GB2267320A

GB2267320A - Pressure-equalising delivery valve assembly.

Info

Publication number: GB2267320A
Application number: GB9309989A
Authority: GB
Inventors: Theodor Stipek; Stanislaw Bodzak
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1992-05-15
Filing date: 1993-05-14
Publication date: 1993-12-01
Anticipated expiration: 2013-05-14
Also published as: GB9309989D0; JPH0633848A; DE4216068A1; GB2267320B

Abstract

A pressure-equalising delivery valve assembly (1) for installation in a delivery line (3) between a pump working chamber (5) of a fuel-injection pump and a fuel-injection point (7) of the internal combustion engine being supplied, has a feed line (13) which accommodates a delivery valve (17) and a return line (15) which accommodates an oppositely opening non-return valve (19). The valve (19) acts to reduce the pressure waves which are caused in the delivery line (3) at the end of the high pressure delivery by virtue of the delivery valve (17) suddenly closing. The valve closure element (43) of the valve (19) is opened rapidly by the pressure wave and this leads to a high mechanical load on its return spring (47). In order to retard opening of the valve closure element (43), a restrictor (55) is connected downstream thereof, the restrictor causing retardation of the flow of fuel away from the spring chamber (37) of the valve (19) thereby counteracting the opening movement of the valve closure element (43). Embodiments having differently disposed restrictors are described. <IMAGE>

Description

2267320

DESCRIPTION PRESSURE-EQUALISING DELIVERY VALVE

The invention relates to a pressure-equalising delivery valve for use with a fuel injection pump.

In the case of a pressure-equalising delivery valve known from EP 0 261 102 Bl, the pressureequalising delivery valve is disposed in a delivery line between a pump working chamber and a fuelinjection point. Two through-going ducts, which extend in parallel with each other and issue into the identical respective space in advance of and beyond the pressureequalising delivery valve, are disposed inside the pressure-equalising delivery valve and the through-going ducts each contain a valve, which opens in the opposite direction to the other valve, so that the throughgoing ducts form respectively a feed duct to the fuel-injection point and a return duct.

A valve closure element is raised from its valve seat, against the force of a spring, by virtue of the highly pressurised medium which is directed to the delivery valve in the feed duct from the pump working chamber, causing the delivery valve in the feed duct to open and the medium to flow to the fuel-injection point. The pressure in the pump working chamber drops at the end of the high pressure delivery and the delivery valve closure element of the delivery valve -2in the feed duct returns to its seat. Shortly afterwards, a fuel- injection valve at the fuelinjection point closes, causing pressure waves to move to and fro in the enclosed volume between the pressure-equalising delivery valve and the fuelinjection valve and these pressure waves are in a position to be able to open the fuel-injection valve again. In order to avoid this, a valve is disposed in the return duct and this valve enables the pressure level in the delivery line to the fuel-injection valve to reduce. even after the delivery valve in the feed duct has closed. to a static pressure which is determined by virtue of the pre- stress force of the return spring of the valve in the return duct and the effective surface area of the valve.

In the known fuel-injection pump, the returning pressure wave which is highly energised, causes at the same time an extremely rapid opening movement of the valve closure element of the valve in the return duct until -%&.-he valve closure element rests against a filler piece which is located in the valve chamber and limits this opening movement, producing a high mechanical load on the return spring of the return valve.

In order to retard this rapid opening movement and therefore to increase the serviceable life of the return spring, restrictors are connected in advance of 1 1 -3the return valve, as are known, for example, from Us-ps 398 513, in which this restrictor is formed by virtue of a reduction in the cross section of the return duct directly in advance of the return valve. The possibilities of varying the opening pressure of the valve in the return line and the diameter of the restrictor connected in advance thereof are essential when adjusting the entire fuel-injection system to suit the requirements of the internal combustion engine being supplied, wherein the diameter of the restrictor bore is to be changed in general more than once when carrying out these adjustments, which in the existing design results in each case in high manufacturing costs. In addition to this, the restrictor bore causes a small jet which arrives at the valve ball and therefore has an adverse effect when raising the valve ball uniformly from its valve seat, so that the individual fuel-injection processes can be irregular.

The present invention resides in a pressureequalising delivery valve for installation in a delivery line between a pump working chamber of a fuelinjection pump and a fuel-injection point on an internal combustion engine being supplied by the fuelinjection pump, comprising a valve housing having disposed therein parallel operating through-going 1 1 -4ducts which, by virtue of a valve closure element disposed in each of the through-going ducts, with each of the valve closure elements opening against a resilient force and in the opposite direction to the other valve closure element, form respectively a feed line to the fuel- injection point and a return line to the pump working chamber, wherein these through-going ducts open in advance of and beyond the pressureequalising delivery valve into the same respective chamber, and a restrictor is connected downstream of that valve closure element in the return line and opening in the direction towards the pump working chamber.

This has the advantage that, by arranging the restrictor after the valve in the return line, it is possible to produce a smaller jet of out-going flow on the valve closure element when the valve closure element is opened simultaneously more gradually. The restrictor can be formed by a reduction in cross section in the region of the return line leading through a second part of the valve housing which is at the side of a first part of the valve housing facing the pump working chamber. The restrictor causes the medium to be held back in the valve chamber of the return valve, which causes the opening movement of the valve closure element to be retarded against the force -5of the return spring. In addition to this, when a restrictor is located in this region, the adjustment work is less costly than when a restrictor is provided in the first housing part, which accommodates the springs and closure elements of the valves. This manufacturing and assembly expenditure during the adjustment process can be further reduced if the restrictor is formed by a bush inserted in the return line.

A further possibility of minimising the assembly and manufacturing expenditure of the restrictor during the adjustment work and still guaranteeing that the valve closure member opens reliably more slowly, can be provided by virtue of arranging restrictor bores in the filler piece limiting the opening travel of the valve closure element. This arrangement has the advantage, that the adjustment work can be carried out more economically and quicker by virtue of an existing and reusable selection of filler pieces having restrictor bores of various diameters. without at the same time having to change the valve housing. An arrangement designed in this way can also be of advantage when using pressure-equalising delivery valves, where the return line leads through the valve closure element of the delivery valve in the feed line and the closure element as well as spring and filler -6piece of the valve in the return line are disposed as known within this valve closure element. In addition to this, it is substantially simpler in this arrangement to check the geometry of the diameter of the bore and the through-flow.

The invention is further described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a longitudinal sectional view through a first embodiment of a delivery valve formed as a pressure-equalising delivery valve, wherein the restrictor is formed as a radial bore in a filler piece; Fig. 2 is a similar sectional view of a second embodiment analogous to that of Fig. 1, wherein the restrictor is formed by virtue of a reduction in the cross section of the axial bore of the filler piece; Fig. 3 is a longitudinal sectional view of a further embodiment with a restrictor bore in the return duct in the region of the valve housing; Fig. 4 is a section of a valve body of a fourth embodiment, wherein the restrictor bore extends through the entire valve housing; and Fig. 5 is a similar section of a fifth embodiment with a restrictor bush inserted into the return line.

In Fig. 1 a pressure-equalising delivery valve 1, is inserted into a housing (not illustrated) of a fuel-injection pump and is situated in a delivery line 3 between a pump working chamber 5 of the fuelinjection pump and a fuel-injection point in the form of a fuel-injection valve 7, of the internal combustion engine (likewise not illustrated) being supplied.

The housing of the pressure-equalising delivery valve 1 comprises a.first part, a valve holder 11 and a second part, a valve body 9 which is adjacent to the pump working chamber 5. These components are screwed together in a sealing manner to the pump housing and the part of the delivery line 3, which serves as the fuel-injection line to the fuelinjection valve 7 is screwed thereto at the side of the valve holder 11 remote from the valve body 9. The pressure-equalising delivery valve l has in its interior two through-going ducts which are disposed in parallel with each other and which jointly issue into the pump working chamber 5 and/or into the delivery line 3. one through-going duct forms a feed line 13 in the direction towards the fuel-injection valve and the other through-going duct forms a return line 15 in the opposite direction. For this purpose, a valve is disposed in each throughgoing duct. The delivery valve 17 is disposed in the -8feed line 13 in the direction towards the fuelinjection valve 7 and the return valve disposed in the return line 15 is a non-return valve 19, which opens in the direction towards the pump working chamber 5. These valves can be formed both as ball valves and also as valves having valve closure elements with conical or flat sealing surfaces.

The delivery valve 17 is disposed in an enlarged diameter part of the delivery line 13 forming a spring chamber 21 and comprises a valve closure element 23 having a conical or flat sealing surface 25 by which the valve closure element 23 is pressed by a valve spring 27 against the valve seat 29 in the valve body 9. The valve seat 29 is formed by a conical enlarged diameter part or a flat sealing surface of the part 31 of the feed line 13 which extends in the valve body 9 and leads from the pump working chamber 5. The opening movement of the valve closure element 23 of the delivery valve 17 which is triggered by virtue of the highly pressurised fuel, which is compressed in the pump working chamber 5, is limited to a predetermined value by virtue of a stop sleeve 33 in the spring chamber 21. The stop sleeve 33, which is slit in a cruciform manner in its upper stop region at the delivery valve holder 11 for the purpose of improving the fuel flow, also serves to guide the -9valve spring 27 and as a valve guide for the valve closure element 23. The non-return valve 19 disposed in the return line 15 is likewise located in an enlarged diameter part of the return line 15 forming a second spring chamber 37 in the region of the valve holder 11. A slightly reduced diameter part 39 of the return line 15, which does not restrict the fuel-flow, is located in advance of the non-return valve 19. The reduced diameter part 39 enlarges again in a conical shape towards the spring chamber 37 and thus forms a valve seat 41 for the valve closure element of the non-return valve 19, the valve closure element being formed as a valve ball 43. The valve ball 43 is guided at the other side by a spring abutment plate 45, against which engages a return spring 47, which presses the valve ball 43 against the valve seat 41. This return spring 47 is supported at the side remote from the spring plate 45 against a shoulder of a cylindrical filler piece 49 which is disposed centred in the second spring chamber 37. The filler piece 49 guides the return spring 47 in the spring chamber 37 and in addition to this limits, by its front face towards the spring plate 45. the movement of the return spring 47 and thus limits the opening distance of the valve ball 43 of the non-return valve 19. The filler piece 49 lies by its front face remote from the -10valve ball 43 in a sealing manner against the front face of the valve body 9 remote from the pump working chamber 5. The return spring 47 holds the filler piece 49 in position against the valve body 9. The part 51 of the return line 15 extending in the valve body 9 has a smaller cross section than the part in the valve holder 11. so that the filler piece 49 has sufficient resting surface around the part 51 of the return line 15, in order to ensure that it can rest thereon in a reliable manner. The filler piece 49 has in its interior, an axial blind bore 53 which issues from the front face adjacent to the valve body 9 and the blind bore 53 issues in the assembled condition into the part 51 of the return line 15. In order to connect the spring chamber 37, into which the returning fuel initially flows after passing the nonreturn valve 19, and by way of the part 51 of the return line 15, to the pump working chamber 5. radial transverse bores 55 are provided in the filler piece 49 and these radial transverse bores 55 issue into the blind pocket 53. These radial transverse bores 55 are of particular importance in the first embodiment illustrated in Fig. 1. By reason of their small cross section, they assume the function of throttling the fuel flowing away from the spring chamber 37, so that the opening movement of the valve ball 43 and of the -11spring abutment plate 45 is retarded, since the fuel located in the spring chamber 37 cannot be displaced at a sufficiently rapid rate.

The second embodiment illustrated in Fig. 2 is constructed analogously to the first embodiment shown in Fig. 1 and differs merely in the arrangement of the restrictor after the non-return valve 19. The axial blind pocket 53 of Fig. 1 is designed here as an axial through-going bore 57, whose diameter tapers severely on the side contiguous to the valve body 9, so that the fuel flowing-away from the spring chamber 37 is throttled within the axial through-going bore 57 of the filler piece 49 which issues into the part 51 of the return line 15 extending in the valve body 9. The cross section of the radial transverse bores 55 is sufficiently large, to avoid the fuel-flow being restricted at this point. The embodiments illustrated in Figs. 3 to 5 are likewise constructed as described with reference to Fig. 1 and differ likewise only in the type and arrangement of the restrictor after the non-return valve 19, and for this reason a complete illustration of the pressure-equalising delivery valve 1 is not included in the illustration of Figs. 4 and 5.

In the third embodiment illustrated in Fig. 3, the restrictor for the flowing-away fuel is formed by -12virtue of a reduced diameter part 59 of the part 51 of the return line 15 extending through the valve body 9 in the region of the filler piece 49. The fuel flowing-away from the spring chamber 37 is also restricted here, causing the opening movement of the non-return valve 19 to be retarded.

Figs. 4 and 5 illustrate two further variants of the design of restrictor within the return line 15, wherein the reduced cross section 59 in Fig. 4 extends over the entire region of the part 51 of the return line extending in the valve body 9, whereas the restrictor in Fig. 5 is formed by virtue of a bush 61 inserted into the return line 15. This bush 61 has a severely reducing cross section 59 at its end towards the non-return valve 19 and this severely reducing cross section 59 enlarges again further on by way of a shoulder. The bush 61 is screwed into the part 51 of the return line 15 by way of an external thread and is secured to prevent it rotating independently. At the same time, this fifth embodiment has the particular advantage that, when carrying out adjustment work on the restrictor cross section, the bush 61 can be replaced by various restricting measures rapidly and at a low cost.

The pressure-equali-sing delivery valve 1 in accordance with the invention functions as follows.

-13When, during the operation of a fuel-injection pump, in which the above-described pressure-equalising delivery valve 1 is installed, fuel is delivered from the pump working chamber 5 to the fuel-injection valve 7 of the internal combustion engine, the delivery valve closure element 23 is raised from the valve seat 29 of the valve body 9, under the pressure of the fuel flowing away from the pump working chamber 5 against the force of the valve spring 27 and the existing static pressure in the delivery line 3. The delivery valve 17 thus opens and fuel flows towards the fuelinjection valve 7 and arrives there for the purpose of being injected into the combustion chamber of the internal combustion engine being supplied. When the delivery pressure of the fuel in the pump working chamber 5 drops at the end of the fuel delivery, the force of the incoming fuel is no longer sufficient to hold the delivery valve closure element 23 open against the force of the valve spring 27 and the delivery valve closure element 23 returns to its valve seat 29. Thus, the delivery valve 17 and consequently also the fuel-injection valve 7 close. Following this sudden interruption of the fuel delivery, pressure waves flow to and fro in the enclosed volume between the pressure-equalising delivery valve 1 and the fuelinjection valve 7. In order to avoid further fuel -14being injected at the fuel-injection point, which this would cause by virtue of reopening the fuel-injection valve 7. the pressure level of the pressure wave peak pressures in the delivery line 3 is now reduced to a predetermined amount by way of the non-return valve 19. in that the fuel raises the valve ball 43 from its valve seat 41 against the force of the return spring 47 and flows back by way of the spring chamber 37, the filler piece 49 and the part 51 of the return line 15 extending in the valve body 9 into the pump working chamber 5 which is now relieved of pressure at the termination of the high-pressure delivery phase. In order to prevent the non-return valve 19 from opening too far and the associated high load on the spring, the non-return valve 19 can only be opened as far as the stop for the spring abutment plate 45 formed by the filler piece 49. In order to avoid the non-return valve 19 opening too rapidly and an associated high mechanical load on the return spring 47. the restrictor is connected downstream of the non-return valve 19, by means of which the fuel flowing away from the spring chamber 37 is throttled, which in turn causes the opening movement of the non-return valve 19 to be retarded. The cross section of this restrictor retarding the flowing-away process from the spring chamber 37 must be chosen to suit the requirements of -15the internal combustion engine being supplied. The restrictor is formed by a reduced cross section 59 of the transverse bores 55 and/or of the blind bore 53 in the filler piece 49 or in the part 51 of the return line 15 extending through the valve body 9 and the described arrangement of the restrictor has at the same time the advantage of being easily interchangeable.

Claims

-16CLAIMS

1. A pressure-equalising delivery valve for installation in a delivery line between a pump working chamber of a fuel-injection pump and a fuelinjection point on an internal combustion engine being supplied by the fuel-injection pump, comprising a valve housing having disposed therein parallel operating throughgoing ducts which, by virtue of a valve closure element disposed in each of the through-going ducts, with each of the valve closure elements opening against a resilient force and in the opposite direction to the other valve closure element, form respectively a feed line to the fuel-injection point and a return line to the pump working chamber, wherein these through-going ducts open in advance of and beyond the pressure-equalising delivery valve into the same respective chamber, and a restrictor is connected downstream of that valve closure element in the return line and opening in the direction towards the pump working chamber.

2. A pressure-equalising delivery valve according to claim 1, in which the opening distance of a spring abutment plate of the valve in the return line, the spring abutment plate receives the valve closure element which opens in the direction towards the pump working chamber, is defined by virtue of a -17cylindrical filler piece which is disposed in a spring chamber.

3. A pressure-equalising delivery valve according to claim 1 or 2, in which the valve housing is in two parts, comprising, as a first part, a valve holder which receives the valve closure elements and as a second part. a valve body lying at the pump working chamber side and clamped in a sealing manner against the first part and against the housing of the fuelinjection pump, a valve body.

4. A pressure-equalising delivery valve according to claims 2 and 3 in which the restrictor is formed by small diameter transverse bores in the filler piece. the transverse bores opening into an axial blind bore which is connected to a part of the return line in the valve body.

5. A pressure-equalising delivery valve according to claim 3, in which the restrictor is formed by a reduced cross section of an axial throughgoing bore in the filler piece at the side towards the valve body.

6. A pressure-equalising delivery valve according to claim 3, in which the restrictor is formed by a reduced cross section of the part of the return line which is adjacent to the delivery line at the pump working side and which extends through the -18second part of the valve housing.

7. A pressure-equalising delivery valve according to claim 6, in which the restrictor in the part of the return line extending through the valve body is formed by a sleeve inserted therein, and its through-going cross section is smaller at the side towards the non-return valve, than the part of the return line in the valve body and its through-flow cross section is greater after this reducing cross section. than the cross section of said part of the return line.

8. A pressure-equalising delivery valve according to claim 7. in which the sleeve is screwed into said part of the return line and is secured to prevent it independently rotating.

9. Pressure-equalising delivery valves, constructed and adapted to operate substantially as herein described, with reference to and as illustrated in the accompanying drawings.