All Volvos use a full powershift, direct-drive transmission designed to maximize fuel efficiency and eliminate surging or wind-up associated with torque converter drivetrains as the load on the grader comes on and off. In addition to the standard eight-speed forward/four-speed reverse transmission, the company offers a version with 11 forward and six reverse speeds. This has several advantages.
"It provides for slower ground speeds in fine grading applications, faster travel speeds and exceptional fuel efficiency in every gear, since the engine can be operated in the most economical RPM range in every application," says Brian Lowe, Volvo Construction Equipment.
Obviously, fuel efficiency is a primary concern. "The rate that fuel is consumed is a function of many factors," says Lowe. "Apart from the load, most influential is the engine speed. Selecting a lower engine speed and raising the gear can yield significant improvements in fuel economy, while allowing the operator to get the job done to spec and on time."
For its larger grader, LeeBoy uses a six-speed powershift transmission, which Lee indicates is better suited for long grading pulls or road work. But its two smaller models use hydrostatic drive for better speed and direction control when grading in confined areas.
Champion graders all use hydrostatic drive. "You are basically limitless in your speed-to-rpm ratio and can adapt your grader to any condition," explains Abernathy. "With powershift, you are limited to just how slow you can go and still have power to work. Also, the part count in a hydrostatic pump is a fourth of the count in a powershift transmission. The pumps are also very inexpensive compared to powershift."
Keep it tight
When fine grading, precise control is crucial. "Precise control of the motor grader extends beyond the actual levers the operators use to position the moldboard," says Lowe. "All of the systems and design elements must work in concert in order for the operator to be most productive and be able to produce an accurate finish grade."
For Alpine Services, everything revolves around precision. The majority of its projects require extremely tight tolerances. "For the National Hockey League, we are
+/- 1/16th measured over 304 ft., or we don't get paid," says Teates. "All of the fields we have done for the NFL are +/- 1/8th over 400 ft."
These tolerances require a tight machine. "Champions are very easy to keep tight because they are made with that in mind," says Teates. "You can adjust and shim out."
The older Blade-Mor unit takes a little more effort. This grader is used a lot due to its small size. "We rebuild that one every two to three years. We simply take it to a machine shop and re-machine everything. We actually redo the entire bushing," Teates explains. "There is nothing original on it."
According to Porter, a motor grader must have the ability to keep the drawbar, circle and moldboard extremely tight - removing any type of unwanted movement - in order to allow the operator to maintain the tightest grades.
For example, Caterpillar uses a shimless moldboard retention system and top-adjust drawbar wear strips. "The patented top-adjust wear strips dramatically reduce drawbar/circle adjustment time. By removing access plates on top of the drawbar, shims and wear strips can easily be added or replaced," Porter points out. "The unique shimless moldboard retention system reduces the potential for blade chatter. Vertical and horizontal adjusting screws keep the moldboard's wear strips aligned for precise blade control and dramatic reductions in service time."
Benefits of AWD
When working to tight tolerances, speed can also be an issue. Being able to run at virtually a crawl is sometimes an advantage.
For example, on Volvo's all-wheel-drive (AWD) models, there is a Creep mode where only the hydrostatic front wheels drive for precise fine grading control. "The operator can easily control his starts and stops via the foot throttle. He can attain a top speed of 2.5 mph and maximum aggression in Creep mode at 1,600 rpm," says Lowe. Volvo set the 1,600-rpm limit, since this is above peak engine torque and running the engine any faster just wastes fuel.
Likewise, the Hydrostatic mode on Caterpillar AWD graders disengages the transmission and provides hydraulic power to the front wheels only. "The ground speed is infinitely variable between 0 to 8 km/h (0 to 5 mph), perfect for precise finish work," says Porter.