External gear pump

Abstract

An external gear pump, having a driving first pump gear and a second pump gear driven by the first pump gear, which intermesh to convey a fluid from a suction side to a pressure side of the external gear pump. The first pump gear and the second pump gear each have a plurality of teeth, each having a leading tooth flank leading in the rotation direction of the corresponding pump gear and a trailing tooth flank. The leading tooth flank of the first pump gear interacts with the trailing tooth flank of the second pump gear to drive the second pump gear via the first pump gear. The trailing tooth flanks of the first pump gear extend concavely to form a fluid pocket at at least one axial position in the radial direction at least in sections in each case.

Claims

1. An external gear pump, comprising: a driving first pump gear and a second pump gear driven by the first pump gear, which intermesh to convey a fluid from a suction side to a pressure side of the external gear pump, wherein the first pump gear and the second pump gear each have a plurality of teeth, each having a leading tooth flank leading in the rotation direction of the corresponding pump gear and a trailing tooth flank, wherein the leading tooth flank of the first pump gear comes into physical contact with the trailing tooth flank of the second pump gear to drive the second pump gear via the first pump gear, wherein the trailing tooth flanks of the first pump gear extend concavely to form a fluid pocket at at least one axial position in a radial direction at least in sections in each case, wherein the fluid pocket extends directly out of a tooth root circle of the first pump gear, and wherein a cross-section of the trailing tooth flanks is identical throughout in the region of the fluid pocket, in the axial direction.

2. The external gear pump according to claim 1, wherein the trailing tooth flanks of the teeth of the second pump gear are symmetric in design to the leading tooth flanks of the teeth of the second pump gear.

3. The external gear pump according to claim 1, wherein as viewed in the axial direction, the fluid pocket in the respective trailing tooth flank of the first pump gear is formed open-edge at least on one side.

4. The external gear pump according to claim 1, wherein as viewed in the axial direction, the trailing tooth flanks of the first pump gear each have a fluid pocket region, which accommodates the fluid pocket, as well as a contact region, which directly adjoins the fluid pocket region, wherein the trailing tooth flanks extend convexly in the contact region.

5. The external gear pump according to claim 4, wherein the first pump gear and the second pump gear are shiftable in position relative to each other in the axial direction with respect to a rotation axis of one of the pump gears to adjust a specific superposition, and wherein a contact region is present in superposition with the second pump gear for each position of the two pump gears relative to each other in the axial direction.

6. The external gear pump according to claim 4, wherein, in a contact region, the trailing tooth flanks extend symmetrically to the respective leading tooth flanks of the corresponding teeth.

7. The external gear pump according to claim 1, wherein a tooth flank wall region that delimits the fluid pocket of the respective trailing tooth flank of the first pump gear extends directly from the tooth root circle, and wherein, as viewed in the cross section, the tooth flank wall region delimits the fluid pocket in the circumferential direction.

8. The external gear pump according to claim 7, wherein the teeth of the first pump gear each have a tip region, in which the trailing tooth flank is convex, and wherein a tooth height of the teeth of the first pump gear is composed of a pocket height of the fluid pocket and a tip region height of the tip region, the tooth height being greater than the pocket height.

9. The external gear pump according to claim 8, wherein in relation to the difference between tip circle radius and root circle radius of the teeth of the first pump gear, the dimensions of the tip region in the radial direction are at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, or at least 40%.

10. The external gear pump according to claim 8, wherein the tooth flank wall region adjoins the tip region via a rounding.

11. The external gear pump according to claim 8, wherein, in the tip region, the trailing tooth flank is symmetric in form to the corresponding leading tooth flank.

12. The external gear pump according to claim 7, wherein as viewed in the cross section, the tooth flank wall region takes the form of a segment of a circle.

13. The external gear pump according to claim 7, wherein the tooth flank wall region that delimits the fluid pocket of the respective trailing tooth flank of the first pump gear extends tangentially out of the tooth root circle.

14. The external gear pump according to claim 1, wherein as viewed in the axial direction, the fluid pocket in the respective trailing tooth flank of the first pump gear is formed open-edge only on one side.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be explained in detail below on the basis of the exemplary embodiments illustrated in the drawing, without any limitation of the invention thereby ensuing. Shown are:

(2) FIG. 1 a region of an external gear pump, namely, a first pump gear as well as a second pump gear, wherein the two pump gears are present in a first position relative to each other;

(3) FIG. 2 the region of the external gear pump, wherein the two pump gears are present in a second position relative to each other;

(4) FIG. 3 a cross-sectional illustration of the first pump gear; and

(5) FIG. 4 a detailed illustration of a region of the first pump gear.

DETAILED DESCRIPTION OF THE DRAWING

(6) FIG. 1 shows a part of an external gear pump 1, namely, a first pump gear 2 as well as a second pump gear 3. The first pump gear 2 is designed as a driving pump gear and can therefore be driven directly. In contrast, the second pump gear 3 can be driven only indirectly via the first pump gear 2. A forward rotation direction of the first pump gear 2 is indicated by the arrow 4. The first pump gear 2 has teeth 5, while the second pump gear 3 is equipped with teeth 6, only a few of which are marked respectively by way of example. The pump gears 2 and 3 or their teeth 5 and 6 intermesh, so that, for a rotational movement of the pump gears 2 and 3 in the direction of the arrow 4, a fluid is conveyed from a suction side 7 to a pressure side 8 of the external gear pump 1.

(7) Each of the teeth 5 has a leading tooth flank 9 extending in the rotation direction as well as a trailing tooth flank 10. This is indicted only for one of the teeth 5. Analogously, for this purpose, each tooth 6 of the second pump gear 3 is equipped with a front-lying leading tooth flank 11 leading in the rotation direction and a trailing tooth flank 12. If the rotational movement of the first pump gear 2 occurs in the direction of the arrow 4, then this leading tooth flank 9 of one of the teeth 5 interacts with the trailing tooth flank 12 of one of the teeth 6 in order to drive the second pump gear 3 via the first pump gear 2 and to convey the fluid from the suction side 7 to the pressure side 8.

(8) Whereas both pump gears 2 and 3 are mounted rotatably in, for example, a pump housing (not illustrated here) of the external gear pump 1, they can additionally be shifted in position relative to each other in the axial direction with respect to a rotation axis 13 of the first pump gear 2 or a rotation axis 14 of the second pump gear 3, for example. Preferably, the first pump gear 2 is arranged in fixed position in the axial direction, whereas the second pump gear 3 can be shifted in position in the axial direction. This is indicated by the double arrow 15. In the axial position of the pump gears 2 and 3, illustrated here, there is a maximum superposition of the pump gears 2 and 3 relative to each other in the axial direction. Preferably, the pump gears 2 and 3 have the same dimensions in the axial direction. Obviously, however, it is possible to create different dimensions.

(9) It can be seen that the trailing tooth flanks 10 of the first pump gear 2 extend concavely in the radial direction at least in sections to form a respective fluid pocket 16. This means that, as viewed in cross section with respect to one of the rotation axes 13 and 14, the trailing tooth flanks 10 of the first pump gear 2 are arched in the direction of leading tooth flank 9 of the corresponding tooth 5, so that the fluid pocket 16 or the fluid pockets 16 are created. As a result of a design of this kind, it is possible to reduce markedly the cavitation tendency of the external gear pump 1 and thereby positively affect the noise behavior. In addition, in the embodiment of the external gear pump 1 illustrated here, in which the pump gears 2 and 3 can shift in position relative to each other in the axial direction, it is possible to achieve a very fast vibration decay behavior following a cold start of an internal combustion engine for which the external gear pump 1 is utilized, for example, as a lubricating oil pump.

(10) FIG. 2 shows the region of the external gear pump 1, that is, the two pump gears 2 and 3, in a second axial position of the pump gears 2 and 3 relative to each other. In particular, in this case, there exists a position in which the superposition between the pump gears 2 and 3 is minimal in the axial direction. The pump gears 2 and 3 are thereby arranged in such a way, however, that they do not become disengaged relative to each other in any position. Instead, the teeth 5 and 6 are intended to be engaged relative to each other in any possible position of the pump gears 2 and 3. It can clearly be seen that the fluid pocket 16 or the fluid pockets 16 each pass through the teeth 5 only in part in the axial direction, that is, is/are designed to be open-edge only on one side in the axial direction.

(11) For this purpose, the trailing tooth flanks 10 each have a fluid pocket region 17 as well as a contact region 18. Whereas, in the fluid pocket region 17, the trailing tooth flank 10 extends concavely in the radial direction at least in sections, the trailing tooth flank 10 in the contact region 18 is convex at least in sections, that is, is arched in the direction facing away from the respective leading tooth flank 9. For example, in the contact region 18, the trailing tooth flank 10 is symmetric in form to the leading tooth flank 9. The dimensions of the contact region 18 in the axial direction are chosen in such a way that, also in the position of the two pump gears 2 and 3 relative to each other that is illustrated here, in which the minimum superposition is present, the contact region 18 is present in superposition with the second pump gear 3. The contact region 18 should therefore be present in superposition with the second pump gear 3 for each position of the pump gears 2 and 3 relative to each other.

(12) In this way, a good reverse rotation ability of the external gear pump 1 and, in addition, a constant clearance in the circumferential direction between the pump gears 2 and 3, regardless of the superposition, are realized. The clearance can be equal to zero, for example. Alternatively, it is greater than zero and, with respect to one of the rotation axes 13 and 14, for example, it is at most 0.1°, at most 0.25°, at most 0.5°, at most 0.75°, at most 1°, at most 2.5°, or at most 5°. It can also lie between two of the values mentioned; that is, it can be, for example, at least 0.25° and at most 0.75°.

(13) FIG. 3 shows a cross-sectional illustration of the first pump gear 2. It can be seen that the fluid pocket 16 is delimited in the circumferential direction by a tooth flank edge or wall region 19. As viewed in cross section, the tooth flank wall region 19 preferably takes the form of a segment of a circle. The tooth flank wall region 19 in this case preferably extends from a tooth root circle 20, which is present in each case between two teeth 5 of the pump gear 2, all the way to a tip region 21 of the respective tooth 5.

(14) The tooth root circle 20 has a tooth root circle diameter d.sub.f. A tip circle diameter is indicated as d.sub.k in the exemplary embodiment illustrated here. The difference between the tip circle diameter d.sub.k and the tooth root circle diameter d.sub.f corresponds to twice the tooth height h, which is not illustrated here. Therefore, d.sub.k−d.sub.f=2 h applies. In the embodiment of the external gear pump 1 shown here, the tooth height h is composed of a pocket height h.sub.t and a tip region height h.sub.k of the tip region 21. As a result, the fluid pocket 16, in turn, directly adjoins the tooth root circle 20 in the radial direction. Especially preferred, the fluid pocket 16 or the tooth flank wall region 19 delimiting the fluid pocket 16 extends directly out of the tooth root circle 20. Preferably, it extends tangentially out of the latter.

(15) As viewed in cross section, in this case, the tooth flank wall region 19 can take the form of a segment of a circle, in particular over its entire extent or at least a large part of its extent in the radial direction, in particular over at least 50%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 100%. On the side that faces away from the tooth root circle 20, the tooth flank wall region 19 extends out of the tip region 21 or transitions into it. The transition can be made via a rounding 22, for example, in order to attain a high strength of the first pump gear 2. The dimension h.sub.k of the tip region 21 is at least 5% in relation to half of the difference between the tip circle diameter d.sub.k and the tooth root diameter d.sub.f, but it can also be greater. It is clearly seen here once again that, in the first pump gear 2, the fluid pocket 16 is formed open-edge only on one side. On one side, as viewed in the axial direction, said fluid pocket is delimited by the wall 23 formed by the contact region 18.

(16) FIG. 4 shows a detailed illustration of a region of the first pump gear 2. Clearly seen here is the rounding 22, via which the tooth flank wall region 19 transitions into the tip region 21. The rounding 22 can be a part of the tooth flank wall region 19 or of the tip region 21. The embodiment of the external gear pump 1 presented here exhibits an extremely small cavitation tendency, because fluid that has been forced into the fluid pocket 16 can leave it in the axial direction at least in part. At the same time, however, the reverse rotation capability of the external gear pump 1 and a constant clearance in the circumferential direction are ensured, regardless of the superposition, by the presence of the contact region 18.