P09310- Automatic Shift Control for ATV

Design Review- System Level Design

Friday October 3, 2008, 1pm, 09-3119

Project Family:

Modular, Scalable, Open Architecture Control Systems

Track:

Systems and Controls

Group Members:

Ashley Shoum, Team Leader, ME

Matt Dombovy-Johnson, Lead Engineer, ME

Keith Cobb, ME

Bibhu Shah, ISE

Jon Willistein, EE

Feng Li, EE

Sarah Bicho, ID

Faculty Consultants:

Professor George Slack

Dr. Alan Nye

Project Sponsor:

Joel Notaro

Performance ATV Project Engineer

Polaris Industries

System Level Design Review Agenda:

  • Review customer needs
  • Previous project needs met and unmet
  • Newly established needs
  • Concept Component Summary
  • Mechanical Components
  • Electrical Components
  • Target Specifications
  • Functional Diagram of Mechanical Subsystem
  • Initial Flow Chart for Program Operation
  • Initial Microcontroller Board layout
  • Review Estimated TPS vs. RPM Shift Characteristics
  • Selected Handlebar Design Concept
  • Action Items
  • Proposed Schedule
  • Additional Suggestions and Feedback
  • Concept Selection and Benchmarking Data [if necessary/requested]

Introduction:

Team P09310 has decided to use a pneumatically controlled cylinder to actuate the existing OEM shift lever on the Outlaw 525. Based on benchmarking from the previous design P08310 and other pneumatic and electronic shift systems on the market the team has decided to use the following components in our design:

  • Air Compressor
  • Pressure Switch
  • Regulates tank pressure
  • Activates pump to recharge tank if a ΔP of 10 psi occurs
  • Pressure Vessel
  • Contains required air volume and pressure
  • Solenoid Valves
  • 3 Way Direct Acting Valve
  • Mounted directly to cylinder
  • Cylinder
  • Double Acting Cylinder
  • Specifications determined from analysis
  • Shift Tab
  • Provides moment arm to translate linear motion into rotational

The engineering manifested within the current design by the team P08310 was investigated through on line research and through product tear down. Due to lack of paper work reverse engineering was used to figure out the system. After Bench testing the pneumatic shifter system numerous problems were identified immediately. There have been several complaints regarding air lines “popping” off during use as well as several tears in the line. The mounting brackets for the previous team were neither robust nor easy to assemble and they lacked any sort of professional touch that one would expect from an after market product of this caliber. Much of that fault can be contributed to time constraints as the inner workings of their design was more valuable than the finish product. Proposed replacement components are described below and will be tested for the final system design.

Component Selection:

Air Compressor:

Our team is investigating the use of a physically smaller pump as compared to the previous team’s selection. We would still need to meet the required pressure, but during benchmarking we have come across smaller sized pumps. This will potentially reduce design weight and size for packaging. Since we are limited by the amount of current that the stator puts out, a smaller pump might have less current draw on the total system and reduce our design risk. Further investigation is required.

Pressure Switch:

Our design will most likely incorporate the previous design teams pressure actuated switch. It may be required that we activate the pump on a lower pressure differential to maintain the tank pressure in a more consistent manner. This could potentially increase the number of shifts per tank. The ultimate goal would be to maintain cylinder volume and pressure to obtain a full cycle of shifts, 10 total. The only downfall to this would be increased activation of pump causing premature wear.

Pressure Vessel

The design will incorporate a pressure vessel to contain the volume of air required to complete specified number of continuous shifts before recharge. Based on the data from the previous design we are investigating either a dual tank system in parallel or simply a larger pressure vessel to contain an increased volume to assist in the number of shifts per tank.

Solenoid Valves

Benchmarking of other systems has led the team to decide on using two small three way solenoid valves mounted directly to the cylinder. The weight will be less, compared to the previous design and it will also decrease the amount of space required to package the system as the size of the valves are much less. (See solenoid comparison sheet) The reduction in length of the air line will also reduce frictional flow losses and increase the velocity of the fluid through the system. A direct exhaust from the valve will increase the shift time overall. Additionally, the design will plan to have both exhaust valves normally closed so that the cylinder will be open to the atmosphere between shifts. This will allow us to use the internal transmission spring to return the cylinder back to the neutral position. It will also reduce the resistive pressure forces during activation because the cylinder will not have such a large pressure remaining in the cylinder that needs to be pushed out during a shift, as compared to the previous design in which both sides were equally pressurized and to complete a shift one side was exhausted. The cylinder being open to the atmosphere will allow manual override at anytime for safety and malfunction reasons. Overall, these design changes should increase the shift time. Analysis of the shift time is not fully completed and will be used to determine whether the assumptions are correct.

Cylinder

The design will use a double acting cylinder with the possibility of a pivot mount system. The actual mounting location will be determined after the selection of the cylinder. The team is investigating the use of a smaller cylinder for weight and packaging reasons. The required bore size has been determined by the analysis of proposed shift tab actuator length. With a 1.5” tab the required force was determined to be 100 lbs. The current design is using a 150 lb cylinder, so there may be a smaller cylinder that meets our requirements. Depending on the shift mounting system there will be a few mounting options for the cylinder.

Shift Tab

The shift tab design will incorporate either the current shift lever or a redesign. The goal is to maintain the manual override ability. The tab length will be determined based on space requirements and required activation force. Proposed length will be 1.5” long. See analysis.

Air Lines:

Investigating last year’s teams design a couple issues were found. The system spanned the entire vehicle, resulting in long lengths of hosing in exposed areas; this led to excessive wear on the hoses which resulted in tears. Also the ends of the hoses weren’t cut appropriately for the fittings that were used. There is merit to the use of push to connect fittings as they are small, cheap, and easily modified. Our plan is to keep the quick connect fittings and use them properly to start out. Once everything is laid out (mounting positions of all the components) we can look for a more permanent solution if this one doesn’t seem sufficient (either the Jiffy-Tite or bent metal hose).

Bracket Design:

As mentioned earlier the main problem with the brackets on the current design is their functionality. There is no easy way to assemble the system and no way to attach it to the vehicle without modifying the frame of the ATV. Striving for a system that is easily installed and completely removable this is far from ideal. Until final components are chosen any sort of initial bracket design would be premature however thought has been and will continue to be placed in this category. The goals of this are simplicity and durability without sacrificing the function it’s needed for, and that is to keep all of the components where they need to be.

Microcontroller Schematic

The microcontroller schematic shows a block-level circuit diagram to be used as the shifting-mechanism’s controller. All of the inputs (sensors, switches) are to the left of the MSP430 block (microcontroller), and all of the outputs (indicators, drivers) are to the right. The voltage regulator is shown above the MSP430, which supplies 3.6V to it from the 12V ATV battery.

Legacy (previous teams) items are shown as white blocks, where new (for this year) items are shown as gray blocks. There are not any legacy blocks that won’t be used. There are only additions. Of course, many of the components that make up the legacy blocks will be replaced/modified, but they will perform the same functionality (only better and cheaper).

Design Considerations

  • Why MSP430?
  1. To continue using previous team’s code, IDE, and familiarity (in case we have questions for the previous teams).
  2. It has max clock frequencies of 8MHz (only at 3.6V, reason we chose 3.6V supply).
  3. Also has variety of on-board peripherals (ADC, DAC, hardware mult. for table interpolation) that we need.
  4. Can program in C and can have good correlation to assembly because it’s a 16-bit processor (no insane assembly routines to do, for example, 16x16 multiply)
  5. Multiple interrupt vectors for easy ISR’s writing (many asynchronous things going on).
  • TPS (throttle position sensor)
  • To more accurately control shift points from user input. Forms a 2-D shift map with RPM.
  • What’s with the gear sensor?
  • Allows for the ATV to be manually driven (shifting is done with the foot lever). If the user decides mid-ride to turn the system on, the controller knows what gear it’s in.
  • Allows for simple up/down shift checking (easier code to write).
  • And the clutch signal?
  • Monitors when the user pulls in the clutch manually; autoshifting is disabled (ex. when at redline and starting line).
  • Won’t shift out of neutral (by pushbutton) unless clutch is pulled in. Note: This could not be the case if the auto-clutch that is installed allows for clutch-less shifting.
  • Indicators? (bad shift and about-to-shift)
  • Bad shift if the user wants to shift (push-button) down/up and the RPMs will go into unsafe range. (Ex. shifting down from 3rd @ 7500 to 2nd, or into R at high RPM)
  • Bad shift will blink if a shift doesn’t actually happen (by reading gear sensor). Something went wrong (no air, solenoid doesn’t fire).
  • About-to-shift is informative to user when system is about to shift (customer need). A bit safer for user…
  • Spark-cut circuit
  • Tells CDI to cut spark to engine while the system is shifting. Makes for much smoother (and less force required on shift lever) shifting. Saves transmission wear-and-tear.

Need met
Need not met
New need

Proposed RPM vs. TPS relationship is our estimated concept for designing shift points for