FR3093445A1 - Agricultural sprayer and its control method - Google Patents

Abstract

Title: Agricultural sprayer and its control method Sprayer (1) for distributing liquids, in particular for agricultural use, comprising at least one spray nozzle (4) for spraying the liquid and a mixer (15) with a mixing chamber (16) , having at least a first inlet (20, 21) for a carrier liquid (TF), at least two second inlets (17, 19) for different active agents (A, B, C) and at least one outlet (22) connected to the spray nozzle (4); a controlled valve (23, 27) is associated with each inlet (17, 21). An installation (28) controls the valves (23-27) for a use in accordance with that determined, by pulse width modulation so as to obtain a constant volume flow in the outlet independently of the actuation of the valves (23-27 ). Figure 3

Description

Agricultural sprayer and control method thereof

Field of invention

The subject of the present invention is a sprayer for dispensing liquids, in particular for agricultural use, comprising at least one spray nozzle for spraying the liquid and a mixer with a mixing chamber having at least one first inlet for a vector liquid, at least two second inlets for different active agents and an outlet connected to the spray nozzle, as well as a controlled valve associated with each inlet.

The invention also relates to a method for managing such a sprayer.

State of the art

For agricultural phytosanitary protection, it is necessary that the spray mixture composed of at least one active agent, in particular an active liquid such as, for example, a phytosanitary agent, and a vector liquid, in particular water, premixed before to be applied to the field. At the end of the application, the tank of the respective agent must generally be completely emptied on the spot and cleaned. Under these conditions, it is very difficult to react to the characteristics of a field and to the actual local demand for a phytosanitary agent. Thus, this mixed spray mixture is completely distributed in the field.

Systems are known that transport undiluted active liquids in their reservoir and it is only on demand that the active agent is mixed with the carrier liquid to be distributed on the field. It is necessary, for this mixture, to appropriately dose the active liquid to the vector liquid.

This dosage, also called direct feeding, requires a complicated sprayer equipped with valves and other accessories.

Sprayers of the above type are, for example, described in document WO 00/59321 which presents a sprayer comprising a mixer having a controlled valve associated with each inlet.

Description and advantages of the invention

The subject of the present invention is a sprayer for dispensing liquids, in particular for agricultural use, comprising at least one spray nozzle for spraying the liquid and a mixer with a mixing chamber having at least one first inlet for a vector liquid, at least two second inlets for different active agents and at least one outlet connected to the spray nozzle, and a controlled valve associated with each inlet, this sprayer being characterized in that it comprises an installation which controls the valves for a use in accordance with that determined , by pulse width modulation, so as to obtain a constant volume flow at the outlet, independent of the actuation of the valves.

The sprayer according to the invention has the advantage of applying an appropriate phytosanitary action very quickly; it guarantees that the overall quantity dispensed or the volume flow supplied to at least one spray nozzle remains constant, regardless of the number of active agents to be dosed, in particular active liquids. This allows optimal application of crop protection agents in the field. As indicated above, the subject of the invention is a sprayer comprising an installation which switches the valves by pulse width modulation according to the use determined so as to have at the output a constant volume flow, independently of the actuation valves.

According to the invention, the valves are switched by pulse width modulation. This means that to adjust the volume flow, the valves are not controlled to have a passage section varying between the maximum possible passage section and the closed position, necessary for the adjustment of the volume flow, but so that the opening and the closing pulses give the desired volume flow on average over time. For this, in a switching cycle, the respective valve is switched at least once to the open position. By convention, the switching position of a valve is the open (or on) position of this valve. The switching time in the switching cycle thus determines the volume flow set on average. If the valve is switched for the full duration (100%) of the switching cycle, the maximum volume flow will be obtained. If the valve is, for example, only switched over 50% of the switching cycle time, the volume flow will be halved. This switching by pulse-width modulation, which is not to be confused with the control by pulse-width modulation of an actuator, by which the pulse-width modulated current influences the passage section of the respective valve, the desired volume flow passing through this valve is obtained on average; by switching all the valves of the sprayer or mixer to pulse width modulation, an overall constant volume flow will be provided from the outlet to the spray nozzles. The operation switched by the pulse width modulation makes it possible to regulate separately the concentration of each active liquid, and also the carrier liquid at the outlet, even if in the lines of arrival of the liquid, the ratio between the carrier liquid and the active liquid is constant. Thus, by a volume flow rate remaining constant, and thus a constant spray pattern, the composition of the liquid dispensed (or mixture to be sprayed) is continuously controlled. In the event that only one active agent, for example a fungicide, is dispensed, it is possible to load the active liquid lines with a single active agent so that the adaptation of the concentration takes place without operating the various valves. with pulse width modulation.

In particular, the installation is designed for a determined application, by varying the switching frequency, the switching time and/or the switching time of the valves in the switching cycle. This makes it possible to operate the valves in cadence or in a time-shifted manner and/or at the same switching frequency or at a different switching frequency. This allows different switching times which regulate the volume flow through the respective valve, averaged over time. Thus, the volume flow increases especially if the switching time is increased. To keep the total output volume flow constant, when increasing the volume flow of one valve, the volume flow of at least one other valve in the mixer is reduced.

According to a preferred development of the invention, the valves associated with the inlets are identical. There are thus many identical elements which simplify assembly and allow economical manufacture of the sprayer. In addition, thanks to the identical realization of the valves, these will have the same pressure drop and the same passage section.

Preferably, an electric actuator, electrically adjustable, is associated with the valves, in particular, an electromagnetic actuator or an electric motor actuator for actuating or switching the respective valve. This allows a simple command and its execution by the command installation. The installation comprises in particular a control unit, preferably a microprocessor which controls actuators according to the necessary phytosanitary measures or the required mixing ratio.

According to another advantageous characteristic, a pump installation is associated upstream with each valve to transfer the respective liquid, the pump installations being designed to provide the same transfer pressure. This does not mean that each valve is preceded by its own pump installation, but rather that several valves can be preceded by a common pump installation. It is nevertheless important to associate upstream to each valve, a pump installation, whether common or separate, to have the appropriate transfer pressure for the valve. Thus, and in particular, each time a pump installation is provided upstream of the valves with a common supply line, in particular it is provided that the pump installations are identical. This guarantees the same transfer pressure so that the valves deliver the same volume flow. This is true for both the active liquid inlets and also for the carrier liquid inlet. Thus, the total volume flow is retained if, for example, one valve closes and another valve opens.

According to another preferred feature, the mixer has three inlets for three different active liquids. Thus, the mixer has at least four inputs. This allows different switching combinations where each time one or more working liquids are mixed with the carrier liquid and the switching between the working liquids takes place without changing the total volume flow through the outlet.

According to another particularly preferred development of the invention, the mixer comprises two first inlets for the carrier liquid. As there are thus two first vector liquid inlets, the vector liquid can be metered by switching (open/closed) the two valves associated with the first two inlets. This increases the diversity of mixer variants while maintaining the same output volume rate.

As a further advantageous feature, the valves are switched with pulse width modulation so that the output always delivers the same volume flow to one or more spray nozzles.

Thus, the valves of the mixer are switched with pulse width modulation so that the output has a constant volume flow independent of valve actuation, to supply one or more spray nozzles. This results in the advantages already mentioned above.

According to another preferential development of the invention, at least two valves are switched in rhythm or in a time-shifted manner. In particular, time-delayed switching minimizes the pressure peaks of the total volume flow. Simultaneous or cadence switching of the valves has the advantage of producing a mixture, for example, of different carrier liquids.

According to another advantageous characteristic, at least two of the valves are switched at the same frequency or at different frequencies. The selection of the switching frequency thus advantageously regulates the volume flow through the respective valve, i.e. the separate volume flow and at the outlet a constant total volume flow will be achieved.

According to another advantageous characteristic, at least two valves are switched in the same switching cycle with a switching time (equal or different valve open). This relates in particular to the duty cycle (on-time), which predetermines the volume flow through the valve in the switching cycle, as already described above.

According to another advantageous characteristic, in each switching cycle, in particular, going up to five valves, three valves are opened or switched simultaneously, which guarantees that, during the dispensing phase or spraying operation, there will be a virtually constant total volume flow.

According to another preferred characteristic of the method, at least one of the valves is switched beyond a switching cycle or remains switched. In particular, starting from a switching cycle, the following switching cycle is modified with a succession of valve switchings so that one of the valves remains switched beyond the switching cycle, i.e. say by overtaking in the next switching cycle. This reduces the number of switching operations of the affected valve and increases its service life. Preferably, this operation is done alternately for all the valves of the mixing installation to globally optimize the life of the sprayer.

According to another preferred characteristic, the valves are switched in such a way that if the difference in the switching time of the two valves for the active agent and which have the longest switching time, is shorter after its scaling over the duration of the switching cycle than the switching duration of a carrier liquid valve switched in the same switching cycle, this carrier liquid valve will not be switched in this switching cycle. This is based on the consideration of reducing switching cycles that do not come into the total volume flow. In the above case, it is assumed that, due to its shorter life, the carrier valve must be able to be closed again before it has been fully opened to achieve the short switching time. The actual volume flow released through the carrier valve would be very low. In this case, the switching of this valve has only a very small effect on the total volume, since the volume flow is practically constant.

According to another preferred feature, the switching instant of the valve having the longest switching time in a switching cycle is chosen so that the valve is centered according to time or with respect to the average volume flow.

According to another preferred characteristic, in particular, at high circulation speeds, there will be as regular a switching as possible of the valves, making it possible to have the same time interval between the switching duration of the current switching cycle and the switching duration the upstream cycle and the downstream cycle.

According to another preferential characteristic, the number of times a valve has been switched is counted in order to preferentially control the valves as a function of the number of switchings entered in order to have substantially the same number of switchings over the same predefined period. In particular, the counting of the switching cycles or of the number of switchings is still done before executing the actual process, if according to the desired phytosanitary product, the valve switching plan is calculated, in particular, the duration is adapted switching time, switching time and frequencies or else they are corrected so that all valves are switched as often as possible if possible.

Presentation of drawings

The present invention will be described below, using a sprayer and a sprayer management method shown in the accompanying drawings in which:

simplified representation of an advantageous sprayer,

schematic detail view of the sprayer installation,

schematic representation of an advantageous mixer of the sprayer,

diagram used to describe the advantageous method of managing the sprayer.

Description of embodiments of the invention

Figure 1 shows a simplified representation of a sprayer 1 comprising a vehicle 2 in the form of a tractor carrying a sprayer system 3 composed of a set of spray nozzles 4; the spray nozzles 4 are distributed over a transverse boom 5. The vehicle 2 pulls the transverse boom 5 and the spray nozzles 4 so that the nozzles are above the ground 6 to apply the phytosanitary agent to the ground and where applicable on the plans therein. The vehicle 2 carries several tanks 7, 8, 9, 10. The tanks 7, 8, 9 each contain a liquid active agent A, B possibly C and the tank C or another tank contains a vector liquid TF, in particular l 'water. Reservoirs 7-10 are connected to spray nozzles 4 by one or more mixers which will be described in more detail later. To transfer the respective liquid into each tank, there is provided a pump installation 11, 12, 13 and 14 which picks up the respective liquid and transfers it to the mixer described below. While in the following example embodiment, there are three different active agent reservoirs 7, 8, 9, it is obvious that the sprayer 1 can have a larger or smaller number of active agent reservoirs.

Figure 2 is a simplified diagram of the sprayer 1 with four tanks 7, 8, 9, 10, corresponding pump devices 11-14 as well as two spray nozzles 4. The spray nozzles 4 are each preceded by a mixer 15 connected to the pump device 11, 12, 13, 14 via the liquid lines. Thus, each of the mixers 15 receives liquid; the mixer 15 is made in such a way as to adjust the desired mixing ratio between the different liquids and to supply the mixture to the respective spray nozzle 4.

The mixture to be sprayed supplied by the mixer 15 consists of the carrier liquid and a phytosanitary agent, for example, A, B or C or even a combination thereof. Typically, the composition of the mixture is in the range of 25-200 parts by volume of carrier liquid for one part by volume of phytosanitary agent as liquid or solid agent, of the order of 50-20000 parts by mass of the vector liquid relative to the part by mass of phytosanitary agent. You can also have different values. The fact that the mixer 15 is upstream of the respective spray nozzle 4 has the advantage that the mixing of the different liquids will take place just upstream of the spray nozzle, it is thus possible to supply each spray nozzle with a compound mixture independently, and on the other hand, the volume for an application of phytosanitary agent of the pipes of the sprayer 1 to be evacuated in order to clean the components remains very low.

While the mixers 15 are directly upstream of a respective spray nozzle 4, according to another exemplary embodiment, it is provided that at each fraction of width, that is to say that a predefined number of nozzles spray 4, juxtaposed, is preceded upstream by a single mixer 15; thus this fraction of width corresponding to the spray nozzles 4 distributed over the field, the same mixture. It is also possible to provide the mixer 15 directly downstream of the tanks 7, 8, 9, 10 or of the pump devices 11-14 to obtain the desired mixture in advance and supply all the spray nozzles 4 of the sprayer 1. For individual switching of each nozzle, there is provided as an option, a simple switching valve for each spray nozzle 4 allowing in a simple way, to activate or deactivate, the respective spray nozzle.

For a typical application of a phytosanitary agent with a vector liquid, the overall quantity, in particular the quantity of vector liquid, must remain constant. Thus, when switching in passing, for example, from one phytosanitary agent for four spray nozzles 4 or for a constant surface on which one sprays. The advantageous embodiment of the sprayer 1 makes it possible in particular to have a constant volume flow rate supplying each spray nozzle, independently of the combination of phytosanitary agents and of the vector liquid and even of this combination being modified during operation.

According to one feature, the pump installations 11-14 are designed to provide the same volume flow and/or the same pressure of liquid so that the pump devices 11-14 provide a constant or equal volume flow for all liquids. This also ensures that crop protection agent application is set to an optimum droplet size at each spray nozzle 4.

Figure 3 schematically shows the mixer 15. It comprises a mixing chamber 16 in which the different liquids are mixed. The mixing chamber 16 has several inlets 17.21 as well as at least one outlet 22 connected to the spray nozzle 4.

The inlets 17-21 are each equipped with a valve 23, 24, 25, 26, 27 closing or releasing the passage section for the inlets 17 and 21. For this the valves 23-27 are electrically controlled.

In particular, valves 23-27 each have an actuator 23', 24', 25', 26', 27' to actuate the valve member against the force of a return spring. The valves 23-27 are shown schematically in Figure 3. The valve 23 is between the pump device 11 and the mixing chamber 16; valve 24 is located between pump device 12 and mixing chamber 16; valve 25 is between pump device 13 and mixing chamber 16; valves 26 and 27 are between pump device 14 and mixing chamber 16. Valves 26, 27 thus regulate the carrier liquid or the volume flow rate of carrier liquid to mixing chamber 16; the valves 23, 24, 25 regulate the active liquids A, B, C. The active liquids are diluted beforehand with the vector liquid to be stored in the tanks 7, 8, 9 or they are supplied from a system of appropriate premix.

The valves 23-27 are identical and by controlling the actuators 23'-27' by the control unit of an installation 28, the different flows are combined to have at the outlet 22, a constant volume flow Qges.

In the following table, the first column shows the different combinations of phytosanitary agents A, B, C with the carrier liquid TF or the switching combinations to obtain the volume flow Qges. The following five columns show the basic switching positions of the individual valves 23-27. The expression "AN" means that the valve is completely open; the expression "AUS" means that the valve is completely closed.

Valve 23 Valve 24 Valve 25 Valve 26 Valve 27 A+TF YEAR AU AU YEAR YEAR B+TF AU YEAR AU YEAR YEAR C+TF AU AU YEAR YEAR YEAR A+B+TF YEAR YEAR AU YEAR AU A+C+TF YEAR AU YEAR YEAR AU C+B+TF AU YEAR YEAR YEAR AU A+B+C+TF YEAR YEAR YEAR AU AU

The switching combinations 26=AN and valve 27=AUS can alternatively be represented by the switching combination valve 26=AUS and valve 27=AN.

The pressure drops of the various valves 23-27 are the same because the valves are identical. Thus, in the switching combinations shown in the table, one third of the total volume flow Qges passes through the respective open valves. Typically, for an application, the volume flow rate Qges is predefined by a spray nozzle 4. In addition, the concentration C2, i.e. the volume of the respective components is divided by the total volume in an element of reference (constant density and constant molar mass are assumed); the different phytosanitary agents A, B, C are also predefined. The target concentration of the different switching combinations is respected in that the phytosanitary agents A, B, C are diluted to the concentration C1 by the carrier liquid TF. The respective concentration C1 corresponds in the switching plane of the table above, to three times the final concentration C2.

If, for example, the total volume flow Qges is set at 3 l/min and the concentrations of the different phytosanitary agents A, B, C are set as follows C2A=0.01, C2B=0.02 and C2c=0.001, we obtains for the different switching combinations, in the table above, the following volume flows for the concentrations C1:

The individual volume flow of each valve 23-27 is regulated by the pulse-width modulated switching of the valves 23-27. For pulse-width modulated switching, the valves are switched using actuators 23'-27' at a predefined frequency, switching time and/or switching times. Actuators 23'-27' are, for example, electromagnetic actuators allowing rapid opening and closing of valves 23-27. Pulse-width modulated switching of valves 23-27 ensures the dispensing of a constant amount of product. The preferred embodiment retains the droplet size or droplet size spectrum even when selecting, i.e. changing, the crop protection agents. This will be detailed below.

Figure 4 shows as an example a diagram for switching to pulse width modulation of valves 23-27 in one switching cycle (100%). The switching position of each valve is represented between its closed position (0) and its maximum open (or fully open) position (1) according to the duration of the switching cycle (100%).

In FIG. 4, the characteristic curve KA represents the switching profile of the valve 23 associated with the active liquid A; the characteristic curve KB represents the switching movement of the valve 24 associated with the active liquid B; the characteristic curve KC represents the switching of the switching valve 25 associated with the active liquid C; the curve KTF 1 represents the switching of the first valve 26 associated with the carrier liquid and KTF 2 represents the switching of the valve 27 also associated with the carrier liquid. The respective switching time is measured from the start of the opening phase to the end of the closing phase. Figure 4 shows the chronological sequence of pulse-width modulated switching for the distribution of three active liquids, according to the different switching times (DC) shown in Figure 4.

Switching with pulse width modulation for which the switching time can be shorter than the switching cycle as shown in Figure 4, allows the time-averaged volume flow through the respective valve 23-27 to be reduced. This makes it possible to modify the concentration C2 despite the predefined concentration C1x applied to the inlet of the respective valve 25 for the outlet of the valve 25 referred to the total volume. The method for managing the various valves 23-27 can, for example, take place as follows:

First of all, we set the total volume flow, i.e. the total volume to be dispensed. This is, for example, predefined according to the phytosanitary protection chosen. The quantity to be dispensed, predefined by the user, gives a target volume flow of, for example, 1 l/min for a valve. Next, the individual valves are switched to pulse width modulation as described above. The volume flow which thus passes through each separately activated valve 23-27 is equal and reduced compared to that of a permanently open valve. The valves 23-27 can be switched in cadence or in a time-shifted manner. It is also possible to use valves with different frequencies. For example, valves can be switched at a frequency of 10-50 Hz and a switching time (DC=Duty cycle) of 50%. We thus obtain, for example:

Qges=1 l/min, composition: A+B+TF, volume flow: Qva=1/3 l/min; for DC=50% QVB=1/3 l/min for DC=50%; QVC=0 l/min; QVTF1=1/3 l/min for DC=50%; QVTF2= 0 l/min.

If the concentration of an active agent has to be changed, for example, the concentration of active agent A by 50%, it is important that the total volume flow Qges averaged over the switching cycle does not change or does not change only slightly. Thus, according to the invention, provision is made to increase the volume flow rate of the active material by its concentration, by increasing the switching time with respect to the DC duty cycle. At the same time, the volume flow rate of the other active materials or of the vector liquid is adapted by adapting and in particular by revising.

Example of increasing the concentration of active agent A by 50%:

Qges=1 l/min, composition A+B+TF, volume flow QVA=3/6 l/min for DC=75%;

QVB = 1/3 l/min for DC=50%; QVC=0 l/min; QVTF1=1/6 l/min for DC=25%; QVTF2=0 l/min;

Example of reducing the concentration of active agent A by 50%:

Qges=1 l/min, composition A+B+TF, volume flow QVA=1/6 1/min for DC=25%;

QVB = 1/3 l/min for DC=50%; QVC=0 l/min; QVTF1=3/6 l/min for DC=75%; QVTF2=0 l/min.

As a possible alternative, the carrier liquid TF can also be metered through the second valve 27:

exemplary distribution of volume flow rates TF; QVA= 1/6 l/min for DC=25%; QVB=1/3 l/min for DC=50%; QVC=0 l/min; QVTF1=1/3 l/min for DC=50%; QVTF2=1/6 l/min for DC=25%.

It is no longer possible to envisage controlling or influencing the distribution of the vector liquid by the valves 26 and 27 in that the switching cycles of the two valves 26, 27 are substantially identical during the life of the sprayer 1. Thus, one avoids a failure which would be linked to too many switching cycles of only one of the carrier liquid valves 26, 27.

In order to keep the total volume flow as constant as possible, the time distribution of the valve switchings in a switching cycle (switching intervals) is optimized as follows, even if the valves operate at the same frequency.

Thus, according to another exemplary embodiment, it is provided that at each instant, if possible three valves 23-27 are opened simultaneously. For this, at the start of a switching cycle, all the valves 23-25 associated with active liquids are advantageously opened while the valves 26, 27 of the vector liquid remain closed. If then one of the valves 23-27 is closed, one of the carrier liquid valves is opened, for example valve 26. If the second of the active liquid valves 23-25 is closed, the second carrier liquid valve 27. If the third active liquid valve 23-25 is closed, the two valves 26, 27 are also closed and the distribution of the phytosanitary agent is terminated.

If, according to another exemplary embodiment, only two of the valves 23-25 are opened during a switching cycle, they are preferably opened simultaneously at the start of the cycle and at the same time one of the valves associated with the carrier liquid. When the first of the two active liquid valves 23-25 closes, the next valve 27 of carrier liquid is opened. By closing the second active liquid valve, the two carrier liquid valves 26, 27 are also closed again simultaneously.

According to another exemplary embodiment, only one of the active liquid valves 23-25 is opened during a switching cycle and at the same time the two vector liquid valves 26, 27 are opened, so that one has always three valves open. If the active liquid valve 23-25 is closed again, the valves 26 and 27 associated with the carrier liquid are also closed.

The method has the advantage of avoiding pressure variations at the spray nozzles 4. This further ensures that each of the valves 23-27 will only be opened and closed at most once during the switching cycle. As an option, the carrier liquid valve 26, 27 is thus always chosen which, in combination with the active agent valve 23-25 open, makes it possible to have the best properties of the system such as, for example, the shortest path of the mixing upstream, mixing quality as good as possible or pressure differences caused by the geometry of the mixing valve being as small as possible on the valve outlets of the individual inlets.

Alternatively, in the case of the dispensing of two active liquids, such as, for example, A and B, the total volume flow is kept constant in that one always has two valves open simultaneously instead of three valves. For this, the concentration of the active liquid for the correct dosage on the field will only be premixed according to a double set concentration. The two active liquid valves 23-25 then switched, (in this case it is valves 23 and 24), are again opened simultaneously at the start of the switching cycle. For different switching times (DC) of the valves 23 and 24 for the phase in which only one of the valves 23, 24 is open, only one of the carrier liquid valves 26, 27 can additionally be opened.

In the case of two or more active liquids dispensed per switching cycle, it is possible under certain conditions that the two longest switching times of the switched valves only have a difference of a few percent between them. . Due to the usual switching time of the valves, the carrier liquid valve 27 opened for this purpose should already be closed before it is completely open. To reduce the power demand and the switching cycles and thus extend the life of the valve concerned, before the start of the switching cycle, it is calculated whether, for a given switching frequency and cycle time, the difference of the two longest switching times of the active agent valves 23-25 scaled to the cycle time is shorter than the switching time of the present carrier liquid valve 26, 27 or for a certain fraction, for example, 50%. If this is the case, the vector liquid valve 26, 27 concerned by this case is not switched (it is not opened) in this switching cycle. This results in a shorter time during which the total volume flow is only about two thirds of the set volume flow. Due to this shorter time, the reduced volume flow is negligible.

As a variant, the switching duration of the valve 23-25 which is open the longest is offset with respect to the switching durations on the time axis in the cycle so that the duration during which, at the start of the cycle alone, this valve and a carrier valve 26, 27 are open, exactly as long as the time towards the end of the cycle of that valve and a carrier valve 26, 27 which are open (centering).

According to another option, the switching cycles of one or more active agent valves 23-25 are adapted so that the total error of the quantity dispensed for each of the valves 23-25 is minimal and that at the same time the Switching times at the end of the switching cycle end identically. For this, one can, for example, lengthen by half the difference, the switching cycle of the valve 23-25, the longest open second and shorten by half the difference, the switching cycle of the valve 23-25 open the longest. This guarantees a constant total volume flow.

To avoid the formation of bands for a high circulation speed and a low switching frequency, the switching times are distributed in a switching cycle so that, in particular when the switching times of the various valves are modified as a function of time, the the interval between the current switching cycle and the start of the switching time in the next switching cycle is as much as possible equal to the time interval between the current switching instant and the end of the switching operation of the cycle previous switch. If the limits of the individual switching cycles disappear and the valves cannot be opened beyond the cycle limits, the valves with a short effective switching time are operated with a slightly increased switching frequency, which also influences the switching operation. This avoids, with certainty, the formation of bands for each of the active agents.

As an option, the service life of the valves 23-27 is maximized. For this, the different switching times are shifted by a switching cycle so that at least one valve, in particular a valve 26, 27 associated with a carrier liquid, remains open beyond the limit between two switching cycles. In addition, this can also be applied taking into account the active liquid valves 23-25 if the order of the selected valves changes with each cycle so that this advantage is had for all the valves, in particular for the active liquid valves 23-25. Thus, effectively, in each switching cycle, one valve switching is saved, which increases the life of all valves on average by at least 20% and for one switching of all five valves per switching cycle, reducing to four valve cycles per cycle increases service life. In addition, the probability of the risk of failures is thus reduced.

One can also consider, to correct a difference related to the pressure drop for the quantity of liquid distributed compared to the quantity of foreseeable liquid, knowing the volume flow rate of all the individual combinations according to the second table presented above, and using a field of characteristics, a correction of the switching times is carried out so that in the end, the correct, exact volume will be distributed for each switching per switching cycle.

It is also possible to adapt the volumetric flow passing through the mixer 15 globally in order, for example, in curved trajectories, to adapt the quantity distributed to the relative, variable speed on the path for the nozzles traversing the curve.

Switching with pulse width modulation of the valves 23-27 preferably takes place during the entire operation. Alternatively, switching with pulse width modulation can be done only periodically, which has the advantage that valves designed for a reduced number of switching cycles can also be used.

If only one or two active liquids are redistributed, the output combination of the various valves can be adapted, also without operating in pulse width modulation by cutting or opening the active agent lines insofar as these lines serve the same active agent.

If an active agent is added to the reservoir containing the carrier liquid beforehand, it is also possible to no longer add it by dosing, from the various active agent reservoirs. In this case, all the pipes arriving at the mixer 15 which supply the same composition can be combined. The five valves 23-27 then make it possible to vary the volume flow rate of the mixture and thus the quantity of active agent according to five levels, without having to adapt the transfer or distribution pressure. It is also advantageous that by adapting the volume flow rate of the liquid from the appropriate spray nozzle, a nozzle change installation, in particular automatic, is selected to maintain the spray characteristics.

NOMENCLATURE OF THE MAIN ELEMENTS

1 Sprayer

2 Vehicle, tractor

3 Spray system

4 Spray nozzle

5 Arrow

6 Ground

7, 8, 9, 10 Tanks

11, 12, 13, 14 Pump installations

15 Mixer

16 Mixing chamber

17-21 Liquid inlets

22 Liquid outlet

23, 24, 25, 26, 27 Valves

23', 24', 25', 26', 27' Valve actuators

28 Control installation

Claims (14)

Sprayer (1) for distributing liquids, in particular for agricultural use, comprising at least one spray nozzle (4) for spraying the liquid and a mixer (15) with at least one mixing chamber (16), having at least a first inlet (20, 21) for a carrier liquid (TF), at least two second inlets (17, 19) for different active agents (A, B, C), at least one outlet (22) connected to the spray nozzle ( 4), and a controlled valve (23, 27) associated with each inlet (17, 21),
sprayer characterized in that it comprises an installation (28) which controls the valves (23-27) for a use in accordance with that determined, by pulse width modulation so as to obtain a constant volume flow in the outlet independently of actuation of the valves (23-27). Sprayer according to Claim 1, characterized in that the installation (28) is designed to vary the switching frequency, the switching time and/or the switching time of the valves (23-27) in a switching cycle , by use in accordance with what has been determined. Sprayer according to Claim 1, characterized in that the valves (23-27) associated with the inlets (17-21) are identical. Sprayer according to one of the preceding claims, characterized in that upstream of each valve (23-27) there is associated a pump installation (11-14) for transferring the respective liquid and the pump installations (11-14) are designed to provide the same transfer pressure. Sprayer according to one of the preceding claims, characterized in that the mixer (15) has three inlets (17-19) for three different active agents (A, B, C), in particular pre-diluted. Sprayer according to one of the preceding claims, characterized in that the mixer (15) has two first inlets (20, 21) for the carrier liquid (TF). Method for managing a sprayer according to one of Claims 1 to 6, characterized in that the valves (23-27) are switched by pulse width modulation so that the output (22) always provides the same volume flow to one or more spray nozzles (4). Method according to Claim 7, characterized in that at least two valves (23-27) are switched in time or offset relative to each other. Method according to one of the preceding claims, characterized in that at least two of the valves (23-27) are switched at the same frequency or at different frequencies. Method according to one of the preceding claims, characterized in that at least two of the valves (23-27) are switched in a switching cycle with equal or different switching times. Method according to one of the preceding claims, characterized in that in each switching cycle three valves (23-27) are opened simultaneously. Method according to one of the preceding claims, characterized in that at least one of the valves (23-27) is switched according to a switching cycle. Method according to one of the preceding claims, characterized in that the valves (23-27) are switched in such a way that if the difference in the switching time (DC) of the two valves (23-25) for an active agent (A ,B,C), whose longest switching time (DC) on the scale of the switching cycle time, is shorter than the switching time of a valve (26, 27) switched in this same switching cycle, this valve (26, 27) will not be switched in this switching cycle. Method according to one of the preceding claims, characterized in that the valves (23-27) are switched to have at least the same number of switchings in a predefined period.