technology. The most common frequency used is at the range of 77 GHz. Even though high resolution radars are preferred since it enables better tracking of both stationary and moving objects. These radars can acquire data like the distance of the object from our vehicle and the relative speed of the object being tracked.
The common technology now in use is the radar using frequency of 77 GHz. But it is not much efficient when tracking the stationary object. So it is preferred to use a high frequency radar system which can be effectively used to track both the moving and stationary objects.
The Laser Scanner
Even though the radar system is highly effective for vehicle tracking, it fails when pedestrian safety is concerned. For pedestrian tracking we use a laser based scanner which uses a laser beam and its reflections to calculate the size, speed, direction of motion and the position of the object. it can also detect the traffic sign boards and the reflection posts.
Object Tracking and Classification
Using the data from environmental sensing systems, the objects are classified according to their static and dynamic characteristics. The main classifications can be like cars, trucks/buses, motorcycles//bicycles and pedestrians. Additional data like reflexivity can be used to detect signal posts and such objects. The pedestrians are identified by comparing the acquired data with some out lines stored in the history. It is almost like video image processing. If the obstacle is identified as a pedestrian some complicated algorithms are used to track the movements of the pedestrian.
Driver Monitoring Systems
Driver monitoring systems are used to analyze driver behavior. There are many systems which can monitor the driver behavior. But most of them require some sort of physical contact with the driver. So most suited system is which did not want any physical contact. One of the proposed system uses some sensors which can monitor the eye lid motion, facial expressions and neck movements of the driver and the data from the sensors are used as the input to the central computer system which uses some complex algorithms to analyze the data and detect the state of the driver.
The reliability of the system that uses only the above data is very low. So we use a system which can analyze data like time, workload of the driver, driverâ„¢s driving behavior, etc. these datas are stored in the central computer and a suitable program is used to analyze these data and to reach a final conclusion on the state of driver.
Driver support systems
Our aim was to design a driver aid and warning system, which would jump into action only when, it detects an urgent situation or carelessness from the driver. The type of aid given to the driver will vary with case to case. We have data from both environmental sensors and from driver monitoring systems.
Data from the environmental sensors are fed in to a risk calculating circuit. Using some complex algorithms and previously stored data, it analyses the situation and gives a risk value as output. The action taken by the system mainly depends on the risk value.
This risk value and the feed back from the driver monitoring systems are fed in to an integrator to decide the extent of aid to be provided. The driver support system includes driver warning systems and driver aid systems. It provides both warning and operational support.
The driver support systems mainly have four stages of operation normal driving state, warning state, collision avoiding state and collision unavoidable state.
Normal driving state: in this case there are no potential threats to our vehicle. Driver can drive the vehicle as he/she like. No speed limitations, no acceleration controls.
Warning state: in this case the environmental sensors detect an object that may raise a chance of collision with our vehicle. The system warns the driver with the help of seat belt jerks or by the vibration of pedals. If the system detects driver is fully conscious, system waits the driver to take action. Till the fourth stage.
Collision avoidance zone: in this state vehicle detects serious threats and the predictive breaking system comes in to play. The brake pads are imperceptibly brought in to contact with the discs to take up the slack, the hydraulic pressure is built up. Hundred percent brake is applied as soon as the driver hits the brake pedal with any degree of force. This will reduce the total breaking distance. If the driver is in full conscious and he/she is not taking any action to stop the vehicle, the injection pressure is withdrawn to decelerate the vehicle. It increases the collision avoidance zone and if the driver is not reacting, the predictive emergency breaking jump in to action and the brakes are applied automatically to avoid collision.
Collision unavoidable state: in this state collision is unavoidable and the system tries to ensure the safety of the occupants. It tries to reduce the after effects of the collision.
Intelligent Speed Governor
In the case of ordinary speed governors, it just limits the maximum speed, but the accidents due to driverâ„¢s carelessness cannot be avoided just by reducing the speed. In the above discussed system we monitor the driver as well as the environment and analyze these data to reach at certain decisions. It will not restrict the driver from enjoying inspired driving unless a potential threat is detected. The system comes in to action only when it detects a threat. The system is designed to provide timely advice and then aid to the driver. It warns the driver when a critical situation arises, and the driver aid systems are activated to tackle an emergency situation. Brake prefill enables 100% breaking force being applied to the pads as soon as the brakes are applied.
Working of intelligent speed governor
The proposed system consider vehicle as a human machine cooperative system. The working of an intelligent speed governor can be explained with the help of a block diagram.
Output from driver monitoring system, environmental sensors and speed monitor is given as the input to risk calculating circuit. All these data with the risk value is given to the integrating circuit. It determines what the next step is.
If a critical situation is confirmed, the system divides the distance between vehicle and obstacle into three states.
Â¢ Safe distance
Â¢ Collision avoidable distance
Â¢ Collision un avoidable distance
In the safe distance the system constantly monitor the obstacle, and analyses its movements. These data is used to calculate the risk.
As the vehicle enters the collision avoidable zone, the vehicle warns the driver by audio and visual methods. Force feed back pedals and seat belt vibrators are also used to warn the driver. At the same time brake prefill is enabled, which helps to avoid breaking slack. If the driver is not taking till the half of the collision avoiding zone, speed is reduced by reducing the injection pressure. It extends the collision avoidance zone. If the driver is not taking any action till the end of the collision avoidable zone, the collision avoiding system is activated. It will automatically stop the vehicle before collision.
Collision unavoidable distance arises when some obstacle suddenly appears before the vehicle. It activates the predictive breaking system, which helps to apply 100 percent breaking force, as soon as the driver hits the brake pedal. The breaking force is not related to the force being applied at the pedal. In such a stage system concentrates on ensuring the safety of its occupants.
Speed is not only the prior cause for the accidents occurring in our country but it is the human errors which causes much of a concern. More than 80% of the accidents are caused by the carelessness of the driver. So as a conclusion to our study implementation of INTELLIGENT SPEED GOVERNOR is a worth alternative for the speed governor.
Prof. Premachandran (Dept. of mechanical engg. SSET Karukuty)
Autocar India. ( autcarindia.com)