The Electronic Parking Brake System Based On CAN Bus

With the growth of traffic density, the requirements of safety are increasing. Although traditional braking systems in vehicles are good, there are also disadvantages such as low braking performance, slow reaction, complicated pipes, pollutant brake fluids and so on. With the development of electronic and control technology, Brake-by-Wire system is around the corner. Brake-by-Wire system replaces conventional hydraulic braking system with a completely"dry"electrical component system. This occurs by replacing conventional hydraulic disk and drum brake actuators with electric motor driven units. This move to electronic control eliminates many of the manufacturing, maintenance, and environmental concerns associated with hydraulic systems. It is a renovation of the vehicle braking system, and the required electronic systems must evidently be available and safe. In Brake-by-Wire system, electronic control unit receives inputs from sensors connected to the brake pedal or brake button, and controls the electric wheel brake actuator to apply brake. The processing components are likely to be networked using high reliability bus protocols.Electronic Parking Brake is a kind of Brake-by-Wire. It works when vehicle speed is almost zero. EPB reacts quickly, has high braking performance, is easy to install and clean. It can also integrate other driver assistance function, like Hill Staring Aid which is discussed in the paper. When a vehicle on an upgrade starts, HSA can help. If the driver pulls the button, ECU controls the actuator to release the brake in a timely and appropriate manner according to accelerator pedal, clutch and engine speed etc. It makes uphill start easier and prevents backward motion and the stalling, reduces the difficulty of operation. Furthermore, an essential advantage of the EPB is the freedom in design, installation location and functionality of the control element. The electrical actuation allows the use of small forces, which is a special valuable feature for physically weak and disable people. It is mainly discussed hardware and software design of EPB in the paper.The EPB is composed of three nodes, one is collection node, two others are electronic wheel nodes. All of the components are connected together via a CAN bus. Collection node ECU collects the information of brake button, HSA button, braking pedal position, clutch position, accelerator position, vehicle speed and engine speed. Braking node is composed of ECU, braking motor, reducer, worm and worm gear and screw rod. Friction plate is fixed on screw rod. When motor turns around, friction plate does reciprocating movement. The two braking ECUs control the two non-driving wheels. Each electric wheel brake actuator is controlled by an electronic wheel node, which processes data received from the collection node and the other node. The wheel nodes can perform a basic braking function in response to input from the collection node. The system eliminates vacuum booster and hydraulic parts. It is an Electro-Mechanical Braking system. The braking motor is a direct-current motor which can meet system's needs. The MCU is Philips80C592 with the features: 80C51 central processing unit, CAN-controller, 10-bit ADC and two 8-bit resolution pulse width modulated outputs. It is a single-chip 8-bit high-performance microcontroller with on-chip CAN-controller which is like CAN controller 82C200. The CAN-controller has the function of CAN physical layer protocol and CAN data link layer protocol. The MCU cannot direct drive motors, H-bridge module helps to drive. The H-bridge module chosen can support 30A current to meet the needs. The hardware part is mainly composed of ECU, H-bridge module and braking motor.When vehicle speed is zero, driver pushes the button, then braking motor turns forward, after a short time, motor blocks and the actuation is locked. The actuation can be in the state for a long time, the vehicle do not slip backward. When the driver pulls the button, braking motor turns backward, after a short time, motor blocks and stops.Besides the existing physical layer protocol and data link layer protocol, the application layer protocol should be defined according to the special purpose. CAN communication include CAN controller initialization, data sending and data receiving. When collection node sends a frame, both the two wheel nodes can receive it. It prevents sending repeatedly, and increases the efficiency of communication.EPB integrated Hill Starting Aid can help drivers to start on an upgrade. HSA button is to instruct weather to start HSA function. If HSA button is pushed, driver's operation is as follows: cut off clutch then fuel, push the brake button, disengage the clutch slowly, when the torque is rightly equal to drag torque, release the brake, so vehicle starts steadily. It is difficult to decide when to release the brake, namely to find half-junction where clutch torque is equal to drag torque. The most important is to calculate drag torque. Through many experiments, half-junction can be got according to different drag torque. A control list is made to control starting.An EPB system based on computer is designed in hardware and software in the paper. The basic function is realized, and an integrated HSA is discussed. EPB is the direction of development in parking brake. It has high braking performance, light weight, and it is better for environment. Next the HSA experiments should be done to make a control list. The half-junctions are got through neural network algorithm. If electronic moving brake is developed, a Brake-by-Wire system will be completed.