FSAE Electronic Shifter Final Project Report

Transcription

1 FSAE Electronic Shifter Final Project Report by Lee Redstone Lewis Weston Jason Deglint Supervisor: Dr. Ashoka K.S. Bhat Group: 5 Due: December 3, 2012 Dept. Electrical and Computer Engineering University of Victoria All rights reserved. This report may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author.

2 FSAE Electronic Shifter i CONTENTS 1 Project Goals Detailed Project Description UVic Formula SAE Shifting Current Shifter Pneumatic Design Consideration Electronic Shifter Further Project Considerations Workload Distribution Project Discussion Steering Wheel Connector Extendable Connector Removable Connector Conclusions Linear Actuator Selection and Testing Force Measurements Push/Pull Solenoid Microcontroller System Integration Summary and Future Work Bibliography Appendix...13

3 FSAE Electronic Shifter ii LIST OF TABLES AND FIGURES Table 1: Workload distribution... 6 Table 2: Advantages and disadvantages of an extendable connector... 7 Table 3: Force table for shifting down... 9 Table 4: Force table for shifting up... 9 Figure 1: Formula SAE car in action... 3 Figure 2: Transmission pushrod... 3 Figure 3: Shift lever in cockpit... 4 Figure 4: Steering wheel with shift button overlay... 5 Figure 5: ¼ inch jack... 7 Figure 6: ¼ inch socket, single channel... 8 Figure 7: ¼ inch socket, dual channel... 8 Figure 8: ¼ inch jack inserted into single channel socket... 8 Figure 9: Conceptual Block diagram showing The Simple System Operation...11

4 FSAE Electronic Shifter 1 1 PROJECT GOALS There were 3 primary goals for the development of an Electronic Shifter for the UVic Formula SAE team. These were decided upon at the onset of the project and were used to focus our design objectives: 1. Redesign the shifting device for the UVic FSAE team`s prototype car. The current shifting mechanism is a mechanical lever mounted on the side of the driver cockpit. The lever requires the driver to remove one hand from the steering wheel while driving at high speeds on a tight course. Driver performance could be improved by having button actuated shifting from the steering wheel. 2. Maintain the reliability of the mechanical shifter The current shifter is a simple mechanical device with a direct linkage to the transmission at the rear of the car. One of the fundament challenges for the SAE team is system reliability, this cannot be sacrificed, and all new developments need to be tested to ensure they are more reliable than the previous design. 3. Practical Considerations The new shifting device that is developed will play a vital role in the operation of the next car the SAE team builds. Therefore, the design must be driven by the practical considerations that the team will face when building and using the system. This includes the cost, and availability of replacement parts

5 FSAE Electronic Shifter 2 2 PROJECT OVERVIEW The Formula SAE Team s current vehicle uses mechanical linkage to allow the driver to change gears. This configuration requires that the driver remove one hand from the steering wheel to move the shift lever, which has the following drawbacks: If shifting in the middle of a corner, the driver will only have one hand on the steering wheel, reducing the amount of control they have of the vehicle The time required to change gears is currently on the order of seconds The solution to these drawbacks is to implement an electronic shifting mechanism with steeringwheel -mounted buttons to control the up- and down-shifting. This allows the driver to keep both hands on the steering wheel and may reduce the amount of time required for shifting by an order of magnitude. The result of these modifications will be a safer, quicker vehicle. 3 DETAILED PROJECT DESCRIPTION This paper provides a complete report on the Electronic Shifter project undertaken for ELEC 399, during the Fall of The team successfully designed an electro-motive system capable of changing the gears of a Formula SAE style race car. The following provides a background on the UVic Formula SAE team and the intended application for this system. 3.1 UVIC FORMULA SAE The UVic FSAE team competes annually in the Formula SAE competition hosted by the Society of Automotive Engineers. The nature of the competition involves designing, fabricating and constructing a new car each year. The majority of the components are designed specifically for this purpose. The team consists of 30 engineering undergraduate students, with approximately 80% consisting of mechanical engineers. One of the major challenges for the team is system integration, having all of the sub-systems working together in the tight confines of the car is a never ending challenge.

6 FSAE Electronic Shifter 3 FIGURE 1: FORMULA SAE CAR IN ACTION 3.2 SHIFTING The FSAE team powers its car using a Honda 600cc CBR F4i engine. The engine block contains a six speed sequential transmission that is normally shifted using the foot of the motorcycle driver. As the reader can see in Figure 2, in order to shift up and down, two motions in opposite directions are required. 3.3 CURRENT SHIFTER The current device is a mechanical lever placed on the driver s left hand side inside the cockpit. Figure 3 shows the simple operation of the device, and the motion of the is translated to the rear of the car using a heavy duty push/pull cable (shown in green in Figure 2) FIGURE 2: TRANSMISSION PUSHROD

7 FSAE Electronic Shifter 4 FIGURE 3: SHIFT LEVER IN COCKPIT 3.4 PNEUMATIC DESIGN CONSIDERATION The motion required to shift the gears of the engine is a simple bi-directional linear throw. A pneumatic option was considered at the onset of the project; however there were a number of considerations that led to the design being discarded: 1. Hoses: The transmission of the compressed air from the cylinders to the shifter would require an extensive network of small diameter plastic hose. On a quickly moving race car it is necessary to protect the entire length from chaffing on its mounts and touching warm surfaces. It was decided that the risk of losing the ability to shift due to a hose failure was too high to implement on the car. 2. Canisters: The compressed air canisters required for a pneumatic system weigh 8-12lbs. The FSAE team has ambitious weight saving targets for this season, and were not interested in adding excessive weight for a new shifting mechanism. 3. Consumables: Finally, there is only a finite number of shifts that can be stored in the compressed air cylinders. It was deemed to be too high of a reliability risk to be able to store sufficient gas for the entire duration of competition events. It was for these reasons that an electronic shifter were chosen over a pneumatically powered one.

8 FSAE Electronic Shifter ELECTRONIC SHIFTER With two 12V batteries already used to power the on-board electronics, it was a straight forward decision to choose an electronic device. The batteries and wires already exist in the current design of the car, and the batteries are charged during normal operation by the alternator. With the decision to use an electronic device, the team was left to decide between a high powered, bi-directional solenoid and a DC motor with some form of mechanical linkage to actuate the gear change. The design considerations and experimental results will be discussed in a subsequent section. 3.6 FURTHER PROJECT CONSIDERATIONS During the annual competition, that the FSAE team competes at each driver must prove to the safety inspector that they are capable of exiting the car in less than five seconds. In order to do this, the driver must remove the steering wheel from the column, and toss it from the car. All electronic connections from the steering wheel would have to be rugged enough to maintain performance in this type of environment. FIGURE 4: STEERING WHEEL WITH SHIFT BUTTON OVERLAY

9 FSAE Electronic Shifter 6 4 WORKLOAD DISTRIBUTION The workload was evenly distributed among the three team members. Each team member took on one major responsibility and all other responsibilities were worked on either by two or three members. The workload distribution for the project can be seen in Table 1. The initials of the different team members are used to show the allocation of different tasks. A more detailed account of the work load can be found in the team logbook. TABLE 1: WORKLOAD DISTRIBUTION 5 PROJECT DISCUSSION There are three major design topics covered by this project: Steering wheel connector (removable and durable for egress) Linear actuator selection and testing Microcontroller code 5.1 STEERING WHEEL CONNECTOR The steering wheel is required by Formula SAE rules to be removable by the driver. This means that any electronic equipment mounted on the steering wheel must be connected via a removable or extendable connector.

10 FSAE Electronic Shifter EXTENDABLE CONNECTOR An extendable connector would involve a permanent electrical connection made by an extendable cable such as a telephone cord. The following table discusses the advantages and disadvantages of such a setup: TABLE 2: ADVANTAGES AND DISADVANTAGES OF AN EXTENDABLE CONNECTOR Advantages Disadvantages Reliable Easy to implement Bulky Limits distance that wheel can be removed from vehicle Tripping hazard With these points in mind, we decided to investigate the possibility of a removable connector REMOVABLE CONNECTOR A removable connector would involve a temporary electrical connection that is made and broken when the steering wheel is connected and disconnected to and from the steering shaft. Because the connector must be capable of turning with the wheel, typical plug/socket configurations such as a three-prong household power cord are unsuitable. We discovered that due to its concentric nature, the ¼-inch audio jack would be a possible choice. The ¼-inch audio jack connects and disconnects easily, and is capable of turning around infinitely in its socket. It typically comes in single channel (mono) and dual channel (stereo) configurations. Because we have two channels on the steering wheel (shift up and shift down), it appeared to be an ideal solution. FIGURE 5: ¼ INCH JACK

11 FSAE Electronic Shifter 8 FIGURE 6: ¼ INCH SOCKET, SINGLE CHANNEL FIGURE 7: ¼ INCH SOCKET, DUAL CHANNEL FIGURE 8: ¼ INCH JACK INSERTED INTO SINGLE CHANNEL SOCKET Unfortunately, one issue that arises from the design of the ¼-inch jack is that during insertion of the plug into the socket, the tip of the plug will pass over the second channel tongue, potentially causing undesired behaviour. In order to determine whether or not this characteristic will be a real-world problem will require further investigation CONCLUSIONS The ¼-inch jack is nearly as reliable as a permanent connection and not significantly more difficult to implement. It also avoids all the drawbacks seen with a permanent connection, and is cheap and easy to procure. Therefore, we have decided to designate it as our connector of choice until issues with the contacts have been confirmed.

12 FSAE Electronic Shifter LINEAR ACTUATOR SELECTION AND TESTING The linear actuator is a major component of this project. It connects directly to the transmission shift mechanism and functions to replace the force generated by a human operator moving a mechanical lever. In light of this, a significant amount of testing and research was directed towards choosing an appropriate linear actuator FORCE MEASUREMENTS In order to help us with selection of a linear actuator, we made a series of force measurements. Both Shifting Up and Shifting Forces were measured: From TABLE 3: FORCE TABLE FOR SHIFTING DOWN To Shifting Down Force (kilos) From TABLE 4: FORCE TABLE FOR SHIFTING UP To Shifting Up Force (kilos) As seen, the maximum force measured was 11kgF. Since we need a force that will always be guaranteed to shift the transmission, 150% of 11kgF was used.

13 FSAE Electronic Shifter 10 Therefore, 16.5kgF (161.7N, or 581.6ozF) will be used as a minimum required force when deciding on a linear actuator. However, a more elegant solution may also exist PUSH/PULL SOLENOID Though rather more expensive than the automotive lock actuator, a push-pull solenoid capable of 960ozF (267N or 27.2kgF) is available for purchase on the McMaster-Carr website. Because this device has not yet been tested, further discussion of its applicability to this project is entirely hypothetical. Nonetheless, it meets the force requirements, runs on a 12V supply, and draws only 6.67A at full power, which is easily delivered by the automotive power packs installed on the vehicle. Possible issues may be length of stroke (too short to move gear shifter) and physical size (too large to properly fit in constrained motor area) MICROCONTROLLER Where the linear actuator is the muscle, the microcontroller is the brains. The microcontroller chosen is the F28069 Piccolo controlstick from Texas Instruments. It features an easy programming interface via USB, dedicated PWM outputs (if required for motor control), and prewritten code for motor/solenoid control. The code is more-or-less ready for implementation, with some minor modifications to customize it to our specific application. The code file titled buttons.c can be found in the appendix of this report. The entire program is spread over many files, but the interrupt initiation can be found in this particular snippet SYSTEM INTEGRATION The block diagram, as seen in Figure 9, outlines the control system of the electronic gear shifter. As can be seen the 12 volt car battery will supply power to both the micro-controller and the linear actuator. Starting at the steering wheel the driver can either shift up or shift down using the paddle or button shifter which will send a signal through the audio jack to the micro-controller. The micro-controller will then then a signal to the linear actuator which will pull a lever coming out of the car transmission to either shift the transmission up or down.

14 FSAE Electronic Shifter 11 FIGURE 9: CONCEPTUAL BLOCK DIAGRAM SHOWING THE SIMPLE SYSTEM OPERATION

15 FSAE Electronic Shifter 12 6 SUMMARY AND FUTURE WORK In summary, having completed all the design process as well as modeled and confirming the functionality of our design via simulation the electronic gear shifter is now ready to be built. Although this is outside of the scope of the ELEC 399 course requirements, the design outlined in the report could be taken by other members of the UVic Formula SAE team and then be built. Furthermore, this project could be continued as an ELEC 499 project. 7 BIBLIOGRAPHY Amphenol Nexus Technologies. (n.d.). TP-120 Telephone Plug. Retrieved 11 05, 2012, from Drang. (2009, July 5). Poor man's cable release. Retrieved from And now it s all this: McMaster Carr. (n.d.). Solenoid Speciifed. Retrieved 10 28, 2012, from SAE International. (2012). Formula SAE Rules Retrieved 11 20, 2012, from SAE International: Surplus Center. (2012). 12VDC Power Door Lock Push/Pull Solenoid. Retrieved 10 12, 2012, from. Switchcraft. (n.d.). Jack Schematics. Retrieved from

16 FSAE Electronic Shifter 13 8 APPENDIX Below is a sample of the code to be used in this project: /* * buttons.c * * Created on: * Author: Lee Redstone */ #include "buttons.h" extern unsigned int upshift, downshift, neutralshift; void InitializeButtons() { EALLOW; GpioIntRegs.GPIOXINT1SEL.bit.GPIOSEL=2; XIntruptRegs.XINT1CR.bit.POLARITY=0; XIntruptRegs.XINT1CR.bit.ENABLE=1; PieCtrlRegs.PIEIER1.bit.INTx4=1; PieVectTable.XINT1=&XINT1ISR; //Initialize second interrupt GpioIntRegs.GPIOXINT2SEL.bit.GPIOSEL=3; XIntruptRegs.XINT2CR.bit.POLARITY=0; XIntruptRegs.XINT2CR.bit.ENABLE=1; PieCtrlRegs.PIEIER1.bit.INTx5=1; PieVectTable.XINT2=&XINT2ISR; //initialize third interrupt GpioIntRegs.GPIOXINT3SEL.bit.GPIOSEL=4; XIntruptRegs.XINT3CR.bit.POLARITY=0; XIntruptRegs.XINT3CR.bit.ENABLE=1; PieCtrlRegs.PIEIER12.bit.INTx1=1; PieVectTable.XINT3=&XINT3ISR; //interrupt input GPIO02 //See data sheet for //XINTnCR for registers //(FALLING EDGE) //Active high //P1 Int4 = XInt1 (enable //PIE) //This points to the //interrupt routine. //interrupt2 input = GPIO3 //See data sheet for //XINTnCR for registers //(FALLING EDGE) //Active high //P1 Int5 = XInt2 (enable //PIE) //This points to //the interrupt routine. //interrupt3 input = GPIO4 //See data sheet for //XINTnCR for registers //(FALLING EDGE) //Active high //P12 Int1 = XInt3 (enable //PIE) //This points to //the interrupt routine.

17 FSAE Electronic Shifter 14 IER = M_INT1; //First bit field for the CPU intr turns on all of the CPU1 ints IER = M_INT12; //Enable XINT3 } EDIS; //end EALLOW interrupt void XINT1ISR() { EPwm1Regs.CMPA.half.CMPA = upshift; PieCtrlRegs.PIEACK.bit.ACK1 = 1; } // Up Shift // CMPA? // Acknowledge interrupt in PIE interrupt void XINT2ISR() { EPwm1Regs.CMPA.half.CMPA = downshift; // // Down SHIFT } PieCtrlRegs.PIEACK.bit.ACK1 = 1; // Acknowledge interrupt in PIE interrupt void XINT3ISR() { EPwm1Regs.CMPA.half.CMPA = neutralshift; PieCtrlRegs.PIEACK.bit.ACK12 = 1; } // Neutral SHIFT // Acknowledge interrupt in PIE

18 FSAE Electronic Shifter 15 Log book grade (25%): Report grade (75%): Total Grade (100%): Supervisor s Comments: Supervisor s name (Print) Signature Date Notes for the supervisor: 1. Please return the marked hard copy to Prof. Tao Lu by Monday, December Attached additional pages for comments if necessary.