GB2171497A

GB2171497A - Solenoid valve

Info

Publication number: GB2171497A
Application number: GB08601088A
Authority: GB
Inventors: Tatsuhiko Abe; Shinya Nozaki; Tadashi Kobaysahi
Original assignee: Diesel Kiki Co Ltd
Current assignee: Bosch Corp
Priority date: 1985-01-22
Filing date: 1986-01-17
Publication date: 1986-08-28
Also published as: DE3601663A1; KR920006360Y1; JPS61123273U; KR860009873U; GB8601088D0; JPH0237339Y2

Abstract

A solenoid valve (1), to adjust the fuel injection of a distribution pump of an i.c. engine, has a valve member (11) slidably guided by a guide hole (13) and an insulation layer (15) formed on a sliding surface (11b) of the valve member (11) by a physical evaporation method so as to form a switch to indicate the valve state which achieves the ON state when the valve member is seated on a valve seat (16). Large diameter portions (13a, 13b) are formed in the guide hole (13) so as to face edge portions of the sliding surface of the valve member in order to prevent the edge portions (11e, 11f) from coming in contact with the guide surface of the guide hole (13) while the valve member (11) slidably moves in said guide hole. Thus, even if the insulation layer (15) is imperfect at its end portions, the valve member (11) is still prevented from being electrically connected through the edge portions with casing (12) during the movement of the valve member. <IMAGE>

Description

SPECIFICATION Solenoid valve The present invention relates to a solenoid valve which is arranged so as to form a switch by a valve and the associated valve seat.

In the prior art, to obtain an electric signal indicating the open/close state of a valve unit, valve units in which an ON-OFF switch is constituted by a valve and the associated valve seat are widely used. Such a valve unit having a such a switch is needed, for example, for constituting a valve unit driving circuit in which the driving pulse applied to the valve unit is corrected in response to the timing of opening/closing of the valve unit in order to make the open/close timing of the valve unit coincide with a target timing. It is also needed for constituting a fuel injection valve which is capable of producing an electric signal indicating the injection timing of fuel.

As such a valve unit, there is disclosed for example in USP No. 4111178 (corresponding to DE-OS 2748447) a fuel injection valve in which a mechanical switch is constituted by a needle valve and a nozzle body in order to obtain an electric signal indicating the timing of the beginning of fuel injection and the timing of the end of fuel injection in response to the movement of the needle valve. In the disclosed fuel injection valve, a nozzle body and a needle valve smoothly moving in the guide hole of the nozzle body are formed of an electrically conductive material and the outer surface of the needle valve is covered with a ceramic insulation film of a thickness between approximately 0.2 m and 0.3 m, or an insulation film formed by the sputtering of aluminum oxide.

However, when the ceramic thin film is used as the insulation film, the durability is insufficient and when the insulation film formed by the sputtering of aluminum oxide is used, the insulation film is liable to peel off from the outer surface of the needle valve. In either case, consequently, stable use over long periods is impossible.

To eliminate these disadvantages in the prior art, there has been proposed an improved valve unit in which an insulation material is formed on the desired portion of the valve by a physical evaporating method such as a sputtering method, an ion-plating method or the like, whereby the insulation at a sliding portion of the valve is assured of having a sufficient mechanical strongness.

However, due to the nature of the physical evaporating method, there is a disadvantage in that it is difficult by this method to completely form an evaporated film at the edge portion of the member to be coated. Thus, when the insulation material is deposited on the outer surface of the valve by the physical evaporating method, incomplete insulation is liable to occur at the edge portion of the valve.

As a result, when the switch formed by a valve and the associated valve seat operates, it sometimes happens that the edge portion of the valve contacts with the inner surface of the guide hole of the valve guide member for guiding the valve, which causes the switch to produce a noise signal.

The preferred objectives of the invention are to provide an improved solenoid valve having a highly reliable ON-OFF switch for obtaining a signal showing the ON/OFF state of the solenoid valves and to provide a solenoid valve which is able to form an ON-OFF switch which is highly reliable in electrical and mechanical performance and which produces no noise signal even if the insulating layer for the sliding portion of the valve is formed by a physical evaporating method.

According to the present invention, in a solenoid valve having a valve member made of an electrically conductive material, an electri cally conductive body having a guide hole for guiding the valve member slidably, a valve seat provided in said electrically conductive body, and an insulation layer formed on a sliding surface of the valve member by a physical evaporation method so as to establish an insulating condition between the sliding surface and a guide surface of the guide hole, whereby the electrically conductive body is electrically connected with the valve member when the valve member is seated on the valve seat, at least one large diameter portion is formed in the guide hole so as to face an edge portion of the sliding portion of the valve member in order to prevent the edge portion from coming in contact with the guide surface of the guide hole while the valve member slidingly moves in the guide hole.

Due to the large diameter portion or portions formed in the guide hole, the edge portions of the sliding portion of the valve member will not come in contact with the guide surface of the guide hole. Thus, even if the insulation layer formed on the sliding portion of the valve member is imperfect at its edge portions, the valve member is still perfectly prevented from being electrically connected through the edge portion with the electrically conductive body. As a result, when a highly durable insulation layer is formed on the surface of the valve member to obtain a solenoid valve having a switch function, no noise signal is produced during the operation of the switch so that a solenoid valve having a switch that is highly reliable in electrical and mechanical performance can be obtained.

The invention will be better understood and other objects and advantages thereof will be more apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an elevation partly in section showing an embodiment of a fuel injection pump having a solenoid valve according to the present invention; and Fig. 2 is a grossly enlarged sectional view of one portion of the solenoid valve shown in Fig. 1.

DESCRIPTION OF THE PREFERRED EMBODI MENTS Fig. 1 is a partially sectional view showing an embodiment of a distribution type fuel injection pump 2 to which a solenoid valve 1 having an ON-OFF switch according to the present invention is applied as a fuel quantity adjusting member. The distribution type fuel injection pump 2 has an input shaft 3 driven by an internal combustion engine (not shown) and the rotation of the input shaft 3 cause a plunger 5 to rotate with reciprocal movement in a plunger barrel 4. As a result, fuel is taken into a high pressure chamber 6 and the intake fuel is pressurized in the high pressure chamber 6. Fuel pressurized in the high pressure chamber 6 is supplied under pressure through a delivery valve (not shown) into cylinders of the internal combustion engine.Reference number 7 designates a fuel-cut solenoid valve and the fuel supply to the high pressure chamber 6 is ceased when the fuel-cut solenoid valve 7 is in closed state.

In order to supply fuel pressurized in the high pressure chamber 6 into each cylinder of the internal combustion engine in a desired amount, the solenoid valve 1 for adjusting the amount of fuel injection is provided so as to be secured on a casing 8 of the distribution type fuel injection pump 2 by an appropriate means. The solenoid valve 1 comprises a valve rod 11 made of steel, which is an electrical conductive material, and a casing 12 made of steel. The casing 12 includes a valve guide member 14 having a guide hole 13 for supporting and guiding the valve rod 11 so as to allow it to move in its axial direction. The valve rod 11 has an enlarged diameter portion 1 lea corresponding to the guide hole 13 and the enlarged diameter portion 1 1a is guided by the guide hole 13.

An insulation layer 15 is formed on the outer surface 1 1b of the enlarged diameter portion 1 lea by depositing an appropriate insulation material by a physical evaporating method such as a sputtering method, an ionplating method or the like. As a result, the insulating condition between the outer surface 11 b and the inner surface of the guide hole 13 is assured. The inner diameter of the guide hole 13 is selected so as to be slightly iarger than the outer diameter of the enlarged diameter portion 1 lea, taking account of the thickness of the insulation layer 15.Thus, the guide hole 13 is able to guide the valve rod 11 slidably in its axial direction while maintaining an oil tight condition between the guide hole 13 and the enlarged diameter portion 1 1a of the valve rod 11. A valve head 11 c is integrally formed at the lower end portion of the valve rod 11 and a valve face lid of the valve head 1 lc is able to come in oil-tight contact with a valve seat 16 formed at the lower end opening of the valve guide member 14.

A disk-like armature 17 made of a magnetic material is secured on the valve rod 11 at a position above the valve guide member 14 and an expansion coil spring 19 is provided between the casing 12 and a spring shoe 18 arranged on the armature 17, whereby the valve rod 11 is biased downward.

As shown in Fig. 2, a washer 20 for the coil spring 19 and a plate electrode 21 are provided between the coil spring 19 and the casing 12 and are electrically insulated from the casing 12 by an insulation member 22.

Reference numeral 23 designates an adjusting washer for setting the force of the coil spring 19. The washer 20, the plate electrode 21, the insulating member 22 and the adjusting washer 23 are rigidly mounted on the casing 12 by a bolt 24 and an associated nut 25. In addition, to prevent the casing from being electrically connected to the washer 20 through the bolt 24 and the nut 25, an insulating sheet 26 is provided between the bolt 24 and the casing 12.

In order to enable the solenoid valve 1 to close by moving the valve rod 11 upward against the force of the coil spring 19 to seat the valve head 1 Ic on the valve seat 16, an electromagnet 27 is provided in the casing 12 so as to face the armature 17. The electromagnet 27 is composed of a core 28 and an exciting coil 29 wound on the core 28 and the armature 17 can be attracted to the electromagnet 27 by an electromagnetic force produced when an exciting current is passed through the exciting coil 29. Thus, the valve rod 11 moves upward against the force of the coil spring 19 to close the solenoid valve 1.

To prevent the inner surface of the guide hole 13 of the valve guide member 14 from making contact with the upper edge lie and the lower edge 1 1f of the enlarged diameter portion 1 1a when the valve rod 11 is moved in its axial direction by the force of the coil spring 19 and the electromagnetic force produced by the electromagnet 27, there are provided large diameter portions 1 3a and 13b, each of which has a larger inner diameter than that of the guide hole 13.

Consequently, during the movement of the valve rod 11 along the guide hole 13 for the opening/closing of the solenoid valve 1, the valve rod 11 will not be electrically connected through these edges lie and 1 lf with the casing 12 even if the coated condition of the insulation material is insufficient, because the upper and lower edges 1 lie and 1 if face the large diameter portions 13a and 13b, respectively. Thus, a switch that is highly reliable in electric and mechanical performance can be formed by the valve rod 11 and the casing: 12 or the associated valve seat 16.

Since the armature 17, the spring shoe ?, the coil spring 19, the washer 20 and the plate electrode 21 are all made of an electrically conductive material, the valve rod 11 is always electrically connected through these members to the plate electrode 21 which is electrically connected with an outer circuit through a wire (not shown).

An input port 30 of the solenoid valve 1 is communicated with the high pressure chamber 6 through a passage 2b defined in the casing 2a of the fuel injection pump 2. Consequently, the high pressure chamber 6 is communicated with a chamber 31 which is communicated with a fuel tank (not shown) when the solenoid valve 1 is changed over from its closed state to its opened state, so that the fuel pressure in the high pressure chamber 6 is forcibly lowered.

Therefore, as will be understood from the above description, when the solenoid valve 1 is changed-over from its closed state to its opened state at a desired time during the fuel injecting operation, the operation of the fuel injection of the fuel injection pump 2 is stopped. That is, the amount of fuel injection can be controlled by the operation of the solenoid valve 1.

A description will be given of the operation of the solenoid valve 1 shown in Fig. 1. Since the valve rod 11 descends by the force of the coil spring 19 when the electromagnet 27 is deenergized, the valve head 1 ic is kept separated from the associated valve seat 16 so that the solenoid valve 1 is in its opened state. As the insulation layer 15 is provided on the outer surface 11 b of the large diameter portion 11a of the valve rod 11, in this case, the electric insulation condition between the valve rod 11 and the valve guide member 14 is established so that an electrically non-conductive state is established between the plate electrode 21 and the casing 12.

When the electromagnet 27 is energized, the armature 1 7 is attracted to the electromagnet 27 so that the valve rod 11 moves upward. Thus, the valve head 1 ic is seated on the associated valve seat 16 to close the solenoid valve 1. As a result, the valve rod 11 is electrically connected with the casing 12.

As described above, a switch is formed by the valve rod 11, the casing 12 and the insulation layer 15, in which ON-OFF operation is carried out in response to the ON/OFF condition of the solenoid valve 1. In this case, since the large diameter portions 13a and 13b are formed in the guide hole 13 in order to prevent the edge portions 1 lie and 1 1f from being in contact with the inner surface of the guide hole 13, the function of the switch will not be impaired even if the insulation layer 15 provides insufficient insulation at the edge portions 1 1e and 1 1f. As a result, the switch formed as described above has high reliability and no noise signal will be produced.

Since the insulation layer 15 is formed by coating an appropriate insulation material on the desired surface portion of the valve rod 11 by a physical evaporation method, the density of the insulation layer 15 is high and the insulation layer 15 is strongly bonded to the valve rod 11. Thus, the insulating layer 15 has excellent durability so that the desired insulating performance is maintained for a long period. In addition, an appropriate insulation material such as SiO2, An203 or the like can be used for forming the insulation layer 15.

In this embodiment, the large diameter portions 13a and 13b are provided at the upper and lower portions of the guide hole 13 in order to effectively prevent a noise signal from being produced due to insufficient insulating condition at the edge portions 1 1e and 1 1f of the enlarged diameter portion 1 1a of the valve rod 11. It is sufficient for the length of the large diameter portions 13a and 13b along the axial direction to be approximately 0.5 mm each, since this is the distance by which the valve rod 11 moves. Thus there is no danger whatever that the provision of the large diameter portions 13a and 13b will adversely affect the supporting and guiding functions of the valve rod 11.

Claims

1. In a solenoid valve having a valve member made of an electrically conductive material, an electrically conductive body having a guide hole for guiding said valve member slidably, a valve seat provided in said electrically conductive body, and an insulation layer formed on a sliding surface of said valve member by a physical evaporation method so as to establish an insulating condition between the sliding surface and a guide surface of said guide hole, whereby the electrically conductive body is electrically connected with the valve member when the valve member is seated on the valve seat, an improvement comprises at least one large diameter portion formed in said guide hole so as to face an edge portion of the sliding surface of said valve member in order to prevent the edge portion from coming in contact with the guide surface of the guide hole while said valve member slidingly moves in said guide hole.

2. A solenoid valve as claimed in Claim 1 wherein said electrically conductive body includes a valve guide member and said guide hole is defined in said valve guide member.

3. A solenoid valve as claimed in Claim 2 wherein said valve member is a valve rod at the lower end of which a valve head is formed and said sliding surface corresponding to said guide hole is formed on the valve rod.

4. A solenoid valve as claimed in Claim 3 wherein said sliding surface is formed on the outer surface of at least one enlarged diameter portion formed on said valve rod.

5. A solenoid valve as claimed in Claim 4 wherein two large diameter portions are formed in said guide hole so as to face upper and lower edge portions of said enlarged diameter portion provided on said valve rod.

6. A solenoid valve as claimed in Claim 3 wherein a valve face is formed on said valve head and said valve seat is formed on said valve guide member in correspondence to the valve face.

7. A solenoid valve as claimed in claim 1 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawing.