A controller for a solenoid valve and a solenoid valve

Abstract

Described is, among other things, a controller for a solenoid valve. The controller being configured to supply a voltage to a solenoid of the solenoid valve and to monitor a current in the solenoid. The controller is further configured to detect valve activation based on the monitored current, where the current is varied during the valve activation phase.

Description

[0001] A CONTROLLER FOR A SOLENOID VALVE AND A SOLENOID VALVE

[0002] TECHNICAL FIELD

[0003] The invention relates to a controller for a solenoid valve and related devices and methods.

[0004] BACKGROUND

[0005] A solenoid valve is a device that can shut off or allow a fluid flow such as an air flow, when electrically energized or de-energized. It has an actuator that pulls a plunger or pivoted armature or similar against a spring force. The valve can be direct-acting, internally piloted, or externally piloted, and can have different types of port connections and flow paths.

[0006] In a typical implementation for a normally closed valve, when a solenoid valve is energized, a magnetic field builds up which pulls a plunger or pivoted armature (or some other device) against the action of the spring force. This movement opens the valve and allows fluid to flow through it. When the solenoid valve is de-energized, the plunger or pivoted armature is returned to its original position by the spring action, and the valve closes. Solenoid valves can also be used for a normally open valve. A normally open solenoid valve is open in its de-energized state. There are various designs, for example a basic design has the armature positioned high up in the coil. So, when the valve energizes, the armature is pulled down towards the centre of the coil. A plunger or piston attached to the armature moves down, closing the valve.

[0007] Solenoid valves are typically used to control the flow of liquids or gases in a wide range of applications, such as in industrial automation, fluid control systems, and more. Solenoid valves are operated by applying a voltage to an electromagnetic coil / solenoid, which generates a magnetic field, causing the valve to open or close and remove the voltage to allow the plunger or similar device to return. The coil's resistance limits the current to a safe level, and the valve returns to its default state by the spring force when the voltage is removed

[0008] The amount of current that flows through the solenoid coil is determined by Ohm's law (I = U / R), where "I" is the current, "U" is the voltage, and "R" is the coil's resistance / impedance. The resistance of the coil is a fixed property of the solenoid valve and is designed to limit the current to a safe level.

[0009] SUMMARY

[0010] It is an object of the present invention to provide an improved control and or functioning of a solenoid valve.

[0011] This object is obtained by the devices and methods as set out in the appended claims.

[0012] In accordance with the invention, a controller for a solenoid valve is provided. The controller being configured to supply a voltage to a solenoid of the solenoid valve and to monitor a current in the solenoid. The controller is further configured to detect valve activation based on the monitored current, and to control the valve based on the detected valve activation. The controller is configured to during a valve activation phase, before valve activation is detected, supply a first voltage to the solenoid. The controller is further configured to supply a second voltage lower than the first voltage to the solenoid when valve activation is detected. Hereby, a lower voltage can be supplied when the valve is activated whereby energy can be saved. The controller is configured to during the valve activation phase first supply the first voltage during a first time period and to then supply a third voltage being lower than the first voltage during a second time period following the first time period, where the third voltage is higher than the first the second voltage. Hereby a voltage control that allows for an improved detection of the valve activation can be provided.

[0013] The controller can be configured to control the voltage supplied to the solenoid based on the detected valve activation. Hereby, a more efficient voltage supply can be obtained. For example, a more energy efficient control can be provided.

[0014] In accordance with one embodiment, the controller is configured to control the flow of the valve using pulse width modulation PWM, and where the controller is configured to control the PWM based on the detected valve activation. Hereby a more precise PWM control can be obtained that can take into account the actual activation time of the valve. For example, the controller can be configured to set the closing time or the opening time of the valve based on the time of the detected valve activation. This is particularly useful when the switching of the PWM controlled valve is performed at a high rate such as more than io Hz such as 50 or 100 Hz

[0015] In accordance with one embodiment, the controller is configured to determine a system pressure based on the detected valve activation, and to control the valve based also on the determined system pressure. Thus, for example the activation time for the solenoid valve typically depend on the pressure over the solenoid valve. The pressure over the solenoid valve typically corresponds to the system pressure whereby the system pressure can be determined from the time of opening of the solenoid valve. Hereby control of the valve can be based on a determined system pressure without the need for a dedicated pressure sensor.

[0016] In accordance with one aspect of the invention, a controller for a solenoid valve is provided. The controller being configured to supply a voltage to a solenoid of the solenoid valve and to monitor a current in the solenoid. The controller can be further configured to detect valve activation based on the monitored current, and to determine a system pressure based on the detected valve activation. Hereby system pressure can be determined without a dedicated pressure sensor. The valve can be controlled based on the determined system pressure or different types of diagnosis of the pressure system can be performed without the need for a dedicated pressure sensor.

[0017] The invention also extends to a solenoid valve comprising the controller according to the above. The solenoid valve can in some implementations be a PWM controlled solenoid valve. The solenoid valve can advantageously be a low-inductance solenoid valve.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention will now be described in more detail, by way of example, and with reference to the accompanying drawings, in which:

[0020] - Fig. la illustrates a schematic view of a solenoid valve,

[0021] - Fig. lb is a schematic diagram illustrating a pneumatic system,

[0022] - Figs. 2a and 2b are diagrams illustrating voltage and current curves in a first implementation,

[0023] - Figs. 3a and 3b are diagrams illustrating voltage and current curves in a second implementation, - Figs. 4a and 4b are diagrams illustrating voltage and current curves in a third implementation,

[0024] - Fig. 5 is a flow chart illustrating some steps performed when controlling a solenoid valve, and

[0025] - Fig. 6 illustrates a controller.

[0026] DETAILED DESCRIPTION

[0027] The invention will now be described more fully hereinafter with reference to the accompanying drawing, in which certain exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. For example, like or similar components of different embodiments can be exchanged between different embodiments. Some components can be omitted from different embodiments. Like numbers refer to like elements throughout the description.

[0028] In Fig. 1, a schematic view of a solenoid valve 10 is depicted. The solenoid valve 10 can typically be a pneumatic solenoid valve. The solenoid valve 10 typically comprises a core 11 of a magnetizable material such as materials used in transformer plates. The core 11 can be magnetized by supplying a voltage to the solenoid 12 driving a current in a coil or solenoid 12 wound around the core 11. When magnetized, the core 11 can attract a plunger 14 or some other magnetic member from a valve seat 15 over a gap 13 to activate the valve 10. The plunger is typically spring biased and will return to its initial position at the valve seat 15 when the supplied voltage is deactivated.

[0029] Fig. la also depicts a voltage source 31 and a controller 32. The controller 32 can be operative to control the valve 10 as will described below by controlling the voltage supplied from the voltage source 31. The valve 10 can be any type of solenoid valve. In accordance with some embodiments the flow through valve 10 can be controlled using a Pulse Width Modulated, PWM, signal. The PWM control can be used to control the flow in the solenoid valve by switching the solenoid valve between open and closed positions at a high rate such as several Hz. For example, the solenoid valve can be switched at a rate of 10 Hz or more such as 40, 50 or even 100 Hz.

[0030] In addition to using PWM for controlling the flow through the valve, PWM can also be applied to regulate the voltage supplied to the solenoid coil itself. In this approach, rather than supplying a continuous DC voltage, the voltage is rapidly switched on and off at a high frequency. By adjusting the duty cycle of this switching, the effective voltage seen by the solenoid can be controlled. This method can be beneficial for reducing power consumption and managing heat dissipation while still maintaining the plunger in its activated state. For example, after the initial activation phase, instead of applying a steady holding voltage, PWM control can be used to maintain an average voltage sufficient to keep the valve open while reducing overall energy usage.

[0031] In Fig. ib, is a schematic diagram illustrating a pneumatic system is depicted. The diagram shows a compressor generating a system pressure. The system pressure is supplied to the valve 10. The valve 10 can then be used to control the pressure to a pneumatic tool.

[0032] In Fig. 2a, a diagram illustrating supply of a voltage U to the solenoid 12 during the time t. The voltage can be supplied from the voltage source 31 and controlled by the controller 32. The voltage supplied to the solenoid 12 will cause a current I to flow in the solenoid 12. In Fig. 2b, a diagram of the current I in the solenoid 12 is illustrated over the time t. As current builds up over time in the solenoid 12, the core 11 will be magnetized and at some point, the magnetic force will attract the plunger 14 to leave its position at the valve seat. Thus, as voltage is applied, current begins to build up in the solenoid 12. Initially, the plunger 14 will not move. The current is limited by the resistance and inductance of the solenoid 12. Initially, the current buildup is predominantly influenced by the inductance. As current increases, the magnetic force on the plunge is increased. The force is working to close the magnetic circuit by closing the air gap 13.

[0033] When the magnetic force is larger than the forces holding the plunger 14 in place, the plunger will start to move. There can for example be a spring force, and also there can be a force from a pressure difference over the valve sealing and other forces that have to be overcome by the magnetic force. When the magnetic force is strong enough, the plunger 14 will start to move from a position with an open magnetic circuit to a closed magnetic circuit. This will give a counter electromagnetic force EMF. This counter EMF will work against current build up. As a result, current build up will decrease as a result of this movement. In other words, the increase rate (derivative) of the current will be reduced.

[0034] When the plunger 14 reaches its final position, closing the magnetic gap, the counter EMF disappears instantaneously. This leads to a discontinuity in the derivative of the current over time, represented as a sharp bend or sudden change. This is indicated by reference numeral 50 in Fig. 2b.

[0035] As has been realized, the voltage required to activate the plunger 14 is higher than the voltage required to keep the plunger in an activated state. Thus, energy can be saved by reducing the voltage once the plunger has been activated. In other words, there is typically a need for a relatively high voltage to cause activation of the plunger. However, once the plunger is activated, the required voltage to maintain the plunger in an activated state is much lower. Consequently, a high voltage should only be applied long enough to ensure that valve goes from deactivated state to activated state. By detecting when the valve is activated energy can be saved by lowering the applied voltage during the remaining time of the activated state. This is illustrated in Figs. 3a and 3b.

[0036] In Fig. 3a, a diagram illustrating the current when applying such a control scheme. Thus, when the activation of the plunger is detected at 50, the voltage can be reduced resulting in a lower current in the solenoid 12. The lower voltage will result in lower energy losses and energy can be saved. The detection of the activation of the plunger can be performed by monitoring a parameter such as the derivative, increase rate, or similar of the current and compare the parameter to a threshold value to determine activation of the plunger.

[0037] Fig. 3b is a diagram showing the applied voltage when detecting an activated plunger and then reducing the applied voltage. Thus, during a valve activation phase before valve activation is detected, a first voltage is supplied to the solenoid. Then, when valve activation is detected, a second voltage lower than the first voltage is supplied to the solenoid.

[0038] In order to facilitate detection of the activation of the plunger 14, the voltage can be somewhat reduced at a time prior to when the plunger is expected to be activated. For example, one problem that can arise is that in fast valves with low inductance, the counter-EMF is low compared to the voltage applied to activate valve. To reduce this problem, an initial full voltage can in accordance with one embodiment be applied to the solenoid valve for a set duration to initiate valve opening. In another embodiment, an initial full voltage is applied until a preset current is detected. However, this predetermined time or preset current is chosen so that the valve is not fully open yet. Then, the voltage is reduced to a lower level to enhance the ability to observe current spikes that occur during the valve's opening process. This transition to the lower voltage level occurs before the valve reaches its fully open position, allowing for precise monitoring. Once the valve is fully open, the control system enters a "hold phase," maintaining the valve's open position using reduced voltage or current. This approach ensures both efficient energy usage and accurate control of the valve's opening process. The lower voltage level during the last part of the opening phase is lower than the full voltage but higher than the voltage required for maintaining the valve in an activated state.

[0039] One advantage of using a low-inductance solenoid valve is that it allows for faster operation, enabling quick response times in applications requiring rapid actuation. However, a key drawback is that the initial opening of the valve can be more challenging. As discussed earlier, low-inductance coils generate a weaker counter-electromotive force (EMF) during activation, making it harder to detect the exact moment the plunger moves.

[0040] To improve detection, the voltage can be lowered before the plunger is expected to activate. This increases the proportion of the counter-EMF relative to the externally applied voltage, making the current response more pronounced and easier to monitor. However, reducing the voltage too early slows down the valve's opening. A balance must be struck between improving detectability and maintaining a fast response. One effective strategy is to apply a high voltage until the current reaches a certain threshold, then lower the voltage to facilitate detection before finally switching to a holding current once activation is confirmed.

[0041] Fig. 4a illustrates a diagram of how the supplied voltage can be supplied in accordance with an exemplary embodiment. First, during an initial phase, a high voltage is supplied to quickly build up a current in the solenoid. After some time, before the plunger us expected to be activated, the supplied voltage is lowered. This will result in a slower build up of current in the solenoid 12. As a result, the ratio of the voltage from counter EMF compared to voltage from external voltage applied is increased. Hereby, the discontinuity in the derivative in the current curve at reference numeral 50 will be more pronounced and easier to detect. Once the activation of the plunger 14 is detected the supplied voltage can be even further reduced in accordance with the example described in conjunction with Figs. 3a and 3b. The corresponding diagram for the current I is shown in Fig. 4b.

[0042] In most solenoid valves, the current required to transition from the closed to the open state is significantly higher than the current needed to keep the valve open. This is because overcoming the initial mechanical resistance — such as spring force or friction — requires a strong electromagnetic force.

[0043] Once the plunger has moved and the valve is fully open, much less current is needed to maintain its position. For a solenoid valve designed to be operated with 24 V that requires 5 A to transition from closed to open state and 1 A to keep the valve open, an optimized activation sequence can be as follows:

[0044] - Apply 24V until the current reaches 4A. This ensures a rapid buildup of force to initiate movement.

[0045] - Reduce the voltage to 12V to slow the current increase and enhance detection of the plunger movement.

[0046] - Once plunger activation is detected, transition to a holding phase by regulating the current to 1A, ensuring energy-efficient operation.

[0047] This method balances speed, detection accuracy, and power efficiency, ensuring the valve opens quickly while minimizing excess power consumption.

[0048] The speed at which a solenoid valve operates is influenced by its electrical time constant r which is given by r=L / R where L is the inductance of the coil R is its resistance. A lower inductance results in a smaller time constant, allowing the current to build up more quickly and enabling faster actuation of the valve. For practical reference, low-inductance solenoid valves typically have time constants below 5 ms, meaning they respond quickly to changes in voltage. In contrast, higher-inductance valves, with time constants in the range of tens or hundreds of milliseconds, exhibit slower response times due to the delayed buildup of current.

[0049] The time of activation as determined at point 50 can also be used for control of a pulse width modulated PWM solenoid valve. Thus, to regulate flow of the medium, for example air. passing through the solenoid valve, Pulse Width Modulation PWM, can be used. The solenoid valve is then rapidly cycled between fully open and fully closed positions. By varying the duration of "on" time (duty cycle) in proportion to the desired flow rate. Longer "on" periods allow more flow, while shorter "on" periods restrict it. By adjusting the duty cycle based on the desired flow rate, precise flow control can be achieved without the need for a continuously variable valve, making it a cost-effective and efficient method in many applications.

[0050] However, as has been realized, the time at which the solenoid valve is activated, which corresponds to the start of the “on” time, can vary thereby making the duration of the “on” time less precise. By detecting the actual activation time of the valve, a more precise duty cycle can be obtained in that the actual time for valve activation is known in the PWM control of the solenoid valve.

[0051] Thus, if the time to open the valve varies, the resulting flow from the valve when controlled using PWM varies. The information from detecting time to open valve can be used to compensate the electrical signal to the valve. Example of a procedure where a valve is desired to be activated during a set time.

[0052] 1. Valve activation procedure is started

[0053] 2. Valve is detected to have activated

[0054] 3. Valve is held in activated state during the desired set time “on” time”. Time starting from the time when valve is detected to have activated.

[0055] 4. Valve is deactivated

[0056] Consider a case where a 50% duty cycle is applied at a valve operating frequency of 100 Hz. This means the valve is activated at o ms and deactivated at 5 ms, with the cycle repeating every 10 ms.

[0057] - If the valve opens exactly on time, the intended flow rate is achieved.

[0058] - However, if the valve takes 1 ms longer to fully open (i.e., instead of opening immediately at o ms, it fully opens at 1 ms), the effective open time is reduced to 4 ms instead of 5 ms, leading to a lower-than-intended flow rate.

[0059] - Conversely, if the valve opens 1 ms faster, it will allow flow for 6 ms, causing a higher-than-intended flow rate.

[0060] This variation in flow can be problematic, especially in precise control applications.

[0061] To address this, the control system can detect the actual valve opening time and adjust the PWM duty cycle accordingly.

[0062] - If the valve is detected to open 1 ms later than expected, the closing command can be delayed to 6 ms instead of 5 ms, ensuring the effective open time remains 5 ms.

[0063] - If the valve opens 1 ms earlier, the closing command is instead sent at 4 ms, keeping the flow rate stable.

[0064] By dynamically adjusting the PWM signal based on the detected valve response time, flow variations due to opening delays are minimized, ensuring a more stable and predictable system behavior.

[0065] Hereby the duty cycle of a PWM solenoid valve can be controlled with higher precision.

[0066] In another embodiment, the detection of valve activation is used to estimate the pressure difference over the valve. The pressure difference over the valve can in some applications be the system pressure, i.e. the pressure supplied to the valve. One factor that will impact time to activate valve is pressure. The information of time to activate valve can therefore be used to calculate pressure. For a specific valve and coil and voltage, the time to activate valve as a function of pressure difference over valve can be mapped and stored. The mapped information can for example be stored in a look-up table that can be used by the controller 32 when controlling the valve 10. The mapping information can be used, when the time to activate valve has been determined, the pressure can then be calculated / read from the stored map based on the activation time of the valve.

[0067] The pressure difference over valve can hereby be determined and can be used to reduce the number of pressure sensors. Since the pressure difference over a valve can be determined by using only stored parameter values and the time for activation of the valve, the need for additional physical pressure sensors can be reduced or in some implementations eliminated. For systems, where pressure information is required, this is cost saving.

[0068] Also, the detected valve activation time can be used to detect a pressure loss. Loss of pressure in a system can result in system not working as intended. A large deviation, above some threshold value, in the activation time can be used to indicate a pressure drop or similar. Detection of pressure loss increases safety and possibility of diagnosis. Further, flow control of the valve can also be improved. Fig. 5 is a flow chart illustrating some steps performed when detecting valve activation in a solenoid valve supplied with a voltage to a solenoid of the solenoid valve.

[0069] First, in a step 501 current in the solenoid is monitored. Valve activation is then detected based on the monitored current in a step 503 for example by detecting a current derivative over / under some pre-determined threshold value. In accordance with one embodiment, multiple threshold values are employed to detect valve activation. For example, activation can be determined when the detected derivative is first above a first threshold value, then below a second threshold value and thereafter above a third threshold value. The solenoid valve is then controlled based on the detected valve activation in a step 505.

[0070] For example, the voltage supplied to the solenoid can be controlled based on the detected valve activation in a step 507. The voltage can for example be controlled to, during a valve activation phase before valve activation is detected, supply a first voltage to the solenoid, and to supply a second voltage lower than the first voltage to the solenoid when valve activation is detected. Also, during the valve activation phase, the first voltage can be supplied during a first time period and then a third voltage being lower than the first voltage is supplied during a second time period, where the second voltage is lower than both the first voltage and the second voltage.

[0071] In another example, when the flow of the valve is controlled using pulse width modulation PWM, the PWM control can be based on the detected valve activation in a step 509. For example, the closing time or the opening time of the valve can be based on the time of the detected valve activation. Thus, the “on” time of the PWM cycle can be controlled based on the detected valve activation. Also, in another example, a system pressure can be determined based on the detected valve activation in a step 511. The valve can then be controlled also based on the determined system pressure. The determined system pressure can also be used to determine a pressure drop or when performing other forms of system pressure diagnosis.

[0072] In Fig. 6, a controller 32 for controlling the valve 10 in accordance with the above is depicted. In particular the controller can be provided to control the voltage supplied to the valve 10. The controller 32 can comprise an input / output 81 for receiving input signals for parameters used for controlling the valve as set out above. For example, the input signals can be a current sensor signal representing the current flowing in the solenoid 12. The output signals can be a control signal for controlling the voltage supplied to the valve or it can be switching times for a PWM switched valve or some other parameters such as a determined system pressure. The controller 32 further comprises a micro-processor or some other suitable data processing device such as a Central Processing unit (CPU) or a Digital Signal processor (DSP) that also can be referred to as a processing unit 82. The processing unit 82 is connected to and can execute computer program instructions stored in a memory 83. The memory 83 can also store data that can be accessed by the processing unit 82. The data in the memory can comprise pre-stored data relating to the valve 10 such as normal activation times etc. The computer program instructions can be adapted to cause the controller to control the valve and to generate other output in accordance with the teachings herein. The controller 32 can be located at any suitable location. For example, the controller 32 can be integrated in the valve or be a separate unit. The controller 32 can also be distributed at different locations.

Claims

Claims1. A controller (32) for a solenoid valve (10), the controller being configured to- supply a voltage to a solenoid of the solenoid valve- monitor a current in the solenoid,- detect valve activation based on the monitored current, and- control the valve based on the detected valve activation, wherein the controller is configured to:- supply a first voltage to the solenoid during a valve activation phase, before valve activation is detected,- supply a second voltage, lower than the first voltage, to the solenoid when valve activation is detected, and wherein the controller is configured to during the valve activation phase: first supply the first voltage during a first time period and to then supply a third voltage being lower than the first voltage during a second time period following the first time period, wherein the third voltage is higher than the second voltage.

2. The controller (32) according to claim 1, wherein the controller is configured to control the voltage supplied to the solenoid based on the detected valve activation.

3. The controller (32) according to claim 1 or 2, wherein the controller is configured to control the flow of the valve using pulse width modulation, PWM, and wherein the controller is configured to control the PWM based on the detected valve activation.

4. The controller (32) according to any one of claims 1 - 3, wherein the controller is configured to set the closing time or the opening time of the valve based on the time of the detected valve activation.

5. The controller (32) according to any one of claims 1- 4, wherein the controller is configured to:- determine a pressure over the valve based on the detected valve activation, and- control the valve based also on the determined pressure over the valve.

6. A solenoid valve (10) comprising the controller (32) according to any one of claims 1 - 5.

7. The solenoid valve (10) according to claim 6, wherein the solenoid valve is a PWM controlled solenoid valve.

8. The solenoid valve (10) according to claim 6 or 7, wherein the solenoid valve is a low-inductance solenoid valve.

9. The solenoid valve (10) according to claim 8, wherein the solenoid valve has a time constant of 5 ms or less.

10. The solenoid valve (10) according to any one of claims 6 - 9, wherein the solenoid valve is a pneumatic solenoid valve.

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