Positive displacement machine with kinematic synchronization coupling and with driven moving parts having their own individual drives

Abstract

Positive displacement machine such as a compressor, expander, pump or the like, for displacing a gaseous or liquid medium, the machine containing an element with at least one inlet and at least one outlet for the medium and at least two cooperating driven moving parts. The mutual periodic movement of the moving parts displaces the medium from the inlet to the outlet. Each of the at least two driven cooperating moving parts is provided with its own individual drive. The element is provided with a kinematic synchronisation coupling between the at least two cooperating moving parts for the mutual kinematic synchronisation of their movements.

Claims

1. A positive displacement machine for displacing a gaseous or liquid medium, the machine comprising: an element with at least one inlet; at least one outlet for the medium; and at least two cooperating driven moving parts, wherein a mutual periodic movement of the moving parts displaces the medium from the inlet to the outlet, wherein each of the at least two cooperating driven moving parts is provided with its own individual drive, and wherein the element is provided with a kinematic synchronisation coupling between the at least two cooperating driven moving parts for a mutual kinematic synchronisation of their movement, wherein the machine is provided with a synchronisation controller to mutually synchronise the individual drives, wherein the synchronisation controller contains a primary control algorithm for controlling the speed of one of the at least two individual rotative drives, referred to as a master drive, as a function of a set primary control criterion, wherein the synchronisation controller contains a secondary control algorithm for controlling the speed of the other of the at least two individual rotative drives, referred to as the slave drive, in such a way that the speeds of the master drive and of the slave drive are mutually synchronised, and wherein the secondary control algorithm is such that the ratio between the speed of the master drive n.sub.a and the speed of the slave drive n.sub.b is practically constant at a set value (n.sub.a/n.sub.b)set.

2. The positive displacement machine according to claim 1, wherein the cooperating moving parts of the element are rotative parts.

3. The positive displacement machine according to claim 1, wherein the individual drives are rotative drives.

4. The positive displacement machine according to claim 2, wherein the cooperating rotative parts are each provided with a shaft and the individual drives are each provided with a drive shaft directly connected to the shaft of a respective one of the cooperating rotative parts.

5. The positive displacement machine according to claim 1, wherein the kinematic synchronisation coupling contains a gear transmission with a fixed transmission ratio between the at least two cooperating moving parts of the element.

6. The positive displacement machine according to claim 1, wherein the machine is a screw compressor or tooth compressor or a screw expander with an element with two helical or tooth shaped cooperating driven rotors with screws or teeth which partly engage to compress or expand a gaseous medium between the screws by their mutual movement.

7. The positive displacement machine according to claim 1, wherein the machine is an oil-free screw compressor or an oil-free screw expander.

8. The positive displacement machine according to claim 1, wherein the individual drives are rotative drives with a variable adjustable speed and the machine is provided with means to determine the speed of the individual drives, said means being connected with said synchronisation controller for a feedback of the speeds.

9. The positive displacement machine according to claim 1, wherein the machine is provided with means to determine the pressure and/or the flow rate of the displaced medium and the primary control criterion is a desired pressure or a desired flow rate.

10. The positive displacement machine according to claim 1, wherein a ratio between the speed of the master drive and the speed of the slave drive is practically constant at the set value (n.sub.a/n.sub.b).sub.set with a maximum deviation which is less than 5%.

11. The positive displacement machine according to claim 10, wherein the ratio between the speed of the master drive and the speed of the slave drive is practically constant at the set value (n.sub.a/n.sub.b).sub.set with the maximum deviation which is less than 2%.

12. The positive displacement machine according to claim 11, wherein the ratio between the speed of the master drive and the speed of the slave drive is practically constant at the set value (n.sub.a/n.sub.b).sub.set with the maximum deviation which is less than 1%.

13. The positive displacement machine according to claim 5, wherein the set value (n.sub.a/n.sub.b) set of the ratio between the speed of the master drive and the speed of the slave drive is equal to the transmission ratio of the kinematic synchronisation coupling.

14. A method for displacing a liquid or gaseous medium by means of a positive displacement machine with an element with at least two cooperating driven moving parts which can displace the medium by their mutual periodic movement, the method comprising the following steps: individually driving the at least two cooperating driven moving parts by means of an individual drive for each of the at least two cooperating driven moving parts; and providing a kinematic synchronisation coupling between the at least two cooperating driven moving parts to prevent that said moving parts interfere with each other; synchronously driving the individual drives; primarily controlling the speed n.sub.a of one of the at least two individual drives as a function of a set primary control criterion; and secondarily controlling the speed n.sub.b of the other of the at least two individual drives to keep a ratio (n.sub.a/n.sub.b)set between these speeds practically constant.

15. The method according to claim 14, further comprising the step of determining the pressure and/or the flow rate of the displaced medium, wherein the primary control criterion is a desired pressure or a desired flow rate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) With the intention of better showing the characteristics of the invention, hereafter, by way of an example without any limiting nature, a preferred embodiment is described of a positive displacement periodic machine according to the invention and of a method thereby applied for displacing a liquid or gaseous medium, with reference to the accompanying drawings, wherein:

(2) FIG. 1 schematically shows a known positive displacement machine;

(3) FIG. 2 schematically shows a positive displacement machine according to the invention with comparable capacity as that of the known machine of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(4) In this case, by way of an example, the known positive displacement machine 1 shown in FIG. 1 is an oil-free screw compressor 1.

(5) In this case the machine 1 contains one single and sole drive 1 in the form of an electric motor 2 and an element 3 with two cooperating moving parts 4, respectively a first and a second moving part 4a and 4b, in the form of two helical rotors which partially engage with their screws 5 and which have been rotatably mounted in a housing 3′ of the element 3 with therein two overlapping cylindrical compression chambers 6 in which the cooperating moving parts 4 have been mounted closely fitting.

(6) The cooperating moving parts 4 are provided with a shaft 7, respectively 7a and 7b, which are mounted on bearings by means of radial and axial bearings 8 in the housing 3′ to secure the moving parts 4 in this case axially and radially.

(7) The machine 1 contains a torque transfer transmission 9 with an input shaft 10 which is coupled directly or by means of a coupling 11 to the aforementioned single drive 2 and an output shaft 12 which may or may not be connected by means of a coupling 13 to the shaft 7a of the first moving part 4a.

(8) The input shaft 10 and the output shaft 12 are mounted in the housing 5 by means of extra bearings 14.

(9) In this case the transmission is a gear transmission with two engaging gearwheels 15, respectively a floating gearwheel 15b on the input shaft 10 and a driven gearwheel 15a on the output shaft 12, which is connected to the first moving part 4a.

(10) In operation, the machine 1 is driven by means of the drive 2 which drives the first moving part 4a via the transmission 9.

(11) The second moving part 4b is driven via a second torque transfer transmission 16 by the shaft 7a of the first moving part 4a, for which purpose a floating gearwheel 17a is mounted on the shaft 7a which engages with a driven gearwheel 17b on shaft 7b of the second moving part 4b.

(12) Thanks to the drive both moving parts 4a and 4b are synchronously driven, for example at the same speed with the same number of revolutions, such that a gaseous medium is sucked in via an inlet 18 in the housing 3 and compressed between the screws 5 and is displaced to an outlet 19 in the housing to be supplied at a higher pressure to a pneumatic consumer.

(13) The power required to supply the gaseous medium at a given pressure to the outlet 19 and a given flow rate to the consumer passes entirely over the transmission 9 and a significant part of this power passes over the transmission 16 and the moving parts that must be designed to cope with it. The bearings also have to be able to cope with it.

(14) FIG. 2 shows a positive displacement machine of a comparable power to displace the medium at a certain pressure to the outlet 19 and flow rate, whereby the moving parts 4a and 4b in this case have the same dimensions as those of FIG. 1.

(15) Specific to the invention is that, in this case, each of the two cooperating moving parts are provided with their own individual drive 20, 20a and 20b respectively, each of which in this case is directly coupled by means of a coupling 21, 21a and 21b respectively, to a respective shaft 7a and 7b of the cooperating moving parts 4a and 4b and that the element 3 is provided with a kinematic synchronisation coupling 22 between the at least two cooperating moving parts 4a and 4b for the mutual kinematic synchronisation of their movements.

(16) The couplings 21a and 21b do not necessarily have to be separate couplings, but can also be a direct mechanical connection whereby the shafts of the drives 20a and 20b are one with the shafts 7a and 7b.

(17) The shafts 7a and 7b are mounted in the housing 3′ by means of bearings 8.

(18) In the example the synchronisation coupling 22 is formed by two engaging gearwheels 23, a gearwheel 23a on the shaft 7a of the first moving part 4a and a gearwheel 23b on the shaft 7b of the second moving part 4b respectively.

(19) The synchronisation coupling 22 has a fixed transmission ratio between the gearwheels 23a and 23b.

(20) In this case the drives 20a and 20b are located at one axial end of the element 3, while the synchronisation coupling 22 is located at the other axial end of the element 3. However, it is not excluded that both drives 20a and 20b are located on the same axial end of the element 3 as the synchronisation coupling 22 or that one drive 20a is located at the same axial end as the synchronisation coupling 22 and the other drive 20b is located at the other end.

(21) Analogue to FIG. 1, the element 3 is provided with an inlet 18 and an outlet 19.

(22) The drives 20a and 20b are drives with a variable adjustable speed n and the positive displacement machine is provided with a synchronisation controller 24 which is connected to the drives 20a and 20b for the synchronous control of the speeds n.sub.a and n.sub.b of the cooperating moving parts 4a and 4b with a fixed ratio between the speeds n.sub.a and n.sub.b, at least apart from the possible errors of the controller.

(23) To this end, the element 3 is provided with means 25, respectively 25a and 25b, to determine the speed n.sub.a and n.sub.b of the individual drives 20a and 20b, said means 25 being connected with the aforementioned synchronisation controller 24 for the feedback of the speeds.

(24) Furthermore, the positive displacement machine 1 is provided with means 26 to determine the pressure p at the outlet 19 of the element 3 and/or the flow rate of the displaced medium.

(25) Preferably the synchronisation controller 24 contains a primary control algorithm for controlling, for example, the speed n.sub.a of one of the individual drives 20a, referred to as the master drive here, and this as a function of a set primary control criterion which is, for example, a desired pressure p or a desired flow rate as is already traditionally applied in positive displacement machines.

(26) A secondary control algorithm of the synchronisation controller will then control the speed n.sub.b of the other individual drive 20b, referred to as the slave drive here, and this in such a way that the speeds n.sub.a and n.sub.b of the master drive and of the slave drive are mutually synchronised.

(27) The secondary control algorithm is for example such that the ratio n.sub.a/n.sub.b between the speed n.sub.a of the master drive 20a and the speed n.sub.b of the slave drive 20b is practically constant and equal or practically equal to a set value (n.sub.a/n.sub.b) which is equal to the fixed transmission ratio of the kinematic synchronisation coupling 22, with a maximum deviation which is preferably less than 5%, more preferably less than 2% and most preferably less than 1%.

(28) The method for using the positive displacement machine 1 according to the invention is simple and as follows.

(29) The speed of the individual drive is controlled by the primary control algorithm such that a set pressure p at the outlet of 19 of the element 3 or a set flow rate is maintained.

(30) Further, the secondary control algorithm ensures the second individual drive 20b is driven synchronously with the first individual drive 20a, i.e. making sure that the ratio between the speeds n.sub.a and n.sub.b always remains equal to the set value (n.sub.a/n.sub.b) set which is equal to the transmission ratio of the kinematic synchronisation coupling 22. In other words, the speed n.sub.b of the slave drive 20b follows the variations of the speed n.sub.a of the master drive 20a.

(31) With a theoretically perfect controller 24, no torque and therefore no power will be transmitted through the synchronisation coupling 22.

(32) However, in case of a deviation of the synchronisation controller 24, the speed n.sub.b for example will lag slightly behind the speed n.sub.a with a certain deviation in relation to the set speed ratio (n.sub.a/n.sub.b) set.

(33) Without the kinematic synchronisation coupling 22 this would mean that the cooperating moving parts 4a and 4b would interfere against each other, which must be absolutely avoided.

(34) However, the presence of the kinematic synchronisation coupling 22 avoids this forcefully and the moving part 4a with the greatest speed will help drive the moving part 4b with a lower speed via the kinematic synchronisation coupling 22 which will then have to absorb the power difference which is, however, limited and all the more limited such that the control of the speed by the synchronisation controller is more accurate.

(35) It is clear that thanks to this the kinematic synchronisation coupling 22 can be made relatively light.

(36) It is also clear that by applying the invention the relatively robust torque transfer transmissions 9 of the known positive displacement machine of FIG. 1 can be left out and/or the transmissions 9 and 16 of FIG. 1 can in any case be made much lighter.

(37) For the primary control other criteria can be applied than a set pressure or flow rate such as a power control or the like.

(38) The secondary control can also be based on other control criteria such as minimising the power transmitted via the kinematic synchronisation coupling 22.

(39) It is also clear that the positive displacement machine does not necessarily have to be a rotative machine but also applies to, for example, machines with periodically linear moving parts between which a gaseous or liquid medium is displaced and which are each provided with their own individual drive and the frequency of the drives of which needs to be synchronised to avoid collisions.

(40) The present invention is by no means limited to the embodiment described as an example and shown in the drawing, but a positive displacement periodic machine according to the invention and a method applied thereby for displacing a liquid or gaseous medium can be realised in all kinds of ways and forms without departing from the scope of the invention.