Environment for Brake by Wire System Development Katharina Wennerström Master’s thesis 20 p D-Level

Environment for Brake by Wire System Development Katharina Wennerström Master’s thesis 20 p D-Level Department of Computer Science and Electronics Mälardalens University, Västerås Examiner: Denny Åberg Supervisor: Peder Norin October 5, 2006 Abstract In the automotive industry the safety critical systems in cars are increasing These systems are called X by Wire system and their purpose is to assist the driver in different situations These systems must be fail operational as they are deemed safety critical If the system develops a fault, it might have catastrophic consequences such as injury or death of humans I have looked closer on one of them, the “Brake by Wire system” which is based on a time-trigged protocol The purpose of this thesis has been to study the Brake by Wire system and the ABS application A part of this thesis has been dedicated the study of the communication system, the time trigged TTP/C real time communication protocol and compare it with two other time trigged solutions, TTCAN and FlexRay Design of a Brake by Wire system with ABS based on TTP/C and also implement a very simple Brake by Wire system with ABS but without TTP/C where the hardware description language VHDL is used Sammanfattning Inom bilindustrin ökar de säkerhetskritiska systemen i bilar Systemen kallas ”X by Wire” och deras syfte är att hjälpa föraren i olika situationer Systemen måste vara felfunktionsdugliga, eftersom de är bedömda säkerhetskritiska, om systemet utvecklar ett fel kan det katastrofala konsekvenser som skada eller död på människor Jag har tittat närmare på ett av dem ”Brake by Wire” systemet som är baserat på ett tidsstyrt protokoll Syftet med detta arbete är att studera ”Brake by Wire” och ABS applikationen En del av arbetat har varit att studera kommunikationssystemet, det tidsstyrda TTP/S realtids kommunikations protokoll och jämföra med två andra tidsstyrda lösningar som TTCAN och FlexRay Designa ett ”Brake by Wire” system med ABS baserat på TTP/C och också implementera ett mycket enkelt ”Brake by Wire” system med ABS, men utan TTP/C där det hårdvarubeskrivande språket VHDL används Acknowledgement The work has been performed by Katharina Wennerström and it is the final part of the education at Mälardalens University in Västerås, Sweden, that leads to a Master of Science degree in Electronics I would like to thank my examiner Denny Åberg and my supervisor Peder Norin at Mälardalens University I would also like to thank Susanna Nordström and Mika Seppänen at Mälardalens University for there advices Table of contents Introduction 1.1 Background 1.2 Problem formulation 1.3 Delimitations 1.4 Guide to Thesis TTP/C and two other potential time-trigged alternative 2.1 TTP/C 2.1.1 TTP/C architecture 2.1.2 TTP/C communication 2.1.3 Fault tolerance strategy 11 2.1.4 TTP/C software 12 2.1.5 Hardware CNI: AS8202NF TTP-C2NF Communication Controller 13 2.1.6 Advantages with TTP/C 14 2.2 FlexRay 15 2.2.1 Architecture 15 2.2.2 Frame Format 16 2.2.3 Data transmission 17 2.2.4 Protocol operation 17 2.2.5 Error handling 18 2.3 TTCAN 18 2.3.1 Data transmission 18 2.3.2 TTCAN Implemention 20 2.3.3 Error handling and fault tolerance 21 2.4 Comparison between the TTP/C, Flexray, and TTCAN Protocol 22 Brake by Wire System with ABS 24 3.1 EHB (Electro Hydraulic Brake) 25 3.2 EMB (Electro Mechanical Brake) 25 3.3 ABS (Anti-Lock Brake System) 25 3.3.1 History 25 3.3.2 How ABS Work 25 3.3.3 What are the advantages and disadvantages of using ABS? 26 3.3.4 Wheel speed sensor 26 3.3.5 Calculated brake distance with and without ABS 28 Design of the Brake by Wire System with ABS 29 4.1 The Brake by Wire design with TTP/C 29 4.1.1 Communication in the wheel node between the Host and the CNI 30 4.1.2 The brake sensor 30 4.1.3 Pedal node 31 4.1.4 Wheel node with ABS 32 4.1.5 Wheel node without ABS 34 4.2 Design without TTP/C implemented in this theses 34 4.2.1 Direct communication between the pedal node and wheel node 34 4.3 Software 34 4.4 Hardware 35 4.4.1 HOST: Altera UP3 Education kit 35 Implementation of the Brake System with ABS 37 5.1 Pedal node 37 5.1.1 The brake sensor 37 5.1.2 Simulation of the pedal node 37 5.2 Wheel node 37 5.2.1 Wheel simulation in node with locked wheel 37 5.2.2 Wheel simulation in node without locked wheel 39 5.3 Communication between the pedal node and wheel node 39 Summary and conclusions 40 Future Work 41 References 42 Introduction 1.1 Background Fault tolerant systems will become a big business area in the automobile industry in the future The systems will assist the driver in critical situations and also help the driver with routine tasks This is achieved by using fault tolerant techniques both in software [1] and hardware Hardware fault tolerance is based on the used of redundant system Many are hesitating because of the reliability and the safety concerns, because of that the conventional system have stood the test of time and are proven to be reliable but there is a clear trend to substitute mechanical, hydraulic or pneumatic system by computerized components in the automotive systems The electronically controlled automotive systems are known as X by Wire X by Wire is a generic term when bulky mechanical systems are replaced with sophisticated electrical components such as electronic sensors and actuators X by Wire systems must be fail operational as they are deemed safety critical, because if the system develops a fault, it might have catastrophic consequences The basic X by Wire systems are Throttle by Wire, Steer by Wire and Brake by Wire [2] The current 14-volts bus has become insufficient in this new systems and the solution is to integrate a 42-volt bus that provides the necessary power [3] A Brake by Wire system is based on time-trigged protocol, nodes, sensors and actuators The Brake by Wire system transfer electrical signals down to a wire instead of using hydraulic fluid If no hydraulic back-up is available it is a pure Brake by Wire system (Electro Mechanical Brake system) and it is very important that the system must continue to function in the event of a fault occurs This has generated a need for fault tolerant computer systems at low costs [4] A conventional ABS (Anti-Lock Brake system) that is used in must of the cars today is considered fail silent If a fault in the electronic control system is detected, the control system is switched off, leaving the manual hydraulic back-up still operational There is no such hydraulic back-up in the Electro Mechanical Brake system The only safe car is a non-moving car so the task of creating a safe system is to decide an acceptable level of risk and then design the system from that point of view The automobiles changed the world during the 20th century because of the greater mobility for people so the car is here to stay as an integral part of modern society 1.2 Problem formulation The main goal of this Master’s thesis work is to develop a simple Brake by Wire system with ABS that will be used in future laboratory experiment in the course Digital systems The goals for this thesis are to: • Study the TTP/C concept and compare it with other time trigged solutions as TTCAN and Flexray • Study the Brake by Wire and the ABS application • Give a deeper theoretical/practical knowledge about the hardware description language (VHDL) and development tools • Design a Brake by Wire system with ABS based on TTP/C and a system without TTP/C who is implemented in this thesis • • Implement a very simple Brake by Wire system with ABS but without TTP/C Write the Masters thesis report 1.3 Delimitations In my design I have described the system with TTP/C but I am not going to implement the system with TTP/C instead I implement the nodes without TTP/C The wheel node and pedal node will communicate directly to each other 1.4 Guide to Thesis Chapter presents general background theory to most of the subjects touched in this report Chapter treats the TTP/C concept A description of the TTP/C software tools and the TTP/C hardware is also given TTP/C are also compared with FlexRay and TTCAN Chapter presents the Brake by Wire system with ABS Chapter describes the design of the simple Brake by Wire System with ABS based on TTP/C and the design without TTP/C that has been developed and implemented during this Master’s thesis work Chapter describes the implementation of the very simply Brake by Wire System with ABS Chapter describes my personal conclusions and thoughts Chapter gives example of future work on the Brake by Wire developed in this thesis Appendix A contains the VHDL code for the pedal node and the wheel node Appendix B contains simulation results for the pedal node and the wheel node TTP/C and two other potential time-trigged alternative “In contrast to classical event-triggered communication systems, the Time-Triggered Protocol involves a continuous communication of all connected nodes All events are safely processed according to schedule without data collision.” [5] The design ensures that an overload in the bus is prevented even if many important events occur at the same time Because the Brake by Wire system is safety critical you exceed the limitations for event trigged protocol and can’t use them You must use a time trigged protocol I will study the TTP/C that is a time-trigged protocol and compare it with two other time-trigged protocols Flexray and TTCAN who I also describe briefly 2.1 TTP/C TTP/C is a time-triggered class C low-cost communication protocol for fault-tolerant real-time systems It is specially designed for X by Wire applications that are safety critical and is developed by Vienna University of Technology Class C indicates that it satisfies the SAE classifications for safety critical control applications The application domains are automotive control systems, aircraft control systems, industrial and power plants TTP is based on 25 years of development work [5] “In a TT architecture all systems activities are initiated by the progression of a globally synchronized time It is assumed that all clocks are synchronized and every observation of the controlled object is time stamped with the synchronized time.” [6] 2.1.1 TTP/C architecture A TTP/C node (See figure 2.1) consists of a host computer and a communication controller and they are communicating through an interface (CNI) TTP/C is designed for systems with four or more nodes and can contain up to 64 nodes, but systems with two or three nodes that are active members in the clock synchronization work practically well Each node is connected to communication buses Figure 2.1 Node configuration [7] TTP/C topology: The possible topology can be bus, star or any combination of the two (See figure 2.2) Also are multiple stars or sub buses supported You combine the highest safety level with minimal cost when you use a redundant star topology with a Bus Guardian integrated into the star Figure 2.2 A star with central bus guardians and a bus with local bus guardians [8] 2.1.2 TTP/C communication A TTP/C system is built by first defining the message schedule (See figure 2.3) Figure 2.3 The TTP/C communication schedule for the Brake-by-Wire system [6] I-frames are only used for reintegration of lost members A TDMA (Time Division Multiple Access) is a full communication cycle where every meeting member speaks The sequence of sending slots within the nodes is called a TDMA round After a decided (usually two) number of cycles (TDMA) the same message is repeated and that is called a cluster cycle The clock synchronization is based on the TDMA principle and all nodes in the cluster know when a certain node has to send a message The TDMA message schedule is stored locally in each node in the MEDL (MEssage Descriptor List) and each node knows exactly when it’s time for the other nodes to send as they read the schedule No space is allocated for spontaneous messages in the sending cycle and this means that an alarm that is an asynchronous message has to wait until the next cycle before being sent Message descriptor list (MEDL): MEDL that is the schedule of messages that is to be received and sent is stored in a static data structure in the local memory of the communication controller The list contains information of when the node is allowed to send message and when the node is expected to receive message All controllers act according to the list and the global time base keeps them synchronized and this guarantees that the bus is nodes that are assigned a timeslot for sending MEDL contains two data structures: the Configuration Parameters and the Transmission Block Frame format: The TTP/C contains two kinds of frames (See figure 2.4, 2.5, 2.6 and 2.7) Those are I-frame (Initialization frames) and N-frames (Normal frames) I-frames are used to initialized the system and contain the internal state of the TTP controller and the N-frame are used for ordinary messages A frame consists of three fields: a four bit header, a data field and a CRC-field The first bit in the header tells if it is an N or I frame The other three in the header are used for changing mode in the system The data field contains data up to 16 byte and at last the CRC field Information about name of the message and the sender is not included because such information can be read directly from the MEDL-list Figure 2.4 Frame format [7] Figure 2.5 N - frame [7] Figure 2.6 I - frame [7] 10 Wheel velocity sensor (10-0 km/h) 0,016 0,8 0,014 0,7 0,012 0,6 0,01 Series1 0,008 0,006 0,004 cykle length (s) Cykle length (s) Wheel velicity sensor (130-10 km/h) 0,5 0,4 Series1 0,3 0,2 0,1 0,002 0 20 40 60 80 100 120 140 km/h 10 12 km/h Figure 3.4 Wheel speed sensor 130-0 km/h 3.3.5 Calculated brake distance with and without ABS The most common calculation formula in the automotive industry is the ECE rules, Annex 13 [25] Formula for brake distance (on dry road): Stop distance (with ABS) = Velocity*Velocity/25.92*Brake friction maximum (with ABS)*9.92 Stop distance (without ABS) = Time to start braking (without ABS) + Velocity*Velocity/25.92*Brake friction maximum (without ABS)*9.92 Brake friction maximum (with ABS) = 0.92 Brake friction maximum (without ABS) = 0.71 Time to start braking (without ABS) = 0.1*Velocity I have calculated the brake distance with and without ABS The brake slow down is supposed to be uniform so the middle value will be included in the calculations At the velocity 130 km/h it takes 72.17 s to stop the car with ABS (See table 3.2) Velocity Brake distance with ABS (m) Brake distance without ABS (m) 10 0,427037179 1,427037179 25 2,66898237 5,16898237 50 10,67592948 15,67592948 100 42,70371792 52,70371792 130 72,16928328 85,16928328 Table 3.2 Calculated brake distance with and without ABS 28 Design of the Brake by Wire System with ABS This chapter describes the design of a simple Brake by Wire system with TTP/C and a simple system without TTP/C that will be implemented in this thesis 4.1 The Brake by Wire design with TTP/C The Brake by Wire system consists of five nodes and is implemented as an EMB (Electro Mechanical Brake) system (See figure 4.1) Wheel Velocity Brake Force Brake Actuator FR Wheel node FL Wheel node Wheel Velocity Brake Force Brake Actuator Pedal Force Pedal node Wheel Velocity Brake Force Brake Actuator BR Wheel node BL Wheel node Wheel Velocity Brake Force Brake Actuator Figure 4.1 The Brake by Wire design There are four wheel nodes and one pedal node The nodes are connected by two replicated buses A lot of status messages have to be sent over the data bus to keep the Brake by Wire system as fault tolerant as possible The pedal node is the node that contains all important information of the system including the managing of the ABS The pedal node samples sensor values from the pedal, calculation of how much the wheel brake should apply on each wheel and checks if the ABS should be activated When the brake values have been calculated they are sent as messages to the different wheel brake nodes The pedal node also collects status information from the nodes 29 The wheel nodes that are placed at each wheel simulate the wheel velocity and real brake force because wee don’t have any real wheel It also sends status message about the node to the pedal node 4.1.1 Communication in the wheel node between the Host and the CNI This is done in the component FLCNIhost that must be implemented in every node in future work but not in this thesis because we don’t use TTP/C Data FL_BUS_OK FL_NODE_OK FL_BRAKE_OK FL_WHEELVEL FL_BRAKEFORCE FL_BRAKE Address 0000 0101 0000 0000 0100 0000 0000 0011 0000 0000 0010 0000 0000 0001 0000 0000 0000 0000 Mode in in in in in out Comment 1=true, both buses is ok 1=true, node FL is ok 1=true, desired brake value=real value Wheel velocity Real Brake force Desired Brake force Table 4.1 Host Front Left Wheel node It is the same addressed for the other Wheel nodes But for the back right wheel you use BR, for the left right wheel node you use BL and for the front right node you use FR instead of FL Address Data CNI TTP/C CEB WEB OEB READYB INTB RAM_CLK_TESTSE USE_RAM_CLK HOST CNI (Communication Network Interface) – AS8202NF Figure 4.2 communications between the CNI and the host 4.1.2 The brake sensor The pedal force will be simulated with a tri-terminal potentiometer where the mid-terminal output voltage is connected to an A/D converter that translate the analogue value to a digital value and the size of the input sensor value is 10 bits The A/D converter can preferrably be connected to socket J2 [27] I`ve got 11 I/O pins there and also voltage feeding I need 10 bits for the pedal value and an A/D converter with V feeding that convert the input signal The monitoring could be as follow One of the pins is connected to the A/D converters in signal for converting start activated 30 Wait at least the time it takes for the A/D converter to convert a new value Read that value at the other 10 I/O pins 4.1.3 Pedal node The function of the pedal node is to read the sensor value of the brake pedal, calculate the brake force for the four brake actuators and manage the ABS function To sort out the most incorrect values only pedal position value between 100 and 1023 are used when the brake force is calculated The calculated brake value has been calculated according to an earlier thesis work [26] I calculate the brake value in the component Pedalcalbrake as follow when the pedal position is 0-99 and 924 - 1023 the calculated brake force is not valid = “00000000000”, in other case when pedal position is (100 – 899) the calculated brake force is (150 to 949) and when the pedal position is (900 – 923) the calculated brake force will be (1150 – 1173) (See table 4.2, figure 4.3) with one exception and that is when the wheel is locked (the wheel velocity is km/h, the ABS function will start and the calculated brake force value will be set to “00000000001” until the wheel has locked up and that will be independent of the value of the pedal sensor Brake sensor value Brake sensor value Calculated brake force Calculated brake force (base 2) (base 10) value(base 2) value(base 10) 0000000000 00000000000 0011000010 50 00000000000 0001100011 99 00000000000 0001100100 100 00010010110 150 1000100110 550 01001011000 600 1110000011 899 01110110101 949 1110000100 900 10001111110 1150 1110001111 911 10010001001 1161 1110011011 923 10010010101 1173 1110011100 924 00000000000 1111111111 1023 00000000000 Table 4.2 Pedal sensor value and the calculate brake force value 31 Brake force 1000 900 800 Pedal sensor 700 600 500 400 300 200 100 0 500 1000 1500 Calculated brake force Figure 4.3 Calculated brake force 4.1.4 Wheel node with ABS Receive calculated brake force and send real brake force and wheel velocity to the pedal node Depending on the calculated received brake value the actuator brake harder or release the brake The regulation of a brake actuator will typically be controlled using feedback from sensors in the brake actuator As I have no real actuator there will be no code written for how to translate the requested brake force value into control signals for an electromechanical actuator In this node the wheel velocity will be simulated as a pulse where the pulse length depends on the velocity This pulse frequency will be read and translated into a km/h value in the node, a value that is then sent to the pedal node The test case that will be simulated is a situation when you drive in 130 km/h and you have to stop immediately (See figure 4.4 and 4.5) The ABS system will go on twice when you brake after 0.24 seconds and after 0.5 seconds It will be locked in 0.1 seconds each time The brake slow down is supposed to be uniform so I use the mean value in the calculation At the velocity 130 km/h it will take 4.0 seconds to stop the car Brake stop time at 130km/h = 72.17/(65/3.6) = 4.0 s 32 Brake with ABS 140 Wheel Velocity (km/h) 120 100 80 Series1 60 40 20 0 Time (s) Figure 4.4 Wheel velocity simulation S i m u l a t e d whe e l v e l o c i t y ( 10 - k m / h ) S i m u l a t e d whe e l v e l o c i t y ( 13 - 10 k m / h ) 1,2 0,016 0,014 0,012 0,8 0,01 0,008 0,6 0,006 0,4 0,004 0,002 0,2 - 0,002 50 100 150 0 k m/ h 10 12 k m/ h Figure 4.5 Simulated wheel (cycle length) When I simulate I step up the pulse length and I assume that the cog is 1/5 of the pulse At 130 km/h are the cycles 1000/s and the length of each cycle are 1000 (µs) and the clock frequency is MHz (See table 4.3) Cycles/s Pulse length (µs) Low (µs) 1000 1000 200 999-501 + 0.4 500-101 +4 100-51 + 40 50-11 +400 10-6 +4000 5-1 +40000 0 Table 4.3 How the length of the cycles steps up High (µs) 800 + 1.6 + 16 +160 + 1600 +16000 +160000 33 4.1.5 Wheel node without ABS Receive calculated brake force and send some status message When FL wheel is locked the brake force will be shared at the other three wheels None of these nodes will have locked wheel This is done in the component FRWheelsim For back wheel BL and BR are used The wheel simulations are the same as for the wheel with ABS with the exception that the wheels never lock and in component (See figure 4.7) S i m u l a t e d whe e l v e l o c i t y ( 10 - k m / h ) S i m u l a t e d whe e l v e l o c i t y ( 13 - 10 k m / h) 0,016 1,2 0,014 0,012 0,8 0,01 0,008 0,6 0,006 0,4 0,004 0,2 0,002 0 50 100 150 k m/ h 10 12 k m/ h Figure 4.7 Simulated wheel without ABS (cycle length) In component FRpulsevelocity you check the pulse length and translate it to a velocity in km/h that will be sent to the pedal node 4.2 Design without TTP/C implemented in this theses The system that will be implemented in this thesis is very simple and we don’t use TTP/C The system consist of nodes the Pedal node and one wheel node with ABS The nodes will be the same as the nodes with TTP/C the only difference is the communication between the wheel node and the pedal node and that there is only one wheel node 4.2.1 Direct communication between the pedal node and wheel node The communication happens during use of the IC2 bus, as the memory hang on Only two wires are needed I take out the signals on JP18, pin and according to table 17 on page 43 According to table 15 they are connected to pin 21 and 20 on the FPGA and these should be connected between the nodes as and on the pedal node to and on the wheel node The I2C-funktion lies in the FPGA:n Maybe there will be a ready VHDL component to realise the block [27] In this thesis there are only the nodes for a future Brake by Wire system with TTP/C that are implemented The nodes that will be implemented will communicate directly to each other 4.3 Software I use Alteras Quartus II software for designing high performance architectures FPGA and the programming language VHDL (Very High Speed Integrated Circuit Hardware Description Language) 34 4.4 Hardware The design in this thesis will be implemented in a Field Programmable Gate Array (FPGA) The FPGA device is a Cyclone provided by Altera 4.4.1 HOST: Altera UP3 Education kit The Altera UP3 education is shown in (See figure 4.8 and 4.9) Figure 4.8 Altera UP3 Education kit “This board provides a powerful educational support and also a low cost solution for prototyping and rapidly development products The board serves a means for hardware as well as software development It gives scope to a hardware design engineer to design, prototype and test hardware design using VHDL” [27] 35 Figure 4.9 UP3 Board top view 36 Implementation of the Brake System with ABS The implementations of the tasks are made in the programming language VHDL [28], [29] I use Alteras Quartus II All tasks that are used by the pedal node and the wheel nodes are declared in Appendix A and the simulation results are declared in Appendix B In this thesis there are only the nodes for a future Brake by Wire system with TTP/C that are implemented The nodes that will be implemented will communicate directly to each other When I simulate I use device EP1C12F256C6 5.1 Pedal node See the code in Appendix A and the simulation result in Appendix B 5.1.1 The brake sensor Not implemented 5.1.2 Simulation of the pedal node Simulating the pedal node with the input (brakesensor) according to table 4.2 I have the correct output value (calculated brake force FLbrake) When the wheel velocity (FLwheelvel) is km/h I also have the correct output value for the calculated brake force (“00000000001”) independent of the pedal sensor value When reset = or outside the range 100-923 is the calculated brake force = “00000000000” (FLbrake) 5.2 Wheel node See the code in Appendix A and the simulation result in Appendix B 5.2.1 Wheel simulation in node with locked wheel The real brake force value will be set to the calculated brake value that I receive from the pedal node in the wheelnodetop In component FLwheelsim I calculate the total pulse length and high pulse length according to table 4.2 Pulseno is the same as 1000 cycles/ s (See table 5.1) and pulsno 1000 are the same as cycles/s (the car has stopped) The clock frequency 200 ns are used After 0.24 s and 0.50 s will the wheel be locked in 0.1 s In table 5.1 I show some value for the signal Pulseno and the value that will be simulated for Totpulse and Highpulse 37 Pulseno Totpulse 60 61 85 86 124 125 149 150 499 500 501 899 900 901 949 950 951 989 990 991 993 995 996 999 1000 5000 5010 5600 5610 5850 5860 6240 6250 6490 6500 9990 10000 10100 49900 50000 51000 99000 100000 110000 490000 500000 600000 900000 1000000 2000000 5000000 100000 Highpulse Time (s) 1000 1002 1120 0 1172 1248 0 1300 1998 2000 2020 9980 10000 10200 19800 20000 22000 98000 100000 120000 180000 200000 400000 1000000 0.000 0.004 0.240 0.244 0.340 0.344 0.496 0.500 0.596 0.600 1.996 2.000 2.004 3.596 3.600 3.004 3.796 3.780 3.784 3.956 3.960 3.964 3.972 3.980 3.984 3.996 4.000 Table 5.1 Totpulse and Highpulse are calculated in component FLwheelsim Totpulse and Highpulse are the signals that are sent to component FLpulseout that will simulate the pulse Totpulse Highpulse - Total size of the pulse – Size when the pulse is high When the brake is not on or reset is set the output value will be according to Pulseno = Simulating the result was according to table 5.1 (See Appendix B test of wheel) In component FLpulseout the pulse is simulated The total length of the pulse is = Totpulse and length when pulse is high = Highpulse (See table 5.1) The component FLpulsetovelocity counts the pulse and translates it to a value (1000-0) The clock pulses are counted between every time the wheel pulse trigs (positive flank) and translates it to an integer with the range of 1000 to 1000 is 130 km/h, 500 is 65 km/h and is km/h between 0.244 – 0.344 s and 0.500 – 0.600 is the wheel velocity km/h Only if the 38 velocity is greater than 32.5 km/h (300 = ms) I check if the wheel is locked This is due to the fact that if the velocity is lower there will be problems cause of the long pulse length, and if the pulse length is longer than s (0.13 km/h) I assume that the car has stopped Pulse length (ms) (no of Wheel velocity cycles*200ns) 1.000 ms (5000) 1000 (130.00 km/h) 1.002 ms (5010) 999 (129.87 km/h) >1000 ms (> 5000000) km/h 1.200 ms (6000) 900 (117.0 km/h) >1000 ms (> 5000000) km/h 2.000 ms (10000) 500 (65.00 km/h) 10.000 ms (50000) 100 (13.00 km/h) 20.000 ms (100000) 50 (6.50 km/h) 100.000 ms (500000) 10 (1.30 km/h) 200.000 ms (1000000) (0.65 km/h) 1000.000 ms (5000000) (0.13 km/h) Table 5.2 The velocity of the wheel Time (s) 0.000 0.004 0.244-0.334 0.400 0.500-0.600 2.000 3.600 3.800 3.960 3.980 4.000 The test result when I simulate the wheel node is in Appendix B wheelnode where pulseout is only temporary to see the pulse that is simulated from component FLpulseout 5.2.2 Wheel simulation in node without locked wheel This is not implemented in this thesis as wee only got one wheel node FL, but for future use I explain the implementation The brake force is shared when FL wheel node is locked and the wheel will never be locked in those nodes 5.3 Communication between the pedal node and wheel node Not implemented 39 Summary and conclusions One of the goals with this thesis was the development of a simple platform that will be applied for educational purpose (practical training) in the course Digital System given at Mälardalens University, specific a very simple Brake by Wire system In this moment there are only the pedal node and the wheel node with ABS that are implemented, but the communication between them is an important part and one solution is to implement TTP/C as the communication system between the nodes in a complete Brake by Wire system with four wheel nodes The simpler way to solve the communication is that the pedal node and the wheel node will communicate directly to each other The function in the nodes can also be developed further where more thing are checked etc The other goal was to study the communication system The requirements on class C real time communication systems makes it impossible to use the wide spread event driven communication protocols The time trigged architecture and its fault tolerant time trigged protocol provides a solution for new functions as Brake by Wire I don’t think TTCAN is adequate for safety critical application, but TTP/C and FlexRay offers a solution I think that FlexRay is the biggest opponent to TTP/C in the future car industry The reason why TTCAN is not considered a possibility is because it is solely event based and does not eliminate the risk in the way that TTP/C and FlexRay does My guess is though, that in the future, it will still be used by the car industry as a complementary system Even if it is not an alternative to the safety critical systems, the cars may carry a mixture of TTCAN along with TTP/C or TTCAN along with FlexRay Human control is essential and for most safety critical systems, when they are developed, the safety must be acceptable There are many aspects to be considered: cost, weighed both to organizational goals as profit and acceptability risk for humans 40 Future Work Implement a complete system with TTP/C Wheel simulation in node without locked wheel is not implemented in this thesis because wee only got one wheel, but for future use it is explained in 5.3.2 It would be possible to steer a real wheel with the simulated wheel velocity value that are simulated in the wheel node A unit that brake the wheel could be connected to the wheel and that brake value could be read to the wheel node as the real brake force instead of today when the real brake force value will be set to the calculated brake value from the pedal node Implement the status messages and it is possible to send the status message to some display at the driver’s instrumental panel 41 References [1] Michael R Lyu, Software Fault Tolerance, ISBN 471 95068 8, John Wiley & Sons Ltd, 1995 [2] E Touloupis, J A Flint and D D Ward, Safety-Critical Architectures for Automotive Applications, University of Loughborough, 2003 [3] Nathan Ray Trevett, X-by-Wire, New Technologies for 42V Bus Automobile of the Future, April 2002 [4] E Touloupis, J A Flint, V A Chouliarias and D D Ward, A TMR_PROCESSOR ARCHITECTURE FOR SAFETY-CRITICAL AUTOMOTIVE APPLICATIONS, University of Loughborough, [5] http://www.tttech.com [6] Th Ringler, J Steiner, R Belschner and B Hedenetz, Increasing System Safety for by-wire Applications in Vehicles by using a Time Triggered Architecture, University of Stuttgart, 1999 [7] http://staff.iha.dk/foh/Foredrag/TTPFlexRay-LunaForedrag.pdf [8] A Platform for Safety-Critical Applications, TTTech Computer technik AG, 2005 [9] Pimentel, Juan R A Fault Management Protocol for TTP/C, The 27th Annual Conference of the IEEE Industrial Electronics Society, 2001 [10] AS8202NF TTP-C2NF Communication Controller Data Sheet Rev.1.4, July 2005 [11] http//embsys.technikum-wien.at/projects/steacs/publications/pubs/preprint_DDECS04.pdf] [12] Kosov, Sergey, FlexRay communication protocol, (Wakeup and Startup), 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Brake by Wire developed in this thesis Appendix A contains the VHDL code for the pedal node and the wheel node Appendix B contains simulation results for the pedal node and the wheel node TTP/C... with ABS The Brake by Wire system means that the mechanical system is replaced by an electromechanical braking system Brake by Wire was originally used for aircraft and military purposes only It... Calculated brake distance with and without ABS 28 Design of the Brake by Wire System with ABS This chapter describes the design of a simple Brake by Wire system with TTP/C and a simple system without