GB2312925A

GB2312925A - Fuel-injection valve for internal combustion engines

Info

Publication number: GB2312925A
Application number: GB9708469A
Authority: GB
Inventors: Johann Warga; Erguen Filiz; Friedrich Boecking
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1996-05-09
Filing date: 1997-04-28
Publication date: 1997-11-12
Anticipated expiration: 2017-04-28
Also published as: GB9708469D0; DE19618650A1; GB2312925B; DE19618650B4

Description

2312925

DESCRIPTION FUEL-INJECTION VALVE FOR INTERNAL COMBUSTION ENGINES

The invention relates to fuel-injection valves for internal combustion engines.

A fuel-injection valve for internal combustion engines is already known which has a piston-shaped valve member which is axially displaceable in a bore of a valve body, which valve member comprises on its combustion chamber-side end a valve sealing surface which cooperates, for the purpose of opening an injection orifice, with a valve seat provided on the combustion chamberside end of the bore and furthermore comprising on the valve member a pressure shoulder which is directed in the direction of the valve sealing surface and protrudes into a pressure chamber which is formed in the valve body by virtue of an increased diameter of crosssection of the bore, which pressure chamber is connected to the valve seat by way of an annular gap formed between the valve member and the wall of the bore and adjacent to said pressure chamber at the end remote from the valve seat is a guide portion of the bore, which guide portion receives the valve member in a sliding manner, and further comprising a pressure duct which penetrates the valve body in an axial manner and issues radially outwards of the bore into the end of the pressure chamber remote from the valve seat, wherein a wall crosspiece is formed between the bore and the pressure duct disposed inclined thereto and said wall cross-piece forms a wedge-shaped region of reduced diameter in the region of the intersection between the bore and that portion of the pressure duct proximate to the pressure chamber.

In the case of a fuel-injection valve of the aforegoing type disclosed in DE-OS 43 41 102, a piston-shaped valve member is guided in an axially displaceable manner in a bore of a valve body against the force of a closing spring. The valve member comprises on its combustion chamber-side end a valve sealing surface with which for the purpose of opening and closing an injection orifice it cooperates with a valve seat provided on the combustion chamber-side end of the bore.

For the purpose of the introduction under force of the high pressure fuel

2 in the opening direction, a pressure shoulder directed in the direction of the valve sealing surface is provided on the valve member and by means of the said pressure shoulder the valve member is moreover subdivided into a guide part, which comprises a greater diameter and is guided in a sliding manner in the bore, and into a free spindle part which comprises a smaller diameter, the said spindle part being guided as far as the valve sealing surface. In the region of the pressure shoulder on the valve member there is provided in the valve body a pressure chamber formed by an increase in the cross-section of the bore. The said pressure chamber is connected to the valve seat by way of an annular gap formed between the free valve member spindle and the wall of the bore. A guide portion of the bore which receives the guide part of the valve member is adjacent to the end of the pressure chamber remote from the valve seat. The supply of high pressure fuel from an external high pressure fuel pump into the pressure chamber of the valve body occurs by way of a pressure duct which penetrates the valve body in an axial manner and issues radially outwards of the bore into the end of the pressure chamber remote from the valve seat, wherein the pressure duct extends inclined to the axis of the bore. In so doing, a relatively thin-walled wall cross-piece is formed in the valve body in the region of intersection between the entry region of the pressure duct into the pressure chamber and the wall of the bore, which wall cross-piece is influenced on one side by the high pressure fuel in the pressure duct. This cyclic and pulsating manner in which the pressure acts on one side of the cross-piece causes fractures in the wall cross-piece, which as a consequence can lead to a total failure of the entire injection system, especially in the case of the high injection pressures of above 1000 bar which are required by the modern direct-injection diesel engines.

In accordance with the present invention, the valve body comprises a higher residual compressive stress at the wall cross-piece in the region of the wedge-shaped region than in the remaining region.

In contrast to the prior art, a fuel-injection valve according to the present invention has the advantage that as a result of increasing the residual compressive stress of the valve body in the wall cross-piece region at the level

3 of the wedge-shaped region between the pressure duct and the valve body bore it is possible to increase the compression pulsating fatigue strength on the wall cross-piece to in excess of 2000 bar, which even in the case of direct injection diesel engines renders it possible without any problem to inject high pressure fuel over a long serviceable life.

This increase in the residual compressive stress is achieved in an advantageous manner by heat treating the wall cross-pieces in the valve body in a controlled manner, wherein the wall cross-piece is heated in a first step and rapidly cooled (quenched) in the second step. The heat treatment can be performed by a so-called vacuum hardening process using nitrogen quenching or oil quenching. It is, however, also possible as an alternative to use equivalent heat treatment methods.

Tests with the fuel-injection valve according to the invention demonstrated, for example in the case of an increase in the residual compressive stress of the wall cross-piece in the wedge-shaped region of 167 to 222 N/m M2 by means of a controlled heat treatment, an increase in the compression pulsating fatigue strength from 1520 bar to 1640 bar. Particularly advantageous are compressive stress values which are greater than 222 N/m M2 for compression pulsating fatigue strength values in the wedge-shaped region of approx. 2000 bar.

Further advantages and advantageous embodiments of the subject matter of the invention are evident in the description, the drawing and the claims.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawing, in which:- Figure 1 shows a longitudinal sectional view through a fuel-injection valve in accordance with the invention in the closed state.

In the case of the fuel-injection valve for internal combustion engines illustrated in Figure. 1 only with its components essential for the invention a valve body 1 protruding with its one end in the combustion chamber of an internal combustion engine comprises a bore 3 formed as a blind bore closed at the combustion chamber-side, in which bore a pistonshaped valve member 4 is guided in an axially displaceable manner.

The valve member 5 comprises at its combustion chamber-side end a conical valve sealing surface 7 with which it cooperates in a sealing manner with a conical valve seat surface 9 which is formed at the closed end of the bore 3. An injection orifice 11 leads off from the valve seat surface 9 and issues into the combustion chamber [not further illustrated] of the internal combustion engine being supplied, preferably a direct injection diesel engine.

Furthermore, the valve member comprises a pressure shoulder 13 which is formed by a reduction in cross-section in the direction of the valve sealing surface 7 and which pressure shoulder subdivides the valve member 5 into an upper guide part 15 which is greater in diameter and is guided in a sliding manner in the bore 3 and a free spindle part 17 which is of a smaller diameter, wherein the spindle part 17 extends with a constant cylindrical crosssection as far as the valve sealing surface 7.

Furthermore a pressure chamber 19 is provided in the valve body 1, the said pressure chamber is formed by virtue of an increase in the crosssection of the bore 3 and is connected at its lower end facing the valve seat by way of an annular gap 21 formed between the free valve member spindle 17 and the wall of the bore 3 to the valve seat 9. At the upper end remote from the valve seat 9 the pressure chamber 19 is adjacent to a guide portion 23 of the bore 3 which receives in a sliding manner the guide part 15 of the valve member 5.

The high pressure fuel is supplied from an external high pressure fuel source, preferably an injection pump into the pressure chamber 19, by way of a pressure duct 25 which penetrates the valve body 1 in an axial manner and which extends inclined to the axis of the bore 3 and issues radially outwards of the bore 3 into the end of the pressure chamber 19 remote from the valve seat. Between the bore 3 and the pressure duct 25 is formed a wall crosspiece 27 in the valve body 1, which wall cross- piece forms in the region of the intersection between the bore 3 and the mouth of the pressure duct 25 leading into the pressure chamber 19 a wedge-shaped region 29 which comprises the smallest wall thickness of the cross-piece 27.

In order to increase the compression pulsating fatigue strength of the wall cross-piece 27 in the region of the wedge-shaped region 29 the wall crosspiece 27 comprises a higher residual compressive stress than the remaining valve body 1. This increased residual compressive stress at the wall crosspiece 27 especially in the region of the wedge-shaped region 29 is achieved by virtue of heat-treating the wall cross-piece in a controlled manner, wherein the wall cross-piece 27 is heated during a first step and then quenched during a second step.

The fuel-injection valve, according to the invention, for internal combustion engines functions in the following manner.

In the inoperative position the valve member 5 is held with the valve sealing surface 7 in position against the valve seat surface 9 by a closing spring [not illustrated] so that the injection orifice 11 which issues into the combustion chamber is closed. At the commencement of the high pressure injection, high pressure fuel passes via the pressure duct 25 into the pressure chamber 19 and via the annular gap 21 further as far as the valve seat 9. In so doing, the hydraulic force which engages the pressure shoulder 13 in the opening direction of the valve member 5 rapidly exceeds the closing force of the spring so that the valve member 5 is raised from the valve seat 9 and the fuel passes via the orifice cross-section which is open between the valve sealing surface 7 and the valve seat 9 via the injection orifice 11 for injection into the combustion chamber of the internal combustion engine. The injection process is terminated by terminating the supply of high pressure fuel so that the pressure engaging the valve member 5 in the opening direction drops again below the restoring force of the closing spring which then displaces the valve member 5 again into position against the valve seat 9.

In so doing, the compression pulsating fatigue strength is increased by virtue of the higher residual compressive stress of the wall cross-piece 27 in the region of the wedge-shaped region 29 in such a manner that even in the case of high injection pressures fractures in the wall cross-piece 27 can be reliably prevented over a long serviceable life.

6

Claims

1. A fuel-injection valve for an internal combustion engine, having a piston-shaped valve member which is axially displaceable in a bore of a valve body, which valve member comprises on its combustion chamber-side end a valve sealing surface which cooperates, for the purpose of opening an injection orifice, with a valve seat provided on the combustion chamber-side end of the bore and furthermore comprising on the valve member a pressure shoulder which is directed in the direction of the valve sealing surface and protrudes into a pressure chamber which is formed in the valve body by virtue of an increased diameter of cross- section of the bore, which pressure chamber is connected to the valve seat by way of an annular gap formed between the valve member and the wall of the bore and adjacent to said pressure chamber at the end remote from the valve seat is a guide portion of the bore, which guide portion receives the valve member in a sliding manner, and further comprising a pressure duct which penetrates the valve body in an axial manner and issues radially outwards of the bore into the end of the pressure chamber remote from the valve seat, wherein a wall cross-piece is formed between the bore and the pressure duct disposed inclined thereto and said wall cross-piece forms a wedge-shaped region of reduced diameter in the region of the intersection between the bore and that portion of the pressure duct proximate to the pressure chamber, and wherein the valve body comprises a higher residual compressive stress at the wall cross-piece in the region of the wedgeshaped region than in the remaining region.

2. A method for manufacturing a fuel-injection valve according to claim 1 wherein the higher compressive stress of the wall cross-piece of the valve body between the bore and the pressure duct is achieved by virtue of additionally heat-treating the valve body in the region of the wall cross-piece.

3. A method according to claim 2, wherein the heat treatment is performed in two steps, wherein during a first step the wall cross-piece is heated to a predetermined temperature and during a second step the heated wall cross-piece region is cooled extremely rapidly.

4. A fuel-injection valve substantially as hereinbefore described, with 7 reference to and as illustrated in the accompanying drawing.

5. A method for manufacturing a fuel injection valve, substantially as hereinbefore described, with reference to the accompanying drawing.