A FORAGE HARVESTER

Abstract: In a forage harvester with a height adjustable cutting head having ground engaging means in the form of slide shoes, one of these or another machine member, caused to be deformed by the pressure of the slide shoe against the ground, mounts a strain gauge (21) which, in response to variation of the engagement pressure, applies an electric signal actuating via an amplifier (42) one or the other of two magnet valves (43 and 44), which controls the supply and discharge, respectively, of oil to and from a hydraulic cylinder (16), which thereby raises and lowers, respectively, the cutting head until the desired pressure between the slide shoe and the ground has been re-established. Thus, the cutting head is kept at a substantially constant height above the ground irrespective of irregularities in the surface of the ground, so that also the stubble height is kept substantially constant.

Description: A forage harvester The invention relates to a forage harvester of the type defined in the introductory portion of claim 1. Such a forage harvester makes it po'ssible automatically .to keep the height of the cutting head above the ground and thus the stubble height essentially constant, ir¬ respective of irregularities in the surface of the ground. The US Patent Specification 2 750 727 discloses a forage harvester of the present type, where the ground engaging means are formed by slide shoes mounted on a rotatable shaft. An adjustable link mechanism connects this shaft to an arm which, in one embodiment, can be caused to contact one or the other of two contact means and thus actuate an electric motor to raise or lower the cutting head, and which, in another embodiment, actuates a hydraulic valve inserted in an oil line which shunts a hydraulic cylinder- to raise and lower the cutting head, thus varying the oil pressure in the cylinder and thereby the height of the cutting head above the ground. The object of the invention is to provide a forage harvester of the present type whose height adjusting mechanism is more sturdy and can thus cope better with the tough working conditions to which it is subjected than the prior art ones, and which moreover responds more quickly to irregularities in the surface of the ground than the prior art height adjusting mechanisms. This object is achieved in that the forage harvester is constructed as stated in the characterizing portion of claim 1 since, in this structure, pressure sensing and control of the height adjusting mechanism take place without any use of moving members, viz. by means of a firmly mounted strain gauge, which moreover responds instantaneously to any change in the pressure of the ground engaging means against the ground. Claims 2 and 3 define various possibilities for the mounting of the strain gauge, and simple embodiments of the means for controlling the height adjusting mechanism, when this is formed by a hydraulic cylinder, are defined in claims 4 and 5. The invnetion will be explained more fully below with reference to the drawing, in which fig. 1 is a schematic side view of an embodiment of the forage harvester of the invention, coupled to a tractor, fig. 2 is a section along the line II-II in fig. 1, and fig. 3 is a diagram of an electric -hydraulic control system. In figs. 1 and 2 the numeral 10 designates a forage harvester in the form of a windrower which is coupled to a tractor 11. The windrower has a cutting head with a beam 12 suspended between two gable members 20; the beam rotatably mounts a plurality of disc-shaped cutters 13, here four, which are caused to rotate in a generally known, not shown manner during travel. The windrower has two ground wheels 14 mounted on the outer end of their respective pivot arms 15. A hydraulic cylinder 16 is mounted between each pivot arm and the frame of the windrower to raise and lower the windrower with respect to the wheels. Each cylinder is connected with an oil/air accumulator 17 mounted directly on the cylinder. A slide shoe 18 is mounted below each cutter 13, said shoe being rotatably suspended from the machine frame at its leading edge 19 in a manner not shown. Fig. 1 shows a strain gauge 21 placed on the top side of a slide shoe 18, and, in response to any change in the pressure of the slide shoe against the ground, the strain gauge applies an electric signal depending upon the size of the pressure change. As shown in fig. 3, the strain gauge 21 is connected to an amplifier 42 with two outputs, which are in turn connected to electromagnets in their respective ones of two magnet valves 43 and 44. These valves, when actuated, connect the cylinder 16 with an oil supply conduit 32 and a reservoir 35, respectively. The amplifier 42 is so arranged as to actuate, upon actuation of the strain gauge- 21 in one or the other direction from an average state corresponding to the desired pressure against the slide shoe, one or the other, respectively, of the two magnet valves 43 and 44 with a view to supply and discharge, respectively, of oil to and from the hydraulic cylinder to raise and lower, respectively, the cutting head until the desired engagement pressure has been re¬ established. The magnet valves 43 and 44 may be either cut-off or regulating valves. The details of the shown and described structure may be varied in many ways. As examples of readily performed changes may be mentioned that the shown relatively narrow slide shoes may be replaced by two disc-shaped shoes, each of which extends approximately half the width of the machine. Also wheels may be used instead of slide shoes. Moreover, instead of a single strain gauge, two might be used, which are actuated upon deviation in their respective directions from the desired average state of the deformable machine member. The strain gauge might also be placed on other machine members than a slide shoe, e.g. as shown at 22 in fig. 2 on one of the gable members 20. An additional possibility is the mounting of the cutting head in the' frame in such a manner that the head is movable vertically by means of the hydraulic cylinders, instead of moving the entire machine frame up and down. The hydraulic cylinders might be replaced by other forms of height adjusting means, e.g. mechanical jacks driven by electric motors whose power supply is controlled by the amplifier 42.

Claims: P a t e n t C l a i m s: 1. A forage harvester, comprising a, cutting head which is equipped with at least one ground engaging means and whose height above the ground can be regulated by means of a height adjusting mechanism in response to the pressure of the ground engaging means against the ground, c h a r a c t e r i z e d in that a strain gauge is placed on a machine member which is caused to be deformed by the pressure between the ground engaging means and the ground, said strain gauge controlling the height adjusting mechanism via an amplifier. 2. A forage harvester according to claim 1, wherein -the ground engaging means is formed by a slide shoe attached to the cutting head, c h a r a c t e r i z e d in that the strain gauge is placed on the slide shoe. 3. A forage harvester according to claim 1, wherein the cutting head extends between and is supported by two gable members, c h a r a c t e r i z e d in that the strain gauge is placed on one gable member. 4. A forage harvester according to claim 1, 2 or 3, wherein the height adjusting mechanism is formed by a hydraulic cylinder, c h a r a c t e r i z e d in that the amplifier is designed to actuate one or the other of two magnet valves controlling the supply and discharge, respectively, of oil to and from the hydraulic cylinder, in response to deformation of the machine member in question caused by changes in the pressure of the ground engaging means against the ground. 5. In a forage harvester according to claim 4, the modifi¬ cation that two strain gauges are provided, controlling their respective magnet valves through their respective amplifiers.

Inventors: LARSEN BOERGE, RIIS ARNE, LARSEN, BOERGE, RIIS, ARNE
Applicants: TAARUP AS MASKINFAB, MASKINFABRIKEN TAARUP A/S
Application year: 1985
Main classification: A01D34
IPC codes: A01D41