THE TRANSMISSION OF PISTON FORCES TO THE MOUNTS OF AN ENGINE

An experimental and theoretical study was made of the transmission of piston inertia and gas pressure forces to the mounts of a conventional four-cylinder in-line engine. Of particular concern is the transmission of forces at frequencies which are second order and twice engine speed. The results refer mainly to the forces at the rear mounts of the engine at a gearbox extension. The vibrations of the crankshaft and flywheel were found to have a significant effect on the transmission of the forces to the vehicle body structure at high engine speeds. Measurements also show that "beam" resonances of the engine/gearbox assembly affect the transmission of the forces. Theoretical models of the crankshaft and the engine/gearbox explain the increase of the force transmission at high engine speeds. The crankshaft whirl causes the engine/gearbox to shake in the horizontal and vertical directions. To avoid excessive transmission of engine forces, changes to the crankshaft design should be considered at an early stage. If the crankshaft is optimized or if design changes are unacceptable and the force transmission is high, then the rubber mounting stiffnesses should be as low as possible and they should meet the design specification. An increase of stiffness and damping of the engine mounts with frequency should be avoided.

• Supplemental Notes:
  • Also published in HS-029 137 (IMechE-CP-1979-10), "Noise and Vibrations of Engines and Transmissions," Bury St. Edmunds, 1979 pp 1-8. Presented at conference, Cranfield Institute of Technology, England, 10-12 July 1979.
• Corporate Authors:

  Institution of Mechanical Engineers

  1 Birdcage Walk
  London SW1H 9JJ,   England 

  Society of Automotive Engineers (SAE)

  400 Commonwealth Drive
  Warrendale, PA  United States  15096
• Authors:
  • Hodgetts, D
  • McDonald, A M
• Publication Date: 1979

Media Info

• Features: References;
• Pagination: 8 p.

Subject/Index Terms

• TRT Terms: Crankshafts; Engines; Flywheels; Pistons; Transmissions
• Old TRIS Terms: Gear boxes
• Subject Areas: Safety and Human Factors; Vehicles and Equipment;

Filing Info

• Accession Number: 00385667
• Record Type: Publication
• Source Agency: National Highway Traffic Safety Administration
• Report/Paper Numbers: IMechE-C116/79, HS-029 138, SAE-MEP-109
• Files: HSL, USDOT
• Created Date: Jun 28 1984 12:00AM