Early horsepower experiments in tractors

From its humble beginnings as a modified steam traction engine (in which an internal combustion engine was plopped on a simple frame), the tractor has been a never-ending experiment in the making. That experimentation continues today, as engineers finalize plans on one of the most significant changes in tractor design since the Charter tractor (one of the first tractors ever built) was created in 1889.

Soon, the autonomous tractor will be introduced to farmers, ushering in the age of the driverless robotic vehicle, minus a steering wheel, seat, and cab.

Eras of development

While the tractor has undergone continual experimental changes, general investigation into its design usually falls into three eras.

As mentioned, the first tractors were copycats of steam traction engines. Behemoths weighing multiple tons, these machines consisted of little more than a single-cylinder engine equipped with a massive flywheel, and a one-speed transmission attached to a channel iron frame sitting atop a set of rear-drive wheels and front steering wheels. Marked by the 1902 experimentation by McCormick in the lithe Auto-Mower, engineers began envisioning smaller machines, some of which used a single, front steering wheel.

The tricycle-type tractor wouldn’t become popular until the 1930s. But tractors went on a massive diet, thanks to the development of more powerful and compact four-cylinder engines.

Unit-frame design

Wallis Tractor Company pushed tractor design further in the early 1910s, experimenting with unit-frame construction. This approach, which all tractor builders adapted over time, employed a single-unit frame, with the engine mounted on top and the transmission attached to its rear. Introduced in the Wallis Cub, this advance not only trimmed tractor weight but also streamlined its manufacturing.

At this point, engineers began evaluating configurations, with a single rear-drive wheel and two front steering wheels; a single front drive wheel with two rear steering wheels; dual front-drive wheels and rear steering wheels; and other combinations.

Manufacturers, including John Deere, played with the concept of what was then called motor cultivators or motor plows, marking the continuous reduction in tractor size. The motor cultivator craze reached a peak in the late 1910s and disappeared by the early 1920s, replaced by the multiple-purpose tractor concept, introduced to farmers in the Farmall Regular in 1924.

Era of refinement

After the Farmall came on the market, configurations settled into four-wheel affairs. The exception was the increasing appearance of tracked tractors in agriculture, which found favor on steep hillsides and in softer soil conditions.

The next couple of decades were marked by refinements that improved tractor performance and longevity. Manufacturers began experimenting with a dizzying array of mechanical advances that included:

• replaceable wearing parts
• antifriction bearings
• carburetor manifolding
• advanced air cleaners
• force- and pressure-gun lubrication
• alloy and heat-treated steel
• pneumatic tires
• pushing horsepower

The multiple-purpose tractor continued to dominate design as farmers’ demand grew for a machine that could plow and cultivate. With the lifting of the Great Depression, they also demanded
more power.

Engine displacements grew exponentially, while their operating speeds rose. Transmissions expanded to include multiple gears in ranges designed to put more power to the ground. World War II slowed engineering advances. With its end came even more demand — not only for power but also for conveniences such as electric starting, lights, and cabs.

The gasoline engine, however, was maxed out when it came to power generation, which inspired engineers to investigate revolutionary engine technologies.

Oliver, which pioneered much of the early work in diesel engines on tractors, took a stab at pushing gas engine output in 1953. The Oliver XO-121 employed an engine featuring an amazing 12:1 compression ratio.

To reach those pressures, Oliver engineers modified a four-cylinder Hercules diesel, equipped with specially designed cylinder heads and pistons that nearly doubled the compression ratio of other gas engines. The motor burned a special high-octane fuel developed by the Ethyl Corporation.

The tractor generated an amazing 92% more horsepower and consumed 35% less gas compared with similar displacement gas engines. But the diesel offered great horsepower generation burning a cheaper fuel, so the XO-121 never went to market.

Turbines in tractors

Turbine technology, which had advanced greatly during the war, found a proponent in Ford, whose engineers attempted to build a turbine-powered tractor. Ford’s 1957 Typhoon hosted a “free piston” turbine that used two pistons; they slid back and forth within a single-cylinder combustion chamber. The pistons had no connecting rods to transfer power. Instead their purpose was to produce exhaust gases to spin the turbine. Double-reduction gears fed power to the power-shift transmission.

The engine never panned out, but the transmission reappeared two years later, when Ford introduced its Select-O-Speed, the world’s first power-shift transmission.

IHC engineers came as close as anyone to incorporating a turbine engine in a tractor. The 1961 HT340 put out an astonishing 80hp, but the power plant consumed too much fuel and was never marketed.

However, the tractor’s hydrostatic transmission found its way into future IHC equipment.

Sometimes, tractor experimentation was prophetic. Take the Allis-Chalmers 1959 fuel-cell tractor. Fuel-cell technology is now the rage in cars. Yet, more than 50 years ago, Allis researchers created a machine that churned out power using a mixture of gases (predominantly propane) to cause a chemical reaction in the fuel cells, generating electricity.

Unlike today’s hybrids, the Allis fuel cell was hulking, employing 1,008 individual fuel cells that contributed to the machine’s 5,270-pound bulk.

The tractor had an engine and transmission with no moving parts, generating twice the efficiency of a combustion engine, and “ran like a whisper.” Even so, the tractor was never marketed.