GB2210940A

GB2210940A - Seals for fuel injection pumps for internal combustion engines

Info

Publication number: GB2210940A
Application number: GB8829138A
Authority: GB
Inventors: Andre Brunel; Jean Leblanc; J Paul Morel-Fourrier
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1987-12-15
Filing date: 1988-12-14
Publication date: 1989-06-21
Also published as: GB8829138D0; FR2624558A1; DE8716536U1; JPH01195965A

Abstract

In a fuel injection pump which is to be sealed off from the outside by a shaft seal, there is a risk that the seal will be subjected to heavy stress by leakage flows because of the high internal pressure in the chamber, and will hence wear rapidly. The leakage flow is reduced by an element 6 which surrounds the drive shaft 2 in the manner of a sliding bearing and is both axially and radially displaceable against surrounding housing parts, as well as by a relief line 12, which connects the relief chamber 8 to the suction side 13 of the feed pump 4 and draws off the leakage flow by the vacuum, prevailing at this location. This solution is particularly suitable for designs in which, for reasons of cost, a roller bearing 3 is provided in place of a sliding bearing for guiding the drive shaft 2. <IMAGE>

Description

DESCRIPTION A FUEL INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES The invention relates to a fuel injection pump.

Fuel injection pumps are known from DE-P 35 19 029, where the drive shaft enters the housing through a shaft seal and is guided in the housing by a sliding bearing (plain journal bearing). The drive shaft is coupled to a fuel feed pump, which subjects part of the inside of the housing to pressure. This pressure also acts on the sliding bearing, to which a relief line is connected approximately half way along the length of the bearing.

As a result of its cross section, the quantity of leakage oil is drawn off substantially without line resistance. The remaining length of the sliding bearing from the relief line to the shaft seal is, as a result of the narrow bearing clearance and the high flow resistance associated therewith, not supplied with a sufficient quantity of the lubricating leakage oil, which can lead to the pump running dry and jamming. This effect is made worse by the risk of blockage due to the intake of dirt.

The invention resides in a fuel injection pump for an internal combustion engine, having a housing, a drive shaft journalled in the housing, a fuel feed pump disposed in the housing and driven by the drive shaft, so as to deliver fuel to a fuel chamber disposed in the housing beyond the feed pump, a relief chamber being formed between a lip seal, which has a prestressed sealing lip abutting the shaft, and a floating sealing element which encircles the shaft and is axially and radially displaceable, a sliding seal being formed between the sealing element and either the shaft or the housing and the sealing element being sealed to either the housing or the shaft, respectively, the relief chamber being connected by a relief line to the suction side of the feed pump, whereby fuel which passes the sealing element is withdrawn from the relief chamber.

This has the advantage that in some embodiments the sealing element slides in the manner of a sliding bearing on the shaft, but is displaceable axially and radially with respect to the surrounding housing parts and hence does not have to have the machining quality of a sliding bearing which is used for guiding, and, by virtue of the fact that there is no need to observe close tolerance, can be manufactured inexpensively.

Through the vacuum prevailing at the pump inlet, the connection between the relief line and the suction side of the feed pump changes the passive flow of the leakage oil into an active suction. As a result, it is possible to reduce wear to the shaft seal by way of smaller pressing forces on the drive shaft and, as a result of the eliminated leakage oil flow, to mount the drive shaft using a rolling bearing between the shaft seal and the drive shaft outlet on the housing and in this way to reduce the amount of machining on the fuel injection pump.

It is particularly advantageous to vary the quantity of leakage oil by way of graded sealing quality without this impairing the drive shaft bearing and hence the ability of the fuel injection pumF to operate.

The invention is described further hereinafter, by way of example only, with reference tc the accompanying drawings, in which: Fig. 1 is a schematic view of a ;artial longitudinal section through a distriLutor-type fuel injection pump of a first embodiment cf the present invention; Fig. 2 is a detail of the position of the drive shaft seal, the element with surrounding components, and the suction of the pump according to second embodiment of the invention; Fig. 3 is a schematic view of th- element for prevention of leakage flow of a third embodiment of the present invention; and Fig. 4 is a schematic view of the element for prevention of leakage flow of a fourth embodiment of the present invention.

As illustrated in Fig. 1, a drive shaft 2 enters a housing 1 and is guided therein through a rolling bearing 3 and drives a feed pump 4, which delivers fuel into a fuel chamber 5. As a result of leakage along the drive shaft 2 in the direction of the rolling bearing 3, the fuel chamber 5 is connected to an element 6, which is located on the side of the feed pump 4 remote from the pressure side.

This element 6 surrounds the drive shaft 2 as a rotationally symmetrical part and, since it is axially and radially displaceable on the drive shaft 2 in the manner of a sliding bearing, it has a gap between its inner bore and the drive shaft 2. This gap thus forms the only way for the leakage flow to flow out of the working chamber 5 along the drive shaft 2 in the direction of the roller bearing 3. If element 6 has a shoulder 9 with an axially directed end face extending radially of the drive shaft 2 and is axially supported on the side remote from the fuel working chamber 5 on a housing shoulder 7, which is directed radially to the drive shaft 2, and in this way blocks off the leakage flow from the fuel chamber 5 along this path. However, leakage may take place from the fuel chamber 5 even here.

Beyond the element 6, the leakage flow enters a relief chamber 8 which is defined by the side of the element 6 remote from the delivery pump 4, the drive shaft 2, a shaft seal 11, the housing 1 and a relief line 12. The essential feature of the shaft seal 11 is a prestressed sealing lip in the form of a cuff, which abuts on the drive shaft 2 and protects the rolling bearing 3 from the leakage flow. The relief line 12 leads from the relief chamber 8 to the suction side 13 of the feed pump 4, as a result of which the leakage flow is reliably drawn off, as a result on the vacuum on the suction side 13. In this way, the relief chamber 8 and, at the same time, the sealing lip of the shaft seal 11 are reliably and substantially uncoupled from the internal pressure of the fuel chamber 5 and relieved thereof, which lengthens the period of functional efficiency of the shaft seal.

The second embodiment, shown in Fig. 2, shows a somewhat more detailed embodiment of the main representation of the element 6 in Fig. 1, and is an alternative solution with respect to the blocking off of the leakage flow along the shoulder 9 of the element 6 and the housing shoulder 7. To do this, on its side facing the shoulder 9, the housing shoulder 7 has an annular groove 15, in which there is a resilient seal 16. In conjunction with an energy store 14, in this case a leaf spring, which is supported on the feed pump 4 and presses axially against the element 6, the shoulder 9 is pressed against the seal 16 and, when the seal has yielded elastically into the annular groove 15, it abuts firmly against the housing shoulder 7, thus blocking the way of the leakage flow to enter the relief chamber 8.Furthermore, in order to protect the seal 16, rotation of the element 6 on the drive shaft 2 is prevented by one or more pins 18 retained in the housing 1 engaging with a corresponding number of grooves 17 provided on the periphery of the shoulder 9. Leakage from the fuel chamber 5 to the relief chamber 8 thus takes place in this case, only by way of the gap between the inner bore of the element 6 and the drive shaft 2.

Alternatively, the annular groove 15 may also be disposed in the end face of the shoulder 9.

In the embodiment shown in Fig. 3, the annular groove 15 and the seal 16 are not provided in the position described in the embodiment of Fig. 2. But rather, a corresponding annular groove 19 and a resilient seal 20 inserted therein are disposed in the region of the inner bore of the element 6 in the drive shaft 2 in such a way that the gap between the element 6 and the drive shaft 2 is closed by the resilient seal 20 and leakage flow along the drive shaft 2 is prevented. Alternatively, the seal 20 may also be disposed in the outer surface of the inner bore of the element 6.In the region of the face of the element 6 opposite the drive shaft 2, said element has a longitudinal groove 21, into which a pin 22 engages, which is retained in the drive shaft 2, as a result of which the element 6 is prevented from rotating with respect to the drive shaft 2 and hence the seal 20 is protected from wear.

The energy store 14, which acts in the same way as described with respect to Fig. 2, is in this case in the form of a helical spring. In addition, the pressure of the fuel chamber 5 acts as a sealing force on the element 6, as in the embodiment of Figs. 1 and 2.

Fig. 4 shows an element 106 which, like the element 6, is disposed on the drive shaft 2 in the manner of a sliding bearing, but which differs from the element 6 in that it does not have a shoulder. As a result, the prevention of relative rotation between the element 106 and the drive shaft 2, which is realised in the same way as described in Fig. 3 with respect to the element 6 and the drive shaft 2, has the additional function of preventing displacement, in that in the groove 21, the pin 22 abuts against the side boundary face facing the fuel chamber 5, wherein the axial displacement force on the element 106 is generated by the internal pressure prevailing in the fuel chamber 5.

In the case of the element 106, the sealing function is carried out by an annular groove 23, which is on the outer surface remote from the drive shaft 2, and the resilient ring 24 inserted therein, which is supported at one side on a collar 25, which is on the housing side and is concentric with respect to the drive shaft 2, and on the other side is pressed by the internal pressure prevailing in the fuel chamber 5 against the lateral boundary of the annular groove 23 remote from the fuel chamber 5. Alternatively, the ring 24 may also be disposed in the inner peripheral surface of the element 106.

Claims

1. A fuel injection pump for an internal combustion engine, having a housing, a drive shaft journalled in the housing, a fuel feed pump disposed in the housing and driven by the drive shaft, so as to deliver fuel to a fuel chamber disposed in the housing beyond the feed pump, a relief chamber being formed between a lip seal, which has a prestressed sealing lip abutting the shaft, and a floating sealing element which encircles the shaft and is axially and radially displaceable, a sliding seal being formed between the sealing element and either the shaft or the housing and the sealing element being sealed to either the housing or the shaft, respectively, the relief chamber being connected by a relief line to the suction side of the feed pump, whereby fuel which passes the sealing element is withdrawn from the relief chamber.

2. A fuel injection pump as claimed in claim 1, in which the sealing element is sealed to the housing or the shaft, as the case may be, at opposing radially directed faces on the element and on the housing or the shaft.

3. A fuel injection pump as claimed in claim 2, wherein the sealing element is biased in the axial direction by means of an energy store.

4. A fuel injection pump as claimed in claim 2, wherein a resilient seal is disposed between the opposing abutment faces.

5. A fuel injection pump as claimed in claim 4, wherein the sealing element is restrained from rotation relative to the housing or the shaft, as the case may be, by means of a key and keyway arrangement.

6. A fuel injection pump as claimed in claim 1 or 2, in which the sealing element is sealed to the shaft by means of a sealing ring disposed between an internal bore in the sealing element and the drive shaft.

7. A fuel injection pump as claimed in claim 2 or in claim 6 when appendant to claim 2, wherein the outer surface of the element has an annular groove, one of the lateral boundaries of which forms one of said axially directed faces and into which a ring is fitted which is outwardly resilient and one of whose axial faces forms the other of said axially directed faces and whose peripheral face is in sealing contact with a collar of the housing.

8. A fuel injection pump as claimed in claim 6 or 7, wherein the element is coupled to the drive shaft so as to be non-rotatable relative thereto.

9. A fuel injection pump as claimed in any preceding claim, wherein the drive shaft is journalled in the housing in a rolling bearing contiguous to the lip seal and to the outside thereof.

10. A fuel injection pump for internal combustion engines constructed and adapted to operate substantially as described herein with reference tb and as illustrated in Figs. 1 to 4 of the accompanying drawings.