In Canada, the industry is working together to popularize “enviroTrucks” that reduce fuel consumption and greenhouse gas emissions by utilizing the latest technologies. In the US, truck builders are focused on meeting new Environmental Protection Agency (EPA) regulations that address diesel engine emissions and idling times.
One way OEMs in the industry are building better trucks is by challenging suppliers to design components and sub-systems that reduce weight and improve fuel economy. When those suppliers can also provide products that lower cost, reduce inventory and simplify installation, partnering with them isn’t just good for the environment.
Threaded cup bearing
At Timken Company, a global friction management and power transmission solutions provider headquartered in Canton, Ohio, engineers are constantly looking for ways to improve overall system performance through smart bearing design. One of their recent innovations for trucking and off-highway pinion and differential shafts is the threaded cup bearing.
The threaded cup was originally designed to eliminate early service warranty problems occurring on heavy truck differential shafts when the originally-specified transition cup fits would come loose and turn, causing the housing to wear. The threaded cup design eliminates the turning cup, and its design also results in more benefits. It can improve fuel economy, reduce parts and inventory costs, and simplify differential shaft assembly.
“On differential shafts in the traditional bearing cup design, two standard-tapered single bearings are split-fit in the housing using threaded cup followers for bearing and gear mesh adjustment. The design also included separable locking devices with fasteners to prevent the followers from unthreading,” says Glenn Fahrni, principal application designer at Timken. “Because the differential shaft requires an adjustable cup, the cup fits must be originally-specified as partially loose in the housing. This causes the cups to eventually work themselves loose rotationally until they begin wearing on the cup adjuster and housing.”
To solve these problems, Timken integrated the threaded cup follower, tapered-single cup and rotational locking device into one component – the threaded cup assembly. The threads were moved from the old cup adjuster onto a portion of the cup outside diameter (OD).
“To provide an anti-rotational feature, we weld a low-carbon sheet metal ring to the carburized cup’s backface. Timken has been issued a patent for the threaded differential bearing cup”, Fahrni adds.
By combining the individual components of the traditional cup design into one, the threaded differential cup offers less complexity because there are fewer parts to inventory and handle during axle assembly. The result is easier and quicker assembly and less time spent adjusting the bearings and gear mesh.
Threaded cup designs also help OEMs reduce fuel consumption and maximize engine performance by creating less drag coming from the axles.
The threaded cup features Timken high-performance bearings, sometimes referred to as P900. These bearings feature ultra-clean steel, which reduces the risk of fatigue spalling and bearing failure. The bearings also have smoother surface finishes that improve lubricant film thickness, resulting in up to four times the predicted bearing life compared to standard finishes. The smoother surfaces also reduce friction, contributing to improved fuel economy.
Special internal bearing profiles also spread the load more evenly across the bearing contact surfaces, keeping contact stress to acceptable levels.
Mr. Fahrni further observes: “By combining clean steel, smoother surface finishes and special raceway profiles, we’ve been able to integrate several traditional components into the threaded cup bearing, making it capable of handling heavier loads without making the bearing bigger or heavier. It’s what we call power density – increasing the bearing capacity-to-weight ratio, so that a smaller bearing can carry a greater load.”
Since the integrated threaded cup weighs less than the traditional design, and also diminishes the overall housing width needed to support it, axle weight is saved. The overall weight savings help contribute to fuel economy and reduced engine emissions.
Reducing assembly time
Currently, Timken engineers are investigating the usage of a threaded cup bearing on the pinion shaft.
He says: “On the pinion shaft, to correctly adjust the traditional pinion bearings the axle OEM has to keep anywhere from 40 to 55 different sizes of a variable length cone spacer at their assembly station. How the pinion head and tail bearing tolerances stack up determines which spacer size is used.”
According to Mr. Fahrni, rolling torque is used as the bearing setting measurement method, and the tight-fitted cones are clamped through the spacer with a nut tightened to a very high clamp torque. If the wrong spacer size is initially used, you have to teardown the pinion shaft and rebuild with another spacer size.
