Conventional agricultural planters include a tow behind material dispensing implement that deposits planting material, such as seed and fertilizer, onto a furrowed farmland or similar planting surface. The implement may consist of multiple dispensing units that are supported by a common or shared frame that is towed by a tractor or similar vehicle. The dispensing units, commonly referred to as row units, for some planters may be grouped into two sets—a left side set and a right side set. Each of these sets may be independently controlled, which allows the operator to selectively dispense material from either of the left and right side units or both.
Each dispensing unit is associated with a material hopper and includes a material metering system that regulates the flow of material from the associated material hopper. The amount of material that is deposited is generally a function of the rotational speed of the seed meter. The rotational speed is transmitted from a transmission assembly that includes a friction or drive wheel that is maintained in frictional engagement with a carrying wheel. A planter will typically include at least two carrying wheels that collectively support the planter above the planting surface. For material to be deposited, the drive wheel and the carrying wheel must be engaged with one another.
The dispensing units of a planter can be separated into multiple sets, with each set associated with a respective friction drive. The transmissions can be separately controlled using electric clutches. Thus, when the transmissions are both engaged, all the dispensing units are allowed to deposit material onto the planting surface. When one or both of the transmissions are disengaged, the respective dispensing units will not deposit material onto the planting surface. This effectively allows the operator sectional on/off control during the planting or fertilizing process.
The rotational speed set by the transmissions controls how much material is deposited. Generally, if no rotation is transmitted by a transmission, i.e., from a disengaged transmission, the dispensing units associated therewith will not dispense any material. As noted above, an electric clutch can be used to disengage a transmission, but is also possible for no torque to be transmitted even when the transmission is engaged. During wet or muddy conditions, the carrying wheel may slip. Similarly, when the carrying wheel engages an obstruction and is momentarily suspended above the planting surface, no rotation is transmitted by the transmission. For rotation to be transmitted, the drive wheel must be rotated. Thus, when the carrying wheel is slipping, rotation is not passed through to the metering system resulting in no material being deposited. Conventional friction ground drive planters have used springs mounted to the frame to pull the drive wheels down into frictional engagement with the carrying wheels. Since the pull strength of the springs is constant, the degree of frictional engagement, if any, cannot be varied. As a result, there is very little flexibility in adjusting to match the operating conditions and torque generated by the seed meters. For example, during ideal operation conditions, less frictional engagement may be tolerated as the operator may not be expecting the carrying wheel to slip. For normal operation, the carrying wheel must overcome the bias placed thereon by the drive wheel to rotate and propel the planter forward. If the bias is set for less than ideal operating conditions however, more work is required for the towing vehicle to pull the planter. On the other hand, if the bias is set for ideal conditions, it may be difficult to plant or fertilize effectively during non-ideal conditions, such as wet or otherwise muddy conditions.
Additionally, the amount of torque required to drive the material metering systems is not universal for all seeds and granular fertilizers. For example, for some planters, more torque may be required for dispensing cotton seed than corn seed.