Continuing improvements in transmission design, the emergence of new transmission technology, and the importance of improved lubricating fluids to support performance and durability – these are all crucial elements in the field of off-highway transmission design. These were the key messages delivered by the webcast, Designing Off-Highway Drivetrains to Meet End User Demands, part of the 2013 Global Powertrain Virtual Summit co-hosted by SAE and Lubrizol in December last year. Contributing to the webcast were experts from John Deere, Dana, and Lubrizol. Read the article below to see what they had to say or click here to see the webcast.
The webcast was opened by Paul Meyer, responsible for tractor drivetrain and hydraulic engineering at John Deere, who explained how feedback revealed that reliability, durability, operating costs, fuel economy, and performance are all priorities for John Deere customers. “Transmission design can have a huge influence on fuel economy, so we need to continually look at ways to optimize the efficiency of the drivetrain,” he said, adding that the operating characteristics of the drivetrain can influence performance. Ease of use of the transmission control systems is also rated highly by customers. The combination of performance and avoiding downtime has a major effect on increasing yield and return for the customer.
Agricultural tractor transmissions now have greater demands upon them than ever before. “In EU markets, transport speeds can be as high as 50 km/h,” explained Meyer. However, a transmission must also be capable of achieving slow speed through an IVT or high-reduction design when used off-highway, during harvesting for example. The transmission must also withstand high loads when a vehicle is used for primary tillage such as plowing.
“We need to support a high number of global applications and duty cycles for our global customer base,” said Meyer. “Future design goes beyond hardware; we can influence productivity and fuel economy through design and drive strategy.” Increased gains can be made in the future with further electronic control and system integration of the powertrain. Meyer cited the example of a new 23-speed powershift transmission designed for two large tractor platforms, which can operate in three different modes. Automation will also improve performance and efficiency, he said.
In the future, Meyer expects even more sophisticated off-highway transmissions to emerge, with productivity and fuel consumption being the main focus. “There will continue to be a place for the IVT and powershift transmission,” he maintained, “but there will also be increased electrification and more advanced control features. High power density will be offset by advancements in materials, heat treatment technology, and manufacturing processes.”
Meyer concluded by saying that simulation and modeling will play an even greater part in future transmission design and stressed the importance of considering the complete tractor and implement system when designing transmissions.
Rob Smithson, responsible for powertrain innovations engineering at Dana Limited, revealed details of a new continuously variable planetary transmission that is scalable and could be adapted for off-highway applications. The VariGlide Continuously Variable Planetary (CVP) resembles a large ball race, where each ball revolves on an axle and on its own axis, the angle of which can be varied. Angling in one direction provides a low ratio and in the other, a high ratio. When the axles are leveled, the ratio is 1:1. The transmission follows the same principle as a conventional planetary transmission, except that none of the “gears” have teeth.
There is a “sun” at the center surrounded by the balls, which form the planets. There are two outermost rings, one providing input from the engine and the other, output. A thin layer of traction fluid transmits torque between the components and there is no metal-to-metal contact. “The ratio change is quick, at just 350 milliseconds,” said Smithson, “and the system provides the same power path flexibility as a conventional planetary.”
No fewer than 100,000 VariGlide transmissions have been built so far for bicycle and e-bike applications and the design is subject to 600 US and international patents. “We have carried out a total of 67,000 hours durability testing and analysis so far,” revealed Smithson. Larger scale versions include one for a medium-sized agricultural tractor, with two planetary sets and 63 mm balls. “The CVP is the only variator technology with true planetary characteristics,” explained Smithson, who claims it matches the functionality of a hydrostatic transmission, with cost on a par with a hydrodynamic drive, to improve both productivity and fuel economy.
Fuel economy, durability, and performance formed the basis for the final presentation by Lubrizol Driveline off-highway project manager, Simon May. May outlined the major role lubricating fluids play in improving fuel economy and reducing cost of ownership through providing better protection for equipment. He explained to the webinar audience that lubricating fluids consist of three main components: The primary or underlying fluid, usually a refined petroleum fraction or a selected synthetic material, into which additives are blended to produce finished lubricants., A measure of a fluid's resistance to flow. A fluid with a higher viscosity flows less easily. modifiers, and an additive package containing The resistance to motion of one object over another. Friction depends on the smoothness of the contacting surfaces, as well as the force with which they are pressed together. modifiers, detergents, inhibitors to protect copper parts, and emulsifiers to keep water droplets in suspension. Viscosity modifiers improve the flow at low temperatures and provide increased viscosity at higher temperatures. “Balance is the key,” said May. “All these components compete against each other and too much of one will affect the others.”
Significant market drivers for improving lubricants include the need to increase productivity and reduce cost of ownership, with the latter encompassing durability, reduced downtime and fuel consumption, all of which demand more effective lubricating fluids. “Equipment is more powerful so at the same engine speed, torque has massively increased. This puts more strain on gears, bearings, and the fluid. Drain intervals are increasing, so fluid must last longer while coping with that extra power,” May explained.
Today, the use of superior base oils and advanced additives improves thermal stability and extends fluid life. Modern hydraulic systems place additional demands on fluid, which must withstand extreme pressures without breaking down. However great the challenge, May is confident fluids can continue to be improved with increased shear stability and longer fluid life. Lower viscosity fluids capable of delivering the same level of protection while reducing internal losses have been introduced in on-highway vehicles and, according to May, a reduction in off-highway fluid viscosity is also possible.
To conclude the webcast, presenters answered questions from audience members. Asked about the efficiency of the Dana Mechanical IVT system, Rob Smithson said it was significantly better than hydromechanical and hydrostatic transmissions, with no heat issues. Once the efficiency gains had been quantified, he said, the system could be scaled up toward even larger applications.
Paul Meyer of John Deere predicted that tractor horsepower would continue to rise in North America, bringing with it an increase in implement size and operating speeds. All of these trends would bring a demand for increased power density in off-highway transmissions. In the cost-competitive markets of China and India, by contrast, Meyer said that the outlook in the medium term would be one of continuing simplicity, with baseline transmissions remaining dominant for a long time.
Questioned on future trends for off-highway lubricant viscosity, Lubrizol’s Simon May said that with SAE 30 fluids now commonplace and the market focusing on the 11 to 12 centistokes area, moving to 7.5 to 8 cS was “unlikely to be a problem” for future fluids. When asked about the main difference between tractor and axle fluids, May cited the frictional responses needed to make tractor wet brakes operate smoothly, and also the need for water compatibility in tractor applications, where water ingress is much more likely.