The first purpose-built, self-propelled wheel grader was the Auto Patrol, introduced by Caterpillar in 1931. This machine embodied several major design breakthroughs. Rather than adapting a grader to a separate wheeled or crawler tractor, the grader and power unit have been designed as a complete, integral unit, rolling on a common frame on pneumatic tires with puncture-proof inner tubes.
Compared to a motorized patrol, the driving position and the engine were essentially exchanged. The engine was at the very rear of the machine and the operator was positioned at the top of the frame, midway between the blade and the rear tires. It had a clear view of the blade, while the location of the engine reduced its exposure to dirt and put more weight on the drive axle, resulting in more reliable operation and better balance. The powertrain was designed specifically to propel the grader with the greatest possible traction, blade pressure and stability. In addition, the weight and positioning on the powertrain frame served to distribute the weight over the front and rear axles and the blade, and the weights of the operator compartment, the power control mechanism and the blade and circle assembly have been designed to produce maximum blade. pressure, traction and resistance to lateral thrust.
The Auto Patrol was the first motor grader to use motorized blade controls, eliminating handwheels and cranks and allowing small adjustments to be made faster. The controls were operated by a series of levers: one to raise and lower each end of the blade, one to move the circle sideways, and one to turn the circle. A fifth lever raised and lowered the scarifier or a front v-plow. A shaft drive transmitted power from the flywheel to the central case via worm gears and a vertical shaft, bypassing the flywheel clutch and allowing the controls to be used whenever the engine was running. Inside the box, two sets of gears distributed power to the levers, which transmitted power to the moving parts through sliding-shoe clutches, universal joints, and telescoping shafts. The clutches disengaged at the limit of work piece movement and the control levers returned to neutral when not in use.
The circle was rolled from angle steel, welded and machined into a true circle, and a length of high carbon steel was riveted around its front half to provide reinforcement. A set of screw clamps with locknuts prevented vertical play and loss of motion while allowing the circle to rotate freely, and another set below the circle prevented side play. The circle was turned by a motorized, self-locking worm gear with a brake that held the circle against back pressure caused by heavy loads on the blade. Although the circle and blade assembly was designed not to move under a heavy load, a crossbar could be unbolted to allow the assembly to float more freely when working under a light load at higher speed. Auger-driven sideshift allowed the grader to carve shoulders, and blade-tip extensions further increased its reach.
The positioning of the blade along the length of the machine was determined by finding a balance, so to speak, between the actions of the front and rear wheels. The further away from the front axle, the less vertical motion was imparted to the blade when the front wheels rolled over rough ground. The further away you went from the rear axle, the less chance there was of the drive tires being forced out of the ground by downward pressure on the blade. Similarly, the wheelbase length was optimal between a longer length to produce a smooth blade action while minimizing the effect of road surface roughness, and a shorter length to provide a radius shorter turning.
Despite all its innovations, Auto Patrol #9 was discontinued a year after its introduction. Although grader design has evolved considerably since 1931, the basic concepts of the Auto Patrol are the standard for today’s graders.
About the HCEA
The Historical Construction Equipment Association (HCEA) is a 501(c)3 nonprofit organization dedicated to preserving the history of the construction, dredging, and surface mining industries. With over 3,800 members in 25 countries, our activities include publishing a quarterly educational magazine, Equipment Echoes, from which this article is adapted; operation of the National Construction Equipment Museum and Archives in Bowling Green, Ohio; and hosting an annual working exhibition of restored construction equipment. Our next international convention and antique equipment expo will be held September 23-25, 2022 at the National Construction Equipment Museum in Bowling Green, Ohio. The HCEA is raising funds for the construction of a new purpose-built building to house its collection of equipment, and the Convention will feature a first for it. Individual HCEA annual memberships are $35 in the United States and Canada, and $55 elsewhere. We seek to develop relationships in the equipment manufacturing industry and offer a college scholarship for engineering and construction management students. Information is available at www.hcea.netor by calling 419.352.5616 or by sending an email [email protected].