I'm currently working on a reasonably new Toyota Landcruiser which is suffering from a bad vibration that can be felt through the steering wheel. The vehicle in question is fitted with a Diesel V8 engine and automatic transmission.
Using the Picoscope with the Pico NVH kit, I was able to determine that the vibration was of the fourth order. When the vibration is the most severe (engine RPM approx. 1980Rpm) the vibrations being transmitted to the base of steering column can be in the vicinity of 30mg in amplitude.
Understanding that a E4 vibration is normal for a V8 engine vehicle, I started to look for a reason for the vibration being excessive at the steering wheel.
Even with the engine idling, with the A/C cycling engine RPM from 600 to 800 RPM, I'm picking up an increase of 26mg at the steering wheel (NVH accelerometer held against the steering wheel)
The question is - why have I got so much vibration being transmitted to the steering wheel?
I managed to get a comparable vehicle to check vibration values between the two vehicles.
The comparison vehicle has the same Body, Engine, Transmission, etc - but is a lower grade (plastic coated steering wheel as opposed to the leather / wood grain steering wheel of the luxury subject vehicle)
After measuring the E4 vibration at multiple locations (Engine, LH chassis, RH chassis, Steering shaft engine side and steering wheel side, LH and RH steering rack ends and of course - at the steering wheel itself) I have come to the conclusion that my diagnosis of the transmission path of the vibration is inconclusive!
That being said - I have really only done a static comparison between the two vehicles. I figure that would be ok as the ability for the Picoscope to pick up the smallest levels of the vibration would still show varying levels of the vibration - but the severity would increase when the engine was driven and put under load.
Below is the measurements taken from the comparison vehicle and subject vehicle.
Both vehicles had reached operating temperature and were left to idle with the air conditioning left on for RPM variation.
Comparison Vehicle Subject Vehicle
600RPM 800RPM 600RPM 800RPM
Engine 144mg 118mg 149mg 133mg
Steering Column, Bracket 2.4mg 4.1mg 3.27mg 5.47mg
Steering Column, Shaft 3.5mg 5.27 0 0
Steering Column, Washer 3.26mg 5.57 2.12mg 4.38mg
Steering Column, Uni Joint 806ug 19.1mg 836ug 11.2mg
Steering Column, Engine side 9.14mg 10.6mg 3.58mg 12.1mg
Steering Wheel 12.3mg 4.43mg 4.8mg 38.4mg
LH Steering Rack End 8.79mg 16.7mg 4.22mg 15.2mg
RH Steering Rack End 2.6mg 7.22mg 2.12mg 24.12mg
Front Prop Shaft 8.79mg 22.3mg 9.56mg 19.5mg
Transfer Case 94mg 104mg 107mg 108mg
#3 Crossmember, LH 6.22mg 12.6mg 744ug 15.2mg
#3 Crossmember, RH 2.47mg 7.28 mg 4.59mg 12.3mg
My question is - Am I even heading in the right direction in terms of gathering information that will help lead me to the cause of the vibration being felt so badly in the steering wheel of the subject vehicle?
Would there be a simpler, more direct way to chase down the path that this 'normal' vibration is being transferred along?
Thanks for reading!!