Gear pump having a multishaft drive and method of operating same

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of European application 98 115 962.7, filed in the European patent Office on Aug. 25, 1998, the disclosure of which is expressly incorporated by reference herein.

The present invention relates to a gear pump having two mutually meshing gears which are each assigned to a shaft and which are each driven by means of a driving unit, the driving units each being drivable by a control unit such that the shafts rotate at a definable rotational velocity.

Normally, gear pumps are driven by a single shaft which extends out of the pump casing. In cases with very high torques or when the flow medium is charged with fillers, two-shaft arrangements are occasionally also used in order to protect the tooth surfaces from wear or excess strain.

Known multishaft drives include timing gears which ensure that the tooth surfaces do not come in contact with one another. In the case of the known multishaft drives, a single driving unit is used, the force distribution onto the individual shafts taking place by means of the engaging gears by way of the above-mentioned timing gear.

Furthermore, a teaching is known from German Patent Document DE-32 30 550C2 in which a two-shaft drive is described which has two driving units. In this case, direct-current motors are used with a control unit which is based on current measurements in the exciting circuit of both driving units and on a rotational velocity measurement in the case of one driving unit. In this known teaching, a desired rotational velocity and a desired power ratio can be defined.

The last-mentioned driving concept has the disadvantage that, as the result of the rotational velocity monitoring taking place only on one side, in the event of a clutch, transmission or pump gearing damage, the line in which the rotational velocity is not monitored may cause consequent damage by endeavoring to reach the desired power. Furthermore, the power ratio can be adjusted only in a narrow range of from 0.5 to 1. Finally, this system is not suitable for appropriately detecting and taking into account torque pulsations because of the intervention point shifting on the intervention line, because of minimal gearing inaccuracies or differences in the rigidities of the engine mounting and transmission mounting.

It is therefore an object of the present invention to provide a gear pump which does not have the above-mentioned disadvantages.

This object is achieved by providing a gear pump of the above noted type, wherein the control units are operably connected by way of a data line. Further advantageous features of preferred embodiments of the present invention are described below and in the claims.

Preferred embodiments of the invention have the following advantages. In that a completely symmetrical structure for the control units for controlling the driving units is provided and, in addition, a fast data transmission is provided between the two control devices contained in the control units, it is achieved that, despite possible torque pulses on the shafts, the tooth surfaces will neither lift off, nor can an excess torque which is too high be transmitted by way of the tooth surfaces.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The single drawing FIGURE is a schematic representation of a gear pump having two identical control units according to preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The drawing figure schematically depicts a gear pump having a two-shaft drive and two control units SE

1

and SE

2

according to the invention. The gear pump has two mutually meshing gears Z

1

and Z

2

which are assigned to two different gear shafts W

1

and W

2

. The gears Z

1

and Z

2

and the shafts W

1

and W

2

are contained in a pump casing G. The shafts W

1

and W

2

extend to the outside and the projecting ends of the shafts W

1

and W

2

are each coupled with a driving unit AE

1

and AE

2

.

According to the invention, the control units SE

1

and SE

2

have a symmetrical construction and include one control device KE

1

and KE

2

respectively, one inverse rectifier WR

1

and WR

2

respectively as a power converter, and one rotational velocity measuring unit DME

1

and DME

2

respectively as measuring units which are each connected with a signal generator of the known type mounted on the shafts W

1

and W

2

. In the rotational velocity measuring units DME

1

and DME

2

, the signal measured in the signal generator is processed for the determination of the angular velocities &ohgr;

1

and &ohgr;

2

, these then being transmitted to the control devices KE

1

and KE

2

.

In the control devices KE

1

and KE

2

, the respective control signals SS

1

and SS

2

are generated for controlling the respective inverse rectifiers WR

1

and WR

2

. For this purpose, in addition to the angular velocity &ohgr;

1

and &ohgr;

2

, output signals for the driving units AE

1

and AE

2

are also used which are generated by the inverse rectifier WR

1

and WR

2

, whereby possible non-linearities or asymmetries of the inverse rectifiers WR

1

and WR

2

are automatically compensated.

In a preferred embodiment of the invention, the driving units AE

1

and AE

2

are of the electric asynchronous machine type (Rolf Fischer, “Electric Machines”, 5th Edition, Carl Hanser Verlag, 1983, pages 170 to 260). The output signals generated by the inverse rectifier WR

1

and WR

2

are indicated in the drawing figure by U

1

and U

2

for the electric voltage, and by I

1

and I

2

for the electric current and by F

1

and F

2

for the frequency.

As mentioned above, the output signals U

1

, I

1

, F

1

and U

2

, I

2

, F

2

are returned into the control device KE

1

and KE

2

for a precise adjustment. This provides a first internal control circuit for adjusting the rotational velocity of the shafts W

1

and W

2

. Specifically, if the driving units AE

1

and AE

2

are conceived as electromechanical converters, the voltage frequencies F

1

and F

2

are imaged on the angular velocities &ohgr;

1

and &ohgr;

2

, and the voltages U

1

and U

2

and currents I

1

and I

2

are imaged on corresponding driving torques (vector drives). Another control circuit is created by measuring the rotational shaft velocity by means of rotational velocity measuring units DME

1

and DME

2

and returning the measured signals into the respective control devices KE

1

and KE

2

. In the context of the present invention, this second control circuit will be called an external control circuit.

According to the invention, a fast data line DL, preferably in the form of a data bus, is provided between the two control units SE

1

and SE

2

, by way of which the angular velocities &ohgr;

1

and &ohgr;

2

of the two shafts W

1

and W

2

and the position of the gears Z

1

and Z

2

can be precisely coordinated or adjusted with respect to one another. The data line DL is provided so that angular velocity differences can be reliably processed within the control units SE

1

and SE and that, despite possible torque pulses, neither a lifting-off of the tooth surfaces, which are to remain in contact, is caused, nor is an excess torque, which is too high, transmitted by way of the tooth surfaces.

In another embodiment of the invention, it is provided that a computer unit is connected to the data line DL constructed as a data bus, by means of which computer unit a rotational velocity adjustment can, for example, take place, particularly in connection with other process components, with which the gear pump is connected.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.