WO2005057012A1

WO2005057012A1 - Gear pump, particularly a fuel pump

Info

Publication number: WO2005057012A1
Application number: PCT/DE2004/002324
Authority: WO
Inventors: Marcus Marheineke; Thomas Fuhrich
Original assignee: Robert Bosch Gmbh
Priority date: 2003-12-05
Filing date: 2004-10-20
Publication date: 2005-06-23
Also published as: DE10356949A1

Abstract

A gear pump (10) comprises at least two gears (28, 30), which are mounted inside a case (20) and mesh with one another. The gears enable a fluid to be delivered from a suction area (50) to a pressure area (54). At least one fluid connection (60) is situated inside the case (20) and connects a tooth space (40) of a gear (28) approaching the pressure area (54) at least indirectly with this pressure area (54). The invention provides that the fluid connection has a recess (60), which is situated to the side of the gear (28) inside the housing (20) and which connects the tooth spaces (40) located in the vicinity thereof directly to the pressure area (54).

Description

Gear pump, in particular fuel pump

State of the art

The invention relates to a gear pump, in particular a fuel pump, with at least two gear wheels, which are arranged in a housing and mesh with one another and convey a fluid from a suction area into a pressure area, and with at least one fluid connection, which is arranged in the housing and adjusts itself to the At least indirectly connects the tooth space of a gear wheel approaching the pressure area with the pressure area.

A gear pump of the type mentioned is known from DE 100 18 348 AI. It serves as a pre-feed pump in a fuel system and has a housing in which a pump chamber is present. In this two gears are arranged side by side, which mesh with each other. A boundary wall of the housing is arranged directly adjacent to the exposed edges of the gear wheels. Between a full cross section (base circle) and the boundary wall, two delivery channels are formed, in which fuel is conveyed from a suction area into a pressure area by means of the interdental spaces of the two gear wheels.

The speed of the known prefeed pump is rigidly coupled to the speed of an internal combustion engine. The gear pump is designed so that it is already at low Speed promotes a sufficient amount of fuel. In order to prevent too much fuel from being delivered at high speed, a flow restrictor is arranged in the suction area, which limits the delivery rate. However, this leads to a low pressure at high speed in the suction area, so that subsequently fuel vapor is present in the interdental spaces at a comparatively low pressure (for example approximately 0.3 bar). If such a tooth space reaches the pressure range in which, for example, a pressure of 6 to 9 bar can prevail, there would be the risk that the pressure in such a tooth space suddenly increases and cavitation damage to the gear wheels and / or the housing occurs.

To avoid this, in the known gear pump in the housing there is a groove arranged radially outside of the gear, which extends a certain distance from the pressure area along a conveying channel in the direction of the suction area and thereby connects a tooth space approaching the pressure area to the pressure area immediately before the interdental space opens towards the pressure area. As a result, a certain pressure equalization can take place in this interdental space beforehand. If the groove extends in the circumferential direction over more than one interdental space, pressure equalization can only take place between the last partially filled interdental space and the adjacent fully filled interspace, since vapor pressure is always present in a partially filled interdental space. Therefore, only a part of the available angular range can be used for refilling, and as a result the filling must take place relatively quickly, which leads to a rapid increase in pressure and the associated noise. The object of the present invention is to develop a gear pump of the type mentioned at the outset in such a way that it works particularly quietly and has a long service life. The gear pump should also be highly efficient.

This object is achieved in the case of a gear pump of the type mentioned at the outset in that the fluid connection comprises a recess arranged laterally in the housing in the housing, which recess has the recess in its area

Interdental spaces directly connects to the pressure area.

Advantages of the invention

Due to the direct fluid connection, an interdental space that is still comparatively far from the pressure area can be filled slowly. This allows slow pressure equalization over a maximum period of time. Due to the slower filling of one

Between the teeth, even before it opens to the pressure area, the running noise of the gear pump is further reduced, and cavitation damage to the gear and / or the housing of the gear pump are avoided. In addition, such a gear pump can be manufactured comparatively inexpensively, since the recess can be milled with high precision, for example, in a side cover of the gear pump, which must be machined anyway.

Advantageous developments of the invention are specified in the subclaims.

First, it is proposed that the recess with a between a root circle and a tip circle of the gear enclosed area overlaps in such a way that the overlap forms a defined flow restrictor to an interdental space located in the area of the recess. With this gear pump, the filling of the interdental spaces approaching the pressure range can take place in a precisely defined manner, since only a certain amount of fluid can flow into the interdental space during the period during which there is an interdental space in the area of the recess.

In principle, the overlap can also change in the circumferential direction in order to be able to set a desired optimal pressure profile in an interdental space approaching the pressure area. An initially smaller cross-section can, for example, reduce pressure pulsations in the pressure chamber. In this case, the cross section of the flow restrictor depends at least in regions on the angular position of the gear.

But it is also possible that the cross section of the

Flow throttle is independent of the angular position of the gear, so the degree of overlap does not change in the circumferential direction. This results in a volume flow into the interdental space that is initially larger and then decreases with a decreasing pressure difference.

In a further development it is proposed that the flow restrictor be dimensioned such that the pressure in the interdental space at a certain speed

Time of entry into the area of the recess until the pressure area is reached rises at least approximately to the pressure level prevailing in the pressure area. This speed is preferably a speed range in which the gear pump is operated frequently becomes. With such a gear pump, cavitation is completely excluded, at least in the specific speed range, and the operating noise is thereby significantly reduced.

It has been found to be particularly advantageous if the cutout extends in the circumferential direction from the pressure area over an angular area which corresponds approximately to three times the pitch angle of the gearwheel. Such a gear pump has a very high degree of efficiency and at the same time the interdental spaces approaching the pressure area have been in the area of the lateral recess sufficiently long that a gradual and thus noise and wear-reducing filling of the interdental spaces is possible.

For the efficiency of the gear pump, it is most favorable if the recess opens into the foot area of an interdental space.

Due to the recess provided on the side of the gear wheel, a slide bearing of a gear wheel can also be supplied with lubricant. Since a separate lubricant channel can thus be dispensed with, this measure reduces the manufacturing costs of the gear pump.

It is also advantageous if the depth of the recess corresponds to at least twice the overlap of the area enclosed by the top and bottom circle. Thus, the flow in the recess itself is not or not significantly throttled.

drawing An exemplary embodiment of the present invention is explained in more detail below with reference to the accompanying drawing. The drawing shows:

Figure 1 shows a schematic section through a gear pump; and

2 shows a section along the line II-II of Figure 1.

Description of the embodiment

A gear pump bears the overall reference number 10 in FIG. 1. It delivers fuel from a storage container 12 to a high-pressure pump 14. From there, the fuel reaches a fuel injection device 16, which injects the fuel directly into a combustion chamber 18 assigned to it.

The gear pump 10 comprises a housing 20, which one

Includes base body 22 and a lid 24 (Figure 2). FIG. 1 shows a top view of the housing 20 when the cover 24 is lifted off. A generally oval pump chamber 26 is present in the base body 22. In this two gears 28 and 30 are arranged side by side. The gears mesh with one another in a region 32. They are mounted in the housing 20 by means of shafts 34 and 36, respectively. The shaft 34 of the left gear 28 in FIG. 1 is driven in a manner not shown by an internal combustion engine to which the combustion chamber 18 belongs.

The two gears 28 and 30 are identical. They have a total of ten teeth 38, between which tooth spaces 40 are formed. A root circle with the radius Rl is indicated by a dash-dotted line and bears the reference number 42. A corresponding tip circle with the radius R2 bears the reference number 44. The angle between two teeth 38 is referred to as tooth pitch Z. The directions of rotation of the two gear wheels 28 and 30 are indicated by two arrows 46 and 48.

A lower region of the pump chamber 26 in FIG. 1 forms a suction region 50. This is connected to the reservoir 12 via a flow restrictor 52. An upper region of the pump chamber 26 in FIG. 1 forms a pressure region 54 which is connected to the high-pressure pump 14 via an outlet 56. The left and right edges of the pump chamber 26 in FIG. 1 are semicircular with a radius which corresponds approximately to the radius R2 of the tip circle 44 of a gear 28 or 30. A corresponding radial boundary wall bears the reference number 58. There is only a very small gap between it and the tips of the teeth 38.

A recess 60 is present in the cover 24 of the housing 20. This is indicated in Figure 1 by a dashed line. The recess 60 extends in the manner of two wings from the center of the pump chamber 26 to the side. It is designed symmetrically on both sides of the pump 10. For the sake of simplicity, only that area of the recess 60 that lies in the area of the left gear 28 is described below.

A radially outer edge region 62 of the recess 60 is coaxial with the gear 28 and extends approximately in the

Area of the upper left quadrant of the gear 28 over an angular range of slightly more than 90 °. Approximately from the point of intersection with a 12 o'clock line 64 of the gear 28, which also corresponds to the beginning of the printing area 54, the outer edge 62 merges into an edge area 65 roughly straight inwards and very slightly upwards at an angle. A radially inner boundary wall 66 of the recess 60 extends approximately straight from a 9 o'clock position of the coaxial edge region 62 inwards and obliquely upwards. It runs just above the shaft 34 of the gear 28.

A radius R3 of the coaxial edge region 62 of the cutout 60 is somewhat larger than the radius Rl of the root circle 42 of the gearwheel 28. This creates an overlap U with which the recess 60 is enclosed in between the root circle 42 and the tip circle 44 of the gearwheel 28 ■ Area protrudes. Those interdental spaces 40 of the gear 28 that are currently located in the upper left quadrant of the pump chamber 26 are therefore connected to the recess 60 and thus ultimately to the pressure region 54 via a gap 68, which is shown hatched in FIG. 1 for clarification. The gap 68 forms a flow restrictor. The depth of the recess 60 is approximately twice the overlap U.

The gear pump 10 operates as follows:

The gear 28 is driven by the shaft 34 and thereby rotates clockwise. Gear 30 is driven by gear 28 and rotates counterclockwise. Fuel present in the suction area 50 is entrained in the tooth space 40 between two teeth 38 when the gear 28 or 30 rotates and forms a closed volume as soon as a tooth space 40 lies completely in the region of one of the radial boundary walls 58 of the pump chamber 26. This volume becomes larger as the gears 28 and 30 rotate along the radial Boundary walls 58 transported from the suction area 50 to the pressure area 54.

When the front tooth 38, viewed in the direction of rotation of the gear 28, for example, of the two teeth 38 delimiting a tooth space 40 passes the 12 o'clock line 64, this tooth space 40 opens towards the pressure area 54. In the course of the further rotation of the gear wheel 28, the tooth space 40 comes into the meshing area 32 between the two gear wheels 28 and 30, in which the fluid present in the tooth space 40 is squeezed out by a tooth 38 of the other gear wheel 30. The pressure in the suction area 50 is a little less than 1 bar when the gear pump 10 is operating at a low speed, whereas in the pressure area 54 there is approximately 6 to 9 bar.

The gear pump 10 is designed such that it already has a high delivery rate even at a low speed of the two gears 28 and 30. To prevent the gears 28 and 30 from being too high at high speeds

Fuel quantity is delivered, the flow restrictor 52 is arranged between the suction region 50 and the reservoir 12. This limits the inflow of fuel from the reservoir 12 into the suction area 50 of the pump chamber 26. However, this has the consequence that at high

Speeds the pressure in the suction area 50 decreases and may only be about 0.2 to 0.3 bar. Correspondingly, the pressure in the interdental spaces 40, which move along the radial boundary wall 58 of the pump chamber 26 from the suction area 50 to the pressure area 54, is likewise only about 0.2 to 0.3 bar. At this pressure, there is only a comparatively small amount of fuel in the interdental space 40, especially at high speeds. The rest of the tooth space 40 is filled with fuel vapor.

If such an interdental space 40 now reaches the region of the recess 60 in the cover 24, it is connected directly to the pressure region 54 via the gap 68 and the recess 60. As the interdental space 40 continues to move toward the pressure area 54, fuel present under comparatively high pressure in the pressure area 54 can therefore flow into the interdental space 40 via the recess 60 and the gap 68. The overlap U or the gap 68 are constant over the angle of rotation of the gear wheel 28 and are selected such that at a specific design speed of the gear wheels 28 or 30 the time during which a

The interdental space 40 is located in the area of the recess 60 without the front tooth 38 of the interdental space 40 lifting off the radial boundary wall 58 of the pumping chamber 26, just enough for the pressure in the interdental space 40 to continuously increase to the pressure prevailing in the pressure region 54 , In an embodiment not shown, the gap 68 could also change over the angle of rotation.

If the front tooth 38 of the two teeth 38 delimiting an interdental space 40 passes the 12 o'clock line 64 and the interdental space 40 opens towards the pressure area 54, an abrupt pressure change in the interdental space 40 is avoided since this already in the pressure area 54 prevailing pressure level prevails. As a result, the operating noise of the gear pump 10 is reduced and cavitation damage to the teeth 38 and to the housing 20 are avoided. The efficiency of the gear pump is very high because the radially outer edges of the teeth 38 until the 12 o'clock line 64 passes the radial Boundary wall 58 of the pump chamber 26 are opposite with a very small gap.

In an exemplary embodiment not shown, a small branch channel leads from the recess 60 to the shaft 34.

As a result, the shaft 34 is lubricated with fuel under high pressure. Separate fluid channels for the supply of lubricant can then be dispensed with. It is also conceivable that the recess is so large that the shaft is at least partially in its area.

Claims

Expectations

1. gear pump (10), in particular fuel pump, with at least two gear wheels (28, 30) which are arranged in a housing (20) and mesh with one another and convey a fluid from a suction area (50) to a pressure area (54), and with at least one fluid connection (60) which is arranged in the housing (20) and connects an interdental space (40) of a gearwheel (28) approaching the pressure area (54) at least indirectly to the pressure area (54), characterized in that the fluid connection comprises a recess (60) arranged laterally of the gearwheel (28) in the housing (20), which connects the interdental spaces (40) located in its area directly to the pressure area (54).

2. Gear pump (10) according to claim 1, characterized in that the recess (60) overlaps with an area enclosed between a root circle (42) and a tip circle (44) of the gear wheel (28) such that the overlap (U) is a Defined flow restrictor (68) to a tooth space (40) lying in the region of the recess (60).

3. Gear pump (10) according to claim 2, characterized in that the cross section of the flow restrictor (68) is at least partially independent of the angular position of the gear (28).

4. Gear pump (10) according to one of claims 2 or 3, characterized in that the cross section of the Flow restrictor (68) is dependent on the angular position of the gear (28) at least in some areas.

5. Gear pump (10) according to one of claims 2 to 4, characterized in that the flow restrictor (68) is dimensioned such that at a certain speed the pressure in the tooth space (40) from the time of entry into the region of the recess (60 ) until reaching the pressure range (54) at least approximately up to the pressure level prevailing in the pressure range (54).

6. Gear pump (10) according to one of the preceding

Claims, characterized in that the recess (60) extends in the circumferential direction from the pressure area (54) over an angular area which corresponds approximately to three times the pitch angle of the gear wheel (28).

7. Gear pump (10) according to one of the preceding

Claims, characterized in that the recess (60) opens into the foot region (42) of an interdental space (40).

8. Gear pump (10) according to one of the preceding claims, characterized in that the fluid connection (60) supplies a slide bearing of a gear (28) with lubricant.

9. Gear pump (10) according to one of the preceding claims, characterized in that the depth of the recess (60) corresponds to at least twice the overlap (U) with the area enclosed between the root circle (42) and the tip circle (44).