Issue link: https://read.dmtmag.com/i/95785
MAINTENANCE MATTERS Get A Lift F Electronic Air Suspension Comes to North American Market or the last several decades, the default configuration for OTR truck tractors in North America has been a three-axle unit with one steer axle and tandem drive axles. This configuration is known by industry insiders as a 6x4, denoting six wheel ends with four of the six powered. The key reason for having two axles at the back of the tractor is to meet the legal weight restrictions imposed on each of a truck's axles. Before gearing and tire technology reached its current state, it was also beneficial to spread a truck's power across a greater number of wheel ends, so virtually all tandem axle configura- tions offered for tractors featured driving power on both axles. As engine horsepower and torque ratings reached a plateau that is likely to extend well into the foreseeable future, the technology behind tires and axle gearing caught up to the point where getting power to the ground can usually be accomplished through a single drive axle, in all but the most extreme weight, grade and horsepower scenarios. While the newer drivetrain technology enables removing the drive function from one of the rear axles, weight carrying capacity still requires two axles at the back of the tractor, even if one isn't powered. This configuration is referred to as a 6x2, six total wheel ends on the tractor, with only two powered. There are two major benefits to using a 6x2 configuration. The larger benefit is weight reduction, about 400 pounds in most cases, due to the lack of a differential and axle shafts in the rear-most axle. The lesser, though still important benefit is a reduction in friction loads on the drivetrain. Every rotating part of the drivetrain adds some parasitic friction 40// OWNER OPERATOR // OCTOBER 2012 load, so eliminating a whole bunch of drive- train components can measurably improve fuel economy. The one downside to a 6x2 configuration is that even with a locking differential or electronic traction control employed on the single drive axle, there are certain situations in which weight transfer to the unpowered rear axle of the tandem pair can reduce the traction at the driven axle. Long popular in Europe, fuel economy concerns are driving increased interest in the 6x2 configuration in North America. Meritor WABCO, long-known for integrated safety systems in the commercial vehicle industry, recently announced the debut of its Electronically Controlled Air Suspen- sion (ECAS) for the North American market. More than 3 million WABCO ECAS systems have been sold worldwide and the company is adapting the product to meet the growing interest in North America. The ECAS system offers automatic load transfer, significantly reducing drive axle wheel spin during aggressive acceleration. This addresses lower traction of 6x2 vehicles compared to 6x4 configurations, providing considerable improvement in traction on low friction surfaces. ECAS also improves air suspension control by electronically maintaining a set ride-height as road and vehicle characteristics change. The pressure control of the air springs is only adjusted when there is a change in the load, so normal axle vibration during driving does not cause height adjustment or consume air. Reduced air consumption decreases the compressor duty cycle, resulting in improved fuel economy. OO By Tom Kelley