GB2339859A

GB2339859A - Testing hydrostatic displacement units

Info

Publication number: GB2339859A
Application number: GB9907724A
Authority: GB
Inventors: Rolf Truninger
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-04-01
Filing date: 1999-04-01
Publication date: 2000-02-09
Also published as: GB9907724D0; DE19914606A1; IT1312159B1; DE19914606C2; ITMI990671A1

Description

2339859 Testing hydrostatic displacement units The present invention

relates to a device for testing hydrostatic displacement units.

Hydrostatic displacement units are today used in almost all areas of technology. They are used, for example, as pumps, motors, volumetric meters and volume dividers in hydraulic drives of industrial machines and earth-moving equipment, in aviation and space travel, in cars and HGVs, in shipping, in forestry vehicles and machine tools, on crude-oil platforms and in many more applications. Hydrostatic pumps are used not only in drive engineering but also for the transport of all kinds of fluids. Thus, for example, they are used as feed pumps in the chemical industry or for the transport of fuels in gas turbines or internal combustion engines.

These known hydrostatic displacement units are, as a rule, tested by their manufacturers on test stands which are built specially for the respective pump or motor. On these test stands, the pump or motor develops a predetermined pressure profile. In the case of variable pumps and motors, the displacement volume is also varied.

In this connection, pumps are, as a rule, driven by an asynchronous motor and loaded with a pressure limiting valve. This procedure has the disadvantage that the whole pump capacity is dissipated as heat, something which, on the one hand, entails energy losses and, on the other hand, necessitates a corresponding cooling capacity; both lead to excessively high operating costs of the test stand. This problem is particularly pronounced for high-capacity pumps.

It is known from www.bauerct.com/hyd.html, for example, that a large portion of the hydraulic power can be recovered by way of a hydraulic motor with a constant or variable displacement volume that is mounted on the same shaft. This leads to substantial energy savings. However, a significant portion of the energy is still dissipated by way of conventional pressure-limiting valves.

The testing of hydrostatic motors is still more expensive. On the one hand, these motors have to be connected to a pressure source and, on the other hand, the shaft has to be loaded, i.e. braked. As a rule one needs to investigate the performance data in the entire speed range, and the braking device therefore has to be operable with variable speeds, in the entire possible operating range. The pressure source has to deliver correspondingly variable feed currents. Here also, a portion of the output power of the hydraulic motor can be used to drive the supply pumps. The pressure load is in turn controlled using a valve, something which brings with it a corresponding energy loss.

These known systems have the disadvantage that they can be used only for a relatively small spectrum of pumps or motors and often have lower and/or upper speed restrictions. The pressure load takes place practically exclusively by way of pressure load valves, something which in turn entails energy losses. A further problem which should not be underestimated is the high inertiae of the drive trains, something which in the case of failure (seizure) of the units being tested can lead to overloading of expensive torque dynamo hubs or to damage in the pump or hydraulic motor. Because of this problem it is often necessary to dispense with the use of a torque dynamo hub.

Starting from this prior art, the object of the invention is to propose a device for testing hydrostatic displacement units in the operating state, in which device, by means of complete electrical and hydraulic recuperation of the energy, considerable savings can be made on operating and investment costs and torque dynamo hubs can be protected from overloading.

In accordance with the invention a displacement unit to be tested is mounted in a drive train, in such a way that it can exchange hydraulic power completely or partially with a complementary second displacement unit on a second drive train which is independent of the first drive train, the second displacement unit is arranged to regulate the system pressure by way of a pressure control loop, and power can be exchanged between the two drive trains by electrical or electronic means.

It is particularly advantageous to drive the drive train by a small electric motor M1 with variable speed, which is able to apply only a portion of the power of the test stand. The electric motor is supported by one or more displacement units, which can be operated both as pumps and as hydraulic motors and act as a type of torque booster. In a particularly advantageous manner, this function is performed by internal gear pumps or motors, because these cover a large speed range and cause only low noise emissions. The speed of the test piece (pump or motor) can thus be specified up to certain maximum speeds in both directions.

A second variable-speed electric motor M2 can be used in order to apply the system pressure, the speed of the motor M2 being controlled by way of a pressure regulator. The two electronic power drivers of the electric motors M1 and M2 can, in accordance with the invention, be interconnected in such a way that the energy or power of the two electric motors M1 and M2 is exchanged.

For a better understanding of the invention embodiments of it will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a diagrammatic representation of an embodiment of the invention in which one motor is operated of a variable speed; Figure 2 shows a diagrammatic representation of an embodiment in which both motors are operated at variable speeds; and Figure 3 shows a diagrammatic representation of an embodiment in which two displacement units can be connected.

Figure 1 shows a displacement unit 1 to be tested, which is driven by a first electric motor (Ml) 2 and draws in a fluid from a tank 11. By way of the pressure line 13, the pump 1 is connected to a hydraulic motor 6, which converts the hydraulic power of the pump into mechanical energy again. The shaft of the hydraulic motor 6 is braked by a second electric motor or generator S. The energy which generated upon braking is output by the power electronics 4 of the braking motor 5 into the alternating-current network 14, where it is again available to the drive motor 2.

In this way, the energy is, in accordance with the invention, exchanged between the two drive trains using electronic means. During operation the speed of the second motor (M2) 5 is controlled by a pressure regulator. The pressure regulator can, for example, be integrated in the electronic drive 4; the desired pressure value 10 and the measured pressure value 8 from the pressure line 13 are used as input variables.

If the drive motor Mi is driving a pump, the braking motor M2 can, by way of a hydraulic motor, convert the hydraulic power generated back into electrical power, which is in turn supplied to the drive motor M1. The two motors are thus electrically and hydraulically in a reciprocal relationship. In this connection, the electrical coupling can, for example, be realised in the two electronic power drivers of the motors by way of the direct-current bus (DC bus) or, however, directly by way of the electrical network supply. Conversely, the displacement unit at the second motor M2 can be operated as a pump and drive a hydraulic motor to be tested, which is braked by the first motor M1. The energy exchange then takes place in the same way with opposite polarity.

As a result of this electrical and hydraulic coupling of the two motors, it is possible to dispense with the use of any control valves, such as pressure control valves, for example. Therefore, no energy has to be dissipated by way of the reducing edges of the valves; rather, a significant proportion at least of the hydraulic energy is recovered hydraulically and electrically. only the power losses of all the components in the system still need to be compensated for.

As a result of the hydraulic recovery of a portion of the energy, the two electric motors M1 and M2 have to apply only a fraction of the drive power, something which renders possible the use of small and reasonably priced motors with a correspondingly low moment of inertia. The electronic power drives in particular can be designed so as to be smaller and more reasonably priced. Particularly advantageous is the use of a servomotor (synchronous motor with permanent magnet rotor), which has a very low inertia, something which reduces further the relatively low kinetic energies of the drive train and additionally means the highest dynamic performance for the pressure load and the speed of the test stand. This renders possible a fast run through of pressure p rofiles and speed profiles, which in turn shortens the test duration. Thus, in the case of continuous tests with pressure cycles, for example, substantial time and energy savings can be made.

In the embodiment shown in Figure 2, the displacement unit 1 to be tested is, in contrast to the embodiment in Figure 1, driven at a variable speed. In this way, the speed of the pump 1 can be specified in both directions of rotation by the first motor (2) (Ml). The pump 1 can accordingly be operated as a hydraulic motor or a pump. The exchange of energy likewise takes place by electrical means. In contrast to the embodiment in Figure 1, the two motors 2, 5 exchange energy in the above example directly by way of the intermediate circuits 7 (DC bus); a reconversion of the direct current (DC bus) into a mains current can thus be avoided.

With comparatively new converter technology, the electrical energy exchange can also take place directly by way of the network, and a DC bus no longer absolutely has to be present for this purpose. A test stand according to the above Figure can gauge hydraulic pumps and motors at any speed in the entire range of performance data.

Figure 3 shows a further embodiment of the invention, in which two displacement units can be connected in as required.

The inner core of the test stand is identical to the embodiments of Figure 1 and Figure 2. The two motors (Ml) 2 and (M2) 5, the electronic power drivers 3, 4, the pressure feedback 8 and the setpoint inputs still have the same function. The two hydraulic displacement units 20, 21, which take on the function of a torque amplifier of the first drive motor (Ml) 2, are new.

If the unit 1 to be tested is, for example, a large pump, the displacement units 20, 21 are connected thereto as hydraulic motors. A portion of the hydraulic power delivered by the pump 1 is hydraulically recovered as a result, which relieves the drive motor (Ml) 2. The second motor (M2) 5 and the corresponding displacement unit 6 control the system pressure. In this connection, however, only a portion of the hydraulic power is recuperated by electrical means.

The valve block 22 produces the correct hydraulic connection of the individual displacement units in the system. In this connection, depending on the volumetric displacement of the unit 1 to be tested, neither, one or both of the additional displacement units 20, 21 are connected to the supply. The latter are designed in such a way that they can be operated in both directions of rotation both as hydraulic motors and pumps (four-quadrant). The principle therefore works in both directions of rotation, particularly also for the case that the unit 1 to be tested is a hydraulic motor.

The section comprising a filter 15, a cooler 16 and a flow 17 indicates that this is not a closed system. The flow of the pump 1 can be measured, the oil accordingly being returned to the tank 11 and being maintained via the cooler 16 and filter 15. The cylinder 27 indicates auxiliary drives which can likewise be controlled and supplied with power from the valve block.

The displacement unit 1 is coupled by way of a quick coupling 19 to a torque dynamo (measurement) hub, with which the current load of the drive is reported via a sensor line 24 to the control computer 25. The control computer 25 controls all the valves and motors in the system, which renders possible an automation of the whole process. A screen with a keyboard 26 can thereby serve as man-machine interface. In a simpler variant of the test stand, it could also be imagined that all functions are controlled by hand and no control computer 25 is integrated.

The simplest embodiment comprises two motors M1 and M2, which exchange the drive energy via the direct current bus of the power electronics (drives). In this connection, the energy is recuperated 100% electrically in all operating states. Both pumps and motors can be tested. The desired speed is set by the motor M1, and the system pressure is controlled by the motor M2 via a pressure control loop, or vice versa. In this way, each operating state of the displacement unit to be tested can be simulated. The properties of the displacement unit can thus be measured for any pressures and speeds.

A substantial improvement of this concept results in accordance with embodiments of the invention if the torque of the drive motor M1 is increased by permanently installed hydraulic displacement units. In this way, only a fraction of the power has to be generated or recovered electrically, the majority of the power being recovered hydraulically. This is particularly advantageous because hydraulic drive elements have substantially lower costs, weights and inertia than comparable electric drive elements. This also means in particular that the power-electronics control units (drives) for the electric motors can be of correspondingly smaller dimensions, which is also a substantial cost factor.

In this way, it is possible to realise a test stand whose drive train has such a low inertia that the delicate measuring device for the drive torque no longer has to be protected against overload. This procedure often permits for the first time the reliable use of such devices, in particular dynamo hubs. A sudden blockage of a pump or a hydraulic motor on the test stand will also immediately reduce the hydraulically recovered torque. The flywheel of the small dynamic motor M1 is not sufficient to overload the dynamo hub. The low kinetic energy in the system also reduces the damage to the test pieces that often arises in such situations in the case of conventional test stands.

The combination of electrical and hydraulic regeneration or recycling in accordance with the invention as described not only results in a minimal energy consumption and low capital costs, but also results in a compact structure. This is the case in particular if dynamic servomotors are used, which by their nature have a slim build.

Claims

1. A device for testing hydrostatic displacement units in the operating state, in particular hydrostatic pumps and motors, comprising: a first drive train for mounting the displacement unit to be tested; this drive train including an electric motor, a second drive train which is independent of the first drive train and includes a second hydraulic displacement unit, a means for exchanging hydraulic power completely or partially with the complementary second unit on the second drive train, and electrical and electronic means for exchanging power between the two drive trains.

2. A device according to claim 1, in which the exchange of electrical power takes place between the said motor and at least one other electric motor by way of the alternating-current network or by way of an intermediate circuit (DC-bus) of the power electronics used for controlling the motors.

3. A device according to claim 1 or 2, in which one or more further displacement units are mechanically connected to the drive train of the displacement unit to be tested in order to recover hydraulically a portion of the power.

4. A device according to any preceding claim, in which recovery of hydraulic power, one or more displacement units with predetermined displacement volumes are used, the feed currents of are capable of being connected to the supply as required by means of relay valves.

5. A device according to any preceding claim, in which one or more of the displacement units that are used has/have variable or constant displacement volumes and is/are constructed according to the radial or axial piston principle, the external or internal gear principle, the G-rotor principle, the vane-cell principle, the propeller principle or according to other generally known displacement principles.

6. A device according to any preceding claim, in which the hydraulic recovery takes place by way of one or more variable-displacement units, so that the amount of hydraulically recuperated power can be varied.

7. A testing device as described herein with reference to any of the embodiments shown in the accompanying drawings.

8. Use of the device according to any preceding claim for testing double or triple pumps or motors, the individual circuits of which can be laid out in a sequential or parallel manner, in which at least one circuit is hydraulically connected to a complementary displacement unit on an independent drive train, and in that, if appropriate, the power of the pumps or motors can be exchanged between the first and second drive trains by electrical or electronic means.

9. A method of testing a hydraulic device by driving it against a load, in which work done on the load is recovered and used as a source of energy for driving the device.