GB2123089A - Gear pump - Google Patents

Abstract

Two pumping gear-wheels (24, 26) are mounted in a housing (10) and each of them has its own motor (40 or 42). The motors may be electric, flange-mounted on the ends of the housing remote from each other, and connected to the associated gear-wheel through a coupling (36 or 38). Thus, each gear-wheel draws power from the associated motor and only a comparatively slight difference of power, if any, is transmitted from one gear-wheel to the other. Accordingly, the gear-teeth are loaded substantially only by forces and moments which are caused by the difference in pressure between the working-fluid inlet (12) and outlet (14), Fig. 2. <IMAGE>

Description

SPECIFICATION Gear pump The invention relates to a gear pump having a housing in which two driven gear wheels meshing with one another are mounted.

In known gear pumps, one of the gear wheels is coupled to a drive motor and transmits the necessary drive power to the other gear wheel meshing with it. The loading by the transmitted torque on the one hand and by the pressure of the medium being pumped on the other hand are experienced additively on the teeth of this other gear wheel, as a result of which those teeth are exposed to heavy bending loads. The Hertzian stress and linear loading caused by the transmitted torque are added to the pressure per unit of area and linear loading caused by the pressure of the pumped medium on the flanks of the teeth of both gear wheels in engagement with one another. This loading, particularly with very high differential pressures between inlet and outlet and with high viscosity of the displaced medium, necessitates correspondingly smaller dimensioning of the depths of the teeth.The consequence of this, however, is that a given delivery can only be achieved with an enlarged width of tooth and/or enlarged diameter of gear wheel which leads to considerable space requirements for the gear wheels. In consequence, the interior of the housing is very large in comparison with the volume delivered on each revolution of the gear wheels and altogether the housing requires a correspondingly large structural volume. In addition, the pump efficiency drops because of the increased frictional effect. As a result, limits are imposed on the deliveries and discharge pressures which can be achieved with known gear pumps, which limits could hitherto not be exceeded without the risk of operational disturbances.

It is an object of the invention to produce a gear pump which, with a given dimensioning of the teeth and without impairing service life, is capable of achieving a higher delivery rate and/or a'higher discharge pressure than the known form of gear pump referred to above.

According to the invention, there is provided a gear pump having a housing-in which two pumping gear wheels meshing with one another are mounted, each said gear wheel being arranged to be driven by its own motor.

With this arrangement substantially only that power need be supplied to each of the two gear wheels which it needs to convey the pumped medium in the gaps between its teeth from the suction side to the delivery side of the pump. If a transmission of power takes place at all between the gear wheels, it is restricted to comparatively small differences, which in some circumstances may be intentional, in the power consumption of the two motors.

It may be advisable for the motors to differ slightly in their power and so the one gear wheel transmits the marginal difference of power to the other gear wheel for the equalization. As a result, definite contact relationships can be maintained between the flanks of the teeth of the two gear wheels.

It is, however, also possible to accept deliberately the fact that sometimes the one and sometimes the other gear wheel is the driving gear wheel, within the range of a predetermined, slight difference of power, so that all the flanks of the teeth of both gear wheels are run in uniformly.

The two motors are preferably interlinked by a common regulator. In this case, the two motors may appropriately be direct-current motors and have allocated to each of them a current-measuring means which provide respective inputs to the common regulator.

In a gear pump according to the invention, as in known gear pumps, one motor may be coupled coaxially to one of the gear wheels and be secured to one end of the housing. It is now very convenient to couple the other motor coaxially to the other gear wheel and to secure it to the other end of the housing. The two motors may each be flange-mounted on the housing via a respective intermediate part which includes a coupling.

One embodiment of the invention is described below, by way of example, with reference to-the accompanying diagrammatic drawings.

Figure 1 shows a gear pump according to the invention in a vertical axial section, Figure 2 is the vertical cross-section ll-ll in Fig. 1, and Figure 3 shows an electrical circuit for controlling the motors of the pump.

The gear pump illustrated has a housing 10 with an inlet 1 2 and outlet 14. The housing 10 contains a pair of upper bearing bushes 1 6 and a pair of lower bearing bushes 1 8 for an upper shaft 20 and a lower shaft 22 respectively. The two shafts 20 and 22 are disposed parallel to one another and, in the example illustrated, vertically one above the other and each carries a gear wheel, 24 and 26 respectively, which is disposed between the two associated bearing bushes 1 6 and 18, respectively, and may be made integral with the associated shaft or be secured thereto.

To the opposite ends of the housing 10 are secured respective side members 28 and 30.

The upper shaft 20 extends through the righthand side member 28 in Fig. 1 whereas the lower shaft 22 extends through the left-hand side member 30. Each shaft 20 and 22 is sealed in the side member (28 or 30) in question by a seal 32 or 34. Outside the side members 28 and 30, the two shafts 20 and 22 are each connected to a motor 40 or 42 through a coupling 36 or 38. The two motors 40 and 42 are arranged coaxially with the associated shafts 20 and 22 and are each flange-mounted on an intermediate part 44 or 46 which in turn is flange-mounted on the associated side member 28 or 30. The two intermediate parts 44 and 46, like the side members 28 and 30, are completely alike.

According to Fig. 3, the two motors 40 and 42 are direct-current shunt-wound motors and a common regulator 50 is associated with them in such a manner that an ammeter 52 or 54 is connected each to one input of the regulator 50 that is in the exciting circuit of each of the two motors. One output of the regulator 50 is connected to a speed reference value transmitter 58 which in turn is connected, through a power amplifier 62, to the ammeter 54 of the associated motor. An input signal x, which determines the power ratio of the two motors 40 and 42 in relation to one another and is adjustable between 0.5 and 1, can be supplied to the regulator 50 via a control line 64.Additionally allocated to the two motors 40 and 42 is a speed controller 56 which compares the actual value obtained from a speed indicator 66 connected to the motor 40 with the DESIRED SPEED fed in and can transmit a corrected controlling quantity to the power amplifier 60.

During the regulation of the power of the two motors, the power amplifier 60 supplies the motor 40 with a current 140 according to the input quantity of the DESIRED SPEED.

The ammeter 52 measures this current and passes on a signal of the measured quantity k.l40 to the regulator 50. The regulator 50 controls the power amplifier 62 via the speed reference value transmitter 58 according to the input signal x and the measured quantity K. 140, k being a reducing constant, and the power amplifier 62 supplies the motor 42 with a current 142. The ammeter 54 measures the current 142 and conveys the measured quantity k.l42 back to the regulator 50. The regulator compares the measured quantity k.l42 with the desired quantity k.l4250" and can correct the controlling quantity at the power amplifier 62.

Claims (7)

1. A gear pump having a housing in which two pumping gear wheels meshing with one another are mounted, each said gear wheel being arranged to be driven by its own motor.

2. A gear pump as claimed in claim 1, wherein the motors differ slightly in their power.

3. A gear pump as claimed in claim 1 or claim 2, wherein speed controlling means receive input signals from both motors.

4. A gear pump as claimed in claim 3, wherein the two motors are direct-current motors and said input signals are provided from respective motor circuit current-measuring means.

5. A gear pump as claimed in any one of the preceding claims, wherein the motors are coupled coaxially to their respective gear wheels and are secured to opposite ends of the housing.

6. A gear pump as claimed in any one of the preceding claims, wherein the two motors are each flange-mounted on the housing through an intermediate part which encloses a coupling.

7. A gear pump constructed and arranged for use and operation substantially as described herein with reference to the accompanying drawings.