GB2099085A

GB2099085A - Engine fuel pump pressure valve

Info

Publication number: GB2099085A
Application number: GB8211086A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1981-04-22
Filing date: 1982-04-16
Publication date: 1982-12-01
Also published as: FR2504597B1; GB2099085B; JPS57181968A; DE3115908C2; CH659109A5; FR2504597A1; DE3115908A1; JPH0411740B2

Abstract

A pressure valve (13), provided in the fuel path between the pump pressure chamber (9) and a high pressure reservoir of an internal- combustion engine, to supply the injection valves, is closed by a compression spring (29) supported in blind bore (24) in the pressure valve and on an abutment (30). The abutment (30) has bottom surface portions (33) and (34) for supporting the compression spring (29) and for restricting the of the pressure valve (13), and an outer annular collar (35) surrounding the rearward end of the latter to define a small gap (36) of predetermined width. The cross- sectional area of the gap is independent of the position of the pressure valve (13) and fuel can flow through the gap in throttled manner into and out of a variable volume damping pressure chamber (37) formed by the blind bore (24) of the pressure valve (13) and the bottom surface (33) of the abutment (30), the throttled flow thereby damping the movement of the pressure valve (13). <IMAGE>

Description

SPECIFICATION Fuel pump for an internal-combustion engine The invention relates to a fuel pump by means of which fuel can be fed to the high-pressure reservoir of an internal-combustion engine for supplying the injection valves, the pressure chamber of which is connected to a pressure valve in the fuel path, which pressure valve is arranged to open in response to pressure in the pump pressure chamber and to close, under spring force, against a valve seat, the pressure valve opening up to an abutment member which limits its opening.

A fuel pump of this general type is known, for example, from British Patent Specification 258 682. As an abutment for the pressure valve there is used a screw inserted behind the latter in the valve carrier; the screw has at the front a central blind bore for guiding and supporting a compression spring acting on the pressure valve in the closing direction, and its front face acts as a stop to limit the height of lift of the pressure valve.

The pressure valve and its abutment are the critical components in a fuel pump, especially when the high-pressure reservoir and the injection valves of an internal-combustion engine have to be supplied with fuel at extremely high pressure, for example in the order of magnitude of 1000 bar.

Since the rearward end of the pressure valve and the front end of the abutment are both sleeveshaped, in operation only the relatively smalldimensioned annular surfaces of the abutment and of the pressure valve that face each other come into contact during the opening stroke, so that both the abutment and the pressure valve are exposed to extreme loads. It is therefore unavoidable that both the pressure valve and its abutment are exposed to a great deal of wear, and at worst break down. In any case the long service life that is required of a fuel pump with a pressure valve and abutment can not be achieved with the known construction; in addition a construction of this type in a high-pressure system does not fulfill the necessary safety requirements.

An object of the invention is to construct a fuel pump of the type mentioned at the beginning in the area of the pressure valve and its abutment in such a way that a long service life of these components is possible even with extremely high fuel pressures and in addition the danger of a breakdown of the pressure valve is reduced to a minimum, without the function of the fuel pump as such being adversely affected.

According to the present invention there is provided a fuel pump for supplying fuel to the high-pressure reservoir of an internal combustion engine from which the injection valves may be supplied, including a piston pump, the pressure chamber of which is connected to a pressure valve in the fuel path, the pressure valve comprising a valve element which is arranged to open in response to pressure in the pump pressure chamber and to close, under spring force, against a valve seat the valve element having a hollow interior, and an abutment member which limits the opening movement of the valve element and which defines with the hollow interior of the valve element a damping pressure chamber which decreases and increases in volume as the valve element respectively opens and closes, which chamber communicates with the fuel path downstream of the valve seat via a gap of a predetermined cross-sectional area of flow which is independent of the position of the valve element so that as the valve element moves in response to pressure changes in the piston pump the throttled fuel flow into or out of the damping pressure chamber through the gap damps the movement of the valve element.

The invention may be put into practice in a number of ways but two embodiments will now be described by way of example with reference to the drawings, in which: Figure 1 is a sectional view through parts of a fuel pump in accordance with the invention showing a first embodiment, Figure 2 is an enlarged portion of Figure 1 in the region of the pressure valve, and Figure 3 is a variant of the arrangement shown in Figure 2 in the region of the pressure valve and its abutment.

In the Figures, like or corresponding parts have been given the same reference numbers.

Referring to Figure 1, a fuel pump 1 has a lower pump housing portion 2, and an upper pump housing portion 3 itself composed of lower and upper parts 4 and 5. A pump cylinder 6 is located in the pump housing portion 2, and is surrounded by a suction chamber 7, with a pump piston 8 working in the pump cylinder 6, above which is a pump pressure chamber 9 connected by suction ports 10 and 11 to the suction chamber 7. Above the pump cylinder 6 is a valve carrier 12 for a pressure valve 13. The pump piston 8 is in working contact, in a way not shown, with the cam of a cam shaft by means of a connecting rod.

The pump cylinder 6 is supported at its lower end (not shown) in the lower pump housing portion 2 and on its upper annular surface 14 the valve carrier 12 is supported with a corresponding lower annular contact surface 1 5. The valve carrier 12 has an outer surface 1 6 formed with a collar 17 located in an inner bore 1 8 of the lower pump housing portion 2, so that it is coaxial with the pump cylinder 6. The upper housing portion 3 is also centered in the inner bore 18 by means of a spigot 1 9 on its lower part 4, which is also coaxial with the valve carrier 12, on the upper annular surface 20 of which the housing portion 3 is supported with its corresponding annular surface 21.

The three pump housing portions 2, 4 and 5 are connected to one another by screws, and the pump cylinder 6 and the valve carrier 12 are thereby securely gripped in the pump housing.

The pressure valve 13, as shown in detail in Figure 2, is inserted into the fuel path inside the pump. It has a cylindrical body 22 with one or more outer fuel outlets 23 in the form of a milled part or longitudinal groove, and a blind bore 24 that is open to the rear and has a closing cone 25 at the front. The pressure valve 13 slides in a bore 26 of the valve carrier 12, which, at its junction with a small-diameter supply bore 27 branching from the pump pressure chamber 9, is constructed as a conical valve seat 28 against which the pressure valve 13 is pressed by a compression spring 29 acting in the closing direction. This spring 29 is located in the blind bore 24 inside the pressure valve 1 3 and is supported at one end against the bottom of the bore 24 and at the other end on an abutment 30 which is surrounded by a fuel collecting chamber 31.This chamber is delimited by formed recesses corresponding with one another respectively on the upper side of the valve carrier 12 and on the lower side of the pump housing portion 4.

The abutment 30 is, according to a feature of the invention, supported on the bottom surface 32 of the pump housing portion 4 in such a way as to be radially movable with respect to this pump housing portion. In addition according to the invention the abutment 30 is constructed as a damping element. It has radially inner bottom surface portion 33 for supporting the compression spring 29 and a radially outer bottom surface portion 34 for restricting the height of lift of the pressure valve 13, and it also has an outer annular collar 35 surrounding the rearward end of the pressure valve 13 like a cap.According to the invention this collar 35 is such that a small annular gap 36 of predetermined radial width is formed between the inner circumferential face of the collar 35 and the outer end of the valve body 22 via which fuel is fed in throttled manner into a damping pressure chamber 37 defined by the blind bore 24 of the pressure valve 13 and the bottom surface 33 of the abutment; the fuel is conveyed out of this chamber in each opening stroke of the pressure valve 1 3 again in throttled manner and with damping of the pressure valve 1 3 being achieved, as will be explained. The cross-sectional flow area of the gap 36 is independent of the position of the pressure valve 1 3.

The inner bottom surface portion 33 on which the compression spring 29 is supported, is arranged on an axial projection 38 of the abutment 30, which projection has a smaller diameter than the blind bore 24 in the pressure valve 13 and dips into it. On the end of the pressure valve 13 that is adjacent the abutment 30, transverse slots 39 are disposed which permit an unhindered flow of the fuel into and out of the damping pressure chamber 37.

The pump housing portion 3 has a highpressure buffer storage chamber 40 which forms an integrated component of the fuel pump 1 and is connected on its inlet-side to the fuel collecting chamber 31 via several ducts 41 leading from the latter and positioned radially beyond the abutment 30, and on its outlet-side via a small diameter choke bore 42 leading to a fuel line 43 which as shown only schematically in Figure 1 - leads to a high-pressure reservoir 44 of an internalcombustion engine for supplying its injection valves 45. The high-pressure buffer storage chamber 40 is thus used in advantageous manner to ensure that pressure peaks in the fuel, which occur during the working stroke of the pump piston 8 are so reduced that they can no longer cause harmful effects in the fuel line 43.

As an alternative to the embodiment of the abutment 30 shown in Figure 1 and 2, this latter element can have, according to the variant shown in Figure 3, a central through choke bore 46 communicating with the high-pressure buffer storage chamber 40 by means of a duct 47 appropriately arranged, which makes it possible to sustain a throttled fuel charging or discharging of the damping pressure chamber 37 taking place via the gap 36; the diameter of the bore 46 is adjusted accordingly to the size of the gap 36.

The function of the pressure valve 13 in conjunction with the abutment 30 is as follows.

As a starting point it is assumed that the pressure valve 13 is in the closed position and the damping pressure chamber 37 is filled with fuel. During the working stroke of the pump piston 8 the pressure valve 1 3 opens after reaching a specific pressure level in the pump pressure chamber 9, and during the opening movement of this valve the fuel in the damping pressure chamber 37 is forced out from this chamber, as its volume decreases, in throttled manner via the gap 36 into the fuel collecting chamber 31; in the variant shown in Figure 3 fusel from the chamber 37 is also forced via the choke bore 46 and the duct 47 into the high-pressure buffer storage chamber 40.

Owing to the throttling effect through the gap 36, the pressure in the chamber 37 is kept relatively high so that the desired damping of the pressure valve 1 3 occurs during the opening stroke movement of this valve and a gentle contact of the same against the bottom surface portion 34 on the side of the abutment is achieved. The fuel then reaches the fuel path, now open to communication through the pressure valve, from the pump pressure chamber 9 via the supply bore 27, the fuel collecting chamber 31 and the outlet ducts 41 into the high-pressure buffer storage chamber 40, in which excessive pressure peaks are reduced, and from this via the choke bore 42 and the fuel line 43 to the highpressure reservoir 44.

When the working stroke has ended and during the suction stroke of the pump piston 8 that then follows, the pressure valve 13 is brought back into its closed position through the exertion of pressure of the compression spring 29 working in the closing direction. The pressure force of the compression spring 29 is selected to be only so great, because of the damping of the fuel in the damping pressure chamber 37 that operates in the opening direction, that bringing back of the pressure valve into the closed position during pressure drop in the pump pressure chamber 9 is ensured. This means that the pressure valve 13 also makes contact relatively gently with its closing cone 25 on the valve seat 28. The actual pressure force working in the closing direction is not effectively delayed until after closing of the pressure valve 13 by the fuel penetrating into the damping pressure chamber 37 from the outside at high pressure, but throttled through the gap 36 or the choke bore 46.

Therefore with simple means a long service life of the pressure valve is guaranteed even with extremely high fuel pressures, and in addition the danger of breakdown of the pressure valve is practically eliminated.

Claims

1. A fuel pump for supplying fuel to the highpressure reservoir of an internal-combustion engine from which the injection valves may be supplied, including a piston pump, the pressure chamber of which is connected to a pressure valve in the fuel path, the pressure valve comprising a valve element which is arranged to open in response to pressure in the pump pressure chamber and to close, under spring force, against a valve seat the valve element having a hollow interior, and an abutment member which limits the opening movement of the valve element and which defines with the hollow interior of the valve element a damping pressure chamber which decreases and increases in volume as the valve element respectively opens and closes, which chamber communicates with the fuel path downstream of the valve seat via a gap of a predetermined cross-sectional area of flow which is independent of the position of the valve element so that as the valve element moves in response to pressure changes in the piston pump the throttled fuel flow into or out of the damping pressure chamber through the gap damps the movement of the valve element.

2. A fuel pump as claimed in claim 1, in which the valve element is generally cylindrical with a blind bore open in a direction downstream of the valve seat, and in which the abutment member is shaped to form an annular gap with the valve element.

3. A fuel pump as claimed in claim 2, in which the abutment member is cap-shaped with an annular collar surrounding the valve element to form the said annular gap therebetween.

4. A fuel pump as claimed in claim 3, in which the inner bottom surface of the abutment member serves to limit the opening movement of the valve element.

5. A fuel pump as claimed in claim 4, in which a closing compression spring is I cated in the hollow interior of the valve elefflent, which acts against the bottom surface of the abutment member.

6. A fuel pump as claimed in claim 5, in which the portion of the bottom of the abutment member against which the spring acts is within the portion of the bottom of the abutment member which limits the opening of the valve element.

7. A fuel pump as claimed in claim 6, in which the inner bottom surface portion, on which the compression spring is supported, is disposed on an axial projection of the abutment member, which projection has a smaller diameter than the blind bore in the valve element and dips into this.

8. A fuel pump as claimed in any one of the preceding claims, in which in the end of the valve element which contacts the abutment member, grooves are arranged to permit fuel flow into or out of the damping pressure chamber in the valve element with the latter in its fully open position.

9. A fuel pump as claimed in any one of the preceding claims, in which a choke bore is provided in the abutment member, which communicates with a high-pressure buffer storage chamber in the fuel path and which with the said throttling gap sustains a throttled fuel charging and discharging of the damping pressure chamber.

10. A fuel pump as claimed in any one of claims 2 to 9, in which the abutment member is supported in such a way that it is radially movable with respect to the valve element.

11. A fuel pump as claimed in any one of the preceding claims, in which the abutment member is surrounded by a fuel collecting chamber from which at least one fuel outlet passage leads.

12. A fuel pump as claimed in claim 11, in which the fuel outlet passage from the fuel collecting chamber leads to a or the high-pressure buffer chamber.

13. A fuel pump as claimed in any one of the preceding claims, in which the valve element has a conical valve closure portion adapted to close against a conical seat.

14. A fuel pump as claimed in any one of the preceding claims, in which the valve element is slidably arranged in a bore in a valve carrier and forms with the bore one or more fuel passages through which fuel flows when the valve element moves to an open position.

1 5. A fuel pump as claimed in claim 14, in which the piston pump has a pump housing in which the valve carrier is located.

1 6. A fuel pump as claimed in claim 1 5 when dependent on claim 12, in which the highpressure buffer chamber is defined within the pump housing.

1 7. A fuel pump substantially as specifically described herein with reference to Figures 1 and 2 or to those Figures as modified by Figure 3 of the drawings.

1 8. An internal combustion engine having a fuel pump as claimed in any one of the preceding claims.