Electronic control for the rear wheel drive of a vehicle

Transcription

1 Electronic control for the rear wheel drive of a vehicle Alfredo Pedroza-Hernández, Osbaldo Vite-Chávez, Roberto Olivera-Reyna, Reynel Olivera-Reyna fello.1@hotmail.com Department of Communications and Electronics Engineering Academic Unit of Electrical Engineering Autonomous University of Zacatecas, Campus Jalpa Abstract There are different types of traction vehicles such as front-wheel drive, rear-wheel drive and fourwheel-drive, also known as 4x4 vehicles. Most cars have built-in mechanism designed to minimize the turning radius. This device is known as a differential, but unfortunately causes loss of traction or ability to progress at the time that one of the driving wheels is suspended or loses it s grip. To improve the traction of a vehicle various mechanisms have been developed such as mechanical, viscosity and currently electronic. In this research it was decided to design and develop an electronic system able to determine which wheel to send the driving force for better progress in places where it would not be possible or under circumstances where it would lose traction completely, obtaining the highest capacity drive a rear-wheel drive vehicle. Finally we present the results and give some conclusions of our work [1]. 1. Introduction Vehicles that have open type differential present greater disadvantage than the differential with limited step and that AWD (commonly called 4x4), Figure 1 shows an illustrative example of an open type differential and some of its components. Figure 1: Components of a differential. 1

2 2. Development The function that performs a differential creates a disadvantage because they are responsible for transmitting the engine power to the wheel that has the least resistance and in many situations causing the slip. This disadvantage can greatly be reduced by using the resources which the same vehicle has appropriately, as the vehicles have two independent activation braking systems. The hydraulic system is composed of the pedal and in most vehicles the brake booster (also known as a booster). Master cylinder, the line leading to the hydraulic pressure to activate the slave cylinder linings also known as brake pads and more. The mechanical hand brake is composed of a lever or pedal depending on the vehicle, a wire wheel to stretch or tighten a lever that activates the brakes (two wires in total). The lever applies the brakes regardless of whether or not to send the hydraulic system pressure. The purpose of vehicles equipped with two independent brakes is that if one fails you can shut down the vehicle with the other system that works [2]. Using this knowledge it is possible to control the loss of traction through the use of brakes, in this case using the hand brake and where as the driver of the vehicle in which the system was fitted in is comfortable knowing that the amendment does not interferes with the main braking system. To design the controller it s necessary to consider various factors such as the control unit, the electromechanical actuator, the work load, the sensors and consider that there might be an external signal between the actuator and the load. The controller block diagram is shown in figure 2. Figure 2: Block diagram for controller. The transfer function relating to the input X(s) with the output W(s) of the diagram in figure 2, is obtained on the principle of superposition and is shown in equation 1. 2

3 (1) 3. Implementation To build the system that controls the loss of traction it is required to design an electronic device to determine which is the wheel that loses traction, turning through the angular velocity sensors in pulses of reference or Hertz, the sensors are composed of a detector Hall effect US1881 series that will be connected to two PIC16F84A microcontrollers (one per sensor) which census the reference of each wheel and then compared to each measured value depending on the outcome measured activate a power amplifier to activate the servo that will control the wheel which loses the traction. The servo system is made up of a motor connected to a worm reduction to transform the rotation angle to a linear displacement motor, it is a servo motor and not a gear motor because it makes reference to the position where it s located and with this reference it will always be able to locate the system when it turns off, in rest or initial position [3]. Figure 3 shows the order of the pins of the microcontroller PIC16F84A, where food is located, the port A, port B, where the oscillator is placed. Figure 3: Connections PIC16F84A. The way to control the traction is relatively simple. The control unit governs the electromagnetic actuator or the actuator that in turn is responsible for controlling the wheel to lose traction, each wheel has a sensor to indicate the speed control unit and comparing the speed of each wheel determines if one slows or remains inactive. Table 1 describes how they are configured each of the microcontrollers used in the control circuit. Table 1: Pin configuration of each PIC16F84A. puertos RA0-RA4 RB0 RB1-RB7 The first microcontroller is connected as follows: Binary output pulses detected. Signal provided by the Hall effect sensor. Not connected. 3

4 RA0-RA4 RB0 RB1 RB2 RB3 RB4- RB7 The second microcontroller is connected as follows: Binary input pulse detected by the first microcontroller. Signal provided by the Hall effect sensor. Indicates whether the pulses measured by the second sensor are less than first Whether they are equal. Whether they are older. Not connected. The RB1 and RB3 port control a power amplifier which is constructed by transistors, diodes and relays to control the servo controlled the wheel loses traction. The servo geared motor can be any sufficient force and complementing it with position references. Figure 4 shows the connections between circuit components to be implemented later, where switch 1 and 2 simulate the references of the sensors and switch 3 and 4 simulate the reference actuator. 4. Results Figure 4: Connections of the components. The control circuit that initially only had two microcontrollers was complemented with digital logic to locate the actuator in the initial position where the system goes off, it has 40 seconds to position itself in the initial place and stabilize, it is a long time but is was determined this way so that despite the conditions and mechanism of the vehicle in which it s fitted, or the dirt it has enough time to settle in the source or at rest and will not intervene with the braking system. Figure 5 shows how the control circuit is now complete. 4

5 Figure 5: Control circuit. The device has the necessary components to determine which wheel loses traction and to control a servo motor to stop the slipping wheel, you can control servo motors up to 5 amperes and with the references which avoids stopping the wheel when shutting off the control system. 5. Conclusions and Outlook This system for traction control is simple and functional it can be control through their references and manually depending on the decision of the driver, this option gives flexibility to the system at the time of having to turn the lowest possible radius. It is hoped that this prototype will solve some of the limitations of a vehicle with open differential and also complement the limited differential or viscous. It is expected to be able to carryout the control by hydraulic circuit and not mechanical in order to rush the response to he loss of traction and the hydraulic and electronic components have the smallest size possible to be installed and go unnoticeable or it may appear a piece more which the vehicle had in it s assemble. Acknowledgements At the Autonomous University of Zacatecas and the National Scholarship Program (PRONABES). To all the people who supported me morally or economically. 5

6 References [1] Mecanicavirtual, la web de los estudiantes de automoción, Recuperado el 20 de abril del [2] D.R. Reader s Digest México, S.A. de C.V., cuarta edición [3] James W. Bignell, Robert L. Donovan Electrónica Digital tercera edición en ingles primera edición en español, Continental S.A de C.V [4] Enrique Palacios Municio, Fernando Remiro Domínguez y Lucas José López Pérez. Microcontrolador PIC16F84, Desarrollo de proyectos, 3ª Edición, Editorial RA-MA, Alfaomega [5] Katsuhiko Ogata Ingeniería de Control Moderna, 4ª Edición, Editorial Prentice Hall