GAS VALVE AND METHOD FOR ACTUATION THEREOF

Abstract

A method for controlling the through-flow cross-section of a gas valve is described. The gas valve comprises a valve body in which a flow channel is provided, a valve element which can be displaced therein between a closed position and an opened position, an armature, a coil, a spring and a control circuit. For opening the flow channel, the control circuit excites the coil with a pulse width-modulated current, the pulse duty factor of which, starting from a starting value, is increased until the armature starts moving out of the closed position against the effect of the spring. Then, the control circuit reduces the pulse duty factor before the valve element has reached the opened position. The control circuit then sets the pulse duty factor at a predefined holding value with which the valve element is held in the opened position.

Claims

1. A method for controlling the through-flow cross-section of a gas valve, which comprises a valve body in which a flow channel is provided, a valve element which can be displaced therein between a closed position and an opened position, an armature, a coil, a spring and a control circuit, wherein the following steps are provided in order to open the flow channel: the control circuit excites the coil with a pulse width-modulated current, the pulse duty factor of which, starting from a starting value, is increased until the armature starts moving out of the closed position against the effect of the spring; the control circuit reduces the pulse duty factor before the valve element has reached the opened position; the control circuit sets the pulse duty factor at a predefined holding value with which the valve element is held in the opened position.

2. The method of claim 1 wherein a current sensor evaluates the current flowing through the coil in order to detect a movement of the armature.

3. The method of claim 1 wherein the control circuit reduces the pulse duty factor gradually as soon as the armature starts moving towards the opened position.

4. The method of claim 1 wherein the control circuit keeps the pulse duty factor constant, once it has been reduced, until it is finally set at the holding value.

5. The method of claim 1 wherein the control circuit varies the pulse duty factor, once it has been reduced, until it is finally set at the holding value.

6. The method of claim 1 wherein the holding current is shut off in order to close the through-flow cross-section.

7. The method of claim 6 wherein the holding current is reduced first, before it is then fully shut off.

8. A gas valve having a valve element, a valve seat with which the valve element can cooperate in order to close or clear the through-flow cross-section, a spring which urges the valve element into a closed position, an armature which is connected to the valve element, a coil with which the armature can be displaced into an opened position against the effect of the spring, a control circuit which can provide a pulse width-modulated signal to excite the coil, and a current sensor with which the current flowing through the coil can be monitored in such a way that the method according to claim 1 can be carried out.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will be described hereinafter with the aid of an embodiment which is illustrated in the attached drawings. In the drawings:

[0024] FIG. 1 schematically shows a gas valve in accordance with the invention; and

[0025] FIG. 2 shows a diagram of the pulse duty factor of the current flowing through the coil of the gas valve shown in FIG. 1 during opening and closing of the gas valve.

DETAILED DESCRIPTION OF THE INVENTION

[0026] FIG. 1 shows a gas valve 10 which has a valve body 12 in which a flow channel 14 for combustion gas is provided. A combustion gas can flow through the flow channel 14 when it is open, said gas being provided via a supply line 16 from e.g. a compressed gas cylinder and being fed via a connection line 18 to a gas burner.

[0027] A valve element 20 is displaceably disposed in the valve body 12 and can cooperate with a valve seat 22 (schematically illustrated herein as a wall of the flow channel 14) in such a way that, when the valve element 20 is in the closed position, the through-flow cross-section is closed by the flow channel 14; no gas can flow through the gas valve 10.

[0028] An armature 24, which can likewise be displaced in the valve body 12, is connected to the valve element 20 (or is formed as one piece therewith). The armature 24 is allocated a single coil 26.

[0029] Furthermore, a spring 28 is provided which urges the armature 24 and the valve element 20 into the closed position shown in FIG. 1.

[0030] The gas valve 10 also has a control circuit 30 which provides actuation electronics 32 with a control signal S. The actuation electronics 32 provide the current which flows through the coil 26.

[0031] A current sensor 34 is also integrated into the actuation electronics 32, the current sensor being used to monitor the current flowing through the coil 26. The current sensor 34 provides the control circuit 30 with a feedback signal R so that information about the level of the current flowing through the coil 26 is available in the control circuit 30.

[0032] The actuation electronics 32 excite the coil 26 with a pulse width-modulated current, i.e. a current which is switched on and off periodically corresponding to a preset ratio. The power regulation is thus effected in that the voltage applied to the coil 26 is switched on and off periodically between 0 and the supply voltage, wherein the effective current flow is produced as the average of the current which flows on average in the phases with the voltage switched off and the phases with the voltage applied. A characteristic variable for such pulse width modulation is the so-called pulse duty factor which specifies the proportion of the phases with the voltage switched on in relation to the total cycle duration. With a pulse duty factor of 0.9, the supply voltage is thus applied for a duration of 90% of a period, while it is switched off for a duration of 10%.

[0033] The opening and closing of the valve element 20 will be explained hereinunder with the aid of an exemplified embodiment and FIG. 2.

[0034] At time t.sub.0, the control electronics 30 begin to open the gas valve 10. For this purpose, an increasing level of current is applied to the coil 26, in this case illustrated by an increasing pulse duty factor.

[0035] In the exemplified embodiment, the current supply begins with a pulse duty factor of 0. It is also possible for a value above 0 to be selected as the starting value.

[0036] The pulse duty factor increases until, at time t.sub.1, the valve element 20 and the armature 24 begin to leave the fully closed position (see the arrow P in FIG. 1). This is detected by the current sensor 34 since the armature 24 moving relative to the coil 26 changes the inductance of the coil so that the current flowing through the coil also changes.

[0037] The pulse duty factor required to open the valve element 20 can be different. For example, when the gas valve 10 has not been activated for a prolonged period of time, a greater force may be required to open the valve element 20, which may be slightly stuck, than when the valve element 20 has been regularly opened and closed during ongoing operation.

[0038] As soon as it is detected that the valve element 20 and the armature 24 are moving, the pulse duty factor is reduced in order to prevent the armature 24 and the valve element 20 from being accelerated further. With the reduced pulse duty factor, the armature 24 and the valve element 20 are displaced further until, at time t.sub.2, the fully opened position is reached.

[0039] At time t.sub.2, the pulse duty factor is reduced further since, in this state, only a holding current has to be provided, with which the armature 24 and the valve element 20 must be held in the completely opened position against the effect of the spring 28 (see the phase from time t.sub.2 to time t.sub.3).

[0040] When the gas valve 10 is to be closed, the pulse duty factor is reduced to 0 (see the phase from t.sub.3 to t.sub.4). In the exemplified embodiment shown herein, the pulse duty factor is not suddenly set to 0 but rather reduced to 0 in a continuous manner.

[0041] In the illuminated exemplified embodiment, during the opening phase of the valve element 20 (phase of time between t.sub.1 and t.sub.2) a constant pulse duty factor is used in this case. However, in dependence upon the framework conditions it can also be possible to use a pulse duty factor which decreases still further so that the armature 24 moves into its fully closed position in the gentlest manner possible.

[0042] Alternatively, provision can also be made for the pulse duty factor between t.sub.1 and t.sub.2 to be increased somewhat in order to compensate for the force of the spring 28 which increases as the degree of opening increases.