Case Studies

Centrifugal Compression Relief Cam Tester

Previous System: A manufacturer of high-performance engines for motorcycles includes a second, very precise, top of stroke compression relief cam modification on the exhaust cams to reduce the starter torque required to start their high displacement engines. Each exhaust cam needs its decompression lobe profile tested dynamically to verify that the decompression cam engages and disengages correctly, and only within a specified engine RPM range, before the cam can be installed in a new engine. A small lathe was modified by the company’s manufacturing engineers to test the cams. Using the lathe, a cam was chucked in the lathe and an operator would manually change the lathe spindle RPM while listening for the decompression cam clicks and noting the speeds at which the clicks were present. This method proved to be very slow and much too inaccurate.

New System Design and Function: Industrial Automation worked with the company’s manufacturing engineering team to develop an Engineering automated method that can accurately measure the cam profiles dynamically, while the cam rotation speed is ramped between preset test RPM limits. Industrial Automation modified the existing test lathe by installing a servo motor to drive the spindle so that cam speed could be precisely controlled and so that the cam high lobe, low lobe, and decompression lobe height and lobes rotational degree angle can be determined and then tracked through multiple cam rotations at any speed.

We added a bar code scanner so that each cam tested is verified to be correct for the model cam that the tester is currently set up to test. Test set ups and test result data for each cam are stored to a database, including the cam model and serial number.

Bar Code SetupFactory engineers designed a mechanical fixture to position a cam testing valve assembly that mimics the intended engine exhaust valve. The testing exhaust valve can be positioned at angles that match the valve angle of the engine for which the cam is intended. An inclinometer verifies that the valve angle is correct for the cam being tested. An extremely accurate optical micrometer is employed to measure the testing valve face movement while a cam under test is lifting the valve as the cam rotates. A color touch screen is employed to enter testing parameters and to monitor the testing. All cam test set up data is saved in memory for each cam grouped by model number. Once cam set up data is entered, it can be easily recalled to test the same model exhaust cam at a later date. Test results along with time and date tested for each cam tested is also saved to a database.

The operator places a new cam assembly in a nest and scans the cam bar code. If the bar code matches the current tester set up, the operator can then depress a foot pedal to start the test. The cam is automatically chucked in the lath, and when chucking is confirmed, the cam is rotated in the intended cam direction slowly. While making the first complete rotation, the high lobe, low lobe, and compression relief lobe angular positions and cam rise profiles are determined and logged. The cam then ramps faster until the compression relief lobe is no longer seen or until the maximum test fail RPM limit is achieved. If the decompression lobe retracts correctly, before reaching the maximum RPM limit, the cam RPM is then slowly decreased until the decompression lobe reappears or until the minimum test fail RPM is achieved. If the decompression cam high or low RPM test have not failed, the process is repeated several more times and the lobe test high pass and low pass RPMs are individually averaged and archived with other cam test and set up data. When the cam test completes successfully, the spindle stops and the cam is automatically un-chucked and drops back into its load/unload nest. If the cam fails any test, the spindle is stopped but the cam is not released from the lathe chuck automatically. The reason for a failed test is displayed on the HMI, and the operator must release the failed cam manually.