IMPROVEMENTS IN THRESHING MECHANISMS

Abstract: A threshing mechanism comprises a threshing drum and downstream thereof a set of straw walkers, wherein the total width of the straw walkers is substantially equal along the full length of the straw walkers, and wherein the said set consists of eight individual straw walkers mounted on a pair of spaced apart crankshafts.

Description: Improvements in Threshing Mechanisms Field of the Invention This invention relates to threshing mechanisms, and particularly to threshing mechanisms comprising a threshing drum and straw walkers downstream of the drum. Background to the Invention Harvesting machines, known as combine harvesters, comprising threshing mechanisms are widely used to gather and process cereal and other crops harvested for their seed. The threshing mechanisms found in combine harvesters fall broadly into two categories, namely those using a threshing drum followed by a group of straw walkers (often referred to as a "conventional threshing mechanism") and those without straw walkers, which simply rely on one or more threshing drums (often referred to as a "rotary threshing mechanism"). Whilst for certain crops in certain conditions rotary threshing mechanisms are more efficient than conventional threshing mechanisms, in certain crops and conditions rotary threshing mechanisms can be much less efficient than conventional threshing mechanisms. Therefore, in regions where numerous different combinable crops are grown, or where varying harvesting conditions can be encountered combine harvesters having conventional threshing mechanisms are much in demand. One of the factors limiting the output of a conventional threshing mechanism is the capacity of the straw walkers. If the amount of straw and grain exiting the drum on to the straw walkers is too great, the grain is not separated from the straw and exits the straw walkers in the straw, and hence is lost. Although a low level of grain loss is inevitable, efforts must be made to keep this to a minimum. Most threshing mechanisms comprise five or six straw walkers across the width of the machine, a six straw walker system being wider than a five straw walker system. In order to increase the capacity of the straw walkers it has been proposed to provide two banks of straw walkers, the second bank comprising a greater number of straw walkers and being wider than the first. In practice there is a first bank of six straw walkers behind the threshing drum and a second bank of eight straw walkers down stream of the first bank. Whilst convention would suggest increasing the overall width of the straw walkers when increasing the number thereof, i.e. the width of an individual straw walker remains the same, this results in either the first or second bank of straw walkers working inefficiently, because for a given volume of straw leaving the threshing drum, the depth of straw on the straw walkers, and hence the efficiency of the straw walkers depends on the overall width of the straw walkers. The invention seeks to provide a more efficient straw walker system which does not suffer from the drawbacks associated with the above described system. According to the invention, there is provided a threshing mechanism as defined in the claims hereto. Brief Description of the Drawings In the drawings, which illustrate preferred embodiments of a threshing mechanism according to the invention: Figure 1 is schematic representation of a combine harvester comprising a threshing mechanism according to the invention; Figure 2 is a side view of a threshing mechanism according to the invention; Figure 3 a shows an end view of a threshing mechanism of the prior art, illustrating the straw walkers thereof; and Figure 3b shows an end view of a threshing mechanism according to the invention illustrating the straw walkers thereof. Detailed Description of the Drawings Referring now to Figure 1, there is shown a combine harvester 1, comprising wheels 2, an operator's cab 3, a header 4 including a reel 5, an elevator 6 which delivers harvested crop to the threshing mechanism of the combine harvester. The threshing mechanism generally indicated by the reference numeral 7 includes a threshing drum 8, a rotary separator 9, and a straw walker assembly 10. The straw walker assembly 10 will be described in greater detail with reference to Figures 2 and 3. Referring now to Figures 2 and 3, the threshing mechanism 7 includes a straw walker assembly 10, which comprises eight straw walkers, each being mounted on spaced apart crankshafts 11, one crankshaft being arranged towards the front of the straw walkers and the other towards the rear of the straw walkers. Each straw walker 12 comprises saw toothed sections 13. The saw toothed sections have two functions, first to allow grain trapped in the straw to escape to be collected, and second to move the straw towards the rear of the combine harvester. As can be seen from Figure 1, the straw exiting the straw walkers is distributed onto to the field. The individual saw toothed sections may have different numbers of teeth, may be inclined at different angles, or be of differing lengths. Turning now to Figures 3 a, the threshing mechanism of the prior art is based on a six straw walker system. The straw mat "A" travelling along the straw walkers is loosened by relative movement between adjacent straw walkers, which gives rise to a tearing action on the straw mat at the points where the mat is supported by the saw teeth of the straw walkers. The straw walkers are mounted on a crank shaft 8' and are arranged at equal angular separation around the crank shaft, and such that adjacent straw walkers exert a tearing action on the straw mat "A" through 120 degrees of rotation of the crank shaft. In the eight straw walker system of the invention illustrated in Figure 3b, the straw walkers are mounted on the crankshaft 8, by means of bearings 13, at equal angular separation, such that adjacent straw walkers exert a tearing action on the straw mat "A" through 135 degrees of rotation of the crank shaft. Increasing the angle through which adjacent straw walkers exert a tearing action on the straw mat increases the distance over which adjacent straw walkers exert a tearing action on the straw mat "B", thereby increasing the separating effect of the straw walkers on the straw mat "B". Furthermore, whereas a six straw walker system provides five points at which the straw walkers exert a tearing action on the straw mat, an eight straw walker configuration produces seven points at which the straw walkers exert a tearing action on the straw mat. Hence, the propensity of a threshing mechanism comprising eight straw walkers to tear the straw mat, and hence release seed trapped therein is greater than a threshing mechanism comprising six straw walkers. However, another factor which determines the efficiency of the straw walkers is the space available between the saw toothed members, since it is through this space that the released seed must fall. Prior art combines using eight straw walker configurations address this problem by using individual straw walkers of the same width as the individual straw walkers used in a five or six straw walker threshing mechanism. Surprisingly, it has been found that when eight straw walkers are fitted in the space conventionally occupied by six straw walkers the capacity of the straw walkers is increased by in the region of 33%., in spite of the width of each individual straw walker being reduced by 25%. This surprising effect gives rise to other benefits compared to the prior art machine using a combination of six and eight straw walkers. First, only two crankshafts are required, whereas the prior art machine requires four crank shafts, two crank shafts for each bank of straw walkers. Second, all the straw walkers perform their function efficiently, since the straw mat is fed onto the walkers such that the mat is the correct depth for the straw walkers, whereas in the prior art example, the depth of straw mat is either correct for the first bank of six straw walkers, resulting in the second bank of straw walkers working under capacity, or it is the correct depth for the second bank of straw walkers and too deep for the first bank of six straw walkers, in which case the first bank of straw walkers serves only to feed the straw mat from the threshing drum on to the second bank of straw walkers. Hence, the threshing mechanism of the invention, comprising eight straw walkers provides significant improvements vis-a-vis prior art threshing mechanisms comprising six straw walkers or a combination of six and eight straw walkers, both in terms of efficiency of threshing and construction.

Claims: Claims 1. A threshing mechanism comprising a threshing drum and downstream thereof a set of straw walkers, wherein the total width of the straw walkers is substantially equal along the full length of the straw walkers, and wherein the said set consists of eight individual straw walkers mounted on a pair of spaced apart crankshafts. 2. A threshing mechanism according to Claim 1, wherein the total width of the straw walkers is substantially equal to the width of the threshing drum. 3. A threshing mechanism according to Claim 1 or 2, wherein the phase angle between adjacent straw walkers is substantially equal 4. A threshing mechanism according to Claim 3, wherein the phase angle between adjacent straw walkers is substantially 135 degrees. 5. A threshing mechanism according to any preceding claim, wherein the crankshafts on which the said straw walkers are mounted are arranged such that upon rotation thereof adjacent straw walkers generate a tearing action on straw supported thereon through 135 degrees of rotation. 6. A combine harvester comprising a threshing mechanism as claimed in any preceding claim. 7. A threshing mechanism substantially as described with reference to, or as shown in, Figures 2 and 3b of the drawings. 8. A combine harvester substantially as described with reference to, or as shown in, Figure 1 of the drawings.

Inventors: HOEG JANS ANKER FRIIS, JULSGAARD JENS, HOEG, JANS, ANKER, FRIIS, JULSGAARD, JENS
Applicants: DRONNINGBORG IND AS, HOEG JANS ANKER FRIIS, JULSGAARD JENS, DRONNINGBORG INDUSTRIES A/S, HOEG, JANS, ANKER, FRIIS, JULSGAARD, JENS
Application year: 2001
Main classification: A01F
IPC codes: A01F12