BLOG: On The Level

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Many manufacturers offer a variety of linkage options for wheel loaders, but have you ever wondered why?  The answer is simple – there are different solutions for different needs.  Let's have a look at a couple of your options.

The traditional Z-bar, nicknamed for the Z shape of the tilt cylinder, lever, and link layout, is generally the most popular option.  Z-bars have the least amount of pins, links and levers to maintain.  They pull the work tool tight to the front tires, and work off the larger, head-end area of the tilt cylinder to deliver high breakout forces. The motion of the linkage is excellent for bucket work as it racks back through the first half of the lift range and starts to dump out near max lift, resulting in an efficient truck loading motion.

For pure bucket work, a Z-bar is an excellent choice, but for material handling, such as fork work, the traditional Z-bar presents some challenges.

I would argue that there are three core requirements to be a good material handler: 1) good visibility to the coupler and work tool (fork tips); 2) predictable parallel lift throughout the lift range with less than 10 degrees of tool pitch variation; and 3) hydraulic tilt forces that exceed machine lift and tip up limits so loads can safely be manipulated throughout the entire lift range. 

The traditional Z-bar falls short of the mark on all three metrics, with poor coupler and fork tip visibility, approximately 25 degrees of tool pitch variation throughout the lift range, and a loss of approximately 60 percent of its hydraulic tilt force near maximum lift. For these reasons, most manufacturers offer a second linkage option, often advertised as a "tool carrier", to meet material handling needs.

Tool carrier linkage designs vary considerably across manufacturers, but in general are more complex with more pins, links, levers and tilt cylinders.  As a result, tool carriers are often more expensive to purchase and maintain than traditional Z-bars, and deliver on the three core material handling requirements in varying degrees.  Examples of tool carriers include Caterpillar’s "IT" or "VersaLink", Volvo's "Torque Parallel", John Deere's "Powerllel", and Case's "XT" linkages.  The right linkage choice for you depends heavily on your application needs...there are plenty of choices.

Caterpillar's new "Optimized Z-bar" eliminates the need to make a linkage choice as it delivers the values of a traditional Z-bar along with the three core material handling requirements. The Optimized Z-bar is standard on the new Cat® Small Wheel Loaders—924K, 930K and 938K.  This new linkage truly combines the best characteristics of all the linkage designs into one.  For more information, please click here http://www.cat.com/equipment/wheel-loaders/small-wheel-loaders .

About the blogger – Joel Grimes is the Small Wheel Loader Product and Application Specialist working as a Marketing Engineer for Caterpillar. His exposure to heavy equipment began at childhood when working on his family's farm. His experience was bolstered by the Mechanical Engineering Degree he received from Ohio State University. His experience in both engineering and marketing at Caterpillar has allowed him to deliver Small Wheel Loader solutions from concept to customer.  

We want to hear from you.  Which linkage option is right for your job?