1. Field of the Invention
The invention relates to a disc harrow farm implement. The disc harrow has a frame with an attached disc gang comprising a plurality of ground engaging discs attached to a gang shaft. In particular, the present invention relates to a novel linkage arrangement for attaching the disc gang to the frame.
2. Description of the Prior Art
The disc harrow is a farm implement that is used to turn and mix soil. The disc harrow includes a frame that is towed behind a tractor with a plurality of earth working disc shaped blades, or discs that engage the ground. Each disc is normally concave and the center of each disc has an aperture for mounting the disc on a gang shaft. A plurality of substantially parallel discs mounted to the shaft at uniformly spaced apart intervals along its length is referred to as a disc gang. Each disc gang is attached to the frame by means of mounts downwardly depending from the frame at suitable intervals along the length of the shaft. Each mount includes a bearing at its lowermost end for receiving the gang shaft to permit rotation thereof. In operation, the frame is lowered, typically by means of hydraulic cylinders powered by a hydraulic pump on the tractor, in order that the discs engage the soil, thereby causing the shaft to rotate in response to forward movement of the tractor. The circumference of each disc is sharpened to allow the disc to cut through any residual plant material from the previous crop remaining on the surface of the soil. Each gang is generally attached at an angle to the direction of travel of the tractor and, due to the concavity of the discs, turns and mixes the soil as it is pulled through the field. Disc harrows may accordingly be used as primary tillage implements or as seedbed-finishing machines.
Due to the weight of the frame, the discs may penetrate the ground by a depth of several inches. Impact of the discs with a sub-terranean obstacle, such as a rock, causes the entire implement to be lifted out of the soil in order to pass over the obstacle and can cause damage to the implement. Types of damage include broken or bent discs, bent or broken gang shafts and bearing failures due to twisting or asymmetric loading of the gang shaft.
In an attempt to reduce this type of damage, a flexible rearward facing C-shaped mount, typically made of spring steel, may be used to permit the gang to upwardly deflect in response to impact with an obstacle. Since the mount must be sufficiently stiff to resist deflection of the gang during normal operation, the C-shaped mount is quite stiff and does not easily deflect. Due to its stiffness, the C-shaped mount is prone to breakage when a particularly large obstacle is encountered. Also, the amount of force required to cause deflection is not readily adjustable and the mount provides very little range of vertical motion for the disc gang. Accordingly, the C-shaped mount has proven relatively ineffective at preventing damage to the implement.
Another type of flexible mount includes a pair of structural support members connected by a coil spring, as shown in U.S. Pat. No. 4,333,535. The first structural support member has an upper end rigidly attached to the frame and downwardly extends therefrom to its lower end. The lower end is pivotally attached to an upper end of the second structural support member, which has a bearing integrally formed within its lower end for receiving the gang shaft. The coil spring connects the first and second members and is normally compressed therebetween by means of a yoke that maintains an acute angle between the first and second members. The second member is allowed to vertically pivot in response to impact of the disc gang with obstacles, and the pivoting movement is resisted by compression of the spring. The amount of compression of the spring in the normal position may be changed by adjusting the yoke to thereby pre-set the amount of impact force required to cause vertical movement of the gang. This mount mechanism permits a greater amount of vertical travel than the C-shaped mount and may be readily adjusted to permit the gang to deflect upon impact.
The coil spring mount functions well to permit vertical deflection of one end of the gang shaft, causing the shaft to adopt an angled orientation with respect to the ground when riding over an obstacle. Since the bearing is fixed with respect to the second structural support member and pivots in the same vertical plane, the angled orientation of the shaft places an asymmetric load on the bearing, leading to premature bearing wear and excessive bearing maintenance. A need therefore exists to solve the problem of excessive bearing maintenance in coil spring mounted disc gangs.
This invention seeks to overcome the aforementioned problem of excessive bearing maintenance in coil spring mounted disc gangs.
According to the present invention, there is provided a disc harrow comprising a frame, a disc gang, and a support assembly for supporting the disc from the frame. The disc gang has a gang shaft adapted for vertical movement with reference to the frame having a plurality of ground engaging discs centrally mounted on the shaft. The support assembly comprises a first structural member, a second structural member, and a resilient means. The first structural member has an upper end and a lower end, the upper end attached to the frame and the lower end remote from the frame. The second structural member has a first end portion and a second end portion. The first end portion is pivotally attached to the lower end of the first structural member. The second end portion has bearing means for rotatably supporting the gang shaft. The resilient means has an upper and lower end, the upper end pivotally attached to the upper end of the first structural member and the lower end pivotally attached to the second structural member. The second structural member is operable to vertically pivot and the resilient means is operable to resist the pivotal movement. The second end portion is rotatably connected to the first end portion by rotational means to permit the second end portion to rotate with reference to the first end portion about the longitudinal axis of the second structural member in response to the pivotal movement of the second structural member and corresponding vertical movement of the gang shaft.
Further features of the invention will be described or will become apparent in the course of the following detailed description.