WO2019025430A1

WO2019025430A1 - Positive-displacement machine

Info

Publication number: WO2019025430A1
Application number: PCT/EP2018/070705
Authority: WO
Inventors: Guido Bredenfeld; Armin RICHTER; Jakob Branczeisz; Matthias RIEDLE
Original assignee: Robert Bosch Gmbh
Priority date: 2017-08-03
Filing date: 2018-07-31
Publication date: 2019-02-07
Also published as: DE102017213506A1

Abstract

The invention relates to a positive-displacement machine (40) comprising an inlet region (27) via which a working medium flows into at least one positive-displacement chamber (29, 30) of the positive-displacement machine (40). In order to create a positive-displacement machine which can be operated without any problem using low-viscosity media such as ORC fluids, at least one flow conducting device (31) which optimizes the inlet region (27) in terms of the flow behavior is placed in the inlet region (27).

Description

description

title

The invention relates to a displacement machine having an inflow region, via which a working medium into at least one displacement space of the

Positive displacement machine flows in.

State of the art

From the German patent application DE 10 2012 216 254 AI is a

External gear, in particular a pump or a motor, with axially opposite a low pressure port and a

High pressure connection, with at least two gears known in the

Combining external engagement with each other, wherein the gears are surrounded by a housing and the one gear has a shaft journal and the other gear has a drive input or output shaft, which are rotatably mounted in each case in a bearing bore of a substantially rotationally symmetrical cross-section bearing bushing about an axis of rotation wherein the bearing bushes are received in corresponding receiving recesses of the housing, wherein the bearing bushes made of aluminum or a

Aluminum alloy and / or the housing made of gray cast iron, wherein in each case the two radially adjacent bearing bushes are connected to a bearing glasses, wherein in the bearing bores of the bearing bushes bearing an axial slot bearing sleeves are used in which the shaft journal and the input or output shaft rotatably mounted are, wherein the bearing sleeves have one or two Verdrehsicherungsansätze, which protrude into a radially opening into the bearing bore securing recess.

Disclosure of the invention The object of the invention is to provide a positive displacement machine with a

Inflow area, over which a working medium in at least one

Displacer of the positive displacement machine inflows, which can be operated with low viscosity media, such as ORC fluids, easily.

The object is in a positive displacement machine with an inflow, via a working medium in at least one displacement of the

Displacement machine flows, thereby achieved that in the inflow at least one flow guide is arranged, through which the inflow is optimized aerodynamically. Optimized in terms of flow technology means, among other things, that undesirable turbulences in the

Inflow area can be avoided. The displacement machine may comprise exactly one displacement space. The displacement machine can also comprise more than one displacement chamber, for example two displacement chambers. The displacement machine may also include more than two displacement chambers.

According to a preferred embodiment, the displacement machine is designed as an external gear machine. The external gear machine can be operated particularly advantageously with low-viscosity media, such as ORC fluids. The uppercase letters ORC stand for the English terms Organic Rankine Cycle. Examples of ORC fluids are ethanol or

Cyclopentane. The claimed external gear machine can also be operated with a refrigerant such as used in automotive air conditioning systems. In the working medium with which the claimed

External gear is operated, it is preferably a poorly lubricating fluid with a low viscosity. The viscosity of the

Working medium of the external gear machine is for example between 0.3 and 1.6 centistokes. Furthermore, the working fluid is subjected to a rather low pressure during operation of the external gear machine. In addition, the working fluid may have an operating temperature in the operation of the external gear, the only a small distance to a

Evaporation temperature of the working medium has. This results in the risk of unwanted cavitation. The working fluid or working fluid is disposed in the working fluid space during operation of the external gear machine. In the working fluid space, the working fluid or working fluid is pressurized

applied when the external gear machine as external gear pump is operated. When the external gear machine is operated as an external gear motor, then comes pressurized working fluid or

Working fluid from outside into the working fluid space to drive the external gear motor. According to a particularly preferred embodiment, the displacement machine is operated as a positive displacement pump, in particular as a constant displacement pump. With a constant pump, the same volume is always displaced with each revolution. With variable displacement pumps, however, can

Displacement volume can be adjusted or adjusted. For constant displacement machines, the volume flow through the

Displacement machine initially proportional to the speed. When in the

Operation of the displacement machine a volume flow spread is required, then determines this flow spreading the spread of the

Drive speed. A volumetric efficiency of the displacement machine is directly dependent on the drive speed. In experiments and investigations carried out in the context of the present invention has become

found that a very large spread of input speed, especially in combination with the use of low viscous

Working media can adversely affect flow conditions and pressure conditions during operation of the positive displacement machine. About the

Flow guide in the inflow of the positive displacement machine can

Working medium advantageously be fed less turbulent. This then has a particularly advantageous effect on the flow conditions and pressure conditions with regard to the volumetric efficiency of the positive displacement machine. A preferred embodiment of the displacement machine is characterized in that the flow guide at least one

Includes flow guide, which is arranged in the inflow, that the inflowing working fluid is divided into at least two directed partial flows. According to a particularly preferred embodiment, the flow-guiding device comprises exactly one flow-guiding element, which is thus in the

Inlet region is arranged, that the inflowing working medium is divided into exactly two directed partial flows. In numerical fluid mechanics calculations and simulations carried out in the context of the present invention, it has been demonstrated that an engine of the displacement engine is ideally flown laminarly at some distance. in the Operation of the displacement machine is, for example, by combing out gears of the external gear machine designed as a displacement machine, according to the size of vacant tooth gaps a volume free.

This creates a local negative pressure area, which causes new working medium or fluid to flow in. At this point it comes

conventional positive displacement machines sometimes very high

Flow rates and turbulence. A part of the working medium or fluid flows back, that is contrary to the actual

Flow direction. For this reason, it may be in the intake tract of a

conventional positive displacement pump operating as a positive displacement machine to turbulent flows and turbulence come. Under unfavorable circumstances, this can lead to undesirable evaporation of the fluid or working medium or to cavitation effects in the suction region and especially in a reversing region of the displacement machine operating as a positive displacement pump in conventional positive displacement machines. The flow guide can also be referred to as filler and is advantageous directly in the flow cross section in the inflow of the

Displacement machine introduced. The flow guide can be particularly advantageous, for example, with the aid of modern manufacturing processes, introduced into the inflow of the positive displacement machine, without changing other components of the positive displacement machine. The flow guide may be integrally formed in the inflow region by, for example, 3D printing, electron beam melting (EBM), laser sintering, alternative lost core casting techniques. These methods provide the advantage that a housing or a connecting piece of the displacement machine in

Inflow or suction can be made in one piece. In addition, the modern manufacturing processes also allow any shape of the flow guide or filler. So can by means of

Fluidic investigations in the context of a numerical fluid mechanics an optimal shape of the flow guide

or filler over the desired operating points of

Displacement machine or positive displacement pump can be determined.

Another preferred embodiment of the displacement machine is characterized in that the flow element in the middle in a Inlet cross section is arranged. This can advantageously be achieved that an unwanted central turbulence no longer disturbs the flow of a displacement chamber, for example a tooth chamber. The

Flow guide or filler shares a particularly advantageous one

Return flow during operation of the displacement machine in two flow areas, each forming a vortex, which is located at an upper or lower edge of the inflow near the wall. This ensures advantageous that the central main flow turbulence poorer in the displacement, for example, the tooth chamber, passes.

A further preferred embodiment of the displacement machine is characterized in that the flow guide extends transversely to the incoming working medium over the entire inflow cross section. As a result, the undesirable turbulence or

Turbulence in the inflow can be effectively prevented.

Another preferred embodiment of the displacement machine is characterized in that the flow guide is designed as a cylindrical pin. The flow guide element has, for example, substantially the shape of a straight circular cylinder. The cylinder pin is simple and

inexpensive to produce and has been found in the tests and experiments carried out in the context of the present invention with regard to the desired improvement of the flow pattern to be advantageous.

A further preferred embodiment of the displacement machine is characterized in that the flow guide element has a drop-shaped cross section. The teardrop-shaped cross section is advantageously designed symmetrically along a longitudinal axis. In this case, the flow of the flow guide advantageously takes place at a tapered end of the teardrop-shaped cross section. As a result, the desired subdivision of the incoming working medium into two directed partial flows can be achieved particularly effectively.

A further preferred embodiment of the displacement machine is characterized in that the flow guide a pointed has tapered inflow cross-section, emanating from the two symmetrical in the flow direction guide surfaces, which are concavely curved. As a result, the undesirable turbulences or turbulences can be suppressed particularly effectively.

A further preferred embodiment of the displacement machine is characterized in that the flow guide is convexly curved at the end. As a result, the desired influence of the return flow can be achieved particularly advantageously.

A further preferred embodiment of the displacement machine is characterized in that the flow guide into a

Connecting piece is integrated. The flow-guiding element is advantageously provided on an end of the connection piece arranged in the interior of the displacement machine. The connection piece is designed, for example, as a socket, which is screwed into an input channel of the displacement machine. As a result, the assembly of the flow guide is simplified.

A further preferred embodiment of the displacement machine is characterized in that the flow-guiding device comprises at least one rounded or beveled transition into a displacement space. As a result, unwanted near-wall backflows and turbulence in the inflow area can be further reduced. If appropriate, the invention also relates to a method for operating a

Displacement machine, in particular an external gear machine, in a WHR system, with a low-viscous medium. Here are the

Capital letters WH R for the English words Waste Heat Recovery. The WHR system is advantageously used to recover energy from an exhaust gas of an internal combustion engine in a drive train of a motor vehicle. to

Utilization of the waste heat from the exhaust gas is in an exhaust tract of the

Internal combustion engine arranged a heat exchanger, which transfers heat from the exhaust gas to a flowing in a heat circulation working medium. The working medium in the heating circuit drives an expansion machine. The thermal cycle is a thermodynamic one Circular process or steam power process, which is also called the Rankine process or Clausius-Rankine cycle process. As an expansion machine, a turbomachine, for example, a turbomachine, or a

Positive displacement machine, for example a piston machine, one

Screw machine or a scroll machine, used. In addition, a condenser and an evaporator are arranged in the cycle. The external gear pump is arranged in the cyclic process between the condenser and the evaporator. The working medium used in the cyclic process is preferably a low-viscosity medium, such as an ORC fluid.

If appropriate, the invention also relates to a flow-guiding device, in particular a flow-guiding element or a connecting piece with a flow-guiding element, for a previously described device

Displacement. The parts mentioned are separately tradable.

If appropriate, the invention also relates to a system for recovering heat from exhaust gas with a previously described displacement machine, preferably an external gear machine, in particular one

External gear pump.

Further advantages, features and details of the invention will become apparent from the following description in which, with reference to the drawings, various embodiments are described in detail.

Short description of the drawing

Show it:

Figure 1 is an exploded view of an external gear machine according to the prior art;

2 shows an enlarged view of an inflow region of a

Displacement machine, which is designed for example as external gear pump, as shown in Figure 1, with a designed as a cylindrical pin Flow guide in cross-section through the flow guide and in longitudinal section through a connecting piece;

Figure 3 is a similar view as in Figure 2 with a teardrop-shaped flow guide;

FIG. 4 shows the flow guide element from FIG. 3 in a side view from the left; and FIG. 5 shows an enlarged detail V from FIG. 3 with a rounded and beveled transition into a displacement space of the displacement machine.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS The prior art external gear machine illustrated in FIG. 1 is an external gear pump and has a housing 1 made of aluminum, which has an interior 2 in which two toothed wheels 4 and 5 made of steel are arranged between two bearing glasses 3, 3 ' , The gears 4 and 5 mesh with each other in external engagement.

The bearing goggles 3, 3 'are received in receiving recesses 23, 23' of the housing 1, whose cross-section corresponds to the outer contour of the bearing goggles 3, 3 '. The gear 4 is rotatably mounted on a freewheel shaft 6, which is connected to both

Pages of the gear 4 projects and with their protruding areas in each case in a bearing bore 7, 7 'of the bearing glasses 3, 3' is rotatably mounted.

The gear 5 is rotatably mounted on a drive shaft 8, which also protrudes on both sides of the gear 5 and with their protruding

Areas in each case in a bearing bore 9, 9 'of the bearing glasses 3, 3' is rotatably mounted.

On the outer side of the bearing glasses 3, an axial seal 10 is held in abutment by a support element 11, this side of the housing 1 is closed by a first cover 12 which is screwed by means of screws 13 to the housing 1.

The interior 2 of the housing 1 is connected via a cover 12 and

Housing 1 arranged ring seal 14 sealed to the outside.

In the same way, an axial seal 10 'is held in abutment on the outer side of the other bearing gland 3' by a support element 11 ', this side of the housing 1 being closed by a second cover 15, which is screwed to the housing 1 by means of screws. The interior 2 of the housing 1 is sealed to the outside via a ring seal 14 'arranged between the cover 15 and the housing 1.

The second cover 15 facing the end of the drive shaft 8 projects sealed from a radial shaft seal 17 through a through hole 16 in the lid 15 to the outside.

This outwardly projecting end of the drive shaft 8 is rotatably driven by a rotary drive, not shown. Thus, the gear 5 and through this the gear 4 is rotatably driven. As a result, hydraulic oil is sucked in at a low-pressure connection 18 and becomes a

High pressure port 19 promoted.

The formed in the housing 1 low pressure port 18 and

High-pressure port 19 are coaxial with each other and lead from the exterior of the housing 1 to the engagement region of the gears 4 and 5.

In the delivery state shown in Figure 1 are the

High pressure port 19 and the low pressure port 18 each of a sealing plug 20, 20 'closed.

In the figures 2 to 5 are embodiments with a

Flow guide shown. The flow-guiding device can advantageously be used in all hydraulic machines, in particular hydraulic pumps, in particular geared machines or gear pumps, for conveying serve a low-viscous medium, which work close to the evaporation or boiling point of the operating medium or working medium and in which the achievement of the highest possible volumetric efficiency while ensuring an acceptable life is required.

In the external gear machine, the engine is usually formed from two mutually meshing gear pairs. The toothed bodies of these gears are usually mounted on shafts which are mounted on both sides in a bearing bush or bearing goggles. In addition to the actual bearing function of the bushings / goggles of a

External gear also taken over the sealing function. Essentially, these are the axial (gear end faces) and the radial (tooth heads, bushes / gland circumference) seals. By combing out the two gears is at the point at the one

Tooth comb combs out of the respective opposite tooth gap, a volume according to the size of the tooth gap free. This results in a negative pressure, which causes the pending on the suction side of the pump fluid flows. The external gear pump absorbs fresh medium through this mode of action.

The system requirements result in a certain bandwidth of a required volume flow. Since gear pumps belong to the constant displacement machines, the volume flow is initially proportional to the drive speed of the pump (pump efficiencies neglected). The required volume flow spread therefore determines the spread of

Drive speed.

Due to the internal leakage of the pump results in a map of the volumetric efficiency. This is directly dependent on the

Drive speed and is usually worse at low than at high

Speeds. Therefore, it is important for the design of the pump (meaning construction and delivery size) that they are at the lower limit of the required

Volume flow still undergoes a drive speed, under which it can achieve a sufficiently good efficiency. If the required volumetric flow spread is very large, this results in a very large spread of the input speed. This can be problematic under certain circumstances, since in this case very high flow velocities and, in turn, unfavorable flow and pressure conditions can occur. This is especially critical on the pump suction side, since it can set highly turbulent flow conditions through which it

Cavitation effects or insufficient filling of the individual tooth chambers (suction limit) can come. The properties of the working medium, such as the viscosity, density,

Vapor pressure, etc. directly affect this effect. The usual in WHR systems low viscous media, such as ethanol, cyclopentane or refrigerant known not only have very low viscosity but also a very low boiling point (or depending on the pressure, a low boiling curve). Therefore, systems with ORC processes (Organic Rankine Cycle) operate very close to the boiling line of the fluid in order to achieve maximum system efficiency. This means for the pump in turn that only very small increases in temperature (for example due to the input of friction power) or very low pressure drops (for example in the suction area due to turbulence) are permissible, otherwise the

Fluid would immediately start to evaporate.

In FIGS. 2 and 3, as in the case of a displacement machine, as illustrated, for example, in FIG. 1, in addition to the long-lasting functionality or service life, above all, a sufficiently high level is also shown

Volumetric efficiency when operating in a WHR system can be ensured. This depends on the one hand significantly on the inner tightness of the external gear from. On the other hand, but also on the possibility of the individual tooth chambers even at very high speeds, so

Fluid speeds on the suction side sufficiently good to fill.

By a flow guide 31; 41, the flow in one

Inflow 27 of the positive displacement machine are guided substantially without turbulence and thus low loss. This allows a sufficiently high even at high speeds or flow rates Volumetric efficiency can be ensured. In addition, the occurrence of unwanted cavitation inside the displacement machine can be prevented. Furthermore, unwanted evaporation of the working medium in the positive displacement machine, and thus unwanted dry running without adequate lubrication, prevented.

By the flow guide 31; 41 in the inflow 27 of the

Displacement machine is this fluid in the inflow, for example in the intake of a working as a pump displacement machine, optimized in terms of flow. The flow guide 31; 41 advantageously comprises a

Flow guide 32; 42, which is also referred to as filler and in the inflow region 27, inter alia with the aid of the Coanda effect leads to a directed flow around this obstacle and thus to a directed flow pattern.

FIGS. 2 and 3 show a section of a displacement machine 40 with a housing 24 in section. The displacement machine 40 is, for example, an external gear pump as shown in FIG. The housing 24 comprises a housing body 25 with a connection 26, via which the displacement machine 40 a working medium or working fluid, for

For example, an ORC fluid is supplied. The connection 26 corresponds to the

Input 18 of the external gear pump in FIG. 1.

The inflow 27 is limited by a connecting piece 28. Via the connecting piece 28, the working medium passes into displacement chambers 29, 30 in the displacement machine 40. In the displacement chambers 29, 30 (not shown in FIGS. 2 and 3) displacement bodies are arranged. The

Displacer may be designed as external gears, as in the external gear pump in Figure 1.

Through the flow guide 31, the incoming working medium, as indicated in Figures 2 and 3 by arrows 33 to 36, divided into two directed part streams 33, 34 and 35, 36. By arrows 37 and 38 it is indicated that a return flow of the working medium in the operation of the displacement machine 40 are divided into two flow areas, each form a vortex, which is advantageously located at the top or bottom of the inflow near the wall, where it is rather uncritical in terms of volumetric efficiency.

In Figure 2, the flow guide 32 is designed as a cylindrical pin and arranged centrally in the inflow. By this arrangement, the two partial streams 33, 34 and 35, 36 from the inflow 27 in the

Displacers 29 and 30 are routed.

In FIGS. 3 and 4 it can be seen that the flow-guiding element 42 of the flow-guiding device 41 is drop-shaped with a tapering point

Flow cross-section in the inflow 27 is executed. From the tapered inflow cross section go out two symmetrical in the flow direction baffles, which are concavely curved. As a result, the desired subdivision of the incoming working medium in the two directed partial streams 33, 34 and 35, 36 realized even more effective.

In Figure 5 is an enlarged detail V of Figure 3 with a

fluidically optimized transition 50 in the displacement of the displacement machine 30 shown in section. The transition 50 is provided with a chamfer 51 and two rounded areas, which are indicated by radii 52 and 53. As a result, an undesirable near-wall backflow and turbulence can be further reduced.

Claims

claims

1. displacement machine (40) having an inflow region (27) over which a working medium in at least one displacement chamber (29,30) of the

Displacement machine (40) flows in, characterized in that in the inflow region (27) at least one flow guide (31, 41) is arranged, through which the inflow region (27) is optimized in terms of flow.

2. Displacement machine according to claim 1, characterized in that the flow-guiding device (31; 41) comprises at least one flow-guiding element (32; 42) which is arranged in the inflow region (27) such that the inflowing working medium flows into at least two directed partial streams (33, 34, 35, 36).

3. Displacement machine according to one of the preceding claims, characterized in that the flow guide element (32; 42) is arranged centrally in an inflow cross section.

4. Displacement machine according to one of the preceding claims, characterized in that the flow guide element (32, 42) extends transversely to the inflowing working medium over the entire inflow cross section.

5. displacement machine according to one of the preceding claims, characterized in that the flow guide (32) is designed as a cylindrical pin.

6. displacement machine according to one of the preceding claims, characterized in that the flow guide (42) has a teardrop-shaped cross-section.

7. Displacement machine according to one of the preceding claims, characterized in that the flow element (42) has a tapered inflow cross-section emanating from the two symmetrical in the flow direction guide surfaces, which are concavely curved.

8. displacement machine according to one of the preceding claims, characterized in that the flow guide (42) is convexly curved at the end.

9. displacement machine according to one of the preceding claims, characterized in that the flow guide (42) in a

Connecting piece (28) is integrated.

10. Displacement machine according to one of the preceding claims, characterized in that the flow guide (41) comprises at least one rounded or beveled transition (50) in a displacement chamber (30).