Electronic Traction Control System - Final Design Report | ECE 441, Exams of Electrical and Electronics Engineering

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ECE 441 Senior Design

Final Design Specification Report

Electronic Traction Control System (ETC)

Group

Chris Troutner

Patricia Abón

Taka Watari

Yu Lau

Table of Contents

1. Revision History

Date Revision # Added Deleted Description 10-17-06 0 N/A N/A Background Research 11-01-06 1 Preliminary Design Report

N/A Preliminary Design Report 11-04-06 2 More Description in 4

N/A Revised Preliminary Design Report 11-30-06 3 Final Design Specification

N/A Final Design Specification

2. Introduction

The product we will develop is the Electronic Traction Control System (ETC system). This device will be installed in the 2006 Baja car and the 2006 Formula car. With this system, cars will be able to turn corners without excess slippage giving more control and safety for the drivers and most of all better time laps in competitions. This system can be achieved successfully with the combination of a power system, computation system, actuation system, and a sensor system.

The power system will be the base of this design as this system will be feeding other devices for it to operate. The sensor system will consist of a wheel speed sensor and an accelerometer which will give information such as the front tire speeds vs. rear tire speeds and send that to the computation system for it to calculate the necessary output. When the computation system gets the information it will calculate the necessary force needed for the actuation system to output towards the tires to lock them up. This system will be utilizing an Atmel 128 8bit-AVR microcontroller board and SystemVision, software that handles various schematics and diagrams. Finally the actuation system will be utilizing a linear actuator. This system will detect and output the necessary force needed towards the tires in order to lock them up from slipping. Experimentation from previous year teams has given us good information that will be useful for our project this year.

Once the ETC system is successfully constructed, it may be applied to nearly all cars including commercial cars, although our system is designed specifically to the 2006 Baja and Formula car.

2.2.1 Product Space Analysis

1. 2004 ETC System The 2004 ETC system uses wheel sensors and a steering wheel angle as inputs to the control system for engaging the electronic traction control system. The system is actuated via a stepper motor coupled to a master cylinder.

Advantages: By having an ETC system, the driver experiences smoother driving experiences and simulation proves better racing performance.

Disadvantages: Unacceptable response times, power requirements are too high, control system algorithm needs improvement.

2. 2006 ETC System The 2006 ETC system is built on top of the 2004 system. The goals for this system are faster response times (0.1 sec), more efficient power use in the actuation system, and scalability between the Baja and Formula cars. Additionally, this system will use a 32bit processor and have an open interface for additional sensors and outputs.

Advantages: Faster response times, faster processing, scalable for future control algorithms, more efficient actuation.

Disadvantages: Open ended system may lead to confusion due to complexity.

3. Commercial Cars The traction control system commercial cars are as complex as the ones the 2004 and 2005 system utilized. They consist of a combination of a braking and engine control.

Advantages: Reliable as they mass produce for sale.

Disadvantages: Very expensive, some systems are insensitive to horizontal motion.

The common themes in ETC systems are traction control through one of 2 means, either braking or engine control or both. There are no other means in traction control. The main intention for every traction control system is to implement a closed loop control system by monitoring vehicle movement and power to the tires. This can be implemented in several ways using wheel position sensors, accelerometers, and other sensors.

The largest missing component in the market place is consistency and reliability. All ETC systems are complex and many are not reliable from car to car. This leaves the product space un-crowded and accessible to innovative new products.

While this is a mature product area, ETC systems are specialized for specific types of vehicles. With our system, we hope to implement an open ended design which decouples hardware from software as much as possible while still remaining rugged and reliable. This design will allow an ETC system to be implemented on cars as different as the Baja and Formula race car with only changing system software and minimal change in sensor systems.

2.2.2 Target Feature Set

One of the main aspects that will distinguish our Electronic Traction Control system is that it will be much more economically accessible than commercial ones. Also the performance of our ETC will be much higher than previous years. This system can be achieved successfully with the following system characteristics:

• Power System o Rugged and efficient rectified system. This ETC will have an alternator which will enter our power system to rectify the signal to a pure DC signal. o Power charge pump for high speed actuation system. Our maximum output will be 40V with 2A of current totaling 80W of power.
• Computation System o Considering loading the code onto a 32bit AVR processor which is the newly released AVR board from Atmel and is much faster than the 8 bit. This AVR will be running embedded Linux (with open source development)
• Actuation System o This ETC will have a higher efficiency compare to previous years’ old system. o Faster response time compare to previous years’ old system.
• Sensor System o Wheel speed sensor and accelerometer which will give vital information, such as front tire speeds vs. rear tire speeds. o The sensors will measure the temperature of the surface of the wheels, that is important information for calculations. o The sensors will measure the steering angle also important information for our ETC. o Open ended for future sensors

2.3 References

• 2004-2005 Formula Car Team Report
• Wikipedia.org

sending out a signal to delay the timing of fire (spark) in the piston which allows us to control the output torque.

Electronic Braking: The electronic braking system is also a traction control device and lends itself best for the vehicle to turn corners smoothly without slipping. As the car makes a turn, the outside wheel must be spinning faster than the inside wheel. Because of this, the inside tire develops more torque and frequently begins to slip. The electronic braking system will brake the inner wheel (side of tire making turn) which will allow the open differential drive system to transfer more power (increased speed and torque) to the outside wheel. This allows more power to be transferred where it is needed and improve overall handling and acceleration of the car.

Figure 2

Ideally we want to use both the launch control and electronic braking in our electronic traction control system for the 2007 Formula Car. However, we are focused on implementing the launch control system first as it is much more practical to implement on the formula car and it will give the team a large competitive edge in the acceleration contest.

3.1 Implementation Approaches

There are two approaches to implement the ETC system.

1. Cutting power from engine Pros: - Easy to implement - Faster response times than braking system (milliseconds) - Less power required Cons: - Must have good design in power system as this approach will be controlling the piston by decreasing the torque.
2. Electronic braking system Pros: - Able to control the speed of each wheel Cons: - Slow response times (half a second) - Heating issues with actuator and power rectifier

We will be using both approaches listed above for our 2006 system. The 1st^ approach has a simple structure and is easy to implement. It not only gives us a faster response time, but will also use less power overall for the system. The electronic braking system will monitor each wheel and control the speed of it for better traction.

4. Top Level Description The top-level system is best broken down into three primary systems: Power System, Control Signals, and Mechanical Actuation.

Power System The Formula ETC system is primarily powered by the on-board flywheel generator, and partially powered by the battery. The generator’s output voltage can range anywhere from 14 volts to 50 volts and the frequency is directly proportional to the engine RPM.

A rectifier, capacitors, and battery are used in the low-power supply to output a fairly clean 12 volt power supply for all low-power electronics. The power signal from the generator is rectified and converted to DC with large capacitors in the high-power supply. This higher, rpm-dependent voltage is used to drive the actuation system.

Control Signals The control signals all use 12 volt logic and all digital information is transmitted via CAN Bus protocol. CAN bus was chosen because of its use in conventional car systems, high noise immunity, and high bandwidth. A CAN bus protocol uses differential (balanced) two wire (twisted pair) connections, where each node has a male 9 pin d-type connector. It can also use the power line for transmission with reduced speed. The bandwidth of this protocol is 1Mbps without fault tolerance, and 125kbps with fault tolerance on a 2 wire connection. The CAN bus uses a bus architecture meaning that a common set of wires connects all the transceivers. This can be laid out as a ring or a star. Our implementation will use a star pattern with the Main Controller at the center.

4.1 Top Level Block Diagram

4.1.1 Top Level Interface Definition

4.1.2 Environment

Electromagnetic noise is the side effect caused by poor grounds and motors in an electronic environment. This problem can be resolved by grounding all data lines and power supply for frequencies outside of the band of interest. Copper mesh or adhesive copper tape should be applied to areas of the enclose not metallic nature.

Excessive shock and vibration will destroy system boards. This can be taken care of by using impact foam and solid state parts. With solid state parts, there is zero concern regarding shock damage. Impact foam helps to prevent loose pieces from jostling about inside of the enclosure.

Heating was one major problem in last year’s design. Since the car will be running in rough conditions, also mud building up will contribute heat to the rectifier power diodes. The maximum temperature for the diode is 150 degrees Celsius. Excessive heat will also burn the integrated circuits. Without proper ventilation, such as sinks and fans, the system will suffocate itself. The same will apply to dust. In addition tires temperature will directly affect the fraction between the tires and the road.

5.1.1 Functional Unit Interface Definition

Pin Designation Pin Description Signal Range AC input one AC power output from the flywheel alternator -50 Volts to +50 Volts AC input two AC power output from the flywheel alternator -50 Volts to +50 Volts Vcc_high Power output of rectification and filters 16 Volts to 50 Volts Ground Reference node for high voltage parts 0 volts

Pin Designation

Signal Validation

Expected Waveform

Expected level at reset time AC input one n/a sine wave -50 Volts to +50 Volts AC input two n/a sine wave -50 Volts to +50 Volts Vcc_high n/a close to flat line 16 Volts to 50 Volts Ground n/a (^) none 0 volts Table 1

5.1.2 Functional Unit Operation The rectifier system consists of 8 diodes and 2 capacitors. During the positive cycle of the AC signal from the flywheel generator, diodes D1 and D3 conducts. During the negative cycle, D2 and D4 conduct to give us a DC value. The 2 capacitors are there to smoothen the ripple to obtain a pure DC voltage.

Main Controller

5 Functional Unit Description The main controller is an Atmega128 micro-controller. This unit will control the DC motor drive and the time delay controller. It will also read off data coming from the steering wheel sensor and Hall-Effect sensor.

5.1 Functional Unit Block Diagram

Figure 5