GB2338993A

GB2338993A - Radial piston pump

Info

Publication number: GB2338993A
Application number: GB9915124A
Authority: GB
Inventors: Wolfgang Kuehne; Rainer Haeberer; Helmut Clauss
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1998-07-02
Filing date: 1999-06-30
Publication date: 2000-01-12
Anticipated expiration: 2019-06-30
Also published as: GB9915124D0; DE19829548A1; DE19829548C2; JP2000038972A; GB2338993B

Description

2338993 DESCRUPTION RADIAL PISTON PIM The present invention relates to

radial piston pumps for use in internal combustion engines.

A radial piston pump for producing high fuel pressure in fuel injection systems of internal combustion engines is known which, in particular in the case of a common rail injection system, has a drive shaft which is mounted in a housing and which comprises an eccentric shaft portion on which a ring is mounted in a sliding manner, which ring cooperates with preferably a plurality of pistons which are disposed in a respective cylinder chamber radially with respect to the drive shaft, which pistons can be moved radially in a reciprocating manner in the respective cylinder chamber by rotation of the drive shaft.

In the case of known internally supported radial piston pumps of this type, the base of the pistons is in each case in contact with the ring mounted on the drive shaft. The pistons are moved one after another in a reciprocating movement as a result of the eccentricity of the drive shaft. The stroke of the pistons is thus constant and corresponds to twice the degree of eccentricity of the drive shaft.

In order to increase the efficacy of the internal combustion engine it is proposed that the quantity of fuel delivered into the respective cylinder chamber be 2 controlled with the aid of a metering unit. In the case of partial filling of the elements it is possible, especially in the case of high rotational speeds, for the ring to become tilted, this being associated with the pistons being lifted off. In the worst case this can lead to the radial piston pump becoming inoperative.

The invention is based on the problem of providing a radial piston pump which overcomes the disadvantages mentioned above. In particular, transfer of the eccentric shaft movement to the pistons should be possible in the case of high rotational speeds and partial filling of the elements.

In a radial piston pump for producing high fuel pressure in fuel injection systems of internal combustion engines, in particular in the case of a common rail injection system, having a drive shaft which is mounted in a housing and which comprises an eccentric shaft portion on which a ring is mounted in a sliding manner, which ring cooperates with preferably a plurality of pistons which are disposed in a respective cylinder chamber radially with respect to the drive shaft, which pistons can be moved radially in a reciprocating manner in the respective cylinder chamber by rotation of the drive shaft, the problem is solved in that the ring is divided into a plurality of ring segments and in each case one ring segment is provided between each piston and the drive shaft. Since, in the case of a multiple piston pump the rolling movement between the bases of the pistons and the ring segments partly takes place in opposite directions it is not possible to produce a pure rolling movement with a ring formed as one piece. If, in the case of a multiple piston pump, the piston movement is introduced via a one-piece ring, opposing sliding movements occur 3 between the ring and the piston bases, which sliding movements can lead to considerable sliding wear. By dividing the ring into one ring segment per piston the ring segments can carry out a pure rolling movement independently of each other on the associated piston bases. The sliding movement between the piston base and the ring segment which causes wear is eliminated.

A particular embodiment of the invention is characterised in that the ring segments are spaced apart from each other in the peripheral direction. 'Me spacing is advantageously selected in such a way that the opposing movement of the ring segments described above is made possible.

A ftu-ther particular embodiment of the invention is characterised in that the friction coefficient between the piston base and the associated ring segme ntis greater than the friction coefficient between the drive shaft and the ring segment In this way it is advantageously ensured that a pure rolling process takes place between the piston base and the ring segment. In contrast, a relative rotation takes place between the eccentric shaft portion and the ring segments and can be improved by formation of a slide bearing.

A further particular embodiment of the invention is characterised in that a groove is provided in the piston base or the ring segment and serves to receive an 0ring. By means of the O-ring the friction coefficient between the piston base and the associated ring segment is increased.

A further particular embodiment of the invention is characterised in that the piston base surface facing the drive shaft, or the ring segment is at least partially 4 gummed. This gumming imposes a pure rolling movement between the piston base and the associated ring segment. Without a feature of this kind the ring segment can carry out a combined sliding-rolling movement on the piston base. The additional sliding portion together with the operational loading would, however, lead to greater sliding wear. If a pure rolling process takes place between the piston base and the associated ring segment the operational loading then acts between the piston base and the ring segment only in the form of surface pressing. 'Me sliding process which causes wear is eliminated. The ring segment and the associated piston base can therefore be purposely designed to take account of surface pressing. The rotational movement predetermined by the drive shaft of the radial piston pump, and the associated sliding process are advantageously limited to the bearing between the eccentric shaft portion and the ring segments.

A ftirther particular embodiment of the invention is characterised in that stops for the ring segments are attached to the housing between the ring segments. The stops advantageously ensure that the tangential working range of the ring segments is fixed.

A further particular embodiment of the invention is characterised in that two stops for the associated piston base are formed on each ring segment. This solution is simple and inexpensive. By means of the stops formed on the ring segment itself the tangential working range of the ring segments is fixed.

A further particular embodiment is characterised in that the piston is coupled to the associated ring segment. Similarly to the stops described above, this feature prevents the individual ring segments from striking against each other during operation. Moreover, the coupling means that a defined rolling process between the piston bases and the ring segments is ensured.

A further particular embodiment of the invention is characterised in that the piston base is formed as a plate. In this way the surface of the piston base is enlarged. This provides the advantage that a larger surface is available for the rolling process.

Further advantages, features and details of the invention are given in the following description in which exemplified embodiments of the invention are described in detail with reference to the drawings. The invention can reside in the features mentioned in the claims and the description individually or in any combination.

Figure I shows the illustration of a cross-sectional view transverse to the drive shaft of a radial piston pump in accordance with a first embodiment of the present invention; Figure 2 shows the illustration of a cross-sectional view longitudinally with respect to the drive shaft of a radial piston pump in accordance with a second embodiment of the present invention; 6 Figure 3 shows the illustration of a cross-sectional view longitudinally with respect to the drive shaft of a radial piston pump in accordance with a third embodiment of the present invention; and Figure 4 shows the illustration of a cross-sectional view transverse to the drive shaft of a radial piston pump in accordance with a fourth embodiment of the present invention.

The radial piston pump shown in a cross-sectional view in Figure I is used in particular in common rail injection systems for supplying fuel to diesel engines. "Common rail" equates to "common line". In contrast to conventional high pressure injection systems in which the fuel is delivered by separate lines to the individual combustion chambers, the injection nozzles in common rail injection systems are supplied from a common line. The radial piston pump shown is provided with an integrated required-quantity control system. The delivery and dimensioning of the fuel supply is carried out by a metering unit, not shown.

The radial piston pump shown in Figure I has a drive shaft mounted in a pump housing, not shown, and having an eccentric shaft portion 1. Three ring segments 2, 3 and 4 are provided on the eccentric shaft portion 1, with respect to which ring segments the shaft portion I can be rotated. Each ring segment 2, 3 and 4 cooperates with a piston 5, 6 and 7. A plate 8, 9 and 10 is formed on the base of 7 each of the pistons 5, 6 and 7. Each of the plates 8, 9 and 10 is located in position against one of the ring segments 2, 3 and 4. A slide bearing I I is formed between the eccentric shaft portion I and the ring segments 2, 3 and 4.

The radial piston pump illustrated only schematically in Figure I serves to exert high pressure on fuel which is supplied from a tank by a presupply pump. The fuel on which high pressure is exerted is then delivered into the afore-mentioned common line. During the delivery stroke the pistons 5, 6 and 7 are moved away outwardly from the axis of the drive shaft as a result of the eccentric movement of the eccentric shaft portion 1, which is transferred by way of the ring segments 2, 3 and 4 to the pistons 5, 6 and 7. During the intake stroke the pistons 5, 6 and 7 move radially towards the axis of the drive shaft in order to take in fuel. The intake stroke movement of the pistons 5, 6 and 7 is achieved by means of springs, not illustrated, which are prestressed against the plates 8, 9 and 10.

As shown in Figure 1, three stops 17, 18 and 19 for the ring segments 2, 3 and 4 are attached to the pump housing indicated by three fixed bearings 14, 15 and 16. By means of the stops 17, 18 and 19 the tangential working range of the individual ring segments 2, 3 and 4 is limited. If one of the ring segments 2, 3 and 4 slides out of its desired position during operation it is automatically returned to the required position by the stops 17, 18 and 19. By deliberately coordinating the friction coefficients between the plates 8, 9 and 10, the ring segments 2, 3 and 4 and the eccentric shaft portion I it is ensured that the ring segments 2, 3 and 4 carry out a pure rolling movement with respect to the plates 8, 9 and 10.

8 Figure 2 shows a partial view of a cross-section taken longitudinally with respect to the drive shaft of a radial piston pump in accordance with a second embodiment of the present invention. An eccentric shaft portion 20 is mounted so asto rotate relative to its ring segment 21. A plate 22 is supported against the ring segment 21 and is attached to a piston 23. The arrow 29 shows the force which acts upon the piston during operation. This force is produced during the intake stroke by means of a spring, not illustrated, which is pretensioned against the plate 22. During the delivery stroke of the radial piston pump the reaction force of the compressed fuel acts in the direction of the arrow 29. The lines 24 and 25 show the flow of fuel. At the edge of the region of fuel flow a groove 26 is provided in the surface of the plate 22 facing the ring. A ring 28 of an elastomeric synthetic material is disposed in the groove 26. The dimensions of the ring 28 are larger than the dimensions of the groove 26. In this way a high friction coefficient is ensured between the plate 22 and the ring segment 2 1.

Figure 3 shows a similar illustration to Figure 2. In Figure 3 reference numbers are used of which the value is increased by 10 with respect to that in Figure 2. In order to avoid repetition, no detailed description' of Figure 3 will be given. The single difference between the illustrations in Figure 3 and Figure 2 is thatthe grooves 3 6 and 3 7 are not disposed in the plate but in the ring segment 3 1. The rings 3 8 and 39 disposed in the grooves 36 and 37 fulfill the same function as the ring 28 in Figure 2.

Figure 4 shows a similar illustration to Figure 1. An eccentric shaft portion 9 is mounted with the aid of a slide bearing 41 in such a way as to be able to rotate with respect to ring segments 42, 43 and 44. The ring segments 42, 43 and 44 are located in position against the plates 48, 49 and 50 which are formed on the pistons 45, 46 and 47. Radially extending stops 51, 52; 53, 54 and 55, 56 are formed on the ring segments 42, 43 and 44. By means of the stops 51 - 56 the movement of the ring segments 42 44 is limited in the tangential direction. -

Claims

1. A radial piston pump for producing high fuel pressure in a fuel injection system of an internal combustion engine, in particular in the case of a common rail injection system, having a drive shaft which is mounted in a housing and which comprises an eccentric shaft portion on which a ring is mounted in a sliding manner, which ring cooperates with a plurality of pistons each of which is disposed in a respective cylinder chamber radially with respect to the drive shaft, which pistons can be moved radially in a reciprocating manner in the respective cylinder chamber by rotation of the drive shaft, the ring being divided into a plurality of ring segments and in each case one ring segment being provided between each piston and the drive shaft.

2. A radial piston pump according to claim 1, wherein the ring segments are spaced apart from each other in the peripheral direction.

3. A radial piston pump according to claim I or 2, wherein the friction coefficient between the piston base and the associated ring segment is greater than the friction coefficient between the drive shaft and the ring segment.

4. A radial piston pump according to any of claims I to 3, wherein at least one groove is provided in the piston base or the ring segment and serves to receive an O-ring.

5. A radial piston pump according to any of claims I to 3, wherein the surface of the piston base, facing the drive shaft, or the ring segment is at least partially gummed.

6. A radial piston pump according to any of the preceding claims, wherein stops for the ring segments are attached to the housing between the ring segments.

7. A radial piston pump according to any of claims I to 5, wherein two stops for the associated piston base are formed on each ring segment.

8. A radial piston pump according to any of claims I to 5, wherein the piston is coupled to the associated ring segment.

9. A radial piston pump according to any of the preceding claims, wherein the piston base is formed as a plate.

10. A radial piston pump substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.