DE102011075415A1 - Gear pump e.g. outer gear wheel pump, for use in fuel injection system of Otto engine to convey fuel from low pressure region into high pressure region, has axially displaceable sealing plates resiliently prestressed in direction of chamber - Google Patents

Abstract

The pump (22) has a pinion (28) and an inner toothed ring gear (30) combing with each other. The pinion, the gear and a housing define a pump chamber (48). Axially displaceable sealing plates (40.1, 40.2) i.e. membranes, are arranged between front sides of the pinion, the gear and the housing. The plates are resiliently prestressed in a direction of the chamber. A side of the plates facing away from the pinion and the gear is sealed against a low pressure side inlet (32) and/or a high pressure side outlet (36). Sealing rings (46) are provided between the plates and the housing.

Description

State of the art

The invention relates to a toothpump according to the preamble of claim 1 and a fuel injection system according to the independent claim 12.

In fuel injection systems of internal combustion engines, for example, for gasoline engines, which operate with a direct injection of fuel, injection pressures of up to 200 bar are needed. Frequently, the required fuel pressure is regulated as a function of an operating point, for example in a pressure range between 40 bar and 200 bar.

To generate the required fuel pressure predominantly valve-controlled piston pumps are used, which are mechanically driven by the internal combustion engine. These piston pumps are relatively expensive to manufacture. In addition, single-piston pumps often generate high pressure pulsations on the high and low pressure sides.

Alternatively, tooth pumps can also be used for fuel delivery or pressure generation. There are various types of tooth pumps, such as internal gear pumps, external gear pumps or gerotor pumps. Tooth pumps generate comparatively low pressure pulsations compared to piston pumps. However, toothed pumps have low volumetric efficiency at low speeds, so they are often oversized to ensure the pressure build-up required at low speeds to start the engine. Owing to their "oversizing", these pumps deliver too much fuel at higher speeds, which then has to be returned to the low pressure area of the fuel injection system. This reduces the efficiency of the fuel injection system.

Many of the flow rate control methods used in reciprocating pumps can not be used with tooth pumps because the delivery rate of tooth pumps is essentially dependent on the geometry of the inlet sections and the outlet sections of the tooth pump. A patent publication in this field is, for example, the EP 1 927 754 A1 ,

To improve the efficiency of toothpumps, it is from the DE 43 45 273 C2 known to arrange the side of the gears of the internal gear pump pressurized sealing plates. Thereby, the internal leakage losses, which are caused by a back flow of the fuel from the pressure side to the suction side in an axial gap between gears and pump housing, reduced.

In the book "Oil hydraulics" by G. Bauer, 7th edition, ISBN 3-519-10144-0 describes an external gear pump of Robert Bosch GmbH, in which the sealing plates simultaneously serve as bearing bushes for the two externally toothed gears and are displaceable in the axial direction. As the operating pressure increases, the axial gap decreases so that good volumetric efficiency is achieved even at high pressures. However, the known pressurized sealing plates are not suitable to improve the performance of the pump during startup or at low speeds.

Disclosure of the invention

The problem underlying the invention is achieved by a dental pump according to claim 1. Advantageous developments are specified in subclaims. Features which are important for the invention can also be found in the following description and in the drawings, wherein the features, both alone and in different combinations, can be important for the invention, without being explicitly referred to again.

In the tooth pump according to the invention at least one sealing plate is resiliently biased in the direction of the pump chamber, so that is minimized during start-up of the pump and at very low speeds and below the operating pressure of the axial gap between the sealing plate and the gears.

To achieve a symmetrical structure, it is proposed to arrange a biased sealing plate on both sides of the gears. However, the advantages according to the invention can also be realized with only one sealing plate. In this case, the pinion and the ring gear are preferably mounted axially displaceable.

As a result, the necessary flow rate or the required pressure at low speeds is also achieved by small pumps. As a result, it is also possible to use a smaller pump. This has the advantage that at medium and high pump speeds, the delivery volume or the delivery rate of the gear pump is relatively small and thus only a relatively small excess amount of fuel is due to the low pressure area. As a result, at medium and higher operating speeds, the efficiency of pump according to the invention better, which has an overall positive effect on energy consumption.

Furthermore, the tooth pump according to the invention has a self-regulation characteristic, which causes the axial gap between the sealing plate and the gears to increase automatically at high operating speeds and high operating pressures. Due to the resulting internal leakage, the flow rate and the pressure of the tooth pump according to the invention are limited, so that the tooth pump according to the invention for the intended use without valves, or with much simpler pressure control valves and without external control, for example, by a control unit of the engine control can work. This reduces the complexity of the system and reduces manufacturing costs. At the same time, the reliability of the system is increased.

In the gear pump according to the invention at least one sealing plate is biased. Because a part of the pump chamber facing away from the side of the sealing plates is decoupled by a sealing ring of the prevailing pressure in the pump chamber, with increasing operating pressure from the pump chamber acting on the sealing plates hydraulic forces are greater than the forces exerted by the spring elements on the sealing plates plus the force of "Outside" on the inside acting on the sealing plates hydraulic forces that would tend to reduce the axial gap.

As a result, at low speeds, the axial gap is minimal, which has a positive effect on the volumetric efficiency. With increasing speed and thus usually accompanied by increasing pressure, the axial gap increases and the demand for drive power is reduced, which has a positive effect on the mechanical efficiency and the wear.

In order to ensure the function of the toothpump in all operating states and at all rotational speeds, it is further provided that a side of the at least one sealing plate facing away from the toothed wheels is sealed against the inlet and the outlet of the toothpump. This can be done according to the invention in that one or more sealing rings are provided between the sealing plate and the housing. Alternatively, it is also possible to make the seal by a bellows seal between the sealing plate and the housing. This bellows seal can be designed as a corrugated pipe.

In order to ensure the inventive bias of the sealing plate regardless of the prevailing pressure in the pump chamber and the speed is provided in the inventive design that the sealing plate is biased by one or more springs, preferably helical compression springs or disc springs, and / or resilient sealing elements in the direction of the pump chamber , It is also possible to form the at least one sealing plate as a membrane, so that the sealing plate is resiliently pressed in the installed state and with an adjustable bias against the gears. In this embodiment can be dispensed with separate spring elements, whether in the form of coil springs, other wire springs or disc springs.

Furthermore, it is possible to sealingly connect the membrane with the at least one sealing plate and the housing. This can be done for example by gluing, welding or by another cohesive joining method. In this case, the membrane also takes over the function of the sealing rings in addition to the function of the spring elements.

It is particularly advantageous if the pretensioning with which the sealing plate is pressed against the gears when the pump is stationary is adjustable. As a result, the operating behavior of the tooth pump according to the invention can be easily adapted to different fields of use. In addition, series variations can be corrected in terms of the spring rate of the spring elements used to bias the sealing plate.

Furthermore, it may be advantageous if the gears are axially displaceable. For then it is possible to provide an axially displaceable sealing plate only on one side of the gears. The sealing gap between the gears and the housing on the side opposite this a sealing plate side is then automatically by an axial displacement of the gears relative to the housing, when the present on the other side sealing plate is resiliently biased against the gears. As a result, the assembly costs and the number of required components are reduced.

It is possible according to the invention, as in the 3 and 4 also shown that on both sides of the gears each have a sealing plate is provided. It is again possible, as in the 3 and 4 also shown that both sealing plates are biased in the axial direction by spring elements against the end faces of the gears. However, it is also possible that in the 3 and 4 shown spring elements are present only on a sealing plate.

The tooth pump according to the invention can be designed as an external gear pump, as an internal gear pump, as a toothed ring pump or as a planetary rotor pump.

Hereinafter, exemplary embodiments of the invention will be explained with reference to the drawings. In the drawing show:

1 a simplified diagram of a fuel system of an internal combustion engine and a toothed pump according to the invention arranged therein

2 an embodiment of a tooth pump according to the invention in cross section;

3 an embodiment of a tooth pump according to the invention with a minimum axial gap;

4 an embodiment of a tooth pump according to the invention with maximum axial gap;

5 Characteristics of a tooth pump according to the invention and a conventional tooth pump with regulated pressure and

6 a plan view of a sealing plate of a tooth pump according to the invention.

The same reference numerals are used for functionally equivalent elements and sizes in all figures, even in different embodiments.

The 1 shows a highly simplified schematic of a fuel injection system 10 an internal combustion engine not shown here. In the drawing from left to right is a fuel tank 12 via a low pressure line 14 with a fuel pump 22 connected. The area upstream of the fuel pump 22 is the low pressure area 17 , The fuel pump 22 delivers fuel under high pressure via a high pressure line 18 in a high-pressure accumulator 20 ("Common Rail"). To the high-pressure accumulator 20 Injectors (not shown) are connected via the fuel is injected into the combustion chambers of the internal combustion engine. The fuel pump 22 is designed according to the invention as a tooth pump. The area downstream of the fuel pump 22 is the so-called high pressure area 25 of the fuel injection system 10 ,

In 2 is a section through an embodiment of a tooth pump according to the invention 22 shown. The cutting plane goes through a housing 26 that, as is evident from the 3 and 4 results from several parts 26.1 . 26.2 and 26.3 , can be composed. Inside the case 26 are a pinion 28 and an internally toothed ring gear 30 arranged eccentrically to each other. The pinion 28 and the ring gear 30 comb each other. The internally toothed ring gear 30 is driven clockwise, resulting in 2 is indicated by a curved arrow without reference numerals.

When the externally toothed pinion 28 is driven in a clockwise direction, then it sucks fuel from an inlet 32 and the fluid in the tooth gaps migrates with the tooth gaps on a filler 34 along and enters the tooth engagement region of the gears 28 and 30 , There, the liquid is displaced and enters the outlet 36 , Since the operation of such a toothpump is known to the person skilled in the art, the description of further details which do not relate to the claimed invention will be omitted. With the reference number 48 becomes a pump space between pinions 28 and ring gear 30 designated.

In 3 is a cross section through an embodiment of a tooth pump according to the invention 22 shown. The section plane is orthogonal to that in the 2 illustrated section plane. From this illustration it becomes clear that the housing 26 from a middle part 26.1 and a first lid part 26.2 and a second lid part 26.3 is composed. The three housing parts are tightly clamped together by screws. Unlike the one in 2 illustrated embodiment, the inlet 32 and the outlet 36 in the first cover part 26.2 arranged.

As is clear from the 3 results, the pinion 28 via a drive shaft 38 driven. The internally toothed ring gear 30 is due to the meshing engagement of the pinion 28 driven. The ring gear 30 is at its outer diameter in the middle part 26.1 of the housing 26 rotatably mounted.

About the drive shaft 38 is the pinion 28 in the housing parts 26.2 and 26.3 rotatably mounted and preferably also axially displaceable.

On the front sides of the pinion 28 or the ring gear 30 are sealing plates 40.1 and 40.2 arranged. These sealing plates 40.1 and 40.2 are axially displaceable and are at the in 3 illustrated embodiment by coil springs 42 against the faces of the pinion 28 or the ring gear 30 biased. The coil springs 42 at one end are supported by the sealing plates 40.1 . 40.2 and at the other end to a screw plug 44 from. Depending on how far the locking screws 44 in the housing part 26.2 respectively. 26.3 be screwed, the bias of the springs changes 42 ,

In general, the gap between the lid part 26.3 and the sealing plate 40.2 significantly larger than the gap between the sealing plate 40.2 and the pinion 28 or the ring gear 30 , The same applies with respect to the sealing plate 40.1 ,

Through the sealing rings 46 the low pressure area and the high pressure area are separated from each other. This will cause a hydraulic short between low pressure area 17 and high pressure area 25 prevented.

In the second cover part 26.3 are opposite the inlet 32 and opposite the outlet 36 Blind holes 47 educated. These blind holes 47 are also made of sealing rings 46 enclosed, so that on the sealing plates 40.1 and 40.2 acting forces are the same.

3 shows the tooth pump according to the invention at a standstill. In this case, no hydraulic forces act on the sealing plates 40.1 and 40.2 and as a result, the sealing plates 40.1 and 40.2 through the spring elements 42 against the front sides of the pinion 28 or the internally toothed ring gear 30 pressed. Thus, the axial gap A between the sealing plates 40.1 and 40.2 on the one hand and the gears 28 and 30 on the other hand minimal. As a rule, it is zero. This means that when starting a rapid pressure build-up in the pump room 48 the tooth pump according to the invention 22 takes place as soon as the drive shaft 38 is driven. The pressure build-up is therefore particularly rapid, because no appreciable internal leaks occur. Therefore, the volumetric efficiency is very high.

In 4 Now, the same embodiment of a tooth pump according to the invention is shown, wherein the drive shaft 38 is now driven with a medium to high speed. This means that the pump 22 already fuel and pumps in the pump room 48 that of the gears 28 and 30 as well as the sealing plates 40.1 and 40.2 is limited, a high pressure prevails. This print is in the 4 through arrows 50 indicated. This pressure causes the sealing plates 40.1 and 40.2 against the of the spring elements 42 applied biasing force can be pushed outward. As a result of this, the axial gap A increases. This enlargement of the axial gap A according to the invention causes a deliberate internal leakage to take place and, as a result, the delivery rate at the outlet 36 declining. In 4 are the sealing plates 40.1 and 40.2 shown in a position in which the axial gap A has a maximum, because the sealing plates 40 outside on the lid parts 26.2 and 26.3 issue. As a result, there is a desired pressure-dependent hydraulic "short circuit" in the pump room 48 instead, so that the mechanical friction and wear decrease significantly.

At medium speeds and depending on the pressure conditions at the inlet 32 and at the outlet 36 are also intermediate positions between the in 3 and 4 shown extreme positions of the sealing plates 40.1 and 40.2 possible. In principle, the delivery rate of the pump according to the invention 22 is proportional to the pump speed. If with increasing flow rate of the pump 22 not an equal amount of liquid through the outlet 36 connected consumer (not shown) is removed, the pressure in the pump room increases 48 , This increasing pressure acts in the manner described on the sealing plates 40.1 and 40.2 and pushes them outwards, ie away from the gears 28 . 30 , so that the axial gap A increases. This leads due to the increased internal leakage to the amount of delivery of the pump 22 and the system pressure will be limited. This reduces the axial gap A again, until a balance between the on the sealing plates 40.1 and 40.2 acting hydraulic forces and the spring forces is achieved.

If the constructive maximum axial gap A, as in 4 shown, is chosen large enough, a zero pump delivery can be achieved. In this case, the tooth pump according to the invention 22 a fully regulated pump, which depends on the system pressure or the pressure at the outlet 36 and the removed flow rate has a delivery rate between 0% and 100%.

In 5 Characteristics of a gear pump according to the invention and a conventional gear pump are shown. From the comparison of the characteristics, the differences in the operating behavior of the tooth pump according to the invention at controlled pressure compared with conventional toothed pumps can be well recognized.

On the abscissa is in 5 the pump speed n [1 / min] is plotted, while on the ordinate the flow rate Q and the torque absorbed by the pump M are plotted. The product of torque M and speed n is a measure of the power consumption of the pump.

A first line 52 represents the flow Q of a conventional gear pump over the speed n. It is clear that the pump only with reaching a minimum speed 60 begins to promote. With increasing speed, the flow Q increases and then approaches asymptotically a maximum.

The associated drive torque M is through a second line 54 shown. The associated drive torque M of a conventional pump is relatively large at the start of delivery (n ≈ 140 1 / min) and then increases slightly with increasing speed.

A third line 56 represents the delivery rate Q of a gear pump according to the invention over the Speed n. It is clear that the pump already at one compared to a conventional gear pump (see the line 52 in 5 ) promotes significantly reduced minimum speed, because in the pump according to the invention due to the spring bias of the spring elements 42 the gaps are substantially smaller than in a conventional pump. With increasing speed, the flow Q increases and then approaches asymptotically a maximum.

The drive torque M of the gear pump according to the invention is through a fourth line 58 shown. The associated drive torque M at delivery start (n ≈ 60 1 / min) is about the same size as that of a conventional gear pump, then decreases rapidly with increasing speed and then remains approximately constant.

From the direct comparison of the lines 56 and 52 as well as the lines 58 and 54 It is clear that the gear pump according to the invention has a much larger flow Q at low speeds and requires less drive power over the entire operating range.

In 6 is a plan view of the sealing plate 40.1 shown. A total area A _{total of} the sealing plate 40.1 is through the two sealing rings 46 divided into three sub-areas, A _HD , A _ND , and A _R.

On the first surface A _HD acts in the high pressure area 25 acting pressure; on the second partial area A _ND acts in the low pressure area 17 prevailing pressure and the third partial area A _R acts in the pump room 48 prevailing pressure.

The total on the pump room 48 opposite side of the sealing plate 40 acting hydraulic force results from the forces acting on the three faces, A _HD , A _ND , and A _R hydraulic forces. This means that by dividing the total area of the sealing plates 40 in three sub-areas, A _HD , A _ND , and A _R using the sealing rings 46 on the pump room 48 opposite side of the sealing plate 40 acting hydraulic force is determined constructively. Thus, the basis of the 5 Exemplary illustrated operating behavior of the gear pump according to the invention varies within wide limits and adapted to different requirements in terms of pressure and flow rate.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1927754 A1 [0005]
• DE 4345273 C2 [0006]

Cited non-patent literature

• "Oil Hydraulics" by G. Bauer, 7th Edition, ISBN 3-519-10144-0 [0007]

Claims (12)

Tooth pump with two meshing gears ( 28 . 30 ), with a low-pressure inlet ( 32 ) and a high pressure side outlet ( 36 ), with a housing ( 26 . 26.1 . 26.2 . 26.3 ), the gears ( 28 . 30 ) and the housing ( 26 . 26.1 . 26.2 . 26.3 ) a pump room ( 48 ), and wherein between at least one end face of the gears ( 28 . 30 ) and the housing ( 26 . 26.1 . 26.2 . 26.3 ) an axially displaceable sealing plate ( 40 . 40.1 . 40.2 ), characterized in that the at least one sealing plate ( 40 . 40.1 . 40.2 ) in the direction of the pump chamber ( 48 ) is biased. Tooth pump according to claim 1, characterized in that one of the gears ( 28 . 30 ) facing away from the at least one sealing plate ( 40 . 40.1 . 40.2 ) against the inlet ( 32 ) and / or the outlet ( 36 ) is sealed. Tooth pump according to claim 2, characterized in that by the sealing of the gears ( 28 . 30 ) facing away from the at least one sealing plate ( 40 . 40.1 . 40.2 ) the sealing plate ( 40 . 40.1 . 40.2 ) is divided into three subareas (A _HD , A _ND , and A _R ). Tooth pump according to one of the preceding claims, characterized in that between the at least one sealing plate ( 40 . 40.1 . 40.2 ) and the housing ( 26.2 . 26.3 ) one or more sealing rings ( 46 ) are provided. Tooth pump according to one of the preceding claims, characterized in that between the at least one sealing plate ( 40 . 40.1 . 40.2 ) and the housing ( 26 . 26.1 . 26.2 . 26.3 ) a bellows is provided. Tooth pump ( 22 ) according to one of the preceding claims, characterized in that the at least one sealing plate ( 40 . 40.1 . 40.2 ) of one or more springs, preferably helical compression springs ( 42 ) or disc springs, and / or resilient sealing elements ( 46 ) in the direction of the pump chamber ( 48 ) is biased. Tooth pump ( 22 ) according to one of the preceding claims, characterized in that the at least one sealing plate ( 40 . 40.1 . 40.2 ) is formed as a diaphragm and in the installed state resiliently against the gears ( 28 . 30 ) is pressed. Tooth pump ( 22 ) according to claim 7, characterized in that the membrane with the at least one sealing plate ( 40 . 40.1 . 40.2 ) and the housing ( 26 . 26.1 . 26.2 . 26.3 ) is sealingly connected. Tooth pump ( 22 ) according to one of the preceding claims, characterized in that the bias of the springs ( 42 ), the sealing rings ( 46 ) and / or the membrane is adjustable. Tooth pump ( 22 ) according to at least one of the preceding claims, characterized in that the gears ( 28 . 30 ) are axially displaceable. Tooth pump ( 22 ) according to at least one of the preceding claims, characterized in that the toothpump ( 22 ) is an external gear pump, an internal gear pump, a gerotor pump, a gerotor pump or a planetary rotor pump. Fuel injection system ( 16 ) of an internal combustion engine, with a pump, the fuel from a low pressure area ( 17 ) in a high pressure area ( 25 ), characterized in that the pump is a tooth pump ( 22 ) according to any one of the preceding claims.

Images