The invention refers to a method and a device for cleaning hydraulic valves according to the preamble of claim 1 and of claim 7.

BACKGROUND During operation of hydraulic systems, particularly within the agricultural machinery sector, the problem arise that dirt in the hydraulic oil leads to the system binding. The control valves in such a system are especially sensitive to dirt. Dirt in the form of small and large particles can be present in the hydraulic oil through dirt such as soil entering the quick release connections, which also contain the connections for the hydraulic oil, during changes of implement. Changes of implement behind the tractor are often carried out in the field, where dirt can thus easily force its way into the hydraulic system, both in the tractor and in the implement. These particles can then flow with the hydraulic oil directly into the control valves, which are very sensitive to dirt and can become unusable if they bind. On an agricultural machine for sowing, such valves control e.g. the marking discs that are positioned on both sides of the machine to show the following driving path for the agricultural machine and at the back of the machine to mark where the driving tramlines are left after sowing. Such valves can also control metering of the seed.

The aim of the invention is to achieve a method and a device for cleaning hydraulic valves, where the cleaning occurs efficiently and rapidly without the need for dismantling of the valve in question.

This aim is achieved by a method and a device that have been given the characteristics presented in claims 1 and 7.

The preferred embodiments of the invention have been given the characteristics presented in the subclaims.

The most important parameter for the function of a hydraulic system is hydraulic hygiene. If this is compromised the operational safety of the system will be jeopardised. Up to 80% of all operational disruptions in a hydraulic system are due to dirt adhering to or mechanically abrading the hydraulic components.

When a dirt particle that is transported with the oil lodges in a seal slot or a valve seat, it can cause the valve to have impaired functioning or to cease functioning completely. The normal way to correct this is to replace the valve or possibly to try rinsing or flushing the valve in the hope that the dirt will dislodge and disappear.

Through the method and the device according to the invention, it is possible that cleaning can be carried out during operation, i.e; in the field at sowing for example, when the driver himself or an automatic detection device detects that the control valve is binding, which as described above is most often due to dirt in the hydraulic oil. The valve consequently does not need to be removed for mechanical cleaning or to be replaced. However, it could be arranged so that the tractor is stationary during the cleaning operation.

The method and the device according to the invention are thus based on a continually alternating signal (tension), such as a square-topped signal, being fed to at least the solenoid valve which binds, at the same time as hydraulic oil is flushed through the valve. The valve will then very rapidly perform full pulses and vibrate. Any dirt that has fastened is then dislodged and flushed away with the hydraulic oil.

DETAILED DESCRIPTION OF THE DRAWINGS

The device is described in more detail in the following with reference to the attached drawings, which show a preferred embodiment.

Fig. 1 shows an agricultural machine, more particularly a seed drill, which can be provided with a device according to the invention. Fig. 2 shows a circuit diagram for a hydraulic system in the seed drill in Fig. 1 to control the movement of the marking discs.

Fig. 3 shows a partial sectional view of a solenoid valve contained in the hydraulic system in Fig. 2.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Fig. 1 shows an agricultural implement, in this case comprising a seed drill 1, which is drawn by a tractor 2. The seed drill 1 is provided with right and left marking discs 3 and 4, which are fully turnably journalled in bearings at the end of the retractable and extendable arms 5 and 6. The arm 5 of the right marking disc 3 is extended to mark the drive path of

the tractor 2 after the next headland turn, while the arm 6 of the left marking disc 4 is retracted against the side of the seed drill to a resting position. There are also rear marking discs 8 and 9 mounted at the ends of raisable and lowerable rear arms 10 and 11 behind the rear harrow tines 12 in order to mark two predetermined driving tracks after the seed drill, i.e. where the seed drill did not place seed in the soil, to later form unsown tramlines in the sown crop, in which a tractor can drive for spraying, etc. Before the sown crop has emerged from the soil these driving tracks must be marked by the rear marking discs 8 and 9 on the sown soil for this purpose. Both these rear marking discs 8 and 9 are therefore lowered during sowing to mark where the tramlines will be created.

Fig. 2 illustrates a diagram of a hydraulic system 13 for a seed drill 1 according to Fig. 1 for e.g. controlling the movements of the arms 5, 6, 10 and 11 of the marking discs 3, 4, 8 and 9. Two piston and cylinder units 14 and 15 influence arms 5 and 6 and one piston and cylinder unit 16 influences the simultaneous movement of the arms 10 and 11. One piston and cylinder unit 17 is activated to raise or lower the seed drill 1 at the tractor linkage to e.g. regulate sowing depth. A valve block 18 contains solenoid valves controllable from a control box 19, of which solenoid valves 20 and 21 activate the piston and cylinder units 14 and 15 of the side arms 5 and 6 and of which solenoid valve 22 activates the piston and cylinder unit 16 of the side arms 10 and 11.

Two solenoid valves 23 and 24 activate the piston and cylinder unit 17 for raising or lowering the seed drill 1 and one solenoid valve 25 is arranged to lock the movement of the side arms and the rear arms in the intended position, such as shown in Fig. 1, where only the right marking disc is active, i.e. lowered and in contact with the soil surface for marking the next driving path of the tractor 2.

A detection apparatus 26 is adapted to receive a signal from not shown sensors via connections 27, when one of the arms 5, 6, 10, 11 of the marking discs cannot be swung out, in or up. This can occur for example through dirt having entered a solenoid valve via the hydraulic oil. Signals can also be sent to the detector 26 when one of the arms is moving sluggishly.

Fig. 3 reveals a partial cross-section through a solenoid valve of the type that in Fig. 2 is labelled with the reference numbers 20, 21, 22, 23, 24 or 25. The solenoid valve in Fig. 3

has an outer valve casing 28, at the upper end of which a top cap 29 is screwed on. Between a lip 30 on the valve casing 28 and a lip 31 on the top cap 29 opposing the lip 30 is an electromagnetic coil or solenoid 32 held in place by tightening of the top cap 29. Between the solenoid 32 and the outer valve casing and the top cap 29, sealing O-rings 33 and 34 are arranged. The reference number 35 denotes electrical connections to the electronic control box 19 in Fig. 2. An inner valve casing 36 is screwed fast into a circular cylindrical cavity 37 in the outer valve casing 28 and is sealed with a sealing O-ring 38. Within the inner valve casing 36 is arranged a valve cone 39. A sphere 40 is contained in a nonreturn valve cavity 41 in the valve cone 39. A pilot pin 42 with a tip 43 is adapted to move forwards and backwards against a seat 44 under the influence of the solenoid 32. The reference number 45 denotes inlet valve ports for hydraulic oil arranged around the periphery and 46 denotes a circular cylindrical outlet valve port.

The valve in Fig. 3 is screwed fast in the valve block 18 in Fig. 2 through an outer threading 47 and sealed in the boreholes in the valve block 18 by means of O-rings 48 and 49.

Dirt in the hydraulic oil can for example adhere on the sliding surfaces 50 between the inner valve casing 36 and the valve cone 39, in the control channel of the pilot pin 42 in the outer valve casing and in a seat 51 where the valve cone 39 abuts the inner valve casing 36.

Even though in the embodiment described above it is stated that detection of dirt occurs when for example the arms 5, 6, 10 and 11 cannot be swung out or bind or move sluggishly, so that the detection apparatus 26 activates the control box 19, in an alternative embodiment this can also be done manually directly by the tractor driver. The detection apparatus 26 can also be omitted completely and activation of the electrical control box can be done solely by the driver.

The invention can of course also be applied in other hydraulic systems than that described above where dirt can force its way into the hydraulic oil via connections or leaking seals.

Although an embodiment of the invention has been described above, the method and the device according to the invention can be modified within the framework of the claims attached.