(under the class definition) Apparatus comprising an earth working element and a propelling device therefor, such as a tractor, the connection between the earth working element and its propelling device being such that (1) the earth working element tends to sink lower into the earth from a median working position when the draft force necessary to propel the element decreases and tends to raise out of the earth when the draft force increases or (2) the earth working element tends to move up and down from a median position relative to its propelling device as its propelling device pitches down and up, respectively, over uneven ground so as to maintain an approximately constant depth in the ground, (3) the earth working element tends to rise from a median position when the downward component or suck of the soil pressure increases and tends to sink from a median position when the downward component or suck of the soil pressure decreases or (4) the earth working element tends to move up from a median position as it approaches or is in a rise of ground and tends to move
down from a median position as it approaches or is in a depression in the ground.
(1) Note. This subclass is intended to provide for linkages or the like which are automatic in action but wholly mechanical so as not to fit the definition of the "Automatic" subclasses. An earth working element which is simply spring-pressed downwardly or which is merely pivoted at a forward point may be analyzable as coming under this definition, but such devices are not so classified. The devices under the definition comprise linkages or equivalent mechanism of greater complexity especially intended to function as stated in the definition. For example, a trailing implement connected to a tractor by a simple hitch including a spring so that the earth working tool is raised or lowered as the spring is stressed due to changes in draft load is classified in subclass 238 or subclass 678.
(2) Note. Apparatus classified under this definition is sometimes known as constant draft or constant depth apparatus.
(3) Note. Apparatus including gauge wheels connected by linkages to the propelling means to perform the functions set out in the definition are included.
(4) Note. Merely holding an earth working element down against a tendency to rise out of the ground is not included. Such devices are classified according to the structure claimed.
SEE OR SEARCH THIS CLASS, SUBCLASS: 2+, for automatically operated power control devices especially subclasses 7+ for automatically operated power control devices responsive to changes in draft load.
238, for ground wheels moved vertically with respect to the running gear by means of the draft force (usually for lifting the earth working element for transport).
261+, for earth working elements which shift on occurrence of an overload.
678, for spring-biased hitches.
779, for a scraper whose position is automatically controlled by a linkage for leveling.
811+, for a scraper positioned in front of a motor vehicle and maintained in a horizontal position as the ground supports of the vehicle move over irregular terrain so that the vehicle tilts sidewise.
SEE OR SEARCH CLASS
280, Land Vehicles,
446.1+, for articulated vehicles with a hitch responsive to change in draft load, there being no disclosure of an earth working element being the cause of the change in draft load.
