R. L. Norton, 11/19/93

Over The River and Through the Woods
WPI ME 3311 Project 2
Term B-93

Assigned 11/19/93 ----- Due 12/17/93

    Tomasello, Mirage Studio’s top Ninja Turtle rider in the Hare Scrambles event, has asked us to design a new motorcycle engine for his racing bikes. Most competitive off-road motorcycles use 2-stroke engines but pending government emission regulations may soon make it necessary to use 4-stroke engines instead. Most of these racing bikes have single-cylinder engines which generate large shaking forces. These shaking forces contribute to rider fatigue in the long 100 mile events. Tomasello believes that a multicylinder design might be a better bet.

    Engine space is limited in a motorcycle of this type and this will limit possible engine configurations. Weight should be minimized as well. A vee engine is a possibility and an inline will clearly fit. A horizontally-opposed engine is another possibility. Given the need for low weight, no more than 3 cylinders are desired. The rules allow two displacement classes, 125cc to 249cc, or 250cc to 500cc.

    Your assignment is to design a superior 4-stroke off-road motorcycle engine, investigating 1-, 2-, and 3-cylinder designs in inline, vee and opposed configurations. Your report will recommend the best design and provide good engineering justification for your choice. The report will also discuss the pros and cons of the various designs not chosen.

    In order to compare "apples to apples", you will design all engines to have the same total displacement. Thus, each engine with a different number of cylinders will have different sized pistons, connecting rods, and crankshafts. Each group is assigned a particular total engine displacement as defined in the accompanying chart. Each group member is expected to design a set of engine parts for a different-sized cylinder to fit one engine.

    Your group is charged only with the design of the mechanical aspects of the engine You will not be involved in the design of the thermodynamics aspects of the engine. Rafael has supplied you with the latest version of the ENGINE computer program. Messrs. Donatello and Michelangelo of the Thermo Design group have defined the gas-force curve for the engine and have included it in program ENGINE. This program is available to you in the Aptlab and all other labs on campus, and is on your textbook's disk. Make sure that you are using version 5.2 or higher. (Please report any bugs to me right away.)

    Tomasello has also generously supplied us with some engines and engine parts for study. These have been partly disassembled and will be available for your inspection and measurement in the Aptlab.

    This design task logically breaks down into several sub tasks which can be addressed sequentially. A chart of these sub-tasks and the due dates for their completion is provided in Table 1 below.

The Goal Statement for this project is:

    Design an improved, multi-cylinder, IC engine of specified displacement, optimizing its torque and dynamic characteristics.

The Task Specifications are:

      1. All engines are to be designed to a common total displacement corresponding to the displacements specified on the attached list for each group.

      2. Your engine is to be designed in various configurations and those configurations compared for best dynamic operation.

      3. All will use the Otto, four-stroke cycle with an idle speed of 1000 rpm and red-line at 8000 rpm.

      4. Various configurations are required as described above (inline, vee, opposed). Compare these designs and discuss their differences.

      5. The torque-time function should be as uniform as is practically feasible.

      6. Shaking forces and moments should be minimized, as much as is practically feasible.

      7. These engines will not have any reciprocating counterbalances, such as are in one of the sample engines.

      8. Engine dimensions, such as bore, stroke, conrod length, counterweight sizes and locations, and masses of all moving parts are to be determined by the designer, consistent with the other task specs. You must design the geometry of the engine parts in sufficient detail to determine their mass properties for input to ENGINE. TKSolver and/or Aries CAD can be of great assistance here.

      9. A flywheel is to be designed and specified as well. Note that weight is a consideration - lighter is better.

      10. Short progress reports are required at each stage of the design as defined in Table 1. These reports must adhere to the Progress Report Specifications supplied with this document. A final report will be required at the end of term, which will detail the complete design and which adheres to the Project Report Specifications supplied. The final report can be considered to include only part of the Design Process as defined in Chapter 1 of Design of Machinery, i.e. you will be beginning this project at step 5 of the Design Process, (Ideation), since you have been supplied a Goal Statement and a set of Task Specifications. Note that this problem is one of Design by Successive Analysis, requiring much iteration between the Ideation and Analysis steps of the Design Process. Background Research material is available in your textbook, and in the several books and documents on reserve in Gordon library. You are expected to read the reference materials! You may, if you wish, also investigate existing engine designs at the local motorcycle or automobile repair shop. Recent issues of motorcycle or automotive magazines (Cycle, Cycle World, N.E. Trail Rider, Road & Track, Car & Driver, Motor Trend, Automobile, Autoweek) may also have useful information.

      11. The programs ENGINE and DYNACAM may be used to do the computations necessary for the analysis, but you must also show in your final report that you all understand the mathematical basis for the analyses. The methods are clearly derived in your textbook and in the lectures, and the computer programs are based on these methods.

      12. Note that this is a group project and you have been assigned to a group of 3 to 4 members. Each group is in "competition" with the other groups. Your group should meet as frequently as possible and assign tasks among yourselves. There will be 3 progress reports and one final report per group. The individual contributions of each member to the overall task must be clearly identified in the final report. Confidential peer evaluation sheets will also be required from each member, to be submitted with the final report. Each group will present its design orally in the section meetings on December 14, 1993. The design needs to be complete by then and the report can be written up in the following three days.

Suggestions for Solution:

    To assist you in getting started, we will provide the means to measure the sample engines and their parts. You can then experimentally determine some starting values to use for input to program ENGINE. Table 1 breaks the problem into four sub-tasks, or stages.

    Stage one will help you understand what needs to be done to design an engine by analyzing an existing example. You should exercise items 1 to 5 on the ENGINE menu until you understand how this engine works and what the equations in your text are telling you. Then apply your understanding to your new design which will have the required cylinder displacement. Thoroughly investigate variations in the parameters described in Table 1 to see their effects on the engine's dynamics. Note that you are still only using items 1-5 in ENGINE's menu. Stage two requires you to balance one cylinder of your design from Stage 1. Use items 1-6 in ENGINE.

    Stage three assembles the multi-cylinders of your engines for the first time. You may find a classic tradeoff here between conflicting demands on the torque-time function versus the inertia (shaking) force function. Also engine balance condition is a factor. Use 1-7 in ENGINE. Compare the various design's configurations and choose one based on a compromise between smoothness of operation, weight, and cost. Note that for a vee or opposed configuration you need to first design one bank as an inline engine and then duplicate it for the other bank. Stage four designs the flywheels for the engines and the cam to drive the valve train.

    Choose the design you recommend to be produced and justify your choice. The final result must be written up in a project report as defined in the Project Report Specifications.

Have fun!

Table 1

        Stage 1. Analyze the sample engines provided, using program "ENGINE". Using specifications for your particular configuration investigate the effects of bore/stroke ratio, and conrod/crank ratio on the dynamic performance of one cylinder only of your proposed design. Look at the equations! Understand the theory! Progress report due (see syllabus).

        Stage 2. Having chosen a bore/stroke ratio and conrod/crank ratio, investigate the effects of adding counterweights of various proportions to the crank to attempt to optimally balance one cylinder of your engine. Progress report due (see syllabus).

        Stage 3. Having balanced one cylinder, assemble the engine with the number of cylinders required, and investigate the effects of different crank throw configurations on the combination of inertial forces, and torque time diagram. Progress report due (see syllabus).

        Stage 4. Design the flywheel to smooth the engine, and design the cam for valve motion. Additional information on the cam specifications will be supplied at a later time. Final report due (see syllabus).