HEADER FLOTATION SYSTEM FOR AN AGRICULTURAL MACHINE

Abstract: A harvester is provided comprising : - a mobile base unit (12) adapted for movement over the ground, - a transversely extending crop harvesting header (20) supported from the base unit (12) for allowing pivotal movement about a generally fore-and-aft axis of the machine, and - a lateral flotation system (57) for pivoting the header (20) about the generally fore-and-aft axis and including . a hydraulic actuator (60) extending between the header (20) and the base unit (12) and operable to position the header (20) in a nominal position prior to starting flotation operation, and . energy storage means (69) connected to the actuator (60). The energy storage means (69) is pressurized at a pressure greater than the pressure in the actuator (60) and is arranged to operate on pivotal movement of the header (20) in one direction and to be inoperative on pivotal movement of the header (20) in the opposite direction, whereby, when the header (20) pivots in said one direction, the actuator (60) retracts so that the energy storage means (69) stores the energy created by the flow of hydraulic fluid out of the actuator (60) and then releases that energy to restore the header (20) to its nominal position when the header (20) is free to move, and whereby when the header (20) pivots in said other direction the energy storage means (69) allows the header (20) so to pivot and return to the nominal position.

Description: The invention relates to a flotation system for a header of an agricultural machine and although it will be discussed primarily in relation to combine harvesters, it is to be understood that it is applicable to any other type of agricultural machine which employs a header, such as a forage harvester, for example. Combine harvesters, particularly the self-propelled type, are equipped to utilise a variety of crop-gathering headers, including headers specifically designed for harvesting corn, cereal grains or soy beans, for example. Normally, these headers are attached to the forward end of a feeder housing which is a structure used to convey crop material from the header to a base unit of the combine harvester for further harvesting treatment. As is shown in U.S. Reissue Patent No. 26,512, the forward end of the feeder housing can be constructed so that the header can be quickly and easily attached thereto. Usually, the feeder housing structure is rectangular in cross section and includes a rectangular crop inlet opening at the forward end which matches with a crop outlet opening of a header attached to the feeder housing. With the modern trend of developing headers of increasingly larger sizes, providing a ready capability for the headers to follow the contours of the ground is vital. One type of prior art levelling or flotation mechanism, such as disclosed in U.S. -A-3,981,125, involves the twisting of the feeder housing structure about the generally fore-­ and-aft extending centreline thereof to effect an associated lateral floating movement of the header. Also hillside combine harvesters have been developed to allow the header to follow slopes of up to 45%. Such hillside combine harvesters have been known to utilise a side pivot mechanism, as disclosed in U.S. -A- 3,731,470, or a centre-mounted pivot connection directly between the header and the feeder housing as disclosed in US. 2.780.903; the latter arrangement involving a specific circular or semi-circular opening between the feeder housing and the header. Problems that have been encountered with these prior art lateral float mechanisms include a difficult sealing situation between the feeder housing and the base unit as the feeder housing is twisted relative to the base unit. The twisting of the feeder housing also results in a twisting of the feeder housing drive mechanism, which in turn also increases wear and reduces the life of the drive chains or the like. Another problem encountered is the matching of different types of headers to different feeder housing structures. This problem is particularly relevant to feeder housings having specially shaped crop inlet openings. In other known header flotation systems use is made of one or two hydraulic actuators connected between the header and the base unit of a machine to pivot the header in a transverse direction around a generaly fore-and-aft pivot axis and which are interconnected hydraulically with a header weight compensation device including control actuators together with a hydro-pneumatic accumulator which effect raising and lowering of the header. In operation, the hydraulic system, inclusive the hydro-pneumatic accumulator is pressurized at a operating pressure such that the ground contact pressure of the header is minimal. This allows the header to follow the irregularities in the ground contour by as well raising or lowering the complete header as by pivoting the header in the transverse direction depending on the size of the irregularities and on the location thereof relative to the header. With headers having a weight imbalance, such as grain headers having the drive means located at one side, a single flotation actuator can be used at the side of the drive means, but with balanced headers, two flotation actuators are used, one at or towards each side of the header. In still another known header flotation system such as disclosed in US. 3.386.235, the header is formed in two parts which can pivot independently from each other and relative to the feeder housing around respective fore-and-aft extending pivot axes. These parts also can be raised or lowered in unison together with the feeder housing upon which they are mounted, around a transverse pivot axis. A hydraulic suspension system, including cylinders supporting the feeder housing with the header thereon on the base unit and further cylinders supporting the header portions on the feeder housing, is coupled to a hydraulic control mechanism which is actuated by variations in hydraulic pressure in the respective cylinders in response to corresponding movements of the header, respectively the constituent portions thereof over undulations in the ground. The arrangement is such that said variations in pressure transmitted to the control mechanism cause the control mechanism to allow hydraulic pressure fluid to flow to or from the respective cylinders so as to compensate for said variations and tend to maintain a substantially constant hydraulic pressure in the respective cylinders. Hydro-pneumatic accumulators, operating at the system pressure, are coupled to the various cylinders for assisting in a smooth following of the ground irregularities by the header and the constituent portions thereof. With the latter two systems, the header must always be in contact with the ground at least at some point along its length so that these headers cannot be set to operate at a given stubble height, for example, which is a disadvantage. This is not so with an automatic header height and lateral flotation control system such as disclosed in the co-pending European patent application no. 86.200.600 and which uses sensors on the underside of the header. Such sensors produce electrical signals for controlling the flotation actuators via electro-­ hydraulic valves, thus making the system automatic. However, other disadvantages arise with such automatic systems, the main one of which is that they are slow acting. Furthermore, these systems are expensive and the sensors thereof can suffer damage when the header encounters a large obstruction and the header tilting is too slow to clear this obstruction smoothly. The slow-acting nature of such automatic systems also can place excessive torsional forces on the header and front end of the machine to which it is fitted (for example the feeder housing of a combine harvester) when the header tilts on meeting an irregularity in the ground and until the system has responded and effected the required flotation to compensate. Although an automatic system can operate with the header off the ground because it is not part of a header weight compensation system, it cannot be set to give any desired initial position of the header which deviates from the nominal position of the header because the electro-hydraulic control valves for the flotation actuators can only be set through the sensors. According to the present invention, a harvester is provided comprising : - a mobile base unit adapted for movement over the ground, - a transversely extending crop harvesting header supported from the base unit for allowing pivotal movement about a generally fore-and-­ aft axis of the machine, and - a lateral flotation system for pivoting the header about the generally fore-and-aft axis and including . a hydraulic actuator extending between the header and the base unit and operable to position the header in a nominal position prior to starting flotation operation, and . energy storage means connected to the actuator. This harvester is characterized in that the energy storage means is pressurised at a pressure greater than the working pressure which is present in the actuator when the header is in its nominal position and meets no obstruction whereby the energy storage means becomes operative upon pivotal movement of the header in one direction and becomes inoperative upon pivotal movement of the header in the opposite direction when the header meets an obstruction causing the one or other of said pivotal movements; the arrangement being such that, when the header pivots in said one direction, the actuator retracts so that the energy storage means stores the energy created by the flow of hydraulic fluid out of the actuator and then releases that energy to restore the header to its nominal position when the header is free to move, and, when the header pivots in said other direction the energy storage means allows the header so to pivot and return to the nominal position. The energy storage means may be a hydro-pneumatic accumulator and valve means may be provided in association with the actuator in order to be able to adjust the nominal working position of the header. If the header to which the flotation system is fitted is balanced, then resilient return means, such as a spring for example, may be provided to return the header to its nominal position. A self-propelled combine harvester incorporating the present invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which :- Figure 1 is a front elevational view of the self-propelled combine harvester having a grain header attached thereto, with certain components broken away, Figure 2 is a cross-sectional view of the forward portion of the combine harvester including the header and feeder housing, taken along the line II-II of Figure 1, Figure 3 is a side elevational view, to a larger scale, of the forward portion of the feeder housing, and Figure 4 is a hydraulic circuit diagram of the header flotation system in accordance with the invention. Figure 5 is a view similar to Figure 4 but showing an alternative arrangement. Referring to Figures 1 and 3 of the drawings, left hand and right-hand references are used as a matter of convenience and are determined by standing at the rear of the machine and facing the forward direction of travel. The combine harvester is generally indicated at 10 and comprises a base unit 12, including crop-treating means (not shown) for separating the desired crop material from the waste crop material, a detachable crop-gathering header 20 located forwardly of the base unit 12, a cab 14 elevated above the header 20 for full view of the crop harvesting process, wheels 16, and a feeder housing 30 for conveying cut crop material from the header 20 rearwardly to the base unit 12 for treatment by the crop-treating means which, for example, can be a conventional threshing unit or the more recently developed rotary type axial flow threshing unit. Referring now to the cross-sectional view of Figure 2, a more detailed view of the general inner workings of the header 20 and the feeder housing 30 can be seen. The header 20 includes a cutterbar 22 operable to sever crop material from the stubble. A reel 24 is disposed above and forwardly of the cutter bar 22 to sweep crop material over the latter and transport it rearwardly to crop consolidating means 26 in the form of a consolidating auger 27. The consolidating auger 27 converges crop material towards a centrally disposed crop discharge opening for discharge to the feeder housing structure 30. A frame 28 of the header 20 includes a transversely disposed main header beam 29 used to support the header 20 from the feeder housing 30. As can also be seen in Figure 2, the feeder housing 30 has a forwardly extending, elongated body portion 32 defined by a rearward end 33 pivotally attached to the base unit 12 and a forward end 34 adjacent the header 20 for connection thereto. The body portion 32 includes a passageway 36 therethrough, terminating in a crop inlet opening at the forward end 34, for allowing crop material to be transported rearwardly from the forward end 34 to the rearward end 33. Crop conveying means 40 in the form of an endless chain and slat apron conveyor 41 is positioned within the passageway 36 and is operable to transport the crop material rearwardly. The apron conveyor 41 is driven by a drive shaft 43 positioned at the rearward end 33 and is supported on a driven shaft 44 adjacent the forward end 34. The height of the header 20 relative to the ground is controlled by a header lift means in the form of a pair of hydraulic actuators 48 interconnecting the feeder housing 30 and the base unit 12. By extending the actuators 48 the rearward end 33 of the feeder housing 30 is pivoted about the drive shaft 43 whereby the header 20 is lifted from the ground without significantly changing the discharge point of the apron conveyor 41 relative to the base unit 12. These hydraulic actuators 48 may be part either of an automatic header height control mechanism of any type known in the art or of a header weight compensation mechanism equally known in the art. Referring now to Figure 3, an enlarged view of the forward end 34 of the feeder housing 30 showing a front face member 50 and a detached header 20 in phanton proximate thereto, can be seen. The front face member 50 includes an offset section 53 substantially registrable with the main header beam 29 for detachably supporting the header 20 in an operable position on a cradle 58 still to be described hereafter. A lateral flotation system 57 for the header is best seen in Figure 3 and comprises the cradle 58 already mentioned and which is pivotally attached to the front face member 50 at the forward end 34 of the feeder housing 30 by a pivot pin 59. The cradle 58 comprises a nesting portion 64 for the main header beam 29 at a position generally within the offset section 53 of the front member 50. The components so far described are similar to those of the combine harvester illustrated in US-A-4,253,295 to which reference is made and which discloses further details of construction which are not relevant to the present invention. In accordance with the present invention, the flotation mechanism 57 further comprises a hydraulic actuator 60 which, in the preferred embodiment, is of the single acting type and the rod 61 of which is pivotally attached to the cradle 58 by a pin 62 extending between a pair of lugs 63 depending from the nesting portion 64 of the cradle 58 which releasably receives the main header beam 29. The cylinder 65 of the actuator 60 is pivotally attached by a pin 66 to a bracket 67 fixed to, and extending rearwardly from the front face member 50 of the feeder housing 30 at the forward end 34 thereof and against which the lower portion of the cradle 58 is movably supported. The header 20 is firmly coupled to the cradle 58 for being transversely pivotable therewith after the main beam 29 of the header 20 is positioned in the nesting portion 64 of the cradle 58. The actuator 60 is thus effectively connected between the main body 12 of the machine and the header 20, the actuator 60 being disposed at the side of the feeder housing 30 corresponding to the side of the header 20 at which the header drive is fitted, i.e. at the side of the imbalance. As can best be seen in Figure 4, the actuator 60 is connected hydraulically via a restrictor 68 to an energy storage device in the form of an accumulator 69 (mounted below the cab 14) and also connected, via a restrictor 71, to a three-position spool valve 72 to which is connected a hydraulic pump 73 for the system and a connection to tank 74. In the central position of the valve 72 (the position illustrated) the pump 73 is vented directly to the tank 74 and the actuator 60 is only connected to the accumulator 69. If the valve spool is moved to the right as seen in Figure 4, the actuator 60 is vented to the tank 74 and if it is moved to the left, the actuator is subjected to system pressure from the pump 73. It should be noted that, under normal operating conditions, the pressure in the accumulator 69 is higher than that in the actuator 60. Preferably this difference is in the range of 10 bar. It also should be noted that the flotation system thus described is totally independent from the header lifting system although it may be used in combination with an automatic header height control mechanism. It even may be used in combination with a header weight compensation mechanism although the combination with an automatic header height control mechanism is preferred. In operation of the machine and provided the hydraulic actuators 48 are not part of a header weight compensation mechanism, the feeder 30 can be set at any required height relative to the ground, including at a height whereat the header 20 makes contact with the ground, by operating the actuators 48 accordingly. In the event the hydraulic actuators 48 are part of a header weight compensation mechanism, the header 20 then of course should be positioned to contact the ground surface. Additionally and prior to commencing operation, the operator also actuates the valve 72 to pressurize the hydraulic flotation circuitry normally so as to position the header 20 in its nominal or level position relative to the base unit 12. By doing so, an operating pressure is established in the actuator 60 which is sufficient to pivot the header 20 away from its rest position towards the intermediate nominal position and thus, which compensates the header imbalance. Indeed, without this pressurizing, the header 20 is positioned in an inclined position with the rod 61 fully retracted within the cylinder 65 of the actuator 60 and with the end of the header 20 supporting the header drive means (i.e. the end of the header 20 at which the imbalance is situated) being situated at a level below the other end due to the header imbalance. As already mentioned, the operating pressure thus established in the actuator 60 is less than the gas pressure in the hydro-pneumatic accumulator 69 whereby the above described initial setting of the header does not vary the gas volume in the accumulator 69 which thus fills the entire accumulator body. Once the operating position of the header 20 has been set, the machine moves forwardly and commences harvesting in the conventional manner. Should the header 20 meet a transverse irregularity in the ground, which may be a temporary transversely offset obstruction or a transverse slope, for example, then one side of the header will rise and the opposite side will drop in view of the pivotal mounting of the cradle 58 about the pivot 59 so as to permit the header 20 to move over and clear said irregularity. Assuming this pivotal movement of the header 20 is such as to move the rod 61 of the actuator 60 into the cylinder 65 (i.e. the actuator 60 contracts) the fluid thus forced out of the cylinder is forced into the accumulator 69 and increases the pressure therein as the connection to the tank 74 is blocked by the central valve position. If the irregularity is only temporary, then when it is cleared by the header 20, the latter will pivot back to its former (nominal) position under the pressure of the accumulator 69, which is sufficient to overcome any frictional resistance in the pivotal mounting of the header. The gas in the accumulator expands until it fills the accumulator volume completely again and thus until all pressure fluid, which previously was urged into the accumulator by the irregularity, is urged back to the flotation actuator 60. Thus, the header 20 always is returned to the same nominal position as initially set by the operator when the header 20 has cleared the obstruction. Should the header 20 pivot in the opposite direction, the actuator 60 is extended as the rod 61 is pulled out of the cylinder 65 and a partial vacuum is created therein (a breather valve may be fitted if desired in this respect). This vacuum is created because the accumulator 69 is unable because of its nominal setting to urge more hydraulic pressure fluid into the actuator 60 to the extent that the gas in the accumulator 69 already occupies the entire volume of the accumulator 69. When the header 20 is free to return to its former position, it does so under the weight imbalance of the header in the illustrated embodiment, this weight imbalance equally being sufficient to overcome any frictional resistance in the pivotal mounting of the header 20, whereby also starting from this side of the nominal position, the header always is returned to its nominal setting when the ground surface beneath the header permits this. From what precedes, it will be understood that the hydro-­ pneumatic accumulator 69 as used in the present invention on the one hand and the header imbalance on the other hand effectively act as "power sources" for always returning, without any hesitation, the header 20 back to the same nominal position previously set by the operator when the ground surface below the header 20 permits this to happen, i.e. when any irregularities in the ground have been cleared by the header. These returning forces are sufficiently large to overcome any frictional resistance in the pivotal mounting of the header which inherently is present and which, in prior art arrangements also using a hydro-pneumatic accumulator, prevent the header to return to the nominal position when the deviation from said nominal position is rather small. Unlike in these prior art arrangements where the hydro-­ pneumatic accumulator has a working pressure which corresponds to the working pressure of the flotation actuator and thus acts mainly to absorb hydraulic pressure fluid urged out of the flotation actuator without substantially varying the working pressure and whereby it becomes a rather "passive" component, the hydro-pneumatic accumulator according to the present invention, is rather "active" in the header flotation operation to the extent that it truely forms a power source in the sense as already described which is operable to always return the header to the same nominal position even when the deviation therefrom is minimal. If the operator wishes to set the header 20 at an angle to the nominal horizontal position, he operates the valve 72 to one side or other of the central position so as to pressurise or vent the actuator 60 to give the desired header tilt perhaps to compensate for a permanent irregularity in the field being harvested. When this control of the header 20 is being exercised, the restricter 71 damps header movement so that the latter is controlled. Also restrictor 68 has a stabilizing function as will be readily understood by any one skilled in the art. In the preferred embodiment as described above, the header is of the type having an imbalance due to the header drive means being provided adjacent one end thereof; this imbalance being used for providing header flotation in one direction. However, the principles of the present invention also can be applied to a fully balanced header (such as e.g. a corn header). In this case the header imbalance may be replaced by a spring force provided by spring means extending between the cradle 58 and the feeder housing 30 at the side of the latter opposite to the side at which the actuator 60 is provided. These spring means are arranged to pivot the cradle 58 with the header 20 thereon in the direction around the pivot 59 so as to retract the rod 61 into the cylinder 65 of the actuator 60. In a further alternative embodiment shown in Fig. 5 the return force acting on the flotation actuator 60 is obtained by a hydraulic coupling of the flotation actuator 60 to the header lifting actuators 48 below the plungers thereof. In this case, the flotation actuator 48 is of the double acting type and is coupled at its plunger rod side to the header lifting actuators 48; the other side of the flotation actuator 48 being coupled to the hydro-pneumatic accumulator 69 and the valve 72 in the same manner as described in connection with Fig. 4. The pressure reigning in the header lifting actuators 48 when the header is in the operative position, is communicated to the plunger rod side of the flotation actuator 60 where it causes a return force oriented opposite to the flotation force resulting from the pressure below the plunger thereof and which acts in the same manner as the imbalance of the preferred embodiment and as the resilient return force of the spring means of the first alternative embodiment. The arrangement again is such that the work pressure below the plunger of the flotation actuator is less than the gas pressure in the accumulator 69. It will be appreciated that this alternative arrangement operates in the same manner as the preferred embodiment and that therefore a detailed description of the operation is not necessary. Finally, the hydraulic coupling between the flotation actuator 60 and the header lifting actuators 48 may comprise a two-position spool valve 80 for enabling the operator either to establish the coupling as described in case the harvester is equipped with a balanced header, or to interrupt this coupling in case the harvester is equipped with an unbalanced header, in which case the header imbalance provides the return force as described in connection with Fig. 3. It will be seen that the present invention provides a very simple but highly effective header flotation system which suffers none of the disadvantages of known systems in that both the operating height and orientation can be set without difficulty. This means that the header can still be operated in a weight compensation mode if desired. This also means that, if the header is set to operate at a height above the ground and thus, if there is no permanent contact of the header with the ground, the header nevertheless always returns to the same nominal position previously set by the operator after the header having cleared an obstruction. This would not be the case in prior art arrangements equipped with a hydro-pneumatic accumulator; this accumulator in these arrangements not providing enough power to overcome frictional resistance in the pivotal mounting of the header when the deviation from the nominal position is minimal. Furthermore, the system is very fast acting, whereby peak loads and high torsional forces on the header and/or front end of the machine to which it is fitted are avoided. This, in turn results in a structure which is less subject to damages and is carefree. Also, the flotation system is very simple in design as well as in operation and is inexpensive to manufacture.

Claims: 1. A harvester comprising : - a mobile base unit (12) adapted for movement over the ground; - a transversely extending crop harvesting header (20) supported from the base unit (12) for allowing pivotal movement about a generally fore-and-aft axis of the machine, and - a lateral flotation system (57) for pivoting the header (20) about the generally fore-and-aft axis and including . a hydraulic actuator (60) extending between the header (20) and the base unit (12) and operable to position the header (20) in a nominal position prior to starting flotation operation, and . energy storage means (69) connected to the actuator (60); characterized in that the energy storage means (69) is pressurized at a pressure greater than the working pressure which is present in the actuator (60) when the header (20) is in its nominal position and meets no obstruction whereby the energy storage means (69) becomes operative upon pivotal movement of the header (20) in one direction and becomes inoperative upon pivotal movement of the header (20) in the opposite direction when the header (20) meets an obstruction causing the one or other of said pivotal movements; the arrangement being such that, when the header (20) pivots in said one direction, the actuator (60) retracts so that the energy storage means (69) stores the energy created by the flow of hydraulic fluid out of the actuator (60) and then releases that energy to restore the header (20) to its nominal position when the header (20) is free to move, and, when the header (20) pivots in said other direction the energy storage means (69) allows the header (20) so to pivot and return to the nominal position. 2. A harvester according to claim 1, characterized in that the energy storage means is a hydro-pneumatic accumulator (69). 3. A harvester according to claim 2 characterized in that, when the header (20) is in its nominal position and meets no obstruction, the gas in the hydro-pneumatic accumulator (69) occupies the entire volume of said accumulator (69). 4. A harvester according to claim 2 or 3 characterized in that when the header (20) is temporarily displaced in the one direction as a result of meeting an obstruction, the gas in the hydro-­ pneumatic accumulator (69) is compressed to store energy which subsequently is released back to the actuator (60) upon the header (20) clearing the obstruction, and when the header (20) is temporarily displaced in the other direction as a result of meeting an obstruction, the gas volume in the hydro-pneumatic accumulator (69) does not vary whereby the accumulator (69) remains inoperative under this condition. 5. A harvester according to any one of the claims 2 to 4 characterized in that, when the header (20) is temporarily displaced in the other direction as a result of meeting an obstruction, this displacement creates a vacuum in the flotation actuator (60). 6. A harvester according to any one of the preceding claims, characterized in that the energy storage means (69) are pressurized at a pressure which exceeds the working pressure in the flotation actuator (60) with a value in the range of 10 bar. 7. A harvester according to any one of the preceding claims characterized in that the lateral flotation system (57) further also comprises a hydraulic pump (73) and an associated reservoir (74) which are coupled to the actuator (60) and the energy storage means (69) via a valve (72); the valve (72) being operable : - in one position to connect the pump (73) to the actuator (60) and the energy storage means (69) and to isolate the reservoir (74) for establishing the working pressure in the actuator (60); - in another position to isolate the actuator (60) and the energy storage means (69) from the pump (73) and the associated reservoir (74) for maintaining the lateral flotation system (57) in the operative condition; and - in still another position to connect the actuator (60) and the energy storage means (69) to the reservoir (74) for draining the working pressure from the actuator (60). 8. A harvester according to claim 7, characterized in that, during flotation operation of the lateral flotation system (57), the actuator (60) and the energy storage means (69) are isolated from the pump (73) and the associated reservoir (74). 9. A harvester according to claim 7 or 8 characterized in that the header (20) is pivotally movable between two extreme positions and has an inoperative rest position coinciding with one extreme position and its nominal position situated between said extreme positions; the header (20), during operation, continuously being subjected to a return force urging said header (20) towards the inoperative rest position and being pivotable toward the nominal position upon actuation of the valve (72) in the one position for establishing the working pressure in the actuator (60). 10. A harvester according to claim 9, characterized in that, when the header (20) is in its nominal position and meets no obstruction, the return force equals the force exerted by the working pressure in the actuator (60) whereby an equilibrium is obtained irrespective of the pressure in the energy storage means (69) being higher than said working pressure. 11. A harvester according to claim 9 or 10, characterized in that the actuator (60) is of the single-acting type and the return force is exerted by a weight imbalance of the header; the return of the header (20) to the nominal position in the direction of the return force, following a temporary displacement from said nominal position in the opposite direction as a result of the header (20) having contacted an obstruction, being effected by said return force upon the clearing of the obstruction by the header (20), and the return of the header (20) to the nominal position in the direction opposite to the return force, following a temporary displacement from said nominal position in the direction of the return force as a result of the header (20) having contacted an obstruction, being effected, upon the clearing of the obstruction by the header (20), by the accumulator (69) releasing energy previously stored therein during said temporary displacement from the nominal position. 12. A harvester according to claim 9 or 10 characterized in that the actuator (60) is of the single-acting type and the return force is exerted by resilient return means extending between the header (20) and the base unit (12); the return of the header (20) to the nominal position in the direction of the return force, following a temporary displacement from said nominal position in the opposite direction as a result of the header (20) having contacted an obstruction, being effected by said return force upon the clearing of the obstruction by the header (20); and the return of the header (20) to the nominal position in the direction opposite to the return force, following a temporary displacement from said nominal position in the direction of the return force as a result of the header (20) having contacted an obstruction, being effected, upon the clearing of the obstruction by the header (20), by the accumulator (69) releasing energy previously stored therein during said temporary displacement from the nominal position. 13. A harvester according to claim 9 or 10 characterized in that the flotation actuator (60) is of the double-acting type with the plunger side thereof being connected to the energy storage means (69) and in that the return force is obtained via a hydraulic coupling between the plunger rod side of the flotation actuator (60) and the pressure side of header lifting actuator means (48) disposed between the base unit (12) and the header (20) for raising and lowering said header (20); the return of the header (20) to the nominal position in the direction of the return force, following a temporary displacement from said nominal position in the opposite direction as a result of the header (20) having contacted an obstruction, being effected by said return force upon the clearing of the obstruction by the header (20); and the return of the header (20) to the nominal position in the direction opposite to the return force, following a temporary displacement from said nominal position in the direction of the return force as a result of the header (20) having contacted an obstruction, being effected, upon the clearing of the obstruction by the header (20), by the accumulator (69) releasing energy previously stored therein during said temporary displacement from the nominal position. 14. A harvester according to claim 13, characterized in that the hydraulic coupling between the header lifting actuator means (48) and the flotation actuator (60) comprises a two-position valve (80) for, in one position, connecting the header lifting actuator means (48) to the flotation actuator (60) and, in the other position, isolating the header lifting actuator means (48) from the flotation actuator (60). 15. A harvester according to any one of the claims 9 to 14 characterized in that the nominal position of the header (20) is selectable from a range of positions inbetween the extreme positions. 16. A harvester according to any one of the claims 7 to 15 characterized in that the valve (72) is connected to the flotation actuator (60) via a restrictor (71). 17. A harvester according to any one of the preceding claims characterized in that the energy storage means (69) is connected to the flotation actuator (60) via a restrictor (68). 18. A harvester according to any one of the preceding claims characterized in that the harvester further also comprises an automatic header height control mechanism. 19. A harvester according to any one of the preceding claims characterized in that the harvester further also comprises an automatic header weight compensation mechanism.

Inventors: DEDEYNE, ALFONS WILLY, DEROO, ROGER CORNEEL, OSSELAERE, GUY HENRI JULIEN
Applicants: FORD NEW HOLLAND N.V.
Application year: 1986
Main classification: A01D41
IPC codes: A01D41, A01D75