WO2008155234A2

WO2008155234A2 - Device for a seed metering device on an agricultural machine

Info

Publication number: WO2008155234A2
Application number: PCT/EP2008/057007
Authority: WO
Inventors: Tommy Bogren; Gert Gilstring
Original assignee: Väderstad-Verken Ab
Priority date: 2007-06-20
Filing date: 2008-06-05
Publication date: 2008-12-24
Also published as: WO2008155234A3; SE532322C2; SE0701507L

Abstract

The invention refers to an agricultural machine comprising at least one seed metering device (8) for distributing seeds to the soil (9) over which the agricultural machine (1) moves, which seed metering device (8) comprises a seed metering element (803) at which a case (802) is arranged, which case (802) communicates with an air pressure device (501, 502) by means of which a pressure difference between a first and a second side (821a, 822a) of the seed metering element (803) can be provided, in addition to which the seed metering element (803) is by means of a drive device (401 ) rotatable around a seed metering axle (805) and provided with a plurality of through retaining recesses (804) disposed at a distance from the seed metering axle (805) for uptake, by means of the pressure difference, of seeds (91), A control entity (451 ) that is adapted through controlling of the air pressure device (501, 502) to control the pressure difference at least partly in dependence on the speed of the agricultural machine.

Description

DEVICE FOR A SEED METERING DEVICE ON AN AGRICULTURAL MACHINE

TECHNICAL AREA

The invention refers to an agricultural machine comprising at least one seed metering device for distributing seeds to the soil over which the agricultural machine moves, which seed metering device comprises a seed metering element at which a case is arranged, which case communicates with an air pressure device by means of which a pressure difference between a first and a second side of the seed metering element can be provided, in addition to which the seed metering element is by means of a drive device rotatable around a seed metering axle and provided with a plurality of through retaining recesses disposed at a distance from the seed metering axle for uptake, by means of the pressure difference, of seeds. The seed metering device also comprises dividing means for release of the seeds after their uptake.

BACKGROUND

An agricultural machine of the type 'precision seed drill' (Eng. planter) is moved, usually towed by a tractor, over the soil that is to be drilled, and comprises a plurality of, in the lateral direction of the machine distributed, row sowing entities, each one adapted to form a seed furrow in the direction of travel of the machine, and by means of a seed metering device to place a row of seeds in the seed furrow. Such a seed metering device is in certain cases shared by several row sowing entities. In order to create good conditions for the crop and yields it is important that the seeds are placed at a constant, uniform distance from each other.

The seed metering device can comprise a case and a seed metering element, commonly circular disc-shaped, which is disposed in the case and adapted to separate two spaces in the case. The case communicates with an air pressure device by means of which a negative pressure can be provided in one of the spaces. At use the seeds are gravity-fed to the other space with a pressure that is somewhat under or equal to atmospheric pressure. Alternative solutions exist with a fan-fed higher pressure on one side of the seed metering element. During use of the machine, the seed metering element is adapted by means of a drive device to rotate around a seed metering axle and is provided with a plurality of peripherally disposed through retaining openings for uptake, by means of the pressure difference, of one seed in each retaining opening. The seed metering device displays an area of through which the retaining openings pass, and in which a decrease in the pressure difference is achieved, by means of a dividing flexible wall or similar, so that the seeds are released as they are moved through the area.

A problem with known seed metering devices of this type is the occurrence of s.c. 'skips', i.e. that a retaining opening bypasses the seeds on one side of the seed metering element without taking up a seed. This means that the desired placement of seeds at a constant, uniform distance from each other is not achieved.

Another problem with known seed metering devices of the mentioned type is the occurrence of s.c. 'doubles', i.e. that two seeds are taken up simultaneously by one and the same retaining opening. To rectify this there is often a s.c. double eliminator which is arranged in the seed metering device to detach any additional seeds that have fastened at a retaining opening. However it has been shown that 'doubles' occur despite seed metering devices displaying such double eliminators. As with 'skips', this means that the desired placement of seeds at a constant, uniform distance from each other is not achieved.

SUMMARY

An aim with the invention is that at sowing with an agricultural machine of the type precision seed drill to create good conditions for the crop and the yield. An additional aim with the invention is that at sowing with an agricultural machine of the type precision seed drill to contribute to a uniform distance between the seeds being achieved.

Yet another aim with the invention is that at sowing with an agricultural machine of the type precision seed drill to permit higher speeds for the agricultural machine at sowing.

These aims are achieved with an agricultural machine of the initially described type wherein a control entity is adapted through controlling of the air pressure device to control the pressure difference at least partly in dependence on the speed of the agricultural machine.

The invention is advantageous particularly in cases where the drive device is adapted to regulate the rotational velocity of the seed metering element at least partly in dependence on the speed of the agricultural machine. The invention is especially advantageous in cases where the drive device is adapted to increase the rotational velocity of the seed metering element at an increase in the speed of the agricultural machine, and vice versa. At known solutions of this type, the occurrence of the above described phenomenon 'skips' increases at relatively high machine speeds and high rotational velocities for the seed metering element Furthermore the occurrence of the above described phenomenon 'doubles' increases at relatively low machine speeds and low rotational velocities for the seed metering element.

Thanks to the invention a compensation for tendencies for 'skips' at high speeds and tendencies for 'doubles' at low speeds can be achieved through controlling of the pressure difference between the first and the second space. In particular the control entity can be adapted to control the air pressure device so that the pressure difference increases at an increase in the speed of the agricultural machine and so that the pressure difference decreases at a decrease in the speed of the agricultural machine.

At a speed increase for the machine the rotational velocity of the seed metering element increases, and through the increased pressure difference, tendencies for seeds not to be taken up by the bypassing retaining recesses due to the high speed are counteracted. Furthermore through the increased pressure difference, tendencies for taken-up seeds to lose contact with the seed metering element, during passage at high speed of and contact with a double eliminator described more closely below, are counteracted.

At a speed decrease for the machine the rotational velocity of the seed metering element decreases, and through the decreased pressure difference, tendencies for one or two seeds to be taken up by the same retaining recess, due to the low speed of bypassing retaining recesses, are counteracted. In the event that, despite the desired single seed, one or several additional seeds are nevertheless taken up by the same retaining recess, the decreased pressure difference causes it to be more difficult, despite the low speed, for the additional seed, or seeds, to stay in place during passage of and contact with the double eliminator.

Through the invention the conditions in the seed metering device are thus adapted to such variations as are caused by speed changes for the agricultural machine. This permits the forward movement of the agricultural machine within a large speed range, while the demand for a uniform placement of seeds in the soil is achieved within this entire speed range. This is of great importance at practical use, where speed variations always occur, e.g. where the machine has to change direction on a field. In addition, through the increased pressure difference in the seed metering device higher driving speeds are permitted.

The invention is suitable on seed metering devices at which the mentioned pressure difference between the first and the second side of the seed metering element is provided in different ways. E.g., as is exemplified below, the seed metering element can be at least partly disposed in the case, and adapted to divide a first and a second space in the case, wherein the mentioned pressure difference arises between the first and the second space. The pressure difference can be achieved through negative pressure or positive pressure. At positive pressure the case can contain a space on the first side of the seed metering element, and through the communication with the air pressure device provide a positive pressure on the first side. Thereby the other side of the seed metering plate does not need to be contained, but can instead be exposed to the surrounding atmosphere.

Preferably the air pressure device comprises a fan, wherein the control entity is adapted to control the speed of the fan.

In certain embodiments the air pressure device comprises a fan, at least one air pipe for the communication with the case, and at least one air flow regulating means arranged in at least one of the air pipes, wherein the control entity is adapted to control the air flow regulating means. With such air flow regulating means a very rapid regulation of the pressure difference over the seed metering plate can be provided.

In embodiments where the agricultural machine comprises at least two seed metering devices, and the air pressure device comprises at least two branch pipes, each one of which communicates with the case at the respective seed metering device, an air flow regulating means can be arranged at each one of the branch pipes. This provides the potential to individually control the pressure difference over the respective seed metering element.

The control entity, which has electronic calculation capacity and which is described more closely below, can be adapted to control the pressure difference on the basis of received signals that correspond to the speed of the agricultural machine. Thus the control entity can be adapted to control the pressure difference at least partly on the basis of the rotational velocity of a carrying wheel for the agricultural machine, in which case e.g. a pulse transmitter arranged at the carrying wheel can be used. Alternatively the control entity can be adapted to control the pressure difference at least partly on the basis of signals from a radar directed towards the soil and adapted to detect movement of the soil in relation to the agricultural machine.

Alternatively the control entity can be adapted to control the pressure difference on the basis of signals corresponding to a parameter that is dependent on the speed of the agricultural machine. In cases where the rotational velocity of the seed metering element is dependent on the speed of the agricultural machine, the speeds of moving parts in the drive device for the seed metering element are also dependent on the speed of the machine. Thus a speed for a moving part in the drive device can be regarded as a parameter that is dependent on the speed of the agricultural machine. In certain embodiments the control entity is therefore adapted to control the pressure difference at least partly on the basis of a movement in one part of the drive device.

In a corresponding way the rotational velocity of the seed metering element can be regarded as a parameter that is dependent on the speed of the agricultural machine. In certain embodiments the control entity is therefore adapted to control the pressure difference at least partly on the basis of the rotational velocity of the seed metering element. An advantage with such embodiments is that the control of the pressure difference is based on a parameter that is closely associated with the problem solved by the invention, i.e. the control of the pressure difference is based directly on changes in the rotational velocity of the seed metering element, which as mentioned above can give rise to an uneven seed distribution in the soil. This constitutes a particularly great advantage at machines where the rotational velocity of the seed metering element is dependent on additional parameters besides the speed of the machine, e.g. in embodiments where the drive device is adapted to increase the rotational velocity of the seed metering element at an upward-directed relative movement of the seed metering device, and to decrease the rotational velocity of the seed metering element at a downward-directed relative movement of the seed metering device, as is specified in Swedish patent application no. 0700529- 1, submitted by the applicant and incorporated herein through this reference.

DRAWING SUMMARY

The invention will be described below in detail with reference to the drawings, in which

- Fig. 1 shows a perspective view of a precision seed drill, seen obliquely from above and obliquely from the rear, according to an embodiment of the invention,

- Fig. 2 shows a perspective view of a row sowing entity that is a part of the precision seed drill in Fig. 1, with a cogwheel (454) displaced along its axis of rotation for clarity of presentation, - Fig. 3 shows a perspective view of a section, vertical and parallel to the direction of travel of the precision seed drill, of a seed metering device that is a part of the row sowing entity in Fig. 2,

- Fig. 4 is a schematic cross-sectional view of the seed metering device, with the section lying along the line IV-IV in Fig. 3, - Fig. 5 shows in a view from the left in the intended direction of travel of the machine details in Fig. 2 with a drive device and a seed metering device (partly sectioned),

- Fig. 6 is a schematic cross-sectional view of the seed metering device, with the section lying along the line VI-VI in Fig.4, - Fig. 7 shows a perspective view corresponding to that shown in Fig. 2 of a row sowing entity according to an alternative embodiment of the invention, with a cogwheel (454) displaced along its axis of rotation for clarity of presentation,

- Fig. 8 shows a view corresponding to that in Fig. 5, with an alternative drive device, - Fig. 9 shows a schematic perspective view of parts of a precision seed drill according to an alternative embodiment of the invention, and

- Figs. 10-14 show parts of air pressure devices in precision seed drills according to alternative embodiments of the invention.

DETAILED DESCRIPTION

Fig. 1 shows a perspective view of an agricultural machine in the form of a precision seed drill 1 according to an embodiment of the invention. The precision seed drill comprises a number, in this example eight, row sowing entities 2, each fastened on a structural member 3 comprising a cross-running steel beam. The structural member 3 forms a part of the frame of the machine which is carried by two carrying wheels 3a. The precision seed drill is, by means of a fastening member S arranged at at least one free end of a longitudinal structure detail 4, adapted to be coupled behind a draught vehicle and brought in a direction indicated by the arrow F in Fig. 1. Each one of the row sowing entities 2 is adapted at movement of the machine 1 over the soil that is to be sown to create a seed furrow in the direction of travel of the machine, to place one seed at a time along the seed furrow in order to create a row of seeds in the direction of travel F of the machine, and to close the seed furrow.

Fig. 2 shows one of the row sowing entities 2 in Fig. 1. This is by means of a linkage device 6 connected with the cross-running structural member 3. The linkage device 6 comprises two upper and two lower primary linkage elements 601, 602, of which only one upper and one lower primary linkage element are visible in Fig. 2. The primary linkage elements 601, 602 form a parallelogram structure so that the row sowing entity 2 can move vertically without rotation in relation to the structural member 3.

The row sowing entity 2 comprises a seed container 7 that communicates with a below more closely described seed metering device 8, adapted via a distribution member (not shown), to distribute one seed at a time to a seed furrow in the soil. Alternatively the agricultural machine can display one or several seed containers, each one of which communicates with more than one seed metering device.

The row sowing entity 2 comprises a seed furrow fonning means, comprising two rotatable discs 10 and adapted to form the seed furrow. The discs 10 are at use of the machine adapted during rotation to partly intrude into the soil, wherein a lower orifice on the distribution member running from the seed metering device 8 is disposed immediately behind the intrusion of the discs 10 into the soil. The row sowing entity 2 is adapted to be carried by two support wheels 11 , disposed on each side of the pair of discs 10. Sowing depth is adjustable according to known technique through adjustment of the height of the support wheels 11 in relation to the discs 10. The row sowing entity 2 in this example also comprises here not more closely described after-cultivating members 202, adapted to close the seed furrow.

Fig. 3 shows a perspective view of a section, vertical and parallel to the direction of travel of the precision seed drill, of a seed metering device 8. This comprises a cylindrical case 802 and a from the case downward directed seed metering pipe 801, which communicates with the distribution member. The seed metering device 8 comprises a seed metering element 803, in the form of a round seed metering plate 803 that is arranged essentially concentrically in the case 802.

As can be seen in Fig. 4 the seed metering plate 803 is adapted to separate a first and a second space 821, 822 in the case 802, which first and a second space 821, 822 are disposed on a first and a second side 821a, 822a of the seed metering plate 803. In this example the first and the second side 821a, 822a are disposed on the left and right, respectively, of the seed metering plate 803 viewed in the intended direction of travel F of the agricultural machine. At use seeds 91 are gravity-fed from the seed container 7 (Fig. 2) into the case 802 on the first side 82 Ia of the seed metering plate 803. The seed metering plate 803 is adapted to rotate in its plane around a primarily horizontally orientated seed metering axle 805, as is indicated in Fig. 3 by the arrow R. This rotation is performed by means of a below more closely described drive device, comprising a seed metering axle 805 concentrically and with the seed metering plate 803 fixedly connected seed metering drive wheel 421 (Fig. 4).

As can be seen in Fig. 1 the agricultural machine 1 comprises an air pressure device comprising a fan 501, and air pipes, comprising a main pipe 501a communicating with the fan 501 and, communicating with the main pipe 501 a, branch pipes 502, each one extending to one respectively of the seed metering devices 8. As can be seen in Fig. 4 the case 802, more precisely the second space 822, communicates at the respective seed metering device 8 with the respective branch pipe 502. The fan 501 is adapted to provide a negative pressure in the branch pipe 502 and in the second space 822, which gives rise to a pressure difference between the first and the second space 821 , 822.

Here reference is to Fig. 5. The seed metering plate 803 as has been mentioned is rotatable around the seed metering axle 805 by means of a drive device 401, comprising a seed metering drive wheel 421 that is mounted on the seed metering axle 805 and concentric with it. The drive device 401 also comprises for each seed metering device 8 a primary drive wheel 411, and a common to all seed metering devices 8 primary axes of rotation 414 (cf. Fig. 1), with which respective primary drive wheels 411 are concentrically and fixedly connected. The drive device 401 further comprises an endless flexible member 443 in the form of a chain 443 (in Fig. 5 partly represented by dashed lines). The seed metering drive wheel 421 is provided in the form of a chainwheel 421 and is adapted to be driven directly by the chain 443, which in its turn is driven by the primary drive wheel 411. The primary drive wheel 411 is driven in its turn via the primary axis of rotation 414 which in its turn is driven by a not shown additional drive element, in its turn driven by one of the carrying wheels 3a (Fig. 1). Thus the rotational velocity of the primary axis of rotation 414, and thereby the rotational velocity of the seed metering plate 803, increases at an increase in the speed of the agricultural machine, and vice versa.

As is shown by Fig. 3, the seed metering plate 803 is adapted to in a circular, with the seed metering axle 805 concentric, seed transport area 806 at a distance from the seed metering axle 805, take, transport and release seeds. More precisely the seed metering plate 803 in the seed transport area 806 displays a plurality of through retaining recesses 804 in the form of retaining openings 804 disposed at the same radial distance from the seed metering axle 805, in this example in the vicinity of the periphery of the seed metering plate 803, which retaining openings 804 are distributed at equal distance from each other in the circumference of the seed metering plate 803.

Through the above described pressure fall over the seed metering plate 803 a seed fastens in each retaining opening 804 and is transported towards the seed metering pipe 801. The seed metering device 8 is adapted to release the seeds on a side of the seed metering axle 80S on which the seeds are transported by the seed metering plate 803 with a downward-directed speed component in relation to the seed metering axle 805.

As can be seen in Fig. 6, release of the seeds is made possible by dividing means 823 comprising a wall 823, which is preferably of a flexible material. The wall 823 is disposed on the second side 822a of the seed metering plate 803. The wall 823 separates off an area of at which the retaining openings 804 pass. The wall 823 brings about a decrease in the pressure fall over the seed metering plate 803 so that the seeds are released as they pass into the area. Fig. 3 shows a release area SL (indicated by broken lines), in which due to the decreased pressure fall the seeds come free from respective retaining opening 804, and fall down through the seed metering pipe 801. Alternatively the wall 823 can be of a rigid material, wherein a slit-sealing is achieved between the wall 823 and the seed metering plate 803. The seed metering device 8 also comprises as shown in Fig. 3 a double eliminator 824, which in known way is adapted to detach additional seeds at a retaining opening. However as is evident in this presentation, the invention decreases the need for such a double eliminator 824.

As is shown in Fig. 1 the agricultural machine comprises an electronic control entity 451, as well as speed determining means 452 adapted to send to the control entity 451 signals which indicate the rotational velocity of the primary axis of rotation 414. The control entity 451 is adapted to control the fan 501 on the basis of the signals from the speed determining means 452. As can be seen most clearly in Fig. 2, the speed determining means 452 are provided in the form of a rotation transmitter 452, arranged at a cogwheel 454 which is fixedly connected with and concentric with the primary axis of rotation 414. The rotation transmitter 452b can be a pulse transmitter of inductive or optical type, adapted to detect the passage of cogs existing at the periphery of the cogwheel. Possible alternatives to such pulse transmitters are in themselves known and are not described more closely here.

The speed determining means 452 can alternatively be provided as a rotation transmitter at a cogwheel which is fixedly connected with and concentric with one of the carrying wheels 3a (Fig. 1) for the agricultural machine. As additional alternatives the speed determining means 452 can be provided as a radar. As yet another alternative the speed determining means 452 can alternatively be provided in the form of a speed meter at the drawbar for the agricultural machine, wherein signals that correspond to the speed are conducted in a suitable way from the drawbar to the control entity 451.

Fig. 7 shows an additional alternative for the speed determining means 452. The control entity is in this embodiment adapted to control the pressure difference on the basis of the rotational velocity for the seed metering element arranged in the seed metering device 8. The speed determining means 452 is provided in the form of a rotation transmitter 452, arranged at a cogwheel 454 which is fixedly connected with and concentric with the seed metering axle 805.

The fan 501 is adapted to be driven by a drive member, e.g. in the form of an electric or a hydraulic motor, with a regulating member adapted to receive control signals from the control entity 451. The controlling of the fan 501 by the control entity 451 on the basis of the signals from the speed determining means 452 is such that at an increase in the speed of the agricultural machine the speed of the fan 501 increases so that the pressure difference between the first and second space 821 , 822 in the seed metering devices 8 increases, and vice versa. This thereby, as is mentioned above, at a speed increase for the machine, counteracts through the increased pressure difference tendencies for the seeds not to be taken up due to the high speed of the bypassing retaining openings, and in addition, at a speed decrease for the machine, counteracts through the decreased pressure difference tendencies for two or more seeds to be taken up by the same retaining opening due to the low speed of the bypassing retaining openings,.

The seed metering device 8 can within the framework of the invention be arranged in a large number of alternative ways. For example the seed metering device 8 can be orientated in alternative ways in relation to the agricultural machine, e.g. so that the seed metering element 803 extends primarily in a plane across the direction of travel of the agricultural machine.

Furthermore the pressure fall over the seed metering element 803 created by the fan 501 can alternatively be achieved with a positive pressure on one side of the seed metering element 803 and an atmospheric pressure on the other side. Such an embodiment can be understood at a comparison with Fig. 4. To achieve a positive pressure in the first space 821, to which the seeds are metered from the seed container, the branch pipe 502 communicating with the fan can communicate with the case 802 on the first side 821a of the seed metering plate 803. The case 802 thereby does not need to contain a space on the second side 822a of the seed metering plate 803, and this can instead be exposed to the surrounding atmosphere.

In addition, instead of retaining openings in the form of through holes, the seed metering plate 803 on the first side 821a can display at its periphery retaining recesses comprising evenly distributed deepenings, each one adapted to take up a seed, in addition to which a through recess in the base of the respective deepening by means of the pressure fall achieves a retaining of the respective seed. Such a recess can be designed as a deepening in the periphery of the seed metering plate 803.

The drive device can be provided in a large number of alternative embodiments. E.g. the drive device can be arranged so that the rotational velocity of the seed metering plate 803 increases at an upward-directed movement of the seed metering device 8 in relation to the structural member 3 or the soil, and decreases at a downward-directed movement of the seed metering device 8 in relation to the structural member 3 or the soil, as is described in the mentioned Swedish patent application no. 0700529-1.

Fig. 8 shows an example of a drive device 401 according to one embodiment in the mentioned Swedish patent application. This drive device 401 differs from that shown in Fig. 5 with respect to the following: Between the seed metering drive wheel 421 and the primary drive wheel 41 1 is disposed a breakwheel 418. The breakwheel 418 is adapted to be in engagement with the endless flexible member 443 in a portion of its path in which it is driving, in this embodiment at its upper path between the seed metering drive wheel 421 and the primary drive wheel 411. Furthermore the breakwheel 418 is arranged, through its position and its radius, so that the upper path 443a of the endless flexible member 443 changes direction downward at the breakwheel 418. The drive device 401 thus displays an angled part 443a of the path for the endless flexible member 443, between the breakwheel 418 and the primary drive wheel 411, at which angled part 443a of the path the endless flexible member 443 is adapted to be driving. The position of the axis of rotation for the breakwheel 418 is fixed in relation to the seed metering axle 805 since the seed metering device 8 and the breakwheel 418 are mounted on a common carrying device 21. The drive device comprises a chain tensioner 417 in engagement with the endless flexible member 443 at its lower path 443b for maintenance of suitable tension in the chain 443.

The distance between the primary axis of rotation 414 and the axis of rotation for the breakwheel 418 is essentially the same as the distances between respective first and second joints 603, 604 (cf. Fig. 8) at the upper and lower primary linkage element 601, 602, respectively. Furthermore, at movements of the seed metering element 8 in relation to the structural member 3, the direction of the relative movement RB for the axis of rotation for the breakwheel 418 is orthogonal to a conceptual line CL which cuts the first and the second joint 603, 604 at the upper primary linkage element 601.

A path angle α between the angled part 443a of the path for the endless flexible member 443, and the direction RB of a movement of the seed metering device 8 in relation to the structural member 3 is less than 90 degrees. This means that at a downward-directed and upward-directed relative movement, respectively, of the seed metering element 8, the length of the angled part 443 a of the path for the endless flexible member 443 decreases and increases, respectively, so that the rotational velocity for the seed metering drive wheel 421 decreases and increases, respectively. The position of the chain tensioner 417 is thereby adjusted in order to compensate for the length change of the upper path 443 a for the endless flexible member 443.

Through suitable choice of the path angle α between the angled path part 443a of the path for the endless flexible member 443, and the direction RB of a movement of the seed metering device 8 in relation to the structural member 3, the radius R2 for the seed metering drive wheel 421 and the radial distance R3 from the seed metering axle 805 for the seed transport area 806, an advantageous compensation KG of the seed metering velocity for vertical movements of the seed metering device 8 in relation to the structural member 3 can be achieved.

Fig. 9 shows a schematic perspective view of parts of a precision seed drill according to an alternative embodiment of the invention, which agrees with that described above with reference to Figs. 1-6, with the exception of certain differences.

Fig. 9 shows one of several row sowing entities 2 in the machine. The drive device 401 for the seed metering device 8 (which is fixedly mounted on the row sowing entity 2), comprises a with the seed metering device 8 fixedly connected drive entity 401 in the form of an electric or a hydraulic motor. As in the embodiments described above, the agricultural machine comprises an electronic control entity 451, speed determining means 452 adapted to send to the control entity 451 signals that indicate the speed of the agricultural machine. The speed determining means is provided in the form of a radar 452. The control entity 451 is adapted to control the drive entity 401 at least partly on the basis of the signals from the speed determining means 452. More precisely, on the basis of the signals from the speed determining means 452 the drive entity 401 is controlled so that the speed of the drive entity 401 increases at an increase in the speed of the agricultural machine, and vice versa.

The fan 501 is as the embodiments described above adapted to be driven by a drive member, e.g. in the fonn of an electric or a hydraulic motor, with a regulating member adapted to receive control signals from the control entity 451. The control of the fan 501 by the control entity 451 on the basis of the signals from the speed determining means 452 is such that at an increase in the speed of the agricultural machine the speed of the fan 501 increases so that the pressure difference between the first and second space 821, 822 (Fig. 4) in the seed metering devices 8 increases, and vice versa. In the embodiments described above the agricultural machine displays a fan 501 that communicates with all seed metering devices 8. Alternatively the agricultural machine can display two or more fans 501 that each one communicate with one or more of the seed metering devices 8.

With reference to Figs. 10-14 additional embodiments of the invention will be described. In the embodiments described above the control entity 451 is adapted to control the pressure difference over the seed metering plate 803 in dependence on the speed of the agricultural machine, through controlling the speed of the fan. Alternatively the air pressure device can comprise one or more air flow regulating means 503, each one e.g. in the form of a butterfly valve, a throttle valve, a gate valve or other flow restricting means, arranged in one or more of the air pipes 501a, 502. With such air flow regulating means 503 a very rapid regulation of the pressure difference over the seed metering plate can be provided.

In Fig. 10-14 air flow directions are indicated by arrows labelled A and directions of movement for the air flow regulating means 503 are indicated by arrows labelled B.

Fig. 10 shows an embodiment in which the air pressure device is adapted to provide a negative pressure at the seed metering element, and in which a flow regulating means 503 in the form of a throttle valve is arranged in the main pipe 501a. The control entity 451 is adapted to control the position of the throttle valve 503 and thereby control the pressure difference over the seed metering plates disposed upstream of the throttle valve 503. Fig. 11 shows an alternative with an air flow regulating means 503 in the form of a butterfly valve. Fig. 12 shows an embodiment in which a throttle valve is arranged in a corresponding way to that in Fig. 10, but in an air pressure device that is adapted to provide a positive pressure at the seed metering element. The seed metering plates are thus disposed downstream of the throttle valve 503 in Fig. 12. Fig. 13 shows an embodiment in which the air pressure device as in Fig. 10 is adapted to provide a negative pressure at the seed metering element, but in which an air flow regulating means 503 in the form of a throttle valve is arranged in each one of branch pipes 502 which each one communicate with a respective case at a respective seed metering element. This provides the potential to individually control the pressure difference over the respective seed metering element. Such a solution with the air flow regulating means 503 in each one of the branch pipes 502 can naturally also be provided in an pressure device that is adapted to create a positive pressure at the seed metering element.

Fig. 14 shows an additional alternative, wherein one and the same valve 503 is adapted to control the flow through two branch pipes.

Claims

1. Agricultural machine comprising at least one seed metering device (8) for distributing seeds to the soil (9) over which the agricultural machine (1) moves, which seed metering device (8) comprises a seed metering element

(803) at which a case (802) is arranged, which case (802) communicates with an air pressure device (501, 501a, 502, 503) by means of which a pressure difference between a first and a second side (821a, 822a) of the seed metering element (803) can be provided, in addition to which the seed metering element (803) is by means of a drive device (401) rotatable around a seed metering axle (805) and provided with a plurality of through retaining recesses (804) disposed at a distance from the seed metering axle (805) for uptake, by means of the pressure difference, of seeds (91), characterised by a control entity (451) that is adapted through controlling of the air pressure device (501, 501a, 502, 503) to control the pressure difference at least partly in dependence on the speed of the agricultural machine.

2. Agricultural machine according to Claim 1, wherein the control entity is adapted to control the air pressure device (501, 501a, 502, 503) so that the pressure difference increases at an increase in speed of the agricultural machine and decreases at a decrease in speed of the agricultural machine.

3. Agricultural machine according to either of the preceding Claims, wherein the air pressure device (501, 501a, 502, 503) comprises a fan (501), wherein the control entity is adapted to control the speed of the fan (501).

4. Agricultural machine according to any one of the preceding Claims, wherein the air pressure device (501, 501a, 502, 503) comprises a fan (501), at least one air pipe (501a, 502) for the communication with the case (802), and at least one air flow regulating means (503) arranged in at least one of the air pipes (501a, 502), wherein the control entity is adapted to control the air flow regulating means (503).

Agricultural machine according to Claim 4, comprising at least two seed metering devices (8), in addition to which the air pressure device (501, 501 a,

502, 503) comprises at least two branch pipes (502), each one of which communicates with the case (802) at the respective seed metering device (8), wherein an air flow regulating means (503) is arranged at each one of the branch pipes (502).

Agricultural machine according to any one of the preceding Claims, wherein the control entity is adapted to control the pressure difference at least partly on the basis of the rotational velocity of a carrying wheel (3a) for the agricultural machine.

Agricultural machine according to any one of Claims 1-5, wherein the control entity is adapted to control the pressure difference at least partly on the basis of signals from a radar (452a) adapted to detect movements of the soil in relation to the agricultural machine.

Agricultural machine according to any one of Claims 1-5, wherein the control entity is adapted to control the pressure difference at least partly on the basis of a movement at a part (414) of the drive device.

Agricultural machine according to any one of Claims 1-5, wherein the control entity is adapted to control the pressure difference at least partly on the basis of the rotational velocity of the seed metering element (803).

Agricultural machine according to Claim 9, wherein the drive device (401) is adapted to increase the rotational velocity of the seed metering element (803) at an upward-directed relative movement of the seed metering device (8), and to decrease the rotational velocity of the seed metering element (803) at a downward-directed relative movement of the seed metering device (8).