EP1832750B1 - Outer gear pump with a pressure relief recess - Google Patents

Description

The invention relates to an external gear pump having at least one discharge pocket for the discharge of pinch fluid from an engagement region of intermeshing conveyor wheels of the pump.

From the DE 198 47 132 C1 goes out an external gear pump with two externally toothed conveyor wheels, which mesh with each other in a rotary drive in meshing engagement. In order to promote a fluid to be conveyed uniformly and with little pulsation, relief pockets are incorporated in the sealing surfaces, which are axially facing the end faces of the conveyor wheels, which extend into the area of the tooth engagement, so that squeezing fluid from the engagement area via the relief pockets both to the outlet high-pressure side as well as to the low-pressure side of the pump, which

The US 5,190,450 A EP-A-0 416 841 discloses an external gear pump having on the high-pressure side of the delivery chamber at least one sealing surface having a discharge pocket extending from a point near the straight line connecting the axes of rotation of the delivery wheels of the pump extends beyond a point where the teeth of the conveyor wheels are no longer engaged. From the EP 1 130 262 A2 is a gear pump with a variable displacement displacement unit known. The US 2005/0276714 A1 describes a gear pump with conveyor wheels with sickle-shaped teeth and adapted to the shape of the teeth inlet and outlet from the pump. The JP 57 065890 shows a generic rotary pump whose conveyor gear teeth are designed so that the pump housing can not be heated by the rotating conveyor wheels. Other generic rotary pumps are from the EP 0 455 059 A1 , of the US 1 719 025 A , of the JP 08 105390 and the US 4 160 630 A known.

Before this prior art, it is an object of the invention to prevent pulsations of the flow even more far.

The subject of the invention is an external gear pump which includes a delivery chamber and at least two rotatably mounted delivery gears which mesh with their external teeth and which separate a low pressure side from a high pressure side of the delivery chamber in the tooth engagement. The delivery chamber has an inlet on its low-pressure side and an outlet for a fluid to be delivered on its high-pressure side. The delivery chamber forms the conveying wheels radially facing sealing surfaces, the so-called wrap, and the end faces of the conveyor wheels axially facing sealing surfaces which form corresponding radial and axial sealing gaps with the conveyor wheels. The high pressure side and the low pressure side of the delivery chamber are pressure moderately separated from each other via the radial and axial sealing gaps and the tooth engagement. In order to relieve the meshing area of crushing fluid is in at least one of the axially facing sealing surfaces, the hereinafter also referred to as axial sealing surfaces, a discharge pocket is provided, through which fluid can escape from a tooth gap located in the area of the tooth engagement.

According to the invention, such a discharge pocket is provided in the relevant sealing surface only on the high pressure side of the delivery chamber, while the respective sealing surface extends on the low pressure side to at least the root circle and the tip circle of the axially facing delivery wheel and forms with this a narrow axial sealing gap, the ensures the separation of high pressure and low pressure. Due to the non-interrupted on the low pressure side sealing surface and therefore on the low pressure side in the direction of rotation of the facing feed wheel long axial sealing gap return transport of high pressure fluid to the low pressure side is prevented safer than the known pump. The high pressure fluid can escape from the meshing only to the high pressure side.

It follows from the above that the discharge pocket nowhere projects beyond the straight axes connecting the axes of rotation of the conveyor wheels to the low-pressure side. The discharge pocket has a certain distance from this connecting line everywhere. An undesirable promotion of pinch fluid from the high pressure side to the low pressure side is safest then prevented when the discharge pocket in the direction of rotation of the axially facing conveyor from the connecting line anywhere a distance of about, preferably exactly half a tooth gap or tooth thickness of the facing conveyor wheel, wherein the Tooth thickness is measured on the pitch circle of the respective conveyor wheel. If the conveyor wheels have different tooth thicknesses and tooth gaps, this dimensioning of the distance is preferably in relation to the larger of the two reference variables. According to the invention, a deviation of half the tooth thickness or the half tooth gap width, which makes up not more than one tenth of the tooth thickness or one tenth of the tooth gap. Such a geometry of the discharge pocket towards the low-pressure side ensures the safest way that squeezing fluid escapes completely from the region of the tooth engagement, but only to the high-pressure side. By avoiding squish fluid drive power is saved as in the known pump, in contrast to the known pump, however, the influx of fluid is less disturbed on the low pressure side and thus kept quieter or more uniform. The suction height the pump rises. Furthermore, a larger portion of the squeeze fluid is beneficially removed to the high pressure side.

The discharge pocket is advantageously flat and preferably has a uniform or a maximum depth of at most 3 mm, optionally at most 3.5 mm, the depth being measured at the level of the sealing surface. More preferably, it is at most 2 mm deep plus tolerance. On the other hand, the bag should have a uniform or greatest depth of at least 0.5 mm.

The at least one sealing surface provided with the relief pocket extends, with the exception of the relief pocket, circumferentially at least to the root circle and to the tip circle of the axially facing delivery wheel. Preferably, with the exception of the discharge pocket, it forms a narrow sealing gap over the entire end face of the delivery wheel up to its tip circle with the delivery wheel. Preferably, it is everywhere with the exception of the discharge pocket plan.

The discharge pocket extends in the radial direction preferably up to the root circle of the axially facing delivery wheel and radially inwardly preferably not beyond it. It can extend against the direction of rotation of this delivery wheel, in particular into the area of the loop, in order to extend the outlet-near high-pressure region of the delivery chamber into the loop. The discharge pocket is measured against the direction of rotation of the feed wheel in such embodiments so long that it extends in all rotational angular positions of the feed wheel to its last in the direction of rotation tooth gap, which is still fully in the loop. However, it does not reach into the next-to-last gap in the direction of rotation. It can, for example, extend over an arc length in the region of the loop, which is about as large as half the pitch of the relevant conveyor wheel. In particular, the discharge pocket of the driven conveyor wheel should not reach too far into the loop. Squeezing fluid should only be able to flow into the loop of the driven conveyor wheel, if the driving at this moment driving tooth of the driving wheel has only on its leading edge contact with the driven impeller, its trailing edge has thus already solved by the driven impeller. Otherwise, there would be a risk that the driven conveying wheel will be delayed by the squeezing fluid flowing into the loop as part of the backlash.

While the axial sealing surface in the region of the tooth engagement preferably in the form of a step, i. abruptly drops at a substantially right angle in the discharge pocket, it is advantageous if the discharge pocket at its relative to the direction of rotation of the feed wheel other end gradually, preferably continuously, up to the axial height of the sealing surface increases, especially if the discharge pocket against the Turning a little way into the loop reaches. Thus, the discharge pocket can be inclined, i. straight, or progressive or degressive rise to the sealing surface. The gradient or inclination angle should be at least towards the end only a few angular degrees, preferably at most 15 °.

In preferred embodiments, a further discharge pocket is provided in at least one further sealing surface, which faces axially one of the conveying wheels, to which the above statements apply equally. The axial sealing surface provided with the further relief pocket is preferably axially facing the same delivery wheel or possibly the other delivery wheel, so that squeezing fluid can escape to the high pressure side on both axial end faces of the delivery wheels. A provided on the other axial side of the conveyor wheels further discharge pocket is always more advantageous in comparison with only a single discharge pocket with increasing width of the conveyor wheels. More preferably, each of the axial sealing surfaces is provided with a relief pocket as described, i. formed in accordance with the invention.

The external gear pump is limited in further developments in the delivery volume in order to adjust the volume flow of the pump as needed. The pump may in particular be formed as a self-regulating pump. For the delivery volume limitation, the axial engagement length of the conveyor wheels can be changed in a manner customary for external gear pumps, by one of the conveyor wheels is mounted relative to the other axially displaceable back and forth. The conveyor wheel in question is in such embodiments part of an axially displaceable unit comprising two pistons in a sandwich-like arrangement and the delivery wheel between the pistons. The pistons are axially linearly guided in a housing of the pump and secured against rotation and each form one of the axial sealing surfaces to the feed wheel. Preferably, the pressure of the high-pressure side always acts on one of the pistons, the corresponding pressurized fluid still acting from the high-pressure side of the delivery chamber, one downstream arranged therefrom connection or advantageously near a unit to be supplied with the high-pressure fluid unit and placed on the relevant piston. The other of the two pistons is acted upon counteracting the high-pressure fluid with a regulating force, preferably a elastic force, which can be generated for example simply by a mechanical spring. If necessary, an auxiliary device may be provided to increase or decrease the restoring force generated by the spring as needed.

In preferred uses, the external gear pump serves to supply a combustion assembly with lubricating fluid. The combustion unit may in particular be an internal combustion engine of an automobile.

Advantageous features of the invention are also described in the subclaims and their combinations. The features described therein and those described above provide further advantageous feature combinations.

Figur 1

eine Förderkammer einer Außenzahnradpumpe mit zwei in einem Zahneingriff befindlichen Förderrädern,

Figur 2

die Außenzahnradpumpe in einem Längsschnitt und

Figur 3

eine Draufsicht auf zwei axiale Dichtflächen der Förderkammer.

Hereinafter, an embodiment of the invention will be explained with reference to figures. The features disclosed in the exemplary embodiment advantageously each individually and in each combination of features form the subject matter of the claims and also the embodiments described above. Show it:

FIG. 1

a delivery chamber of an external gear pump with two gear wheels in meshing engagement,

FIG. 2

the external gear pump in a longitudinal section and

FIG. 3

a plan view of two axial sealing surfaces of the delivery chamber.

FIG. 1 shows an external gear pump in a cross section. In a housing part 3 and a lid 6 ( FIG. 2 ) comprising a pumping chamber, a delivery chamber is formed in the two externally toothed conveyor wheels 1 and 2 are rotatably mounted about parallel axes of rotation R ₁ and R ₂ . The feed wheel 1 is rotationally driven, for example, by the crankshaft of an internal combustion engine of a motor vehicle. The conveyor wheels 1 and 2 are meshed with each other, so that in a rotary drive of the feed wheel 1, the thus meshing feed wheel 2 is also rotated. In the delivery chamber open on a low pressure side an inlet 4 and on a high pressure side an outlet 5 for a fluid to be conveyed, preferably lubricating oil for the internal combustion engine. The housing part 3 forms the conveying wheels 1 and 2 facing in the radial direction in each case a radial sealing surface 9, which wraps the respective conveying wheel 1 or 2 circumferentially to form a narrow radial sealing gap. For the feed wheel 1, the housing 3, 6 further forms on each end side of the feed wheel 1 and this axially facing an axial sealing surface, of which in FIG. 1 the sealing surface 7 can be seen. The conveying wheel 2 is axially facing at its two end faces each formed a further axial sealing surface, of which in cross-section of FIG. 1 the sealing surface 17 can be seen.

By rotational drive of the conveyor wheels 1 and 2, fluid is sucked through the inlet 4 into the delivery chamber and in the tooth gaps of the conveyor wheels 1 and 2 by the respective looping on the high pressure side of the delivery chamber and there through the outlet 5 to the consumer, in the example assumed the internal combustion engine , promoted. During the conveying activity, the sealing gaps formed between the conveyor wheels 1 and 2 and the said sealing surfaces and the tooth engagement of the conveyor wheels 1 and 2 separate the high-pressure side from the low-pressure side. The delivery rate of the pump increases proportionally with the speed of the conveyor wheels 1 and 2. Since the engine receives less lubricating oil from a certain limit speed than the pump would increase according to their proportional to the speed increasing characteristic curve, the delivery rate of the pump is limited from the limit speed. For the reduction, the feed wheel 2 is axially movable relative to the feed wheel 1, ie, along its axis of rotation R ₂ , so that the engagement length of the feed wheels 1 and 2 and, correspondingly, the feed rate can be changed.

In FIG. 2 For example, the feed wheel 2 assumes an axial position with an axial overlap, ie engagement length, which is already reduced compared to the maximum engagement length. The feed wheel 2 is part of a displacement unit consisting of a bearing pin 14, a piston 15, a piston 16 and rotatably mounted between the pistons 15 and 16 on the bearing pin 14 conveying wheel 2. The bearing pin 14 connects the pistons 15 and 16 torsionally rigid with each other. The piston 16 forms the conveying wheel 2 facing the axial sealing surface 17. The piston 15 forms the other axial sealing surface 18. The entire displacement unit is mounted in a sliding chamber of the pump housing 3, 6 axially displaceable back and forth against rotation. The housing is made of the housing part 3 and the thus firmly connected Housing cover 6 is formed. The housing cover 6 is formed with a base, the conveyor wheel 1 facing end surface forms the sealing surface 7. The housing part 3 forms on the opposite end side of the feed wheel 1 axially facing the fourth axial sealing surface 8. The sealing surface 8 is provided on its side facing the displacement unit with a circular segment-shaped cutout for the piston 15. The piston 16 is provided on its side facing the conveyor wheel 1 with a circular segment-shaped cutout for the sealing surface 7 forming base. Apart from the respective section, the sealing surface 7 corresponds to the sealing surface 8 and corresponds to the sealing surface 17 of the sealing surface 18th

The sliding chamber, in which the displacement unit is axially movable to and fro, comprises a limited from the rear of the piston 16 subspace 10 and a limited from the back of the piston 15 subspace 11. The subspace 10 is connected to the high pressure side of the pump and is constantly acted upon there branched off pressure fluid, which thus acts on the back of the piston 16. In the space 11, a mechanical compression spring 12 is arranged, the elastic force acts on the back of the piston 16. The spring 12 counteracts acting in the subspace 10 on the piston 15 compressive force. The reduction of such external gear pumps is known and therefore needs no explanation. The curtailment can in particular according to the DE 102 22 131 B4 be designed.

If the axial sealing surfaces 7, 8 and 17, 18 circumferentially smooth and the axial sealing gaps accordingly circumferentially tight, would be squeezed in the engagement region of the conveying wheels 1 and 2 high-pressure fluid, i. still compressed beyond the pressure of the high pressure side and conveyed to the low pressure side. For the squeezing of the fluid drive power is consumed and further connected to the special compression of the fluid and the transport through the meshing through a delivery flow pulsation.

To avoid the disadvantages mentioned, the sealing surfaces 7, 8, 17 and 18 are each provided on the high pressure side with a discharge pocket 7a, 8a, 17a and 18a, all four in FIG. 2 can be seen.

In the presentation of the FIG. 3 are the conveyor wheels 1 and 2 removed, so that in the plan view of the sealing surfaces 7 and 17 is free. The sealing surfaces 7 and 17 are with Except the respective discharge pocket 7a and 17a formed as a flat, smooth surfaces and each extend to the tip circle of the associated impeller 1 or 2. The discharge pockets 7a and 17a extend radially inwardly towards the respective axis of rotation R ₁ and R ₂ except for the Fußkreis the associated impeller 1 or 2. After radially outward the discharge pockets 7a and 17a are open, ie they extend to the peripheral edge of their respective sealing surface 7 or 17. The sealing surfaces 7 and 17 each fall on a sealing edge, the one to the Rotary axes R ₁ and R ₂ connecting lines R ₁ -R _{2 runs} parallel with a distance a, abruptly in a stage in the respective discharge pocket 7 a or 17 a from. The distance a is half the tooth gap width or tooth thickness e of the associated feed wheel 1 or 2. In FIG. 1 is the essential for the dimensioning of the distance a tooth thickness or tooth gap width e drawn, which is measured as usual on the pitch circle or pitch circle W ₁ or W _{2 of} the feed wheel 1 or 2. The conveyor wheels 1 and 2 have the same tooth thicknesses and tooth gap widths e. If the tooth thicknesses and tooth gap widths are different, which does not correspond to the preferred embodiments, the distance is chosen such that it corresponds at least substantially to the larger of the two.

The relief pockets 7a and 17a extend against the direction of rotation of the conveyor wheels 1 and 2 to the loop, namely until the last in all rotational angular positions of the conveyor wheels 1 and 2 are still fully in the loop located tooth space of the respective conveyor wheel 1 or 2. The discharge pocket 7a goes so far in the wrap that it engages the tooth gap of the driven conveyor wheel 2 only when the driving tooth of the driving impeller 1 has just passed the virtual Wälzpunkt with its trailing edge, so that it clearly only with its leading tooth flank in contact with the driven Conveyor 2 is. In this way, it is ensured that there is a clear drive contact when the squeezing fluid first flows into the tooth space of the driven conveyor wheel 2 which is still in the loop around. The discharge pocket 17a preferably extends just as far into the wrap of the driving conveyor wheel 1. The located in the loop ends of the discharge pockets 7a and 17a are each of the connecting line R ₁ -R ₂ by an approximately 90 ° arc length removed.

While the sealing surfaces 7 and 17 of the respective sealing edge in the engagement region preferably abruptly, ie fall vertically into the discharge pockets 7a and 17a, the discharge pockets 7a and 17a at their other ends against the direction of rotation of the conveyor wheels 1 and 2 continuously flat, preferably with an angle of inclination of at most 15 °, measured to the plane of the respective sealing surface 7 or 17.

The relief pockets 7a and 17a extend in the direction of rotation of the conveyor wheels 1 and 2 equidistant. The discharge pocket 17a extends at its end facing the engagement region of the conveyor wheels 1 and 2 in the circular segment-shaped cutout for the piston 16, so that the sealing edge of the sealing surface 17 is significantly shorter than the sealing edge of the sealing surface 7 located in the engagement region. Apart from this difference, the relief pockets 7a and 17a correspond to each other.

The sealing surfaces 8 and 18 on the axially opposite side of the conveyor wheels 1 and 2 are shaped like the sealing surfaces 7 and 17 and also provided accordingly only on the high pressure side with relief pockets 8a and 18a in the form of the discharge pockets 7a and 17a. With regard to these further discharge pockets, what has been said about the discharge pockets 7a and 17a applies. In that regard, the sealing surface 7 opposite sealing surface 8 corresponds to the sealing surface 17, and the sealing surface 18 corresponds to the sealing surface. 7

Due to the inventive design of the axial sealing surfaces 7, 8 and 17, 18 each with a discharge pocket only on the high pressure side, which further to the project to the respective sealing surface straight lines R ₁ -R ₂ a safety distance a true, it is ensured that the pump is relieved of crushing fluid, but still no crushing fluid can be transported via the meshing or at most in an irrelevant for the practical purposes extent and therefore on the tooth engagement greatest possible tightness is guaranteed.

Claims (12)

1. An external toothed wheel pump, comprising:

   a delivery chamber comprising an inlet (4) and an outlet (5) for a fluid;

   a first feed wheel (1) and a second feed wheel (2) which can be rotationally driven for delivering the fluid and are in a toothed engagement with each other which separates the outlet (5) from the inlet (4);

   sealing surfaces (7, 8, 17, 18) which axially face the feed wheels (1, 2) and form axial sealing gaps with the feed wheels (1, 2) and extend circumferentially up to at least the root circle and tip circle of the axially facing feed wheel (1, 2); and

   at least one relieving pocket (7a, 8a, 17a, 18a) in at least one sealing surface (7, 8, 17, 18) on a high-pressure side of the delivery chamber only,

   which exhibits all over a distance (a) in the rotational direction of the axially facing feed wheel (1, 2) from a straight line (R₁-R₂) connecting the rotational axes of the feed wheels (1, 2) and projected onto the at least one of the sealing surfaces (7, 8, 17, 18),

   characterised in that

   the distance (a) measures e/2 ± e/10 all over,

   wherein e is the tooth gap width or tooth thickness of the axially facing feed wheel (1, 2) as measured to the pitch circle (W₁, W₂).
2. The external toothed wheel pump according to claim 1, wherein the distance (a) measures 6e/10 at most all over, and e is the tooth gap width or tooth thickness of the axially facing feed wheel (1, 2) as measured to the reference circle (w₁, W₂).
3. The external toothed wheel pump according to any one of the preceding claims, wherein the at least one of the sealing surfaces (7, 8, 17, 18) slopes steeply into the relieving pocket (7a, 8a, 17a, 18a) at a front edge in the rotational direction of the facing feed wheel (1, 2) which is preferably parallel to a straight line (R₁-R₂) connecting the rotational axes of the feed wheels (1, 2).
4. The external toothed wheel pump according to any one of the preceding claims, wherein the relieving pocket (7a, 8a, 17a, 18a) becomes gradually flatter at a rear end in the rotational direction of the facing feed wheel (1, 2) and preferably transitions continuously into the assigned sealing surface (7, 8, 17, 18).
5. The external toothed wheel pump according to any one of the preceding claims, wherein the relieving pocket (7a, 8a, 17a, 18a) extends counter to the rotational direction of the axially facing feed wheel (1, 2), up into an enclosure formed by a sealing surface (9) of the delivery chamber which surrounds the feed wheel (1, 2) over a circumferential region.
6. The external toothed wheel pump according to the preceding claim, wherein the relieving pocket (7a, 8a, 17a, 18a) extends counter to the rotational direction up into the last tooth gap of the axially facing feed wheel (1, 2) which is still completely surrounded by the radial sealing surface (9).
7. The external toothed wheel pump according to the preceding claim, wherein the relieving pocket (7a, 8a, 17a, 18a) only extends far enough into the enclosure that it only engages with the last tooth gap when the rear flank of a tooth of the driving feed wheel (1), the front flank of which is in driving contact with the driven feed wheel (2), has passed a pitch point of the feed wheels (1, 2).
8. The external toothed wheel pump according to any one of the preceding claims, wherein the relieving pocket (7a, 8a, 17a, 18a) is 3.5 mm deep at most, preferably 2.5 mm deep at most.
9. The external toothed wheel pump according to any one of the preceding claims, comprising a shifting unit which can be moved axially back and forth and comprises two pistons (15, 16), between which the second feed wheel (2) is mounted such that it can rotate, wherein one of the pistons (15, 16) forms the at least one sealing surface (17, 18) comprising the relieving pocket (17a, 18a).
10. The external toothed wheel pump according to the preceding claim, wherein the pistons (15, 16) each form a sealing surface (17, 18) which comprises a relieving pocket (17a, 18a) on the high-pressure side of the delivery chamber only and except for the relieving pocket, extends circumferentially up to at least the root circle and tip circle of the axially facing feed wheel (1, 2).
11. The external toothed wheel pump according to any one of the preceding claims, comprising a shifting unit which can be moved axially back and forth and comprises two pistons (15, 16), between which the second feed wheel (2) is mounted such that it can rotate, wherein the at least one sealing surface (7, 8) provided with the relieving pocket (7a, 8a) axially faces the first feed wheel (1).
12. The external toothed wheel pump according to the preceding claim, wherein a relieving pocket (7a, 8a) is formed on the high-pressure side of the delivery chamber only in each of the two sealing surfaces (7, 8) which axially face the first feed wheel (1), and except for their respective relieving pocket, both sealing surfaces (7, 8) extend circumferentially up to at least the root circle and tip circle of the axially facing feed wheel (1, 2).

Images