This article focuses on the fact that engineers at Meritor Automotive decided to learn how truck components really held up on the highways. So they outfitted an 18-wheeler with the company’s products for a 24,000-mile trial, in real time and in the real world. According to Meritor, the comprehensive data generated by the test has spurred improvements in brake components, clutches, drivelines, axles, and transmissions. The company claims that the data opens opportunities for improvements in virtually every type of heavy-duty truck component that Meritor builds. The engineers in Meritor’s experimental mechanics unit enlisted support from all the groups in the heavy vehicle division. The use of a channel to record clutch pedal displacement helped engineers improve their model for determining the number of clutch applications in a line-haul duty cycle. Meritor expects that this information will lead to improved durability of several clutch components.
Engineers at Meritor Automotive decided that if they wanted to learn how their truck components really held up, there was no place like the highway. So they outfitted an IS- wheel er with the company's products for a 24,OOO-mile trial, in real time and in the real world.
The truck made fourruns on a cross-section of U.S. highways that ran over the Plains, up the Rockies, across the Great Divide, and into intense desert heat. Meritor's engineers set up 51 data-gathering channels that monitored every second on the road.
Dean Goodwin, a Meritor test driver, drove the truck loaded almost to its weight limit on the four loops stretching from Michigan to California and Oregon.
According to Meritor, the comprehensive data generated by the test has spurred improvements in brake components, clutches, drivelines, axles, and transmissions. What's more, the company has said that the data opens opportunities for improvements in virtually every type of heavy-duty truck component that Meritor builds.
Meritor Automotive, which was spun off from Rock well International Corp. in the fall of 1997 , comprises two major business segments: heavy vehicle systems, which is a leading supplier of key components for medium- and heavy-duty trucks, trailers, off- highway equipment, and specialty vehicles (including buses and fire engines); and light vehicle systems, which makes components for passenger cars and light trucks.
Making the Most of the Effort
When engineers conceived the road test, they knew it would yield more continuous freeway operation information than the company had ever gathered before. Meritor operates a large independent testing laboratory in the company's hometown of Troy, Mich., but the road record would tell more about demands on products than lab or track tests could.
In order to extract maximum value from this undertaking, engineers in Meritor's experimental mechanics unit enlisted support from all the groups in the heavy vehicle division.
The test required more than 50 channels of data in order to evaluate the performance of all the components. Accurate modeling required sampling rates up to 1,000 Hz. The internal memory required for data storage was formidable.
Just a few years ago, it would have been impractical to collect and process data on this scale, because the portable equipment available did not have the capacity or analysis capabilities needed to manage the information.
Meritor used the Series 2500 Field Computer System from SoMat Corp. of Champaign , Ill ., to monitor 16 data channels at sampling rates of 100 to 1,000 Hz. It also converted time history data into time-at-level histograms in real time.
Time histories wererequired, on an intermittent basis, on several channels that monitored accelerometers mounted on axles and other components to detect vibration . A history was required only of the short intervals when the components vibrated enough to cause possible fatigue damage.
Another 35 channels of information, including various temperatures and pressures, were sampled at a rate of once per second by a Campbell Scientific CR 7X computer.
Loads , Instruments, and Drives
Meritor 's vehicle was an instrumented test tractor and a 45-foot van trailer loaded to a gross vehicle weight of 78,440 lbs. The tractor was equipped with Meritor 145 series (3.73) ratio carriers, a Meritor nine-speed overdrive transmission, and a high-torque, low-rpm N1 4-460E Cummins engine that develops 460 horsepower at 1,700 rpm. T h e Cummins engine was also equipped with a Cummins C Brake that develops 454 hp at 2,100 rpm.
Goodwin's routes were plotted to represent the actual conditions, including some of the extremes, that customers face.
The first run, with the engine brake activated , covered 8,200 miles from Troy, Mich., to Salt Lake City, Portland, Sacramento, and Reno, then back to Salt Lake City and to Troy.
The second run was 4,981 miles, with the engine brake off, from Troy to Salt Lake City to Portland, with a return trip by the same route. The third run repeated the second route, with the engine brake on.
Engine brakes hydraulically control the exhaust valves to generate reverse torque, which can be as great as the maximum drive torque exerted by the engine. In recent years, the popularity of engine brakes has grown to the point where possibly more than half of the heavy-duty trucks on the road have them. In this test, Meritor engineers could precisely measure how an engine brake affects loading of the drivetrain .
The 6,232-mile fourth test run was performed using 145 series 2.80 ratio carriers and a Meritor 10-speed direct transmission instead of the 3.73 ratio carriers and nine- speed overdrive transmission that were used for the first three runs. This change was made to compare the engine torque and driveline torque of the two powertrain configurations. The fourth run included a trip from Salt Lake City south to Las Vegas, on to Bars tow, Calif., in the Mojave Desert, and then back to Salt Lake City. The side trip provided a chance to record the performance of components operating in ambient temperatures approaching 120°F.
The data generated during the day was stored in digital memory. An engineer along for the ride uploaded the data to a lap top at the middle and end of each test day. At the close of the day, files were compressed and transmitted by modem to Meritor's technical center in Troy.
Seen as Never Before
The test results provided Meritor engineers with an unprecedented look at their components over long hauls.
Drive axle and air chamber bracket accelerations were used to develop new lab shaker tests for brake components. These new tests provided a greater knowledge of loading conditions and made it possible to adapt designs to increase product life.
Driveline torque data was used to fine-tune Meritor's drivetrain fatigue life analysis software. The result was an improvement in the accuracy of the program, leading to reductions in cost and weight as well as improvements in durability.
The use of a channel to record clutch pedal displacement helped engineers improve their model for determining the number of clutch applications in a line-haul duty cycle. Meritor expects that this information will lead to improved durability of several clutch components.
This 24,000-mile, 51 -channel line-haul has already resulted in a series of product improvements, and the company expects many more in the years to come.