Drive Concept Generation & Selection
Table of Contents
Step 1. Clarify The Task
The team needs to connect the M.E. Dyno Lab Siemen's DC Motor output shaft with the output shaft of the Briggs & Stratton Model 20 10hp engine mounted on our engine stand. This needs to be done with regards to the following parameters:
- Capacity to operate both within the dyno sweet spot and the Briggs dynamic range.
- Ability for drive to allow engine tilt from -30 degrees to +30 degrees
- Easy & quick set-up/take down
- Withstand vibrations
Step 2. Concept Generation
The team started by coming up with the following five drive-line connection methods which are ranked in the Pugh's matrix below.
After narrowing down the high level drive-line concepts to: modifying the existing chain, a new chain system, or a new timing belt system, the team worked hard designing, specifying, and pricing each option to reflect the path of each drive-line concept. This allowed better comparison of the pros, cons, and cost of each of the three options. This can be seen below.
After laying the detailed options out on the table, the team conducted another Pugh's matrix, but this time with weighting of the selection criteria. In this case the timing belt system was used as the baseline since it appeared to be preferred by the customer. This Matrix can be seen below.
Step 3. Concept Selection
After several group meetings and another meeting with the customer, the decision was finally made to go ahead with Option 2, a modification of the existing 525 chain architecture. The team believes that the minor benefits of the timing belt/pulley system were not worth the major system cost increase associated. Although the customer showed preference toward the pulley system, our team sold the customer on the positives of modifying the existing chain drive:
- Cost savings
- Nearly Bolt on operation
- Easier change over, quicker setup time
- Re-use entire Tensioner system
- SAE Formula 600cc proves concept
Step 4. Improvements - Adding More Safety
Safety of a chain system was an initial concern brought up by both advisers and the customer in our design review. To combat this, and answer concerns surrounding the scenario of an extreme overload from the Dyno or an engine failure resulting in the Briggs seizing, we have taken steps with both our mechanical and electronic systems as follows:
- Mechanically, we have designed a safety hub for the Briggs & Stratton engine. The hub will lock to the engine drive shaft via keyway and the smaller sprocket will mount to this hub via bolts designed to shear in an overload scenario. The sprocket will receive a delrin type bushing, but no keyway, allowing it to stay located and continue to spin on the shaft once it has broken away from the hub, but not actually driving anything at that point. This initial hub design can be seen below.
- The team has done preliminary calculations pointing towards using two grade 2, 1/4"-20 threaded bolts, necked down to approximately 3/32" diameter. This design would intend to shear the bolts around 43 lb-ft of torque, preventing the load cell from overloading. This value is about three times the expected out-put of our Briggs engine, but still within the operating range of typical 525 chain & sprocket applications and well under the dynos capacity. For further validation, the team plans to use a test fixture as pictured below in an Instron style test machine on campus to compare expected values with real world results. The team will use trial and error to determine the location and best amount of material removal to result in correct repeatable shear bolt values. The results of the test can be seen in Shear Bolt Analysis.
- Secondly, A chain guard, made from 14 gauge cold rolled sheet steel and designed under OSHA compliance standards, will be used. The chain guard design can be seen below.
- From a control stand point, our LabView program will be used to keep the system in safe operating range. Our interface will receive feedback from the Dyne cell, and will be designed to auto shut down when a safety threat is realized. This will more then likely include Torque, RPM, & HP values that are out side the bounds of our pre-determined safe/normal operating conditions.
Step 5. Results Overview
Our final drive line design decisions thus far are shown below.
Step 6. Finalize & OrderTo see the feasibility of the drive, please follow this link: Engineering Analysis
Step 7. Progress
Please check back for updates.