Building in Safety

Ferguson’s ingenious 3-point hitch used traction to put an end to tractor flip-overs.

| December 2020

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Harry Ferguson and Henry Ford in Dearborn, Mich., during the famous “handshake agreement.”

The 3-point hitch: What’s the big deal? That is a question that might be raised by younger readers who can’t envision a farm tractor without a 3-point hitch. About 100 years ago, though, integration of the tractor and implement was a new idea. It was also about 100 years ago that the first tractor flipped over backward when its plow struck an immoveable object.

It is just a matter of physics. Engine torque and flywheel inertia multiplied by the overall gear ratio means that, if the drive wheels are held stationary, torque on the axle will be enough to rotate the entire tractor backward around the axle. Of course, if the tractor was designed so that its drive axle was in front (front wheel-drive) this would not happen, but that configuration, while good for automobiles, is obviously not so good for tractors.

Continuing with the matters of tractor physics, the force of the tractor applied to the implement is called draft load, or simply draft. The way draft is reflected from the implement (whether it’s a plow or a wagon) to the tractor, and vice versa, can be expressed as a vector, known as the line of draft. If the line of draft passes below the center of the rear axle, it tends to pull down on the entire tractor, increasing traction. When traction reaches the point where there is no slippage of the rear tires, then the front end begins to rise. And that is where the 3-point hitch comes in.



Entrepreneur-turned-inventor

As civilization developed, animal power was adopted on a massive scale to pull plows, rakes, disks, wagons, and buggies. Then, at the turn of the 20th century, the new mechanical “horsepower” arrived on the scene, to be hitched to plows and implements in the same manner as it had been with the horse. One form of motive power was substituted for another. When a horse plow struck a rock or some other immovable object, it simply stopped. When the same thing happened to a tractor-drawn plow, engine torque and flywheel inertia flipped the body of the tractor around the rear axle in rapid fashion.

Harry-ferguson
Harry Ferguson.



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