Gear pump including friction brake ring to generate uniform conveyance flow

A gear pump includes a plurality of gear wheels rotatably retained in a pump housing and that engage in one another for the conveyance of a medium. One of the gear wheels is driven by a pump shaft, which can be coupled to a drive by means of a coupling end. To maintain a uniform conveyance flow, in particular with strongly fluctuating operational pressures, during alternating load states, within a single rotation, a brake ring is disposed on the circumference of the pump shaft, which acts with at least one brake surface on a friction surface of the pump shaft or on a friction surface of the pump housing.

BACKGROUND

The invention relates to a gear pump.

It is generally known that to convey and dose liquid, gear pumps are used in which the medium to be conveyed is transported by means of two gear wheels that engage in one another between a pump intake and a pump discharge. Through the plurality of conveyance units a very uniform conveyance volume can be set, such that gear pumps of this type are preferably used for the generation of uniform conveyance quantities such as the supplying of lacquer in a lacquer facility.

A gear pump of this type is known, for example, from DE 10 2005 059 563 A1. With the known gear pump, two gear wheels that engage in one another within a pump housing are rotatably supported and connected to a pump shaft. The pump shaft extends with a coupling end from the pump housing and can be coupled to a drive shaft of a motor. In the use of gear pumps of this type, having variable pressure loads at the discharge end or the intake end, or both ends, irregularities in the conveyance flow have been observed. Normally, the gear wheels contained in the pump housing are driven by means of torque transferred to the pump shaft. In the case that, as a result of pressure fluctuations, a reversal of the pressure differences between the pump intake and the pump discharge occurs, in addition to the torque of the pump shaft, additional pressure forces act on the tooth surfaces of the gear wheels in the direction of conveyance, such that, depending on the size of the pressure forces applied to the gear wheels, a change from a motorized drive to an internally induced drive can result. In other words, in this situation, the pressure drop from the inlet of the pump to the outlet drives the pump faster than the motor. This change in the load direction is transferred to the entire drive train. Due to the torsional play in the drive train, accelerations then occur, followed by slowing of the rotational speed of the gear wheels within a single rotation of the pump shaft. This occurrence results directly in an irregularity in the conveyance flow during a rotation of the pump shaft.

SUMMARY

It is therefore an objective of the invention to provide a gear pump that, independently of the pressure relationships at the pump intake and the pump discharge, a conveyance flow can be generated that is uniform to the greatest degree possible.

This objective is attained according to the invention by disposing a brake ring on the circumference of the pump shaft which acts with at least one brake surface on a friction surface of the pump shaft or on a friction surface of the pump housing.

Advantageous developments of the invention are defined by the characteristics and combinations of characteristics in the embodiments described below.

The invention is distinguished in that a load reversal to the gear wheels through a braking torque acting on the pump shaft is absorbed and is not be transferred to the entire drive train. As a result only the play between the gear teeth and the gear wheels has an effect, which however affects the conveyance uniformity only to an insignificant degree. Another advantage of the invention is that defined and relatively high braking torques can be generated on the pump shaft independently of the selected gaskets within the pump.

Moreover, in typical known pumps, a higher frictional torque cannot be generated by means of sealing lips on the typical gasket, because the sealing lips seal breakdown within a short period of time. In this respect, the brake ring of the present invention provides the advantage that both the brake surface as well as the material of the brake ring can be adjusted for the generation of the braking torque. Depending on where the brake ring is installed, the corresponding friction surface can be formed on the pump shaft or on the pump housing.

Particularly preferred however, is the designing of the gear pump according to the invention in which the brake ring is retained in a non-rotational manner in the pump housing, and in which the brake surface is designed to correspond to an inner diameter of the brake ring.

In this case, the friction surface of the pump shaft is preferably formed on the circumferential peripheral surface, the outer diameter of which is larger than the inner diameter of the brake ring. In this manner it is possible to create a predefined pre-tension between the brake ring and the pump shaft.

Alternatively, the brake ring can be provided with a plurality of brake segments distributed uniformly on the inner diameter of the brake ring, each of which forms a sub-brake surface. In this manner, stick-slip effects between the brake ring and the pump shaft can advantageously be prevented.

In order, on the one hand, to enable a simple assembly, and, on the other hand, to obtain a defined pre-tensioning between the brake ring and the pump shaft, the design of the invention is preferably carried out in which the brake segments are molded onto a carrier ring to form a unitary component. The brake segments are disposed on the carrier such that they extend axially in a lateral direction and the brake segments are retained by means of an encompassing snap ring on the circumference of the pump shaft. In this manner, each of the brake segments is subjected to a uniform pressure via the snap ring on the circumference of the pump shaft, such that the sub-brake surfaces of the brake segments act together with the rotating friction surface of the pump shaft.

The design of the invention, in which the pump housing includes a plurality of housing plates and a shaft housing, is particularly suited for a subsequent integration in a gear pump of a brake ring of this type, wherein the pump shaft is located in the external housing plates, and extends into the shaft housing with the coupling end, and wherein the brake ring is disposed on a shaft section of the pump shaft within the shaft housing. By this means, there is the possibility of disposing the brake ring outside of the housing plates.

The design of the gear pump, in which a shaft gasket is provided within one of the housing plates and/or the shaft housing on the pump shaft, which is dedicated to the shaft section of the pump shaft between a bearing location and the brake ring, is particularly suited for higher drive pressures. In this manner, the functions between the gasket for the pump shaft and the braking of the pump shaft are clearly separated from one another. The sealing gasket formed on the circumference of the pump shaft can therefore be created and worked on such that it is independent of the rotating friction surface. In this manner, each section of the shaft can be optimally set for the relevant function of sealing or braking.

In order to absorb the pressure forces acting with respect to the brake ring on the pump shaft in the interior of the pump housing, the design of the gear pump according to the invention is particularly advantageous wherein a support bearing within the shaft housing is created for the radial and axial support of the pump shaft. The support bearing is dedicated for this purpose to the shaft section of the pump shaft between the brake ring and the coupling end.

It is also possible to dispose the brake ring on an external surface of the support bearing.

In order to further increase the functionality of the brake ring through the use of suitable materials, the brake ring may include an encompassing sealing lip which lies on the circumference of the pump shaft for sealing purposes and which is separated from the brake surface. In this manner, the two functions of braking the pump shaft and sealing the pump shaft can be combined and executed by means of a brake ring.

In this manner, advantageously high degrees of sealing can be implemented with respect to the coupling end of the pump shaft, wherein the brake ring and the shaft gasket form an annular space on the circumference of the pump shaft between one another, which can be filled with a sealing liquid, such that an additional barrier is formed. In addition, deposits to, and aging processes of the conveyance medium can be prevented. In this manner, gear pumps of this type are particularly suited for the conveyance and dosing of paints.

The gear pump according to the invention shall be explained below, based on some embodiment examples in greater detail, with respect to the attached figures.

DETAILED DESCRIPTION

A first embodiment of the gear pump according to the invention is depicted inFIG. 1. The pump housing1is constructed of numerous pieces, and has a plurality of housing plates1.1,1.2,1.3as well as a shaft housing1.4. A recess for two gear wheels3and4, which engage in one another, is contained inside a central housing plate1.3. The central housing plate1.3is contained together with the gear wheels3and4between the external housing plates1.1and1.2. A gasket1.5and1.6is disposed in each of the end surfaces of the external housing plates1.1and1.2, such that gaps between the central housing plate1.3and the external housing plates1.1and1.2are sealed from the exterior.

One of the gear wheels3is connected in a fixed manner to a rotatable bearing shaft6. The bearing shaft6is retained in two bushings6.1and6.2, which have been recessed in the external housing plates1.1and1.2. The second gear wheel4is supported in a non-rotational manner on a pump shaft5. The pump shaft5is supported at numerous shaft sections in the housing plates1.1and1.2. For this purpose, the housing plate1.1has a first bearing bore7.1and the second housing plate1.2has a second bearing bore7.2, in which the bearing bushings8.1and8.2are contained. The bearing bore7.1is designed as a blind hole in the housing plate1.1. In contrast to this, the bearing bore7.2penetrates through the plate1.2, such that the pump shaft5extends from the housing plate1.2. The shaft section of the pump shaft5extending from the external housing plate1.2forms a coupling end5.1having a profiling5.2thereon.

A pump intake2and a pump discharge, not shown here, are disposed in the housing plate1.2, which form, together with the gear wheels3and4, a conveyance system for the dosed conveyance of a medium capable of flowing.

The shaft section of the pump shaft5extending outward from the housing plate1.2is encompassed by the shaft housing1.4. The shaft housing1.4is connected in a rigid manner to the housing plate1.2. A receiving hole10is formed inside of the shaft housing1.4, in which a coupling sleeve9is inserted such that it can rotate. The coupling sleeve9is connected to the pump shaft5at an end surface via the profiling5.2. At the opposite end, the coupling sleeve9has a profiled opening, such that it can be coupled to a drive shaft of a drive unit. The coupling sleeve9is held in the shaft housing1.4by means of a safety ring12having a receiving opening13in an axial extension toward the coupling sleeve9. In this manner, the pump can be coupled to a drive unit via a plug and socket connection.

The shaft housing1.4has a hole31that is disposed concentrically to the pump shaft5on the side of the housing plate1.2, in which a brake ring11is contained in a non-rotatable manner. The brake ring11has a brake surface11.1on its inner circumference, corresponding to a friction surface5.3formed on the pump shaft5. The friction surface5.3has a circumferential peripheral surface. In one state, the inner diameter of the brake ring11in relation to the outer diameter of the pump shaft5in the shaft section of the friction surface5.3exhibits a defined reduced diameter, such that the brake ring11exerts a pressure on the pump shaft5. In this manner, when the pump shaft5is rotated, a braking torque is generated via the brake ring11.

In order to obtain a defined braking torque, the composition of the friction surface5.3on the pump shaft5and the composition of the brake surface11.1on the brake ring11, and furthermore, the material of the brake ring11, can be adapted to one another. Normally, the brake ring11is formed from a wear resistant plastic.

For the sealing of the pump housing1, a shaft gasket14is provided inside the housing plate1.2in the region between the bearing bushing8.2and the brake ring11, and at the pump shaft5section between the bearing location and the friction surface5.3. The conveyance channel system formed between the housing plates1.1,1.2,1.3is sealed from the exterior in the region of the pump shaft5by means of the shaft gasket14.

With the embodiment of the gear pump according toFIG. 1, the pump shaft5is operated via the coupling sleeve9by means of a drive coupled thereto having a predetermined rotation rate. In this state, the gear wheels3and4engage in one another and convey a medium that has been fed therein via the pump intake2in a continuous manner to a pump discharge. In the case that a discharge pressure existing at the pump discharge is greater than an intake pressure at the intake end of the pump, with each rotation of the pump shaft5a specific continuous conveyance flow is obtained by means of the gear wheels3and4. In the case that, due to a drop in pressure, a reversal of the difference in pressures acting between the pump intake and the pump discharge occurs, additional hydraulic forces act on the gear wheels3and4, which act in the direction of conveyance. For this, states may occur in which a lead with respect to the external drive results, i.e., shaft overrun results, which has an effect in the framework of the, structurally necessary, tolerance clearance. In order to keep operational states of this type within tight limits, a braking torque to the pump shaft5is continuously generated by means of the brake ring11. The braking torque is configured such that an advance on the part of the pump shaft in relation to a drive shaft is prevented. In this manner, undesired load variances can be advantageously suppressed, such that conveyance flow fluctuations cannot occur during a rotation of the pump. By braking the pump shaft5, advantageously uniform conveyance flows are obtained, even with fluctuations in the pressures between the pump intake and the pump discharge.

Depending on the design of the pump, different embodiments for the additional braking of the pump shaft can be used. As such, it would also be possible with the embodiment example according toFIG. 1for the brake ring11to be connected to the pump shaft5in a non-rotatable manner, and to act together with an external brake surface on a friction surface formed in the shaft housing1.4. The friction surface on the shaft housing in this case can be formed by means of a hole or the flanks of a groove. In practice, the alternative variation of the invention has, however, proven to be particularly successful, in which the brake ring is retained in a non-rotatable manner in a housing piece.

Another embodiment of a gear pump according to the invention is depicted inFIG. 2, which is substantially identical to the embodiment according toFIG. 1, such that in the following, only the differences shall be explained, and otherwise, reference is made to the aforementioned description.

With the embodiment according toFIG. 2, the pump shaft5has a cylindrical coupling end5.1, which extends from the shaft housing1.4and can be coupled to a drive unit by means of a fitted tongue.

A brake ring11is disposed on the pump shaft5in a shaft section between the coupling end5.1and a shaft gasket14. The brake ring11is contained in a recess31of the shaft housing1.4, in a non-rotatable manner.

For further explanation of the brake ring11, reference is made, in addition toFIG. 2, toFIG. 3.FIG. 3shows a sectional depiction of the brake ring11on the circumference of the pump shaft5. In this respect, the following description applies to bothFIGS. 2 and 3.

In this embodiment, the brake ring11is formed by a carrier ring15and a plurality of brake segments16disposed laterally on the carrier ring15. The carrier ring15and the brake segments16are united as a single component, wherein the brake segments16are connected in an elastic manner to the carrier ring15. The brake segments extend axially with respect to the carrier ring15, and are distributed evenly over the circumference of the carrier ring15. The individual brake segments16each have a sub-brake surface16.1on an inner surface, which rest against the circumference of the pump shaft5, and which act together with the friction surface5.3of the pump shaft5. In order to guide all of the brake segments16collectively onto the circumference of the pump shaft5, a snap ring17is provided, which encompasses the brake segments16and retains the segments on the circumference of the pump shaft5. Additional parameters are given as a result of the number of brake segments16retained on the carrier ring15, and as a result of the radial expansion of the brake segments16, for generating a specific braking characteristic to the pump shaft5. With the depicted embodiment example, the brake segments16distributed on the circumference are designed to be identical and have a uniform spacing to one another in the radial direction. Both the symmetrical configuration of the brake segments as well as the spacings between the brake segments can be distributed differently over the circumference.

The function of the embodiment depicted inFIG. 2is identical to the embodiment according toFIG. 1, such that no further explanation is required.

Another embodiment of a gear pump according to the invention is depicted inFIG. 4, as it is preferably implemented for the dosing of lacquers in lacquer facilities.

With the embodiment according toFIG. 4, the pump housing1is also designed to have numerous pieces. The gear wheel3is supported on a bearing pin18in a rotatable manner in this embodiment, which is retained in a pin hole19in the external housing plate1.1. A gasket20, concentric to the bearing pin18is disposed in the housing plate1.1, by means of which the pin hole19is sealed from the exterior.

The second gear wheel4is mounted directly on the circumference of the pump shaft5by means of a fastening agent21. The axial gap formed between the circumference of the pump shaft5and the gear wheel4is sealed on both sides of the gear wheel4by means of O-rings22.1and22.2. In this manner, on the one hand, entry of the conveyance medium into the gap between the gear wheel4and the pump shaft5is prevented, and on the other hand, a certain mobility of the gear wheel4on the pump shaft5is obtained, depending on the fastening agent21that is used. In this manner, the signs of wear caused in particular by the intake at the end surface between the gear wheel4and the housing plates1.1and1.2can be advantageously equalized, or minimized, respectively.

The pump shaft5is supported directly in the external housing plates1.1and1.2. In this case, no bearing bushings are provided and the pump shaft5is guided directly into the bearing bores7.1and7.2.

Moreover, numerous rinsing channels23are formed in the pump shaft5, the housing plates1.1and1.2, and the bearing pin18, in order to be able to fully rinse the interior of the pump housing1for the purpose of changing the conveyance liquid. A rinsing system of this type for a gear pump is known from EP 1 164 293 A2, for example, such that at this point, reference can be made to the description given therein, and no further explanation thereto shall be given here.

There is a brake ring11, and a support bearing24formed on the shaft section of the pump shaft5extending outside of the external housing plate1.2, between the coupling end5.1and the location of a shaft gasket14. The shaft gasket14, the brake ring11and the support bearing24are supported, concentric to the pump shaft5, by means of the shaft housing1.4. The shaft housing1.4is connected to the housing plate1.2for this purpose in a fixed manner. With the embodiment inFIG. 4, the brake ring11is also formed by a carrier ring15and numerous lateral, molded brake segments16.

Turning now toFIG. 5, the brake ring11used inFIG. 4is depicted. A cross-section view of the brake ring11is shown inFIG. 5. As can be seen inFIG. 5, the carrier ring15has an encircling sealing lip24on its inner circumference. The sealing lip25is designed to be spaced at a distance from the sub-brake surfaces16.1of the brake segments16on the brake ring11, such that the brake ring11in this case executes a double function on the circumference of the pump shaft5. First, the brake segments16provided on the carrier ring15are pressed by means of a snap ring17against the friction surface5.3of the pump shaft5, in order to generate a braking torque. At the same time, the carrier ring15rests with its sealing lip25, encircling its inner circumference, on the circumference of the pump shaft5, next to the friction surface5.3, and forms thereby a seal in the shaft housing1.4with respect to the coupling end5.1.

With the embodiment depicted inFIG. 4, a closed annular space26within the shaft housing1.4is formed by means of the shaft gasket14and the brake ring11. Channels27open into the annular space26through which a sealing liquid can be introduced in the annular space. The channels27in the shaft housing1.4can be sealed, such that when in operation, a sealing liquid can be contained within the annular space26. Depending on the conveyance medium, a liquid containing a solvent is preferably used as the sealing liquid, in order to dissolve conveyance media exiting though leaks, in this case, lacquer, within the annular space29, such that hardening and adhesion in the gaps is prevented.

The support bearing24formed between the coupling end5.1and the brake ring11is formed in this embodiment by means of a roller bearing, disposed between a shaft shoulder28on the pump shaft5and a housing projection29on the shaft housing1.4. Forces acting in the axial direction on the pump shaft5can be advantageously absorbed by means of the shaft shoulder28and the housing projection29. Likewise, the forces acting from outside, via the coupling end5.1of the pump shaft5, can be absorbed by the support bearing24, and not conducted to the interior of the pump housing1.

The coupling end5.1of the pump shaft5is identical to the embodiment according toFIG. 1, and supports the coupling sleeve9. For this, the coupling sleeve9in the receiving hole10of the shaft housing1.4is retained by means of a bearing sleeve30, which at the same time represents a bearing for a detachable drive shaft. This can be inserted in the drive shaft via the receiving opening13at the end of the shaft housing1.4, and can be connected to the pump shaft5by means of the coupling sleeve9.

LIST OF REFERENCE SYMBOLS

1.1external housing plate

1.2external housing plate

1.3central housing plate