US3753351A

US3753351A - Energy regaining apparatus and method for accelerating and decelerating centrifuges

Info

Publication number: US3753351A
Application number: US00229093A
Authority: US
Inventors: K Pause; W Steprath
Original assignee: Maschinenfabrik Buckau R Wolf AG
Current assignee: BWS Technologie GmbH
Priority date: 1971-03-06
Filing date: 1972-02-24
Publication date: 1973-08-21
Anticipated expiration: 1990-08-21
Also published as: AT321226B; CS161146B2; FR2128308A1; IT946155B; DE2110736B1

Abstract

A set of centrifuges is driven by the hydraulic motors of a set of hydrostatic transmissions whose adjustable pumps have shafts positively connected for rotation with a drive motor. By adjustment of the respective pump, any centrifuge can be accelerated and decelerated. A decelerated centrifuge regains energy for driving the respective hydraulic motor to pump fluid so that the respective pump operates as a motor and aids in driving a centrifuge which is being accelerated.

Description

United States Patent [191 Pause et al.

[ ENERGY REGAINING APPARATUS AND METHOD FOR ACCELERATING AND DECELERATING CENTRIFUGES lnventors: Kurt Pause, Grevenbroich; Werner Steprath, Gohr, both of Germany Maschinenfabrik Buckau R. Wolf Aktiengesellschaft, Grevenbroich, Germany Filed: Feb. 24, 1972 Appl. No.: 229,093

[73] Assignee:

Foreign Application Priority Data Mar. 6, 1971 Germany P 21 10 736.8

US. Cl. 60/420, 60/97 P, 60/486 Int. Cl. Fl6d 33/00 Field of Search 60/97 B, 97 P, 53 R,

[451 Aug. 21, 1973 [56] References Cited UNITED STATES PATENTS 2,846,849 8/1958 Levetus et a1 60/53 R 3,279,172 10/1966 Kudo et a1. 60/53 R Primary Examiner-Martin P. Schwadron Assistant Examiner-Allen M. Ostrager Attorney-Michael S. Striker [5 7 ABSTRACT A set of centrifuges is driven by the hydraulic motors of a set of hydrostatic transmissions whose adjustable pumps have shafts positively connected for rotation with a drive motor. By adjustment of the respective pump, any centrifuge can be accelerated and decelerated. A decelerated centrifuge regains energy for driving the respective hydraulic motor to pump fluid so that the respective pump operates as a motor and aids in driving a centrifuge which is being accelerated.

10 Claims, 5 Drawing Figures mmrwwcer ms 3.753351 SHEEI 1 0f 3 FIG] N=kw n= min 160 Tr Tr -15Q COG O l I I I I I I I I I I I o 5101520253035404550'5560sec 53,2

Pmmenwczl I975 3 753351 SHEET 2 Hi 3 FIG.2

200 sec ENERGY REGAINING APPARATUS AND METHOD FOR ACCELERATING AND DECELERATING CENTRIFUGES BACKGROUND OF THE INVENTION The present invention relates to apparatus for driving a plurality of centrifuges, particularly sugar centrifuges which are provided at a common station, and operate discontinuously.

In modern sugar factories it is the rule to provide several centrifuges for the treating of one product. Each centrifuge is individually driven by an electric motor. Centrifuges, particularly when used for separating sugar crystal and syrup, operate periodically, which means that they fill and empty at low rotary speed, but are accelerated to a high rotary speed, for example about 1,450 revolutions per minute for the purpose of separating, washing and drying the sugar mass, whereupon they are again decelerated to the filling and discharging speed of 60 revolutions per minute.

For driving centrifuges of this type, electric motors are used almost exclusively, which must have high power since in this type of centrifuges, vary great inertia moments are involved.

Modern large centrifuges have moments of inertia of 2,000 kg m or even greater, which are produced by the mass of the centrifuge drum and by the mass of sugar in the ratio of l l. Acceleration time from the discharge and filling speed to the maximum speed is about 60 seconds, so that the electric motor must have a power of over 100 kW.

Induction motors with squirrel rotors havebeen used for a long time, and since in standard induction motors, the rotor losses, disregarding bearing friction, air friction and stator losses, practically correspond to the energy which is stored in the centrifuge at a maximum speed, with corresponding high temperatures of the motor, already years ago special squin'elrotor motors were developed for driving centrifuges.

In the German Trade publicationj z ucker, issue No.4, of February 15, 1950, motors of this type are described and compared with standard motors. While the kinetic energy stored in a centrifuge with the inertia moment of 1,200kg/ m is 0.4 fikwli when the rotary speed of 160 revolutions per minute is reached by a special motor, a standard motor must provide 1, 18 kW h, and a modern special motor still provides 0.785 kW h, without consideration of the efficiency.

While for a standard motor with electric countercurrent braking, again 0.61 kW h must be provided, the new special motor can return 0.1 17 kW h to the power supply when braked and acting as a generator.

Nowadays, special motors for a charge of a large centrifuge requires 2.45 kW h after deduction by regained energy. Half of this energy must be provided for the large mass of the centrifuge drum without being utilized. Furthermore, the motor takes 2.8 kW h from the power supply, and returns only 0.35 kW h, although the centrifuge contains 1.4 kW h stored energy.

The peak loads acting on the power supply are highly undesirable, since the short current peaks are about 650 Ampere in a 380 volt three phase power supply. In the above mentioned electric motors, the rotor losses are directly proportional to the slip relative to the synchronous number of revolutions. This means that a motor upon reaching three-quarter of the synchronous number of revolutions, has already supplied 90 percent of the lost energy so that the rotor is correspondingly heated. During the last quarter of the range of the rotary speed, only 10 percent 37 the total losses occur. That means that a motor whose operational speed varies only in the uppermost range, operates far more economically as far as the energy is concerned, as compared with a motor whose rotary speed is varied for the whole range between zero and the synchronous number of revolutions. Since also the current consumed from the power supply is directly proportional to the slip behind the synchronous number of revolutions if the increments of the phase displacement is disregarded, the fluctuations of current and the current peaks, respectively, are accordingly lower in the last described case.

Each motor in a centrifuge station has to provide lost energy for the following purposes:

1. Acceleration of the discharged molasses,

2. bearing friction and air friction;

3. energy loss corresponding to the electric efficiency;

4. rotor losses due to slip relative to the synchronous number of revolutions; and

5. friction losses during emptying.

Since every centrifuge has its own electric motor, the above explained energy losses take place at each centrifuge, and all losses are combined for the entire centrifuge station.

The disadvantages of the known individual drives for centrifuges by means of pole changeable electric motors are very considerable for discontinuously operating centrifuges, since the acceleration and deceleration requires a great transformation of energy, and accordingly, large cross-sections. During acceleration of the centrifuge drum, the required energy is taken from the power supply. The energy released during deceleration, is fed back into the power supply due to the fact that the motor acts as a generator. The efficiency of electric motors is this form of energy transformation, and the corresponding deviation from the standard rotor speed, is rather bad. During use of the motor as generator, detrimental occurrences, such as reactance currents, cannot be avoided, so that part of the mechanical energy produced by the rotary reciprocal mass, is lost.

SUMMARY OF THE INVENTION It is the object of the invention to overcome the dis advantages of drives for centrifuges in accordance with the prior art, and to provide an energy regaining apparatus for accelerating and decelerating centrifuges and other rotary devices.

Another object of the invention is to mechanically utilize the kinetic energy released upon deceleration of a discontinuously operating centrifuge.

Another object of the invention is to provide a drive for accelerated and decelerated centrifuges in which the disadvantages of electric braking by using the drive motor as generator, are avoided.

With these objects in view, every centrifuge of a set of centrifuges, is individually driven by a hydraulic motor which is driven by a hydraulic pump, and all hydraulic pumps of the thus formed hydrostatic transmissions are mechanically coupled and connected for rotation and driven from a common motor, preferably an electro-motor, such as a slide ring or squirrel cage motor. The arrangement is such that during acceleration and deceleration of the individual centrifuges, a meof the fly-wheel is so dimensioned chanical feed back takes place through the mechanically interconnected shafts so that the kinetic energy released during deceleration of a centrifuge, is supplied to an accelerated centrifuge, relieving the load on the main drive motor, and reducing the power consumed by the same.

The arrangement according to the invention obtains the result that energy, released during deceleration of a discontinuously operating centrifuge is directly supplied to another centrifuge which is to be accelerated, while the electric drive motor varies its rotary speed only slightly, and within the thermally favorable and consequently economical range of the highest rotary speed. Due to the mechanical exchange of energy, the total efficiency of a station with several centrifuges is improved, and not only energy, but also initial investment cost are saved.

The method of the invention comprises accelerating and decelerating at least two centrifuges, or other rotary masses, by hydrostatic transmissions including hydraulic pumps driven by a common drive motor; and decelerating one centrifuge while the other centrifuge is accelerated so that the energy regained by deceleration of one centrifuge causes operation of the respective hydraulic pump as a hydraulic motor, reducing the load on the common drive motor during acceleration of the other centrifuge.

An embodiment of the invention comprises a set of hydrostatic transmissions, each including a hydraulic motor, and an adjustable pump driving the respective hydraulic motor, and having regulating means for varying the flow to the respective hydraulic motor; means mechanically connecting the drive means with the adjustable pumps for rotation together; and a set of centrifuges individually driven by the hydraulic motors, respectively, to accelerate and decelerate depending on the adjustment of the respective hydraulic pump by the regulating means.

In this manner, energy regained during deceleration of a centrifuge, causes the respective hydraulic motor to pump fluid to the respective pump which then operates as a hydrulic motor supplyng the regained energy to an other centrifuge which is being accelerated.

The drive means preferably include an electric motor such as a-squirrel cage motor, a slip clutch and a flywheel. The mechanical connection between the pumps of the hydrostatic trammissions, may be obtained by a common shaft, or by a gear train.

This arrangement prevents a feeding back of electric energy to the electric drive motor and to its power supply. The driving part of the slip clutch runs synchronously with the electric drive motor, while the driven part of the slip clutch runs at a different speed as compared with the electric drive motor. The respective flywheel, which is mechanically coupled for rotation with all hydraulic pumps, can, upon a variation of the rotary speed, store energy and release energy within the speed difference of the slip clutch. The mass inertia moment that the fly-wheel can store the remaining energy within the range of the differences in the rotary speed. This obtains the result that the load variations of the electric drive motor are so small that the motor has to produce only the energy required for the losses, while no feed back of electric energy to the power supply takes place. The electric drive motor runs at almost constant rotary speed, and there is connected by the slip clutch, which may be a hydraulic, or magnetic slip clutch, with the input shaft of a distributor transmission which connects the pumps of all hydrostatic transmissions for synchronous rotation. Each pump is hydraulically connected with a hydraulic motor which drives a centrifuges, and the pumps are adjustable for acceleration or deceleration of the centrifuges at constant pressure, so that the variation of the pumped volume within a time unit, corresponds to the required variation of the rotary speed. Due to the fact that pumps of hydrostatic transmissions are mechanically interconnected for rotation, the regained and released energy of a braking centrifuge can be transmitted to a centrifuge which is to be accelerated. Since in such an energy transformation rarely complete balance between the delivered energy and the required energy prevails, the fly-wheel acting as a mechanical storage, accumulates the available excess energy by increasing its rotary speed and then again provides energy, when more energy is required, by reducing its rotary speed. Since the fly-wheel is positively coupled for rotation with all pumps, variations of the rotary speed of the fly-wheel are transmitted to the pumps without modification. Due to the fact that the pumps are adjusted within the operational range of accelerations and decelerations to a constant pressure, corresponding to a constant output torque of the hydraulic motors, their energy supplies to the variations of the rotary speed are automatically corrected, In operational ranges with constant rotary speed, the variations of the rotary speed of the drive means are corrected by a variation of the pumped volume of the hydraulic pump.

In the preferred embodiment of the invention, the pumps of the hydraulic transmissions have regulating means operated by cylinder and piston means which are operated by pressure fluid supplied from an auxiliary pump in accordance with the position of an electromagnetically controlled valve. Preferably, the cylinder and piston means is provided with pressure limiting valves for acceleration and deceleration, and both pressure limiting valves are connected with the connecting conduits between the respective pump and hydraulic motor of a hydrostatic transmission, and respond to the pressure in the same.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following detailed description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagram illustrating the variation of the energy of the centrifuge over the acceleration and deceleration time;

FIG. 2 is a diagram illustrating the energy exchange between four centrifuges in accordance with the invention;

FIG. 3 is a schematic view illustrating an embodiment of the invention;

FIG. 4 is a schematic view illustrating a modified embodiment of the invention; and

FIG. 5 is a schematic view illustrating control devices for regulating the pumps shown in FIGS. 3 and 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 3, four

centrifuges

18, 19, 20 and 21 are driven by the

output shafts

14, 15, 16 and 17 of hydraulic motors 24 whose inlet and outlet means are connected by connecting

conduits

25, 26 with the outlet and inlet means of four adjustable hydraulic pumps 22, whose speed can be regulated as will be described in greater detail with reference to FIG. 5. Pairs of pumps 22 and hydraulic motors 24 form

hydrostatic transmissions

10, 11, 12 and 13. The

input shafts

6, 7, 8, 9 of the four hydraulic pumps 22, are positively connected for rotation, for example by a gear train of the distributing transmission 5 by which the drive torque of an electric motor 1 is distributed to the input shafts 6 to 9 of the adjustable pumps 22. Motor 1 has a shaft 2 connected by a slip clutch 3 with the input shaft of the distributing transmission 5 which carries a fly wheel 4.

FIG. 4 illustrates a modification of the apparatus, the fly wheel and the slip clutch being omitted for the sake of simplicity. An electric motor is shown which has two coaxial output shafts 2 on opposite sides each of which drives a pair of adjustable pumps 22 which are parts of hydrostatic transmissions to 13 including hydraulic motors 24' having

output shafts

14, 15, 16 and 17, respectively connected with centrifuges 18 to 21, as shown in FIG. 3. The aligned shafts 2' provide a positive coupling and interconnection of the adjustable pumps 22 so that all pumps rotate at the same speed, which is equal to the speed of the shaft means 2'.

F IG. 5 illustrates a control device provided for each hydrostatic transmission 10 to 13, only one hydrostatic transmission including an adjustable pump 22 and a hydraulic motor 24 with an output shaft 14 being shown in FIG. 5. Corresponding control devices are provided for the other hydrostatic transmissions. The centrifuge 18, which is connected to output shaft 14, the distributing means 5, the electric motor 1 and the slip clutch 3 and fly wheel 4 are not shown in FIG. 5.

The control device of FIG. 5 includes an auxiliary pump 23 which is connected with the shaft of the pump 22 and rotates with the same. The discharge flow of the auxiliary pump 23, or other source of pressure fluid, flows through a conduit 31 to a control valve 30 which is also connected to a conduit 30 sucking from an open container 32 with which also the inlet of the auxiliary pump 23 is connected. When shaft 6 is driven from the electric motor 1 the adjustable pump 22 and the auxiliary pump 23 are driven. The fluid pumped by the adjustable pump 22 flows through connecting conduit 25 to the hydraulic motor 24 and through a conduit 26 back to the adjustable pump 22 of the hydrostatic transmission 10. The fluid pumped by adjustable pump 22 drives the hydraulic motor 24, and thereby the respective centrifuge 18.

The pumped volume of adjustable pump 22 is regulated by a servo motor 27 including a piston 27a forming two chambers 27b and 27c in the cylinder of the servo motor 27, and being connected with the regulating means of the respective adjustable pump 22, as schematically indicated by a slanted arrow.

The adjustment of any pump 22 by a regulating means 27 is controlled by a control valve 37 whose valve slide is connected to two

electromagnetic means

33 and 34 for placing control valve 37 is three different positions, which are schematically shown in FIG. 5. In

the illustrated central position 37, no fluid can flow from conduit 31 to conduit 28a, which is connected with chamber 27-so that the pump 22 is not adjusted by the'regulating means 27.

In the position 35, the pressure fluid from the auxiliary pump 23 flows through conduit 32 into conduit 28 and chamber 27b so that piston 27a moves to the left as viewed in FIG. 5, and pump 22 is adjusted to provide such a flow through hydraulic motor 24 that the respective centrifuge l8, driven by shaft 14, is accelerated.

In the position 36, the pressure conduit 31 is connected to its conduit 29a so that the pressure fluid flows into the other chamber 270 and the piston 27a is moved to the right as viewed in FIG. 5, so that the pump 22 is adjusted in the opposite sense so that the speed of motor 24 is reduced, and the centrifuge 18 is decelerated.

It will be seen that in the neutral valve position 37, the output volume of pump 22 is not changed, and the centrifuge 24 rotate at constant speed, that in one control position 36, the output flow of pump 22 is reduced and the centrifuge 18 decelerated, and that in the third position 35 of control valve 30, the output volume of pump 22 is increased and the centrifuge accelerated.

In the conduits 28a and 29a, pressure limiting valves 28 and 29 are provided which are also connected to the connecting

conduits

25, 26, between pump 22 and hydraulic motor 24 and respond to the pressures in

conduits

25 and 26.

Pressure limiting valve 28 measures the pressure in connecting conduit 25 and maintains the same constant so that the hydraulic motor 24 and the centrifuge 18 are accelerated at a constant torque. From program control means, not shown, a pulse signal deceleration arrives at electromagnet 34, control valve 30 assumes the position 36 so that the fluid from conduit 31 flows to the pressure limiting valve 29, and starts the deceleration. The inertia and energy stored in the mass of the centrifuge, drives the hydraulic motor 24 now as a pump so that fluid is pressed into pump 22, which starts operating as a hydraulic motor. The torque of the pump 22 acting as hydraulic motor is transmitted to all other pumps by the positive mechanical connection 5 or 2', so that an other centrifuge, which is accelerated at this time, is also driven by the pump 22 acting as hydraulic motor, whereby the load on the electric motor 1 is reduced.

The rotary speed of the centrifuge is proportional to the piston stroke of piston 27a of the regulating means 27. The acceleration of the centrifuge is proportional to the speed of movement of piston 27a, and to the amount of oil supplied thereto in the time unit.

During acceleration of a centrifuge, the respective pressure regulating valve 28, and during deceleration of a centrifuge, the pressure regulating valve 29 regulates by means of the oil in the cylinder of regulating means 27, and in accordance with the speed of piston 27a, the pressures in connecting

conduits

25 and 26. The pressure acting on the hydraulic motor 24 is thus maintained constant during acceleration and deceleration which has the effect that the centrifuge is accelerated by a constant turning moment or torque, or decelerated, respectively. The speed of the centrifuge is measured and monitored, and if required, corrected by control valve 30.

FIG. 1 illustrates the variation of the energy of a centrifuge 18 to 21 over the time required for acceleration i and again filled. One charge and braking. The graphs N on the right side of FIG. 1 indicates the effective energy required for acceleration of the mass of the centrifuge drum in-filled condition. The graph N represents the energy losses due to air friction and bearing friction and the graph Np indicates the energy to be delivered by the pump 22 considering the hydraulic efficiency. The left side of FIG. 1 shows graphs indicating a decelerating or braking. Since during deceleration the conditions are reversed, the losses have to be deducted from the energy stored in the centrifuge drum, and the energy return is consequently reduced.

The basic conditions in the transformation of energy by a centrifuge as shown in FIG. 1, are illustrated in FIG. 2 for a group of four centrifuges 18 to 21, assuming 18 charges per hour, wherein each centrifuge operates 32 seconds at the highest speed, and then runs 60 revolutions per minute for 55 seconds until emptied takes 200 seconds, and the intervals between the beginning of charges are constant and 50 seconds.

The energy variations of the four centrifuges over the time are illustrated by four graphs a, b, c, d, the energy for acceleration being positively illustrated, and the energy for braking and decelerating being illustrated as negative. The heavy graph e results from the addition of the values of the graphs a, b, c, d. The areas fl and f2, hatched in the negative lower section of the diagram, represent regained energy which are used for increase of the rotary speed of the fly wheel, and reduce the load of the electric induction motor 1 whose squirrel cage rotor operates at a reduced speed, whereby automatically the energy and power peaks of motor 1 are reduced, since the rotor must first reach a slip speed which permits the motor to produce a torque corresponding to the required load. The slip speed of rotation is only reached when the rotary of the fly wheel has been reduced, and the fly wheel has delivered kinetic energy.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of apparatus for accelerating and decelerating rotary masses, differing from the types described above.

While the invention has been illustrated and described as embodied in an energy regaining apparatus for accelerating and decelerating centrifuges including hydrostatic transmissions whose pumps are mechanically interconnected, and operate as hydraulic motors during deceleration of the respective centrifuges, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention ,and therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. Energy regaining apparatus for accelerating and decelerating centrifuges and other rotary masses, comprising drive means; a set of hydrostatic transmissions, each including a hydraulic motor, and an adjustable pump driving the respective hydraulic motor, and having regulating means for varying the flow to the respective hydraulic motor; distributing means mechanically connecting said drive means with said adjustable pumps for rotation together; and a set of centrifuges individually driven by said hydraulic motors, respectively, to accelerate and decelerate depending on the adjustment of the respective hydraulic pump by said regulating means so that energy, regained during deceleration of a centrifuge, causes the respective hydraulic motor to pump fluid to the respective pump so as to operate the same as a hydraulic motor supplying the regained energy to said distributing means and thereby to an other centrifuge which is being accelerated.

2. Apparatus as claimed in claim 1 wherein said drive means includes an electromotor; and wherein said distributing means include mechanical means positively interconnecting said pumps for simultaneous rotation.

3. Apparatus as claimed in claim 1 wherein said distributing means includes a mechanical gear transmission.

4. Apparatus as claimed in claim 1 wherein each of said pumps has a pump shaft; wherein said distributing means include a transmission connecting said pump shafts for rotation together, said transmission having an input shaft; wherein said drive means include a fly wheel on said input shaft, one drive motor driving said input shaft, and a slip clutch between said drive motor and said fly wheel.

5. Apparatus as claimed in claim 1 wherein said drive means include a drive motor having an axis; wherein said pumps have axes aligned with said axis; and wherein said distributor means include shaft means connecting said drive motor with said pumps and having an axis coinciding with said axes.

6. Apparatus as claimed in claim 5 wherein at least one pump is located on either side of said drive motor; and wherein said drive motor has two output shafts on opposite sides for driving said pumps.

7. Apparatus as claimed in claim 1 comprising a set of control devices respectively associated with said hydrostatic transmissions, each control device including a cylinder, and a piston in said cylinder connected with said regulating means for operating the latter, a source of pressure fluid, conduit means connecting said source with said cylinder, and control valve means in said con-. duit means operable for controlling the flow of fluid into said cylinder so that said piston and thereby said regulating means can be moved in opposite directions.

8. Apparatus as claimed in claim 7 wherein said piston forms two end chambers in said cylinder; wherein said source includes an auxiliary pump driven from said drive means by said distributing means; wherein said conduit means include a high pressure conduit and a low pressure conduit connecting said auxiliary pump with said chambers, respectively; and wherein said control valve means controls said conduits, and has first and third positions for reversing the pressure acting in said chambers, and an intermediate second position for holding said piston.

9. Apparatus as claimed in claim 8 wherein each hydrostatic transmission includes two connecting conduits connecting the inlet and outlet means of said drostatic transmissions including hydraulic pumps driven by a common drive motor; and decelerating one centrifuge while the other centrifuge is accelerated so that the energy regained by deceleration of one centrifuge causes operation of the respective hydraulic pump as a hydraulic motor reducing the load on said common drive motor during acceleration of the other centrifuge.

Claims

7. Apparatus as claimed in claim 1 comprising a set of control devices respectively associated with said hydrostatic transmissions, each control device including a cylinder, and a piston in said cylinder connected with said regulating means for operating the latter, a source of pressure fluid, conduit means connecting said source with said cylinder, and control valve means in said conduit means operable for controlling the flow of fluid into said cylinder so that said piston and thereby said regulating means can be moved in opposite directions.

9. Apparatus as claimed in claim 8 wherein each hydrostatic transmission includes two connecting conduits connecting the inlet and outlet means of said pump with the outlet and inlet means of said hydraulic motor; and wherein said control device includes pressure limiting valves in said high pressure and low pressure conduits connected with said connecting conduits, respectively.

10. Method for regaining energy from decelerated centrifuges and other rotary masses, comprising accelerating and decelerating at least two centrifuges by hydrostatic transmissions including hydraulic pumps driven by a common drive motor; and decelerating one centrifuge while the other centrifuge is accelerated so that the energy regained by deceleration of one centrifuge causes operation of the respective hydraulic pump as a hydraulic motor reducing the load on said common drive motor during acceleration of the other centrifuge.