Method for actuating a solenoid valve which is used for flow rate control and is operated in a pulse-width-modulated manner

Abstract

The invention relates to a method for actuating a solenoid valve (12) of an agricultural sprayer which is used for flow rate control and is operated in a pulse-width-modulated manner, the method comprising the steps of: imposing a pick-up current (IAn) in the solenoid valve (12) of the agricultural sprayer in order to effect an opening movement of an armature (24) from a blocking position into a release position and imposing a drop-out current (IAb), having opposite polarity to the pick-up current (IAn), in the solenoid valve (12) in order to accelerate a closing movement, which is supported by a return spring (28) of the solenoid valve (12), of the armature (24) from the blocking position into the release position.

Description

[0001] Description

[0002] Method for controlling a pulse-width modulated solenoid valve used for flow control

[0003] The invention relates to a method for controlling a pulse-width modulated solenoid valve of an agricultural sprayer used for flow rate control, according to the preamble of patent claim 1, and to a system for flow rate control on an agricultural sprayer according to the preamble of patent claim 10.

[0004] Pulse-width-modulated solenoid valves in agricultural sprayers exhibit high-frequency opening and closing behavior. Such solenoid valves can, for example, open and close twenty times per second.

[0005] The ratio of the time periods in which the solenoid valve is open and closed can be used to vary the application rate of spray liquid at a constant spray pressure or the spray pressure at a constant application rate of spray liquid.

[0006] Generic solenoid valves typically have a solenoid coil that attracts an armature to open the solenoid valve. When opened, the armature is lifted from a sealing surface, allowing spray fluid to flow through the solenoid valve. To open the solenoid valve, an attractive current is injected into the solenoid valve, causing the armature to open from a blocked position to a released position. To close the solenoid valve, the coil current was regulated to zero in previous controls, meaning no magnetic field acts on the armature. A return spring then ensures that the armature moves from the released position to the blocked position and is pressed against the sealing surface in the blocked position.

[0007] Due to varying friction inside the solenoid valve, the closing and opening durations of identical solenoid valves can vary considerably, despite identical control. The opening and closing behavior of solenoid valves on agricultural sprayers is also influenced by the properties of the spray fluid being applied. In particular, the viscosity and particle load of the spray fluid can have valve-specific influences on the opening and closing behavior of identical solenoid valves. For example, the deviations in the opening and closing behavior of identical solenoid valves can increase with increasing viscosity of the spray fluid being applied.

[0008] The object underlying the invention is to reduce the deviations in the opening and closing behavior of identically constructed pulse-width modulated solenoid valves used for flow control in an agricultural sprayer. Furthermore, the adjustment range of such solenoid valves is to be expanded.

[0009] The object is achieved by a method of the type mentioned at the outset, wherein, within the scope of the method according to the invention, a waste current having the opposite polarity to the pull-in current is impressed into the solenoid valve in order to accelerate a closing movement of the armature from the release position to the blocking position, which closing movement is supported by a return spring of the solenoid valve.

[0010] By injecting a waste current with the opposite polarity to the pull-in current, the armature is accelerated towards the sealing surface with greater force, thereby reducing the closing time. Because the overall forces are greater, the influence of friction acting on the armature during the closing movement from the release position to the blocking position is reduced. This effectively reduces deviations in the opening and closing behavior of identical solenoid valves. By injecting a waste current with the opposite polarity to the pull-in current, the influence of the properties of the spray liquid being applied on the opening and closing behavior is also reduced. The properties of the spray liquid that influence the opening and closing behavior of the solenoid valves, such as viscosity or particle loading, can thus be effectively compensated. Reducing the closing time also extends the possible adjustment range of the solenoid valve.

[0011] The method may further comprise applying a holding current to the solenoid valve to hold the armature in the release position. The application of the holding current may be initiated as a function of the current flowing through the solenoid valve. The application of the pull-in current and / or the release current and / or the holding current is preferably initiated by a control device for controlling the solenoid valve.

[0012] In a preferred embodiment of the method according to the invention, the pull-in current is impressed by applying a pull-in voltage to the solenoid valve, and the drop-out current is impressed by applying a drop-out voltage to the solenoid valve. The pull-in voltage and the drop-out voltage preferably have different signs. By applying the pull-in voltage, the impressed pull-in current corresponds to the current that occurs when the pull-in voltage is applied. By applying the drop-out voltage, the drop-out current that is opposite in polarity to the pull-in current corresponds to the current that occurs when the drop-out voltage is applied. For example, the pull-in voltage has a positive sign and the drop-out voltage a negative sign. Alternatively, the pull-in voltage can have a negative sign and the drop-out voltage a positive sign.

[0013] Furthermore, a method according to the invention is preferred in which the magnitude of the pull-in voltage and the magnitude of the drop-out voltage differ from each other by less than 20%. The magnitude of the pull-in voltage and the magnitude of the drop-out voltage preferably substantially match. The magnitude of the pull-in voltage is, for example, between 7 V and 15 V. The magnitude of the drop-out voltage is preferably also between 7 V and 15 V. Alternatively, the magnitude of the pull-in voltage can also be greater than the magnitude of the drop-out voltage. Furthermore, the magnitude of the drop-out voltage can also be greater than the magnitude of the pull-in voltage.

[0014] The method according to the invention is further advantageously developed in that the dropout voltage is applied to the solenoid valve for a predetermined, in particular valve- and / or application-specific, closing current supply period. The closing current supply period can be a static, i.e., unchanging, value. Alternatively, the closing current supply period can be a dynamic, i.e., variable, value, which can depend, for example, on current operating and / or control parameters. After the closing current supply period has elapsed, the dropout voltage is removed again.

[0015] Furthermore, a method according to the invention is preferred in which the armature moves from the release position to the blocking position within a closing movement duration. The closing current supply duration is preferably shorter than the closing movement duration. If the closing current supply duration is shorter than the closing movement duration, the closing current supply is interrupted before the armature has reached the blocking position. The closing current supply duration can also be longer than the closing movement duration. If the closing current supply duration is longer than the closing movement duration, the closing current supply is continued when the armature has reached the blocking position. The closing current supply duration can furthermore substantially correspond to the closing movement duration. If the closing current supply duration substantially corresponds to the closing movement duration, the closing current supply is interrupted when the armature has reached the blocking position.The closing current duration is preferably selected to ensure optimal closing behavior. A closing current duration that is too short can result in the solenoid valve not closing as quickly as possible. However, if the closing current duration is set too long, the coil current becomes too high, which can cause the solenoid valve to reopen unintentionally. For example, the armature can move from the release position to the blocking position within a closing movement time of 3 ms.

[0016] Furthermore, a method according to the invention is advantageous in which the application of the drop-out voltage is interrupted as soon as the coercive field strength is generated by the coil of the solenoid valve. The point in time at which the coercive field strength is present can, for example, be detected and / or calculated by sensors. The armature is preferably made of magnetic stainless steel. This is attracted to any magnetic field regardless of polarity. The metal used exhibits hysteresis during magnetization and demagnetization. If the metal is attracted to a magnetic field with a certain polarity, it is itself magnetized in the corresponding polarity direction, thereby creating the attraction effect. If the external magnetic field is removed, a small portion of this magnetization remains; in this context, this is referred to as remanence. The metal itself thus becomes a weak permanent magnet.The remanence is canceled when a magnetic field with the coercive field strength is generated with opposite polarity. The remanence is the magnetic flux density remaining in the iron core when the coil is de-energized. The coercive field strength is the field strength required to cancel the remanence.

[0017] Furthermore, a method according to the invention is preferred in which the waste current is injected into the solenoid valve in such a way that the current flow direction through the solenoid valve is reversed during the closing movement of the armature from the release position to the blocking position. The waste current injection is thus controlled in such a way that the armature moves during the reversal of the current flow direction. Particularly when using a comparatively strong return spring, the armature of the solenoid valve is moved quickly out of the release position, so that it is already performing a closing movement at the time of the reversal of the current flow direction.

[0018] In an alternative embodiment of the method according to the invention, the waste current is injected into the solenoid valve in such a way that the current flow direction through the solenoid valve is reversed, while the armature of the solenoid valve is in the release position. During the reversal of the current flow direction, the armature therefore does not move. In particular, by using a comparatively weak return spring, it can be achieved that the armature is still in the release position at the time of the reversal of the current flow direction and does not yet perform a closing movement.

[0019] In a further preferred embodiment of the method according to the invention, a coil charging current is injected into the solenoid valve while the armature is in the blocking position. The coil charging current preferably results in a magnetic field that counteracts the spring force exerted by the return spring on the armature without causing any armature movement. By injecting a coil charging current while the armature is in the blocking position, the opening duration of the solenoid valve can also be reduced because recharging the coil requires less time. Reducing the opening duration also extends the possible adjustment range of the solenoid valve.

[0020] The object underlying the invention is further achieved by a system of the type mentioned above, wherein a waste stream can be impressed into the solenoid valve to accelerate a closing movement of the armature from the blocking position to the release position, assisted by a return spring of the solenoid valve, and the control device is configured to control the solenoid valve according to one of the methods described above. With regard to the advantages and modifications of the system according to the invention, reference is therefore made to the advantages and modifications of the method according to the invention.

[0021] Preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying drawings.

[0022] Fig. 1 shows a system according to the invention in a schematic representation, wherein the armature of the solenoid valve is in a blocking position;

[0023] Fig. 2 shows the system shown in Fig. 1 in a schematic representation, with the armature of the solenoid valve in a release position; and

[0024] Fig. 3 shows the time courses of the voltage applied to a solenoid valve and the current flowing through the solenoid valve during the control of the solenoid valve.

[0025] Figs. 1 and 2 show a system 10 for controlling a solenoid valve 12 of an agricultural spraying device, specifically a field sprayer, used for flow rate control. The illustrated solenoid valve 12 is arranged in a fluid circuit of the agricultural spraying device, wherein the solenoid valve 12 can be positioned directly in front of a nozzle. The nozzle and the solenoid valve 12 can form a valve-nozzle unit. A plurality of corresponding valve-nozzle units are arranged in the fluid circuit of the agricultural spraying device, via which spray liquid F can be applied to an agricultural field.

[0026] The solenoid valve 12 is connected to a control device 16 of the system 10 via a line 14. The solenoid valve 12 can be opened and closed via the control device 16.

[0027] The solenoid valve 12 has a fluid inlet 18 and a fluid outlet 20. An armature 24 is located in the passage between the fluid inlet 18 and the fluid outlet 20, which can be moved via a magnetic field generated by the coil 22. A return spring 28 is arranged on one end face of the armature 24, with the return spring 28 being supported on a portion of the housing 30 of the solenoid valve 12.

[0028] In the state shown in Fig. 1, the solenoid valve 12 is not energized, so that the return spring 28 presses an end face of the armature 24 onto a valve seat 26, so that the passage between the liquid inlet 18 and the liquid outlet 20 is blocked.

[0029] The solenoid valve 12 can be energized via the control device 16 such that the magnetic field generated by the coil 22 causes an opening movement of the armature 24. To initiate the opening movement, the magnetic field generated by the coil 22 must exert an opening force on the armature 24 that is greater than the restoring force of the return spring 28.

[0030] Fig. 2 shows the solenoid valve 12 in an open state. Applying a pull-in current to the solenoid valve 12 causes the armature 24 to open. Applying a holding current to the solenoid valve 12 holds the armature 24 in a release position, in which the solenoid valve 12 is open. In the open state of the solenoid valve 12, the passage between the liquid inlet 18 and the liquid outlet 20 is open, so that spray liquid F can be dispensed via the nozzle positioned behind the solenoid valve 12. The control device 16 causes the injection of a pull-in current l to open the solenoid valve 12. An , to hold the armature 24 in the release position, the injection of a holding current and to support the closing movement of the armature 24, the injection of a drop current l Ab into the solenoid valve 12.

[0031] Fig. 3 shows the voltage U applied to the solenoid valve 12 and the current I flowing through the solenoid valve 12 over time t.

[0032] During an opening phase fo, the control device 16 causes the injection of the starting current l An into the solenoid valve 12 to cause an opening movement of the armature 24 from a blocking position to a release position. The injection of the pull-in current l An is carried out by applying a pull-in voltage U An to the solenoid valve 12. In the area in which the current curve has a local minimum during the impression of the pull-in current l An, the armature 24 reaches the release position in which the solenoid valve 12 is fully open. The opening phase fo is followed by a holding phase k in which the armature 24 is held in the release position. During the holding phase k, a demagnetization voltage Uem is briefly applied to the solenoid valve 12 in order to prepare the closing process by demagnetizing the armature 24. The opening phase fo and the holding phase k can be combined to form the time period Do in which the solenoid valve 12 is in an open state.

[0033] The closing process is initiated by impressing a starting current l An counter-polar waste stream l A b is initiated into the solenoid valve 12. Through the waste stream l A b, the closing movement of the armature 24, assisted by the return spring 28 of the solenoid valve 12, is accelerated from the release position to the blocking position. The injection of the waste stream l Ab is carried out by applying a drop-out voltage U A b to the solenoid valve 12. The magnitude of the pull-in voltage U An and the magnitude of the dropout voltage U A b are essentially the same. The values ​​of pull-in voltage U An and dropout voltage U A b, for example, are in a range between 7 and 15 V. The dropout voltage L h is applied to the solenoid valve 12 for a predetermined valve- and / or application-specific closing current duration tsB. After the closing current duration tsB has elapsed, the dropout voltage UAb is removed again. The armature 24 moves within a closing movement duration t s from the release position to the lock position. The closing current duration t S B is shorter than the closing movement duration t sAt the current flow reversal time tu, the flow direction of the current flowing through the solenoid valve 12 is reversed during the closing movement of the armature 24 from the release position to the blocking position.

[0034] After the armature 24 has reached the blocking position, the armature 24 is held in the blocking position during the closed phase tc. Towards the end of the closed phase tc, a coil charging current kuf is injected into the solenoid valve 12. At this point, the armature 24 is in the blocking position. The coil charging current kuf creates a magnetic field that counteracts the spring force exerted by the return spring 28 on the armature 24 without causing any armature movement. By injecting a coil charging current kuf in the blocking position of the armature 24, the opening time of the solenoid valve 12 is reduced because recharging the coil 22 requires less time.The control is such that the coil charging current kuf is injected into the solenoid valve 12 so shortly before the following opening phase fo, to avoid unnecessary energy consumption, that the specified coil charging current kuf is reached before the pull-in current kn is injected. Thus, the coil charging current kuf is not injected into the solenoid valve 12 during the entire closing phase tc.

[0035] The closing movement duration ts and the closed phase tc can be combined to form the time period DG during which the solenoid valve 12 is closed. The ratio of the time periods Do, DG during which the solenoid valve 12 is open and closed can be used to vary the applied quantity of spray fluid at a constant spray pressure. Reference symbol

[0036] 10 System 12 Solenoid valve 14 Line 16 Control device 18 Fluid inlet 20 Fluid outlet 22 Coil 24 Armature 26 Valve seat 28 Return spring 30 Housing

[0037] F Spray liquid Do, DG Duration I Current lAn Starting current kb Waste current

[0038] I On Coil charging current t Time to Closed phase tö Opening phase t H Holding phase ts Closing movement duration tsB Closing current duration tu Current flow reversal time U Voltage U A n Starting voltage U Ab Dropout voltage

[0039] Uent demagnetization voltage

Claims

Claims 1 . A method for controlling a pulse-width modulated solenoid valve (12) of an agricultural sprayer used for flow control, comprising the step: Impressing a starting current (l An ) into the solenoid valve (12) of the agricultural sprayer to cause an opening movement of an armature (24) from a blocking position to a release position; characterized by the step: Impressing a starting current (l An ) counter-polar waste stream (l A b) into the solenoid valve (12) to accelerate a closing movement of the armature (24) from the release position to the blocking position, assisted by a return spring (28) of the solenoid valve (12).

2. Method according to claim 1, characterized in that the impression of the starting current (l An ) by applying a pull-in voltage (U An) to the solenoid valve (12) and the injection of the waste stream (l A b) by applying a drop-out voltage (U A b) to the solenoid valve (12), whereby the pull-in voltage (U An ) and the dropout voltage (U A b) have different signs.

3. Method according to claim 2, characterized in that the magnitude of the starting voltage (U An ) and the magnitude of the dropout voltage (U A b) differ by less than 20 percent.

4. Method according to claim 2 or 3, characterized in that the drop-out voltage (U A b) is applied to the solenoid valve (12) for a predetermined, in particular valve- and / or application-specific, closing current duration (B).

5. Method according to claim 4, characterized in that the armature (24) moves from the release position into the blocking position within a closing movement duration (ts), wherein the closing current supply duration (tsß) is shorter than the closing movement duration (ts), longer than the closing movement duration (ts), or substantially corresponds to the closing movement duration (ts).

6. Method according to one of the preceding claims, characterized in that the application of the drop-out voltage (UA) is interrupted as soon as the coercive field strength is generated by the coil (22) of the solenoid valve (12).

7. Method according to one of the preceding claims, characterized in that the injection of the waste current (kb) into the solenoid valve (12) is carried out in such a way that the direction of current flow through the solenoid valve (12) is reversed during the closing movement of the armature (24) from the release position to the blocking position.

8. Method according to one of claims 1 to 7, characterized in that the injection of the waste current (kb) into the solenoid valve (12) is carried out in such a way that the direction of current flow through the solenoid valve (12) is reversed, during which time the armature (24) of the solenoid valve (12) is in the release position.

9. Method according to one of the preceding claims, characterized by the step: Impressing a coil charging current (IAU) into the solenoid valve (12), during which the armature (24) is in the blocking position, wherein the coil charging current (l Au f) preferably leads to a magnetic field which counteracts the spring force exerted by the return spring (28) on the armature (24) without causing an armature movement.

10. System (10) for flow rate control on an agricultural spraying device, comprising at least one solenoid valve (12) into which a starting current (l An ) can be impressed; and a control device (16) for controlling the solenoid valve (12); characterized in that a waste stream (l A b) can be impressed and in that the control device (16) is designed to control the solenoid valve (12) according to one of the preceding claims.

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