This invention relates generally to agricultural machines and, in particular, to a primary drive line and coupling for agricultural implements.
Farm tractors have a power-take-off (pto) shaft which delivers power to implements such as mower conditioners by utilizing a primary drive line consisting of a telescoping shaft with a universal joint at each end. One of the universal joints is connected to the pto shaft of the tractor while the other universal joint is connected to an input shaft on the implement. A drawbar on the tractor is pivotally connected to a tongue on the implement by a hitch pin. During operation, it is often necessary to maneuver the implement by turning the tractor from side to side. This results in the primary drive line, which delivers power from the tractor to the implement, being disposed at a first joint angle relative to the tractor pto shaft and at a second joint angle relative to the implement input shaft. If the difference between these joint angles is too great, torsional vibration will be transmitted through the primary drive line from the tractor to the implement.
U.S. Pat. No. 3,557,892 to Burrough discloses an equal angle hitch designed to maintain the primary drive line at equal joint angles with respect to the tractor pto and the implement input shaft. The equal angle hitch consists of an extension which is mounted on the tractor drawbar in order to locate the hitch pin pivotally connecting the tractor drawbar and the implement tongue at an equal distance from (i.e. exactly halfway between) the universal joints at the ends of the primary drive line. Even when the equal angle hitch of the Burrough patent is used, it is difficult to maintain equal joint angles.
Swivel hitches such as disclosed in U.S. Pat. No. 4,738,461 to Stephenson et al have been designed to overcome the difficulty encountered with the equal angle hitch of the Burrough patent. The Stephenson et al swivel hitch consists of two right angle gear boxes coupled together. One of the gear boxes is connected to the tractor pto shaft while the other gear box is connected to the implement input shaft. Although swivel hitches are vibration free, they have a disadvantage in that they are expensive.