GB2272747A

GB2272747A - Solenoid valve

Info

Publication number: GB2272747A
Application number: GB9323615A
Authority: GB
Inventors: Helmut Rembold; Walter Teegen
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1992-11-17
Filing date: 1993-11-16
Publication date: 1994-05-25
Anticipated expiration: 2013-11-16
Also published as: GB9323615D0; GB2272747B; DE4238727C2; JPH06213357A; DE4238727A1

Abstract

A solenoid valve for use with a fuel injection pump comprises a valve member (11) which is axially guided in a bore, being displaceable by a solenoid (not shown), and whose outer surface tapers from a cylindrical portion to a reduced diameter by way of a conical surface (15), wherein the conical surface (15) cooperates with a conical valve seat (13). The angle of taper of the conical surface (15) is slightly larger than the angle of the valve seat surface (13), so that the valve member (11) cooperates with the valve seat surface (13) by way of a sealing edge (17) produced at the transition between the cylindrical portion of the valve member and the conical surface (15). To avoid cavitation damage in the region of the sealing surfaces, a throttle is disposed downstream of the sealing edge (17). The throttle may be provided by an annular groove (62) in one of the conical surfaces (13, 15). <IMAGE>

Description

a 2272747

DESCRIPTION

SOLENOID VALVE The invention relates to solenoid valves for controlling a connection between a high pressure chamber, such as a pump working chamber of a fuel injection pump, and a low pressure chamber.

In a solenoid valve of the kind known from EP 0 309 797 Bl, which has a valve member axially guided in a guide bore of the valve housing and moved by a solenoid against the force of a return spring to control a flow through a connection between a highpressure chamber and a low- pressure chamber, a flow cross section is formed by the separation of a conical surface, disposed on the valve member, from a conical valve seat in the valve housing, there being incorporated in the valve housing above and below the valve seat a respective annular chamber into which the highpressure line and the low-pressure line open, respectively. The valve member, in the form of a hollow cylinder, is connected by way of a stem to a flat armature upon which the solenoid acts. The flow passage between the high-pressure chamber and the lowpressure chamber is closed by a sealing edge, formed on the valve member by the transition of the conical surface to the cylindrical outer surface being brought -2into contact with the surface of the conical valve seat, the passage between the conical surface of the valve member and the valve seat being such that the largest possible flow cross section may be opened rapidly at the commencement of the opening stroke and is continuously enlarged during the further course of the opening stroke.

In this connection, the flow cross section of the known injection valve has the disadvantage that. as a result of the high velocities of flow, the pressure of the fluid at the sealing edge, and in the flow cross section between the conical surface of the valve member and the valve seat,, drops below the vapour pressure and vapour bubbles or cavities are formed which implode upon coming into contact with a wall where through the known hollow charge effect they cause cavitation damage which may lead to heavy wear on the solenoid valve and to its failure.

The invention resides in a solenoid valve for controlling the flow through a connection between a high-pressure chamber which is at least intermittently brought to high fluid pressure and a low-pressure chamber, having a valve body inserted into a valve housing and a bore in the valve body and in which a valve member in the form of a piston is displaceable by a solenoid against the force of a return spring 1 -3wherein, starting from a circular cylindrical outer surface, the piston tapers to a reduced diameter by way of a conical surface, the conical surface cooperating with a conical valve seat of the valve body, which seat connects a high-pressure chamber, surrounding the circular cylindrical outer surface of the piston, to a low-pressure chamber surrounding the reduced diameter portion of the piston, the cone angle of the valve seat being smaller than the cone angle of the conical surface of the piston, so that the piston cooperates with the valve seat by way of a sealing edge produced at the transition between the cylindrical outer surface of the piston and the conical surface and wherein a throttle which becomes effective upon commencement of the opening stroke is disposed downstream of the sealing edge in the direction of flow from the high-pressure chamber to the low-pressure chamber.

This valve has the advantage that, by disposing a throttle downstream of the sealing edge, in the region of the flow cross section, the local pressure of the fluid is prevented from dropping below the vapour pressure, and thus the formation of cavities and its consequential cavitation damage may be avoided. This throttling effect is effective particularly at the commencement of the opening stroke and decreases -4during the further course of the opening stroke, during which the difference in the flow velocities upstream and downstream of the flow cross section, and in the region thereof, are reduced.

It is particularly advantageous to form this throttle by a throttling path in the region of the flow cross section between the conical surface of the valve member and the valve seat, this being achieved by the construction of the conical surface with an angle to the axis of the valve member only slightly larger than that of the valve seat. the circumference of the flow cross section at the commencement of the opening stroke becoming smaller from the sealing edge towards the axis of the valve member far more rapidly than the height of the gap increases, so that the flow cross section decreases and thus acts as a diffuser throttle.

In order to obtain a reliable throttling action in larger solenoid valves and over a longer period of the opening stroke. it is also advantageous to provide, within the flow cross section, a widening of the cross section andr contiguous thereto,a reduction in the cross section, wherein a labyrinth like transition is obtained which reduces the flow velocity and thus the tendency to cavitation.

A throttling path. formed by an annular gap I between the cylindrical outer surface of the valve member and the wall of the valve body surrounding the said outer surface, is disposed downstream of the flow cross section in order to continue the throttling action even when the flow cross section is fully open. As a further result, the initially acting throttling path is supplemented by a throttling path having an annular cross section whose throttling action persists independently of the opening stroke of the valve member. A throttling path, acting in the early part of the opening stroke and also having an annular cross section, may be connected upstream instead of or alternatively, in addition to the aforementioned throttling path.

A further advantage may be obtained if an axial bore, connected to a lowpressure chamber, is disposed within the valve member for the purpose of pressure equalization and a bore leads from the axial bore and opens into the region of transition between the diffuser throttle and the annular throttle gap so that a portion of the fluid displaced within the axial bore during the opening stroke flows into this transition region and thus keeps any cavities which occur away from the wall of the valve body and flushes them into unendangered regions.

This invention is further described, by way of -6example only, with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal section through the solenoid valve in accordance with the invention; Figure 2 shows a portion of the valve of Figure 1, in which a first embodiment of the throttling path is shown in the form of a diffuser; Figure 3 shows a second embodiment analogously to the illustration of Figure 2, in which the throttling path is interrupted by an annular groove; Figure 4 shows a third embodiment analogously to Figure 3, in which an annular throttle gap is disposed downstream of the throttling path; and Figure 5 shows a fourth embodiment, in which a bore leading from an axial bore in the valve member opens into the region of an annular throttle gap.

In the solenoid valve shown in Figure 1, and whose description is confined to the components material to the invention. a multi-part valve body is inserted in a valve housing 3 and comprises a valve body part 1 and a flange 5, which is mounted thereon and which has a tubular extension 7. The valve body part 1 has. at the end of a stepped bore. serving as a guide bore 9, a blind bore 31 with the smaller diameter of the stepped bore. and the tubular extension 7 has a stepped bore portion with the larger -7diameter of the continuing guide bore 9, in which a valve member 11, in the form of a piston with a stepped diameter, is axially displaceably guided. The end face of the valve body part 1 facing the flange 5 has a conical valve seat 13, which slopes relative to the axis of the guide bore 9. A conical surface 15, produced by a conical transition of the external diameter of the portion of the piston 11 guided in the flange 5 to an annular groove 10 in the valve member 11, cooperates with the valve seat 13 and its angle of taper is slightly, preferably in the range of from 0.5 to 1 degree, larger than the angle of taper of the valve seat surface 13, so that a sealing edge 17. produced by the sharp-edged transition between the cylindrical outer surface of the portion of the valve member 11 guided in the flange 5 and the conical surface 15 of the valve member 11 comes into abutment against the conical valve seat 13 of the valve body part 1. The end of the valve member 11 extending out of the guide bore 9 in the region of the flange 5 on the other side of the valve seat 13 has a flat armature 19, which has an annular shoulder 21 formed as a step, which cooperates with a solenoid 23, annularly surrounding the tubular extension 7 of the flange 5. The solenoid 23 is guided in a groove 22 of a sleeve 25. which is inserted into the valve housing -83 where it forms a cover and which also receives the electrical terminals 27. which are in turn connected to the solenoid 23 by way of electrical leads 29.

A return spring 33, disposed in the portion of the guide, bore 9 in the valve body part 1 forming the blind bore 31. acts upon the end face 30 of the valve member 11 remote from the solenoid 23 and when the solenoid 23 is in its non-energized state, holds the valve member in its open position in which the sealing edge 17 is separated from the valve seat 13.

For the purpose of limiting the lifting movement of the valve member 11, a cylindrical stop piece 35 is inserted into the sleeve 25 in axial alignment with the valve member 11, its end face facing the valve member 11 forming a stop 37, limiting the opening stroke of the valve member 11. The closing movement of the valve member 11 when the solenoid 23 is, energized is limited by the abutment of the sealing edge 17 against the valve seat 13.

The fluid under high pressure, particularly fuel, is fed by way of a highpressure passage 39, which enters at the front, closed end of the valve body part 1 and opens into a first annular chamber 41 which is formed by a recess in the flange 5 and which is defined at the other side by the outer end face of the valve body 1 having the valve seat 13. The flow cross -9section between the valve seat 13 and the conical surface 15 of the valve member 11 forms a passage 42 for the flowing fuel. The fuel, after passing through this passage, flows through an annular gap 44 formed between the cylindrical wall of the annular groove 10, contiguous to the conical surface 15, of the valve member 11 and the wall of the guide bore 9 which is contiguous to the valve seat 13. When the solenoid valve is open, after passing the valve seat surface 13 and flowing through the annular gap 44, the fuel under high pressure is discharged by way of a low-pressure passage 43 which leads from an annular groove in the valve body part contiguous to the annular gap 44. The annular groove in the valve body part forms a second annular chamber 45. The low-pressure passage 43 opens into a low-pressure connection 47.

In order to equalize the pressure on the valve member ll,, the latter also has an axial through-bore 49 which continues into a blind bore 51 in the stop piece 35, which blind bore 51 in turn has radial bores 53, opening into a valve chamber 55 which is under low fuel pressure and which surrounds the stop piece 35 and the solenoid 23, so that communication between the blind bore 31, accommodating the return spring 33, and the valve chamber 55 is ensured even when the valve member 11 abuts against the stop piece 35. Figures 2 -10to 5 show variants of a portion, indicated by a broken circle in Figure 1 and drawn to an enlarged scale, of the solenoid valve, showing the nature of the passage and the transition into the second annular chamber 45.

In this connection. referring to Figure 2, a diffuser-shaped throttling path 60 is disposed downstream of the sealing edge 17, which is seated on the valve seat surface 13 when the solenoid valve is closed and is formed by the slight angular difference. also depicted in Figure 1, between the valve seat 13 of the valve body 1 and the conical surface 15 of the valve member 11. The length of this throttling path 60 is dimensioned in such a way that the cross section of the passage 42 decreases downstream at the copmencement of the opening stroke, for which purpose the circumference of the effective cross section of the passage 42, starting from the largest radius at the sealing edge 17, decreases towards the annular gap 44 far more rapidly than the height of the gap between the two conical surfaces 13, 14 increases. As a result of the throttling of the discharged fuel immediately contiguous to the sealing edge 17 and in the passage 42, a rapid and uniform flow is avoided at this location, so that the pressure difference relative to the annular chamber 41 may be kept small and does not drop below the vapour pressure.

Since the throttling action of the throttling path 60 is effective mainly when the opening cross section is small, that is, at the commencement of the opening stroke, the annular throttle gap 44 is disposed downstream of the throttling path 60 with a smooth transition which opens into the second annular chamber 45 and whose throttling action increases with increasing flow velocity of the fuel flowing through the open passage.

The embodiments depicted in Figures 3 and 4 differ from the embodiment of Figure 2 by virtue of the design of the throttling path 60.

In figure 3, the conical surface 15 of the valve member 11 has a continuous groove 62 as a throttle, which may be incorporated in the conical surface 15 or in the valve seat surface 13, and which forms a large opening across section which, however, decreases again at the end of the passage 42 to the gap dimension, corresponding to the differential angle between the conical surface 15 of the valve member 11 and the valve sealing surface 13 of the valve member 1, thus effecting a reliable throttling action even in the case of a larger opening stroke.

In Figure 4, the throttle is formed by a continuous recess 64 in the conical surface 15 of the valve member 11 and has a boundary wall extending -12radially to the axis of the valve member 11, and a cylindrical wall 66 which extends coaxially to the axis of the piston and which, further downstream when the valve member 11 is seated on the valve seat 13, continues by way of a portion of the cylindrical wall of the valve body part 1 contiguous to the conical valve seat 13, and by way of a shoulder 68, to form the annular gap 44.

In the fourth variant shown in Figure 5, a bore 70 sloping downwardly towards the return spring 33, and directed away from the conical surface 15, is provided in the valve member 11 in such a way that, starting from the axial through-bore 49 connected to the valve chamber 55, it opens into the region of transition between the funnel-shaped throttling path 60 and the annular gap 44 in the flow cross section. A volume equalizing flow occurs by way of the bore 60 during the lifting movement of the valve member 11 and, particularly during the opening stroke,, causes an inflow of fuel into the annular gap 44 which forms a film flowing in the opposite direction to the discharged fuel on the wall of the valve member 11 whereby impingement of the jet on the wall is prevented. In this manner, residual air bubbles formed are prevented from imploding on the endangered surfaces within the flow cross section and are flushed 1 1 awfLy.

Thus,, the measures described make it Possible to avoid cavitation damage at the flow cross section of the solenoid valve without additional expenditure on components.

These measures may also be used on nonelectrically actuated seat valves.

Claims

-14CLAIMS

1. A solenoid valve for controlling the flow through a connection between a high-pressure chamber which is at least intermittently brought to a high fluid pressure and a low-pressure chamber, having a valve body inserted into a valve housing and a bore in the valve body and in which a valve member in the form of a piston is displaceable by a solenoid against the force of a return spring, wherein, starting from a circular cylindrical outer surface, the piston tapers to a reduced diam ter by way of a conical surface, the conical surface cooperating with a conical valve seat of the valve body, which seat connects a high pressure chamber, surrounding the circular cylindrical outer surface of the piston, to a low-pressure chamber surrounding the reduced diameter portion of the piston, a cone angle of the valve seat being smaller than a cone angle of the conical surface of the piston, so that the piston cooperates with the valve seat by way of a sealing edge produced at the transition between the cylindrical outer surface of the piston and the conical surface, and wherein a throttle which becomes effective upon commencement of the opening stroke is disposed downstream of the sealing edge in the direction of flow from the highpressure chamber to the low-pressure chamber.

-is-

2. A solenoid valve as claimed in claim 1, wherein the throttle is formed by a throttling path in the region of overlap between the conical surface of the piston and the valve seat surface, the cone angle of the conical surface of the piston being slightly larger than the cone angle of the valve seat surface, so that the flow cross section between the conical surface of the piston and the valve seat surface decreases uniformly over the entire periphery in the direction of flow to the low-pressure chamber at the commencement of the opening stroke.

3. A solenoid valve according to claim 2, wherein the cone angle of the piston is 0.5 to 1 larger than the cone angle of the valve seat.

4. A solenoid valve as claimed in claim 2 or 3, wherein a continuous groove is incorporated in the conical surface or in the valve seat surface within the throttling path between the conical surface of the piston and the valve seat surface.

5. A solenoid valve as claimed in claim 2, 3 or 4,, wherein a throttle gap is located downstream of the flow cross section between the conical surface and the valve seat surface and is formed by an annular gap between the reduced diameter of the piston and the adjacent wall of the valve housing, which annular gap opens into the low-pressure chamber.

1

6. A solenoid valve as claimed in claim 4, wherein the groove is disposed in the conical surface of the piston and has a boundary wall, extending radially to the axis of the piston, and a cylindrical wall coaxial to the axis of the piston, which, when the valve member is seated on the valve seat, forms, along with a portion of a cylindrical wall of the valve body contiguous to the conical valve seat surface, an annular throttling gap.

7. A solenoid valve as claimed in claim 5, wherein the piston has an axial bore which is connected to the low-pressure chamber and from which a bore extends whose other end opens into the region of transition between the throttling path and the annular gap and through which bore fuel flows into the annular cavity during the opening stroke of the piston.

8. A solenoid substantially as herein described with reference to and as illustrated in the accompanying drawings.

1