Post on 23-Dec-2015
transcript
© 2012 Delmar, Cengage Learning
Objectives• Understand terms related to vibration• Describe the different types of vibration• Test for vibration using test instruments• Check driveshaft runout• Balance a driveshaft• Check driveshaft angle
© 2012 Delmar, Cengage Learning
Vibration Analysis• NVH (noise, vibration, and harshness)
– Specialty area of repair
• Tire and wheel imbalance – Most common cause of vibration concerns– Process of elimination is used to analyze vibration
problems• Vibration: part in motion in waves or cycles• Frequency: number of cycles in a period of time
– Measured in cycles per second or hertz
• Amplitude: vibration intensity• Velocity: combination of amplitude and frequency
© 2012 Delmar, Cengage Learning
Vibration Analysis (cont'd.)• Resonant or natural frequency
– Frequency at which a body vibrates
– Older unibody vehicles often have inherent vibration characteristics
• Severity of vibration – Greatest at its point of resonance
• Suspension frequency always the same– Out of balance driveshaft will have a frequency
that can equal suspension frequency at a particular speed
© 2012 Delmar, Cengage Learning
Types of Vibrations• First order vibration
– Anything that spins at driveshaft speed and vibrates once every revolution
• Second order vibration – Universal joint
• Beat/boom vibration – One vibration interacts with another
© 2012 Delmar, Cengage Learning
Vibration Test Instruments• Reed tachometer
– Senses frequency vibrations from ten to 80 Hz
– Two rows of reeds of different lengths
– Reeds vibrate at different frequencies
• Electronic vibration analyzer (EVA) – Pickup held in place with Velcro®, putty, or a
magnet
– Larger reading means worse vibration
– Handy when vibration occurs quickly and ceases
– Used for balancing driveshafts
© 2012 Delmar, Cengage Learning
Vibration and Frequency (cont'd.)
• During road test – Use a process of elimination
• Vibration usually occurs at a specific rpm and goes away at other speeds
• Drive in high gear at engine rpm where vibration is worst
• Put into different gear to see if vibration changes
• To test first order vibration– Raise tires in the air and run engine in gear to
check driveline– Check front and rear while driveshaft is spinning
© 2012 Delmar, Cengage Learning
Driveshaft Runout• Excessive runout in driveshaft
– Caused by driveshaft or pinion flange• Measure runout of driveshaft• Mark high spot on shaft• Remove and remount 180 degrees away on
flange• Runout is the same: shaft is at fault• Otherwise: flange is at fault
• Driveshafts – Can be aluminum, steel, carbon fiber bonded to
aluminum yokes, or composite
© 2012 Delmar, Cengage Learning
Other Causes of Vibration• Example: engine accessories
– Eliminate out side causes of vibrations
• Vibration present when car is not moving– Not a driveline problem
• Engine accessory brackets – Designed to excite at 400 Hz or higher
• Engine, torque converter, and driveshaft– Change in frequency as rpm changes
• Rebuilt torque converter: often source of vibration
• Check that muffler is not vibrating against frame
© 2012 Delmar, Cengage Learning
Driveshaft Balance• Driveshafts are balanced on the ends
– Weights welded onto ends of driveshaft at least one inch down shaft from weld
– Power takeoffs and shafts that spin at under 1000 rpm need not be balanced
– Correct imbalance with strobe-type balancer
– Transducer tests driveshaft imbalance• Magnet that is spring-loaded on both sides• Moves back and forth in wire coil
– Driveshaft balance can also be checked without special instruments
© 2012 Delmar, Cengage Learning
Driveshaft Angle• Angle of transmission output shaft and front of
differential – Should be within a half degree of each other
• Working angle – Difference between driveshaft angle and angle of
transmission or differential
• Launch shudder – Occurs on acceleration
– Disappears around 25 mph
• Several methods to measure driveshaft angle