Purpose of the Study
This study measured and recorded total vibration and whole body vibration (WBV) levels on a on a wheeled-loader at the Transportation Research Center (TRC), East Liberty, OH. The study examined differences in vibration levels between the use of solid and polyurethane-fill tires on a single piece of equipment on several test tracks selected to approximated conditions that might be found a solid-waste transfer station or landfill.
Vibration transmitted to a vehicle is of great concern. Exposure to constant and severe vibrations will ultimately cause premature fatigue and damage the vehicle components. As vehicles are operated by a riding driver, the effects of vibration on the human component cannot be ignored. The road surface, vehicle components/configuration, and operating speed/style contribute to vibrations within the system. These vibrations are transmitted to the driver from a chassis mounted seat. Reduction of vibration in the vehicle will ultimately reduce the vibration exposure transmitted to the operator.
Environmental WBV is transmitted from the contact surface to the whole human body while standing, sitting or reclining. Occupational seated exposure is found with operators of a variety of vehicle categories such as cars, buses, fork-lifts, tractors, trucks and heavy machinery either on or off paved roads (Padden & Griffin, 2002). Locomotive engineers are also exposed to significant levels of WBV (Johanning, et al., 2006).
While WBV is not a part of current OSHA standards, the National Institute of Occupational Safety and Health (NIOSH) has conducted research in the area of WBV. In its conclusions about WBV, NIOSH (1997) states,
Laboratory studies have demonstrated WBV effects on the vertebra, intervertebral discs, and supporting musculature. Both experimental and epidemiologic evidence suggests that WBV may act in combination with other work-related factors such as prolonged sitting, lifting, and awkward postures to cause increased risk of back disorder. (p. 6-33)
- Johanning, E., Landsbergis, P., Fischer, S., Christ, E., Göres, B., & Luhrman, R. (2006). Whole- body vibration and ergonomic study of US railroad locomotives. Journal of Sound and Vibration, 298(31), 594-600.
- National Institute of Occupational Safety and Health (NIOSH). (1997). Musculoskeletal Disorders and Workplace Factors. DHHS (NIOSH) Publication No. 97-141.
- Paddan, G. S. & Griffin, M. J. (2002). Evaluation of whole-body vibration in vehicles. Journal of Sound and Vibration, 253(1), 195-213.Location/Date
Onsite testing was conducted at the TRC on Tuesday, May 10, 2016. Additional information for the TRC can be found at http://www.trcpg.com/about-trc.aspx.
The vehicle was an approximately 20 year old used Caterpillar 966G Wheel Loader, Series II, Product ID# CAT0966GC3SWO1529, owned and operated by TRC.
Two tire configurations were tested. Tires were installed by a crew retained by Accella.
Solid tires: SG Revolution 26.5-25, and secondly
Pneumatic tires: Firestone 26.5-25 L5 Slicks filled with Accella polyurethane product.
Three separate vibration monitoring systems were utilized.
TRC: An eDAQ data acquisition system with five single axis accelerometers. These were mounted on front and rear axles (both sides) and the cabin floor.
Accella: Three I-phone 6 devices with a Sensor Kinetics application for vibration recording and analysis were used. These were mounted on the rear axle (both sides) and the cabin frame upright.
Paschold: A Larson Davis HVM100 human vibration meter was connected to a triaxial accelerometer seat pad, which also had an Apple I-phone 6 using a WBV monitoring application. The HVM100 is configured to produce data compliant with the International Standards Organization (ISO) requirements 2631-1 for WBV monitoring.
The loader was operated on three different courses at TRC. These were selected in an attempt to approximate conditions which may be found at a solid waste transfer station or landfill.
Bus & Truck Durability Course: Used for durability testing of straight trucks, semi-trailers, motor homes, travel trailers, military vehicles and inadvertent airbag firing tests. The 2,000-foot by 24-foot wide course consists of: staggered bumps, sine waves, chuckholes, chatter bumps and a high crown intersection.
Cobblestone Durability Course: A 1,320-foot roadway features two parallel strips with an average cobble protrusion of 1.5 inches. This track is used to provide input for durability testing of medium to heavy duty trucks.
Skid Pad: This course is used for low speed durability testing. This has two lanes utilized for rough road durability testing. The durability courses contain rough road surfaces such as resonance, impact and chatter bumps, chuckholes, V-ditches, twists and washboards for testing chassis body and suspension components.
This selection includes results and discussion from TRC and Paschold; Accella-generated data and results will be published separately.
TRC published its final report “TRC Inc. Project Number: 20160299” May 31, 2016. This report briefly described the test procedures, summarized vibration results, presented graphs for each accelerometer during the individual test runs, and included test course specifications along with photographs of tires and accelerometer placement. The data appears to have been collected and analyzed without issue. The following is a summary table of data which will be discussed in the following section.
The data collected by Paschold with the HVM100 was flawed due to the instrument defaulting to a setting for the measurement of vibration within buildings prior to use at the test site (a Wm weighting instead of Wd and Wk as prescribed by ISO 2631-1). The Wm weighting is similar to Wd (used for the z-axis), but not sufficiently close to derive a definitive finding. The application on the smart phone device yielded two pairs of readings for z-axis WBV which suggested similar or lower WBV for the polyurethene filled tires over the solid tires. Due to unexpected confounding conditions during the test runs, these data will not be presented.
Discussion of Results
As previously stated, the driver is exposed to vibration transmitted to the buttocks by the chassis- mounted vehicle seat. A reduction of vibration in the vehicle chassis should result in lower vibration doses to the driver.
The TRC summary table clearly shows much lower vibration levels in the cabin (floor-mounted accelerometer at the seat mounting) for polyurethene fill tires versus the solid on the Durability and Cobblestone tracks. There appears to be no significant difference between the tire types on the Skidpad track test. However, the Skidpad comparision is not valid to due a difference in two test drives. The morning test with solid tires covered the entire length of the course, while the afternoon test was shortened to about 200 yards of travel, and did not cover the same obstacles as the morning test. The cabin mounted accelerometer data, vibration expressed as G (gravity, 9.8 m/s2) are highlighted below.
The results are very positive for the vibration reduction on the durability course; it should be noted that features of this course introduce severe shocks to the vehicle. On the cobblestone course, less shock-causing features are present. At 5 mph on both courses, the polyurethene filled tires presented excellent reduction of the peak Gmax force. Interestingly, the Polyurthene filled tires showed greater improvement over the solid tires at 8 mph compared to 5 mph.
With regard to WBV, the lower chassis vibration should result in lower exposure for the driver. In this test, no identifying information was available for the seat which appears to be original equipment. A seat not properly designed, adjusted, or maintained may increase driver WBV levels; therefore, greater value is placed on the chassis vibration adjacent to the seat mount. A second driver operated the vehicle after the tire change, his difference in mass may have altered consistent monitoring of WBV. Due to the condition of the seat and driver change, the WBV findings of similar or lower magnitude for the polyurethene filled tires may not be considered to be absolutely valid.
The findings presented by TRC for the measured cabin Gavg and Gmax values clearly support a claim of reduced vehicle cabin vibration on the Durability and Cobblestone test tracks with the use of Accella’s tire fill product when compared to solid tires.
Respectfully submitted, June 6, 2016
Helmut Paschold, Ph.D., CSP, CIH Assistant Professor
Department of Safety Sciences indiana University of Pennsylvania [email protected]