Able to move tons of earth for landscaping, industrial sites and construction jobs, Bobcat® loaders have been a mini-workhorse for more than 40 years. Throughout the years, Bobcat Company has introduced a number of models and modifications to offer increased power and enhanced performance. One such product is the skid-steer loader, which is known for the ability to stop and turn 360 degrees in place, allowing operation in tight, confined spaces. To further this performance, Bobcat was working on a breakthrough concept that would improve maneuverability and steering efficiency of its loaders.
To turn the idea into reality, Bobcat needed speed and wheel position sensors. To accomplish this task, Bobcat turned to Torrington for its experience in sensor technology. The Torrington and Bobcat sensing solutions allowed for one of the most important breakthroughs in loaders since the invention of skid-steer -- all-wheel steering.
“We were well aware of Timken’s success with sensor technology both in automotive and other applications,” said Jason Osborn, design engineer at Bobcat. “We simply called and asked if they thought they could design a magnetic sensor that would work cost-effectively within the tough internal environment of the Bobcat steering assembly. The rest is history.”
The Bobcat Challenge
Bobcat’s idea for a new steering concept seemed simple enough in theory: implement four independently steerable wheels. The Bobcat engineering team wanted a non-contact sensor designed for long life and reliability that could measure steering angles with extreme accuracy in a system of changing tolerances.
Working together, Bobcat and Timken engineers delivered a major design innovation with non-contact sensors embedded into the kingpin of each Bobcat wheel assembly. The result is a sensor system packaged within the kingpin.
The success of Timken’s sensor technology comes from the use of magnets and Hall effect technology to feed information from each wheel to determine the angle of the wheel. Hall effect is based on the principle that a magnetic field influences the level of voltage within a metal conductor. By introducing a sensor and magnet directly into the wheel system, the direction and strength of the magnetic field are measured at all times to identify the precise position of each wheel. With this information, the steering system can provide reliable wheel-angle feedback.
Timken also designed speed sensors for another rugged Bobcat offering, the Toolcat™ 5600 utility work machine. The speed sensors monitor the rate of motion of a multi-pole ring magnet that rotates on the front and rear axles using a custom encoder ASIC sensor chip. As the wheels turn, the sensor detects the multiple north and south poles within this ring magnet, reading and communicating the speed to the steering system. The steering system uses this information to control the turning rate of the wheels.
The non-contact magnetic sensors and encoder ASIC are capable of producing high-resolution signals comparable to those of larger and less robust contact sensors and optical encoders. In addition, its compact dimensions and ruggedness enable it to function in applications where space limitations previously had made sensing impossible and where harsh environments like high temperatures, oil, dirt, grease and water could damage optical sensors, cause false readings in optical and contact sensors and threaten the effectiveness of angular position sensors. Along with increased durability and precision, the new sensors require no external electronic components to operate. This innovative system dramatically improves the steering and overall performance of both Bobcat vehicles, making them more productive and even easier to operate.
“The engineers at Bobcat brought these challenges to the table and we responded,” said John Santos, Timken team leader for intelligent products and systems. “Our customers have ever-increasing needs for electronic sensing capabilities and we have a proven track record of providing solutions to our customers that make sense for them. In turn, their success is our success.”
Putting the Design to Work
Timken angle and speed sensors are used in the Toolcat 5600 as well as the Bobcat A300 all-wheel steer (AWS) loader. This A-series was the first of its kind to offer dual selectable steering modes. The sensors are critical to enable the system to accomplish AWS and skid-steer maneuverability at the flip of a switch.
In skid-steer mode, each side works independently from one another, allowing the loader to counter-rotate for maximum maneuverability. Alternatively, AWS mode enables each wheel to work independently for precise steering coordination of all four wheels. This allows the inside tires to turn at sharper angles and slower speed than the outside tires. When the right and left sides work together in this fashion, increased tire life results because it is not sliding tires on asphalt and other hard surfaces. This same tire saving motion enables the machine to be gentle on grass and other surfaces where minimal ground disturbance is preferred. Turning in AWS is also smoother, providing the operator enhanced comfort and minimized spillage of loose materials.
“Since 1958, our skid-steer loaders have helped change the way the world works,” Osborn said. “We’re proud that we’ve been able to continue improving our products’ performance. Now, by incorporating Timkens’s sensor technology, we’ve taken efficient operation to the next level.”
Each AWS loader uses six sensors, two speed and four wheel angle sensors. While the angle sensor provides precise steering information from the coordinated action of all four wheels, the speed sensors are used to optimize the proper ratio of the wheel speeds to turn the loader. The AWS loader’s speed sensors monitor the speed of the wheels on the left and right, where the speed sensors on the Toolcat 5600 are used to monitor the speed on the front and rear wheels.
With the integration of Torrington and Timken resources, the company is able to provide Bobcat with steering columns, tapered roller bearings, ball bearings, cam followers, needle bearings, precision assemblies and bushings.
“The expertise we bring to the table, continues to grow and strengthen our relationship with Bobcat,” said Brad Baldwin, Timken regional sales engineer. “The success of our sensors have opened additional doors, making us more than a product provider, but rather a solution provider for Bobcat.”
(All photos couresy of Bobcat)