19-11-2012, 01:21 PM
Brake Assisted Differential Locking System
1Brake Assisted Differential.doc (Size: 52 KB / Downloads: 48)
Abstract –
“It takes 8,460 bolts to assemble an automobile, and one nut to scatter it all over the road.”
Some of the biggest advances in the field of automotive technology in the past 10 years have come in the area of safety. Spurred by the improvements in the microprocessor speed, miniaturization, and software development, the automobile continues to evolve.
In this new approach proposed, I am going to have an electronic and a pneumatic circuit to automatically control the traction of the vehicle.
During ordinary conditions, when the vehicle is driven down a straight road, or if the difference between speeds of the two (rear) wheels is below a specified limit, no signal will be generated by the electronic circuit. This helps the vehicle negotiate the turns with better traction control as differential action is unaltered. But if the difference between speeds is beyond a specified limit, the signal will be generated by the electronic circuit which will actuate the pneumatic circuit. This causes gradual braking on the faster wheel until it gains traction.
Hence, the wheels will never lose traction. This system ensures a reduction of more than 50% in the
capital investment as compared to the already existing system scan tilt the scales in the favour of the manufacturing company and eventually the cost conscious consumer
INTRODUCTION
Are you REALLY comfortable manoeuvring your vehicle through a muddy patch? In dry conditions, when there is plenty of traction, the amount of torque applied to the wheels is limited by the
Engine and gearing; in a low traction situation, such as when driving on ice, the amount of torque is limited to the greatest amount that will not cause a wheel to slip under thoseconditions. So, even though a car may be able to producemore torque, there needs to be enough traction to transmit that torque to the ground .As long as the tyre grips the road, providing a resistance to turning, the drive train forces the vehicle forward.
Driveline torque is evenly distributed between the two reardrive axle shafts by the differential. When one tyre encounters a slippery spot on the road, it looses traction, resistance to rotation drops, and the wheel begins to spin. Because the resistance has dropped, the torque delivered to both the wheels changes. The wheel with good traction is no longer driven. Ift he vehicle is stationary in this condition, only the wheel over the slippery spot rotates. Hence the vehicle does not move.This situation places stress on differential gears. As the traction fewer wheels rotates at a very high speed, amount of heat generated increases rapidly, lube film breaks down, metal to metal contact occurs, and the parts are damaged. Now if the spinning wheel suddenly has traction, then the shock of the sudden traction can cause severe damage to the drive axle assembly.
So presently how do we overcome these difficulties? To overcome these problems, differential manufacturers have developed the –Limited Slip Differential. In automotive applications, a limited slip differential (LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In an automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity. The main advantage of a limited slip differential is found by considering the case of a standard (or "open") differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate at twice its intended velocity – the torque transmitted will be equal at both wheels, but will not exceed the threshold of torque needed to move the vehicle, thus the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use however, such as driving off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the velocity difference between a pair of driven wheels, usefull torque can be transmitted as long as there is some friction available on at least one of the wheels. The clutch type LSD responds to drive shaft torque. The more drive shaft inputtorque present, the harder the clutches are pressed together and thus the more closely the drive wheels are coupled to each other.
PROPOSED INNOVATION-BRAKE ASSISTED DIFFERENTIAL LOCKING
SYSTEM (BADLS)
In this new approach, there is an electronic and a pneumatic circuit to automatically control the traction of the vehicle. During the ordinary conditions, when the vehicle is driven down the straight road, or if the difference between the speeds of the two (rear) wheels is below a specified limit, no signal will be generated by the electronic circuit. This helps the vehicle negotiate the turns with better traction control, as the differential action is unaltered. But if the difference between the speeds is beyond a specified limit, the signal will be generated by the electronic circuit, which will actuate the pneumatic circuit. This causes gradual braking on the faster wheel until it gains traction. Hence, the wheels will never lose traction. The BADLS control module senses that a wheel is about to slip based on the input sensor data and in turn pulses the normally open inlet solenoid valve closed for that circuit.
This allows fluid to enter the circuit. At the same time, the control module opens the normally closed solenoid valve for that circuit. This leads to the application of pneumatic pressure on the brake pads, leading to the artificial braking. Once the
affected wheel returns to the same speed as the other wheel the control module returns both the valves to their respective normal positions releasing any residual pressure in the pneumatic circuit of the affected brake. Flowchart to explain working of the circuit shown in Fig 1 is given above in Fig 2 First flowchart shows working of normal breaking circuit and the latter shows the working when the badls circuit is working. During normal breaking condition solenoid valve 1 is in closed condition so air from master cylinder flows in main braking circuit bypassing the auxiliary circuit through solenoid valve 1 and thus normal breaking action is achieved. .In slipping condition microcontroller actuates normally closed solenoid valve and normally open solenoid valve 2 and thus artificial braking is applied to the required wheel.
The BADLS Control module
The system is provided a control system, at least two driven wheels, a differential for transmitting power from the engine to the driven wheels and permitting relative velocity between the driven wheels. The control system includes two wheel velocity sensor, a comparator circuit and a control circuit. The wheel velocity sensor is configured to detect the angular velocity of the two driven wheels and to generate a signal. The comparator circuit is coupled to the wheel velocity sensor and is configured to compare the signals of the sensors and to generate a slip signal representative of the degree of slip of the driven wheels. The control circuit is coupled to the comparator circuit and to the brake assisted differential locking mechanism and is configured to and to apply the control signals to the differential locking ls mechanism to limit relative velocity between the driven wheel is shown if this flow chart