electronically shifted manual atv transmission...

Multi-Disciplinary Engineering Design Conference

Kate Gleason College of Engineering Rochester Institute of Technology

Rochester, New York 14623

© 2005 Rochester Institute of Technology

Project Number: 07310

ELECTRONICALLY SHIFTED MANUAL ATV TRANSMISSION (MAY 2007)

Jason Botterill (ME) Richard Cheng (EE) Vaibhav Kothari (ISE) ABSTRACT The purpose of this project is to explore the feasibility of an electronically shifted manual transmission for an all-terrain vehicle (ATV). This project explored the possibilities with a semi-automatic concept where the rider will still have input on when the shifts will occur. The concept generated utilizes an electric motor with a positional encoder to actuate the shifts. Controlling the system is a Programmable Logic Controller (PLC). At this date, the project is not complete, and thus detailed results are not available. INTRODUCTION

The main objective of this project is to research the potential of an electronically shifted manual transmission (ESMT) for an all-terrain vehicle (ATV). Manual transmissions are inherently more efficient than automatic transmissions. The primary benefit of automatic transmissions is the ease of use. An ESMT would combine the efficiency of the manual transmission and the ease of use of the automatic transmission. Moreover, the creation of an ESMT would allow for the same core transmission to be used regardless the end user desire for manual or automatic operation. The system needs to be able to integrate into the existing transmission system to avoid the need for large amounts of retooling. Additionally, the system needs to be lightweight due to the nature of the current platform. The Polaris Outlaw 525 is a high-performance ATV and therefore weight is a primary concern as is common in most forms of motor sports.

While the original plan was to produce a working prototype of a fully automated ESMT, time and resource constraints led to the decision to create a semi-automatic proof of concept. The semi-automatic concept allows research to continue regarding the shifting mechanics while eliminating the time and resources necessary for full automation. Full automation remains a possibility should the desire for such a system remain at the conclusion of this project. Within the context of motor sports, one need only look to Formula 1 racing to see the inspiration for this project. In recent years, all cars on the F1 grid have used semi-automatic gearboxes for the efficiency of power transfer, speed of shifts, and ease of use for the driver. This project has the same goals, with faster shifts a possible, though not imperative, bonus outcome. PROJECT OUTLINE Project Scope The main task of this project is to create an electromechanical system that when added to an existing manual transmission provides electronic shifting. Within the twenty weeks allotted, the project included researching any similar systems, researching potential patent issues, designing, and prototyping the system. The end product would be a prototype system retrofitted to the supplied Polaris Outlaw 525 ATV. System Specifications and Features The two critical specifications (design principles) for the project are that the system is safe to use and the system utilizes push-buttons to control up-shifts and down-shifts. To ensure safe use, it was specified that the system shall never take any action the rider has no

Proceedings of the Multi-Disciplinary Engineering Design Conference

Paper Number 07310

expectation of. This means all actions are either user initiated or failsafe conditions presented to the rider prior to riding. Major specifications for the project includes weight, clutch use, and reverse lockout function. The system weight should be less than 7 lbs. One major complaint about the ATV that preceded this model is that it was too heavy. The new model is about 30 lbs. lighter, and ideally, this system would not put much of that weight back on. For a vehicle that weighs less than 400 lbs. 7lbs. is much more significant than it would be on a larger vehicle. Additionally, clutch use shall not be required to use the system. Aside from gear selection, the shifting system shall require no other user inputs. While there are many potential solutions to this requirement, it is necessary to prove that rider inputs can effectively be eliminated from the shifting process. Finally, reverse lockout should be retained or engineered. Currently, the reverse lockout system requires that the clutch be disengaged and a button be depressed before the ATV will shift into reverse. Either this system needs to be retained, or a suitable system needs to be integrated into the design solution. This is to ensure that in aggressive riding situations it is not possible to accidentally shift into reverse. A great number of system specifications were generated, though none have the design implications of the above specifications. In addition to the specifications generated a key feature emerged as well. The need for a gear indicator became clear as the rider would no longer have a direct link into the transmission as they have in the past with the foot lever. Because of this, it is important to have some other device that allows the rider to know the currently selected gear. RESEARCH AND DEVELOPMENT Mechanical Sub-System The responsibility of the mechanical sub-system is to utilize the electrical energy available to physically shift the transmission. In full manual operation, a foot lever is moved by the rider to select the gear. The lever uses a ratchet action to return to a standard rest position. Up-shifting is done by displacing the lever upwards while down-shifting is done by displacing the lever downwards. After each shift, the lever returns via spring action to its center position. To accomplish this task electromechanically, many types of systems were investigated. These systems included pneumatics, hydraulics, solenoids, electric motors, and electromagnets. After evaluating each

system’s ability to actuate the foot lever, it was determined that actuation of the foot lever was not practical due to the high forces required. At the foot lever, approximately 150 in-lb of torque was required. With this in mind, a new concept was explored. This concept involved rotating the shift drum directly. The forces required dropped to approximately 50 in-lb of torque required. With this in mind, it was determined that the best way to apply the necessary torque is with an electric gear motor via a chain and sprockets. In this concept, the electric motor is mounted to the chassis and the shift drum is rotated via a chain and sprockets. See Fig. 1.

Figure 1: View of mechanical shift mechanism. In figure 1, the electric gear motor is mounted on the right hand side of the figure and the sprocket attached to the shift drum is on the left side. Please note the chain has not yet been properly tensioned in Fig. 1.

Figure 2: Internal view of the transmission. Rotating the shift drum (number 1 in Figure 2) the shift forks (number 2 in Figure 2) are moved along the axis of the main gear shafts in the transmission. This allows for different gears to be engaged at different times.

Proceedings of the KGCOE Multi-Disciplinary Engineering Design Conference

Copyright © 2005 by Rochester Institute of Technology

Figure 3: View of shift drum removed from the transmission. In Figure 3, the circumferential grooves can be seen in the shift drum. These grooves are what drive the shift forks axially. By rotating the shift drum, various combinations of fork positions are achieved. Also in Figure 3, the attachment point of the sprocket can be seen on the left of the figure. The center hole is tapped to allow an adapter to be attached. The sprocket is attached to the adapter which also fits into the additional hole seen to drive the rotation of the shift drum. The motor chosen for this application is a MMP-C21-230B-12V GPk52-016 EU-500 electric gear motor produced by Midwest Motion Products. The motor provides up to 89 in-lb of torque (peak), an output speed of approximately 170 RPM, a 500 pulse per revolution encoder, and weighs 5 lbs. The speed of the motor is important due to the desire to complete a shift within 0.1 sec. The shift drum must rotate approximately 60 degrees for each shift, therefore a minimum RPM needed is 100 RPM. The chain and sprockets are ANSI 25 size. Each of the sprockets is the same size and therefore there is no mechanical advantage gained or lost in the transmission of power over the chain. A unique adapter is used to directly connect each sprocket to the shift drum and the motor output shaft. It is noted that there will be backlash inherent to the use of chain and sprockets. This is accounted for in the program written. Additionally, because it is not required that the shift drum rotation have accuracy beyond plus or minus five degrees, some of the backlash may not come into play at all. Clutch use is limited to manual use for starting from a stop and situations where manual use is desired. During a normal shift, the purpose of the clutch is to allow for the transmission to unload and allow free movement of the shift forks. To duplicate this effect,

the ignition is being cut during shifts. The ignition is cut for the length of time it takes to shift the transmission. Ideally, this will be less than 0.1 sec which equates to 7 or 8 missed firings at an engine speed of 9000 RPM. The entire process can be seen in Fig. 4. Electrical Sub-System Using electrical sensors and push-buttons located on the ATV, a transmission control unit was developed to control gear shifting. Data obtained from these sensors and switches is processed by a Programmable Logic Controller (PLC) for ideal shift timing and performance. Shifting is controlled via pushbuttons, while restricting shifting of certain gears by monitoring the RPM’s.

Programmable Logic Controller: The AB 1760-L20BBB-EX PLC from Allen-Bradley’s Pico Controller family was used. While requiring a 24 Vdc input voltage, this controller allows for a higher switching frequency with transistor outputs. To provide for the necessary 24 Vdc, an extra 12 V battery was added in series with the existing 12 V battery. See Table 1 for key specifications of this PLC.

Key Specifications of AB 1760-L20BBB-EX Input Voltage 20.4 to 28.8 Vdc Number of Digital Inputs 8 Digital Input Off < 5.0 Vdc Digital Input On 15 to 28.8 Vdc Number of Analog Inputs 4 Analog Range 0 to 10 Vdc Analog Resolution .1 V Number of Transistor Outputs 8 Rated Output Voltage 24 Vdc Max Output Switching Freq 40 kHz High Speed Counter Freq < 1 kHz Table 1: Key PLC Specifications The PLC was programmed using ladder logic programming. While debugging and simulating was simpler using this language, it was restrictive and limiting in the operators available and its inability to store variables. See Figure 4 for the flow chart of the shifting operation. The PLC monitors the push-buttons for an up-shift or down-shift. When a shift is selected, the RPM is checked for proper range and the reverse lockout button is potentially checked. Next, the spark is cut and the shift is actuated. The shift is verified via the encoder and the spark is restored. Lastly, the current gear is updated and displayed in the gear indicator display.


Paper Number 07310

Figure 4: Shift Operation Flow Chart

Inputs/Output Summary: See Appendix A for Electrical Schematic overview. The Fluke RPM80 Inductive Pick-up RPM (Revolutions per Minute) sensor was utilized to obtain RPM data of the ATV. The resulting waveform pulses were processed through a Low-Pass Filter to reduce noise, and then amplified up to 24 V to conform to the digital inputs of the PLC. Because of the high frequency produced from the sensor, a Divide-by-N circuit was utilized to reduce the frequency below 1 kHz, the highest frequency the High Speed Counter of the PLC can process. The CD74HC4059 Divide-by-N counter from Texas Instruments was used. Looking at the output waveform pulses, each pulse represents a revolution. Knowing the time period of the pulses, the revolutions per minute can be extrapolated. The encoder running off the DC motor will allow the PLC to track the positioning of the motor, subsequently verifying the current gear location. The encoder will output square wave pulses, which the PLC will process to determine location. A Divide-by-N circuit is again used to reduce the frequency, as is an amplifier to allow for a digital input into the PLC. Momentary switches were used for the up-shift, down-shift, and reverse lockout buttons. These Normally Closed (NC) switches are inputted with 24 Vdc to provide for digital inputs into the PLC. As a safety precaution, the reverse lockout button will prevent the operator of the ATV from entering into reverse without first pressing the button. Already existing on the ATV is a mechanical reverse lockout switch. An electrical switch was added to allow for electrical control over gear shifting.

To control the DC motor, an H-Bridge was built. See Figure 4 for H-Bridge schematic. The H-Bridge consists of 2 NPN transistors and 2 PNP transistors, model MJE3055T and MJE2955T respectively. Each transistor is capable of sourcing and sinking 10 A, with the help of heat sinks capable of dissipating 15 Watts. The four STTH1002C diodes are used to protect against back current. Turning on Vin 1 will complete the circuit, driving the motor forward. Conversely, turning on Vin 2 will complete the circuit and drive the motor in reverse. These are controlled through PLC outputs Q1 and Q2.

Figure 4: H-Bridge Schematic To control the ignition attenuation, an electrical relay is used to cut the spark on the primary side of the ignition coil. The relay has a control voltage of 3-28 Vdc, and is controlled through PLC output Q3. The MM74HC138N 3-to-8 line decoder was utilized to indicate the current gear in the gear indicator display. This is controlled through PLC outputs Q4, Q5, and Q6. A voltage regulator was used to drop the output voltage from the PLC from 24 to 5 V. Coming out of the decoder are LED’s corresponding to each gear with current-limiting resistors in series. Interface Sub-System The goal of the Polaris ESMT team is to provide a push-button shifting system that is ergonomically sound, easily accessible to the rider, reliable in the most challenging environments and terrain. This system will be implemented on the Polaris Outlaw 525 high performance ATV. The final design for the gear push buttons is shown in Figure 5. The two gear push buttons are located on the left side of the handle bar, next to the start/light/kill switch controls. The shape for the two push-buttons is circular. The up-shift button triggers the transmission to shift to the next higher gear, and the down-shift



button triggers the transmission to shift to the next lower gear. The reason for placing the gear buttons on the left side is that the driver would not need to remove his thumb from the throttle control to shift, allowing the rider to be more comfortable in controlling the ATV in racing or other challenging environments. There is a sufficient gap between the two push-gear buttons that allows the rider’s gloved hand to activate either button without the risk of pressing both buttons accidentally. The push-button control interface was designed using polypropylene and manufactured using a 3-axis CNC machine. The two push-buttons were purchased off-the-shelf.

Figure 5: Final gear control design The gear indicator screen is located on the center, above the handle bars, providing a clear display of the current gear and operating warning lights. Each gear is indicated as well as a warning light for temperature. The numerical text in this gear indicator screen has bright color that provides easy reading to the driver regardless of operating conditions. The gear indicator interface design was designed in four parts for easy assembly. The clear material for the indicator screen is acrylic, and the casing is ABS. The indicator screen was manufactured using a 3-axis CNC machine. The LED’s are mounted on the back casing of the interface. Installation will require modification to the current cowling.

Figure 6: Gear Indicator Display RESULTS AND TEST PLAN Results As of this writing, the project is not complete. The mechanical and electrical components are still being assembled and therefore many detailed results are not available. One result that is available is the weight of the system. Disregarding items used for the proof of concept that would not be used in a final concept such as the PLC and extra hardware required to run the PLC the weight of the system is still too high. The projected total weight for the motor, chain, sprockets, mounting brackets, adapters, and wiring is approximately nine pounds. This does not meet the specification that was set forth. To reduce the weight of the system it is recommended to use lightweight materials wherever possible. The mounting brackets are made primarily of steel whereas aluminum would likely be sufficient. This design decision was made because of a short time schedule not allowing for the optimization of the design, instead focusing on a highly robust system. Additionally, it may be found that the motor chosen exceeds the actual torque requirement and a smaller motor could be used. The PLC program has been simulated on a PC and has successfully met the requirements of the control system. Additional refinements will be necessary as testing begins, however a solid base has been established. From an ergonomics standpoint the project has been a success. The buttons are easy to reach and the display is easy to read. While actual live testing has not occurred, all test participants have agreed that the system is comfortable and easy to use. Further refinements will need to include the integration of the shift buttons to the current control box. Government regulations require that the engine kill switch be as close as any other control that the rider has access to while riding. The prototype system violates this regulation, however still proves the concept feasible.


Paper Number 07310

If this design is accepted as a final design to go into production, minor retooling would be required to integrate the gear indicator display into the cowl design. Test Plan While results are lacking, there is a test plan in place for when the system is completed. The plan will gradually evaluate the system and increase the demands on the system as the tests proceed. First will be a static system review. The ATV will be put up on jack stands so that the drive wheels do not touch the ground. The system will be tested to see that it shifts gears and functions as expected. This test will have nearly zero load on the transmission since the drive wheels are suspended. Additionally, shifts will be made near the low end of the engine’s RPM range to minimize the potential stresses to the system. Once system function is confirmed and necessary adjustments are made, the second part of the test program will include low speed, low acceleration system tests. Again, shifts will be made in the low to mid-range of the engine’s RPM range and at low to no acceleration. This test will begin to evaluate the system robustness as the load of the ATV will now be in play.

Next is a full system robustness test. In this test, RPM’s and acceleration will not be restricted. This will be the final test to ensure the system can withstand the rigors of full use. The final test will be for data collection. The ATV will be fully instrumented and put on a dynamometer to quantify the system performance results. In this case it is possible to measure the amount of time for each shift. Only at that point will it be clear if the shift time specification has been met.

ACKNOWLEDGMENTS

The team would like to thank Joel Notaro and Polaris Industries for their support. Without them, this project could not have happened. We would also like to thank Professor George Slack for all of his help, support, and encouragement. For their technical expertise and input, the team would also like to extend our many thanks to Dr. James Taylor, Dr. Wayne Walter, and Dr. Matthew Marshall. Finally, we would like to thank the Rochester Institute of Technology, the Kate Gleason College of Engineering, and all of the support staff that made this possible.

.



Appendix A: Electrical Schematic

electronically shifted manual atv transmission...

Documents