Because of the operating efficiencies that can be gained with a 6 x 2 tractor there is “tremendous interest” but little understanding about this type of vehicle configuration, says Matthew Stevenson, general manager, North American Field Operations & Marketing, Meritor.
Meritor is a leading global supplier of drivetrain, mobility, braking and aftermarket solutions for commercial vehicle and industrial markets
A 6x2 is a three-axle tractor equipped with a rear tandem axle that includes one drive axle and one non-driving axle.
Approximately 97 percent of the Class 8 market is made up of 6x4 tractors - a tandem configuration with two drive axles.
Although 6x2 tractors have been available for years, their volumes have been relatively low, Stevenson notes. Recently, however, there is increasing interest in this configuration due to potential fuel economy increases of up to as much as 4 percent or more.
This is possible because on a 6x2 tractor, the non-driving axle has no internal gearing to provide drive to the wheels of the axle. As a result, there is no internal friction or losses due to lubricant churning, which reduces parasitic losses in the drivetrain.
Moreover, a 6x2 configuration is typically between 300 and 400 pounds lighter than a 6x4 configuration.
The key concerns with 6x2s, according to Stevenson, are: traction, resale value, tire wear due to loss of traction and driver acceptance.
New axles
In March, Meritor introduced its FUELite tandem axle - the first member of its SoloDrive Series axles which features 6x2 tandem rear axles. This axle was designed for linehaul applications to maximize weight savings and increase fuel efficiency, usually in a direct drive and fast axle ratio configuration.
Also available is the FUELite ECAS (Electronically-Controlled Air Suspension from Meritor WABCO, a North American joint venture focused on the development and delivery of proven, integrated safety technology and efficiency components.
The ECAS is designed to improve a vehicle’s air suspension control system by electronically maintaining a set ride height between the axle and chassis 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.
ECAS offers automatic load transfer, significantly reducing drive axle wheel spin and traction control events during periods of aggressive acceleration. This feature addresses lower tractive effort of 6x2 vehicles versus 6x4, providing considerable improvement in traction on low friction surfaces to improve performance.
In development is Meritor’s new SmarTandem system which is designed to address simple 6x2 tandem traction deficiencies by actively managing suspension and differential lock, says Charles Allen, the company’s general manager - axles. Scheduled for limited release in 2013, the system will also reduce weight by 30 percent and reduce axle parasitic losses by 40 percent.
The SmarTandem axle will incorporate Meritor’s current European high efficiency 17X carrier technology with laser-welded ring gear and differential case to provide increased torque and efficiency, while electronic control technology will provide comparable tandem traction functionality by sensing operating conditions.
PDC
Another new product under development by Meritor is active oil lube level control facilitated by the company’s exclusive LogixDrive lube management smart technology.
Using a pneumatic control unit (PDC) family developed in-house, Allen says the PDC will measure speed, braking and engine torque to help manage lubrication and optimize axle efficiency.
Controlling the amount of lube in the axle based on operating conditions helps improve improving fuel economy because there is less churning of the lube and thus less drag,
Previewed in September 2010 in Europe, LogixDrive is expected to be introduced in North America in 2014.
Additionally, tire inflation systems, air suspension controls, lift-axle systems and driveline controls utilizing variants of the PCU will follow.
Meritor officials say these products can help balance loads, control trailer height and enhance traction, resulting in a safer, more efficient vehicle.
