WO1999036718A1

WO1999036718A1 - Multi-step valve, especially an electromagnetic valve

Info

Publication number: WO1999036718A1
Application number: PCT/DK1999/000016
Authority: WO
Inventors: Søren LAURSEN
Original assignee: Danfoss A/S
Priority date: 1998-01-16
Filing date: 1999-01-12
Publication date: 1999-07-22
Also published as: AU1960999A; DE19801363A1; DE19801363C2

Abstract

A multi-step valve, especially an electromagnetic valve (14), has an actuating element (solenoid plunger 13) that has at least three defined positions and a closure member (6) which follows the actuating element, which closure member closes the valve in the first position, allows limited flow in the second position and opens the valve fully in the third position. The closure member (6) has a valve disk which co-operates with a valve seat (4) fixed relative to the housing and, in the transition from the second position to the third position, the closure member entrains, from an active position to an inactive position, an aperture member (7) which delimits a flow-determining aperture (8) of fixed dimension. In that manner, the flow rate in the second position can be limited very precisely.

Description

Multi-step valve, especially an electromagnetic valve

The invention relates to a multi-step valve, especially an electromagnetic valve, having an actuating element that has at least three defined positions and a closure member which follows the actuating element, which closure member closes the valve in the first position, allows limited flow in the second position and opens the valve fully in the third position.

Such a multi-step valve is known from DE 37 00 356 Al. It is intended especially for fuel injection installations. The closure member is a slider member that is formed integrally with a solenoid plunger. Two magnetic coils are provided, both or one or neither of which may be supplied with excitation current. Accordingly, under the influence of the magnetic force and counter-directed spring forces, the slider member adopts one of three positions. The slider member has an annular groove which co-operates with an annular groove in the housing. Complete registration of the annular grooves with one another yields the maximum flow; when there is no registration the valve is closed. Partial registration yields a limited flow. The latter case is extremely sensitive to tolerances. Even variations in the position of the slider member by a few tenths of a millimeter result in considerable changes in flow rate, typically by a factor of from 2 to 4. This is especially problematic when a very small fluid flow is to be set.

The problem underlying the invention is to provide a multi- step valve of the type described at the beginning, with which the limited flow can be set very precisely. That problem is solved according to the invention in that the closure member has a valve disk which co-operates with a valve seat fixed relative to the housing, and, during the transition from the second position to the third, the closure member entrains, from an active position to an inactive position, an aperture member which delimits a flow-determining aperture of fixed dimension.

In that construction, the limited flow rate is determined by an aperture of fixed dimension. The flow rate is accordingly determined with high precision. Because the aperture member is entrained by the closure member, the aperture can be rendered inactive in the third position.

Preferably the aperture is formed by the annular gap between the valve seat bore and an aperture member, in the form of an annular disk, mounted on the closure member at a position spaced from the valve disk. Provided that the aperture member is located in the valve seat, the aperture is active; it becomes inactive as soon as the aperture member emerges from the valve seat bore.

In another preferred alternative, the aperture is formed by at least one hole in a plate-shaped aperture member arranged between the closure member and the valve seat and entrained by a stop on the closure member during transition from the second position to the third. In this case, the stop, which is active after an idle stroke, ensures that the aperture is raised from the valve seat and thereby rendered inactive.

It is also recommended that the closure member be connected to a servo element which carries a servo valve seat, and that the actuating element carry the servo valve closure member, pressure being released to the low pressure side from a pressure chamber on the side of the servo element that is remote from the valve seat when the servo valve is opened. As a result of the use of the servo valve, the actuating element is decoupled from any loads that may act upon the valve disk, aperture member and the like. Accordingly, with low actuation forces there is obtained very precise positioning, the closure member immediately conforming thereto.

It is also advantageous for the actuating element to be formed by a solenoid plunger of an electromagnet having a coil, for a control device to be provided which delivers to the coil different excitation currents corresponding to the three positions, and for the solenoid plunger to be acted upon by a relatively weak spring which bears against a stop which is acted upon by a relatively strong spring, which in turn bears against a stop. By setting the appropriate excitation currents, there are automatically obtained the three positions required for controlling the valve.

In that context, it is also recommended that the cooperating faces of the solenoid plunger and of a core plug be conical faces. An approximately linear force/distance characteristic is thereby obtained, so making it is easier to adapt the necessary spring forces to the magnetic forces.

The invention is explained in greater detail hereinafter with reference to preferred embodiments shown in the drawings, in which:

Fig. 1 is a cross-section through a first embodiment of a multi-step valve according to the invention; and

Fig. 2 is a modified construction. A valve housing 1 has an inlet connection 2 and an outlet connection 3 and a valve seat 4. The underside of a servo element 5, in the form of a servo piston, forms a closure member 6 in the form of a valve disk. Between the closure member 6 and the valve seat 4 there is a plate-shaped aperture member 7 which has a number of holes which together form an aperture 8 of fixed dimension. The plate-shaped aperture member 7 can consist of a number of layers. The servo element 5 carries a hollow pin 9 which, at its upper end, has a servo valve seat 10 and which is surrounded by a spring 11 that acts upon the servo element 5 in the closing direction. Co-operating with the servo valve seat 10 is a servo valve closure member 12 carried by an actuating element, in this case, the solenoid plunger 13 of an electromagnetic valve 14.

The electromagnet 14 has a coil 15 and a core 16 which also includes a core plug 17. The co-operating faces 18 and 19 of the solenoid plunger 13 and of the core plug 17 are conical faces. The whole is enclosed in an insulating plastics casing 20. The core 16 is connected to an earth conductor 21. The coil 15 is connected via a connection 22 to a control device 23 which is able to deliver excitation currents of various magnitudes.

The solenoid plunger 13 is acted upon by a relatively weak spring 24 which bears against the shoulder of a pin 25. That pin is pressed against a stop 27 in the core plug 17 by a relatively strong spring 26 and in turn bears against a stop 28 that is fixed relative to the housing. In the rest position, the pin 25 is spaced a little way from a stop face 29 of the solenoid plunger 13.

On the side of the servo element 5 that is remote from the valve seat 4, there is a pressure chamber 30 which is supplied with the inlet-side pressure by way of a throttling bore 31, with the result that the closure member 6 is pressed against the plate-shaped aperture member 7 and the latter is pressed against the valve seat 4. When the servo valve closure member 12 is raised from the servo valve seat 10, the pressure in the pressure chamber 30 is released to the low pressure side 32, as a result of which the servo element 5 moves upwards until the servo valve is closed again. Accordingly, the servo element 5 and, with it, the closure member 6 follow the movement of the solenoid plunger 13.

When no excitation current is delivered, the parts adopt the position shown in Fig. 1. The solenoid plunger 13, which is in the first position, closes the servo valve seat 10 by means of its servo valve closure member 12. The spring 11 presses the closure member 6 onto the plate- shaped aperture member 7 and presses the latter onto the valve seat 4. The valve is closed.

When the electromagnetic valve 14 is supplied with a small excitation current, the solenoid plunger 13 is moved upwards until its stop face 29 comes into contact with the pin 25, with the result that the relatively strong spring 26 becomes active and prevents further movement of the solenoid plunger 13. The aperture 8 thus becomes active.

When a relatively large excitation current is delivered, the force of the relatively strong spring 26 is overcome and the solenoid plunger 13 moves upwards together with the pin 25 until the stop 28 has been reached. The servo element having the closure member 6 follows. Mounted on the servo element 5 is a stop 33 which entrains the aperture member 7 as soon as the servo element 5 moves from the second position to the third. The valve then adopts a large opening position. As soon as the excitation current is interrupted, the servo element 5 returns to the closed position under the influence of the spring 11 and the pressure in the pressure chamber 30.

In the construction according to Fig. 2, there are only a few modifications to be noted. The servo element 105 carries a closure member 6 in the form of a valve disk which co-operates directly with the valve seat 104. An aperture member 107 in the form of an annular disk engages the bore 140 of the valve seat 104. An aperture of fixed dimension is formed by an annular gap 141 between the circumference of the aperture member 107 and the wall of the bore 140 of the seat 104. The annular disk-shaped aperture member 107 is spaced a little way from the closure member 106. It emerges from the bore 140 when the servo element 105 moves from the second position to the third position.

In one example, the following data applied:

In position 1, that is to say without excitation current, the valve was closed. The air gap between the conical faces 18 and 19 was 6 mm.

In position 2, which was achieved by a coil current of 300 mA, the length of stroke of the valve disk 6 was from 0.5 to 1 mm, resulting in an air gap between the conical faces 18 and 19 of from 5 to 5.5 mm in size. The quantity delivered via the aperture 8 was from 2 to 3 litres/minute at a pressure of 1 bar. Accordingly, in comparison with the complete stroke, a very small stroke was sufficient in this case. In position 3, which was achieved by an excitation current of 500 mA, the length of stroke of the closure member 6 was from 5.5 to 6 mm, which corresponded to an air gap between the conical faces 18 and 19 of from 0.5 to 1 mm. This resulted in full flow via the freed valve seat 4. The quantity delivered was 40 litres/minute at 0.3 bar.

Modifications of the embodiments shown are possible in many respects without departing from the basic concept of the invention. For example, the displacement of the valve disks to a number of different positions can be effected also by actuating elements other than a solenoid plunger 13. The servo element may also be a servo diaphragm. Instead of a stop for determining the third position, it is also possible to achieve positioning by selecting the state of equilibrium between the magnetic force and the spring force. It is accordingly possible to alter the maximum opening of the valve by adjusting the excitation current or the spring force.

Claims

Patent claims

1. Multi-step valve, especially an electromagnetic valve, having an actuating element that has at least three defined positions and a closure member which follows the actuating element, which closure member closes the valve in the first position, allows limited flow in the second position and opens the valve fully in the third position, characterized in that the closure member (6; 106) has a valve disk which co-operates with a valve seat (4; 104) fixed relative to the housing, and, during the transition from the second position to the third, the closure member entrains, from an active position to an inactive position, an aperture member (7; 107) which delimits a flow-determining aperture of fixed dimension.

2. Multi-step valve according to claim 1, characterized in that the aperture (108) is formed by the annular gap between the valve seat bore (140) and an annular disk- shaped aperture member (107) mounted on the closure member (106) at a position spaced from the valve disk.

3. Multi-step valve according to claim 1, characterized in that the aperture (8) is formed by at least one hole in a plate-shaped aperture member (7) arranged between the closure member (6) and the valve seat (4) and entrained by a stop (33) on the closure member (6) during transition from the second position to the third.

4. Multi-step valve according to any one of claims 1 to 3 , characterized in that the closure member (6; 106) is connected to a servo element (5; 105) which carries a servo valve seat (10) , and the actuating element (solenoid plunger 13) carries the servo valve closure member (12) , pressure being released to the low pressure side (31) from a pressure chamber (30) on the side of the servo element (5; 105) that is remote from the valve seat (4; 104) when the servo valve is opened.

5. Multi-step valve according to any one of claims 1 to 4, characterized in that the actuating element is formed by a solenoid plunger (13) of an electromagnet (14) having a coil (15) , a control device (23) is provided which delivers to the coil (15) different excitation currents corresponding to the three positions, and the solenoid plunger (13) is acted upon by a relatively weak spring (24) which bears against a stop (27) which is acted upon by a relatively strong spring (26) , which in turn bears against a stop (28) .

6. Multi-step valve according to claim 5, characterized in that the co-operating faces (18, 19) of the solenoid plunger (13) and of a core plug are conical faces.