METHOD AND APPARATUS FOR VIBRATION COMPENSATION IN A PISTON COMPRESSOR

Abstract

The invention relates to a method and to an apparatus for vibration compensation in a piston compressor, the piston compressor of which is driven by means of a crankshaft by a three-phase motor controlled by a frequency converter, wherein the current position the crankshaft of the piston compressor is determined, and based on this the frequency converter, a torque (M.sub.M) for the three-phase motor is predetermined, which torque follows the load torque (M.sub.L) of the piston compressor in order to reduce the vibration stimulation of the entire piston compressor.

Claims

1. A method for vibration compensation in a piston-type compressor, the method comprising: driving the piston compressor of which by a crankshaft of a three-phase motor controlled by a frequency converter; and determining the current position of the crankshaft of the piston compressor, wherein based on the determined current position of the crankshot, a torque (M.sub.M) that follows a load moment (M.sub.L) of the piston compressor is prescribed by a frequency converter for the three-phase motor to reduce the vibration excitation of the piston-type compressor as a whole.

2. The method of claim 1, wherein the torque (M.sub.M) prescribed for the three-phase motor corresponds to the phase position and the load moment profile of the piston compressor.

3. The method of claim 1, wherein the torque (M.sub.M) prescribed for the three-phase motor corresponds to the first order of the load moment profile of the piston compressor.

4. The method of claim 1, wherein the current angular position of the crankshaft of the piston compressor is determined by sensors as the current crankshaft position.

5. The method of claim 1, wherein the deviation of the load moment (ML) of the piston compressor following the torque (M.sub.M) for the three-phase motor is set in such a way that it is less than 30%.

6. The method of claim 1, wherein an increase of the torque (M.sub.M) for the three-phase motor is carried out by a corresponding increase of its operating voltage by the frequency converter.

7. The method of claim 1, wherein to compensate for fluctuations in speed, the torque (M.sub.M) generated by the three-phase motor is produced by the frequency converter by a variation of the feed voltage and/or a variation of the pulse width.

8. An apparatus for vibration compensation in a piston-type compressor which is driven by a crankshaft by a three-phase motor controlled by a frequency converter, the apparatus comprising: a control unit that determines the current position of the crankshaft the piston compressor, wherein, based on this, the frequency converter prescribes a torque (M.sub.M) that corresponds to the load moment (M.sub.L) of the piston compressor for the three-phase motor to reduce the vibration excitation of the piston-type compressor as a whole.

9. The apparatus of claim 7, wherein arranged in the region of the motor shaft or the crankshaft is a position sensor that measures its current angular position, in order to make the measured value available to the control unit.

10. The apparatus of claim 7, wherein the control unit integrated in the frequency converter, which is arranged in or on the three-phase motor.

11. A piston-type compressor for producing compressed air for a vehicle, the compressor comprising: a piston compressor which is driven by a crankshaft by a three-phase motor controlled by a frequency converter; and an apparatus for vibration compensation in the piston-type compressor, the apparatus comprising a control unit that determines the current position of the crankshaft of the piston compressor, wherein, based on this, the frequency converter prescribes a torque (M.sub.M) that corresponds to the load moment (M.sub.L) of the piston compressor for the three-phase motor to reduce the vibration excitation of the piston-type compressor as a whole.

12. The compressor of claim 11, wherein, arranged in the region of the motor shaft or the crankshaft is a position sensor that measures its current angular position, in order to make the measured value available to the control unit.

Description

[0015] Further measures that improve the invention are presented in more detail below together with the description of a preferred exemplary embodiment of the invention on the basis of the figures, in which

[0016] FIG. 1 shows a block circuit diagram of a piston-type compressor with an apparatus for vibration compensation integrated in it,

[0017] FIG. 2 shows a graphic representation of the rotational vibrations produced by the motor and the compressor according to the prior art,

[0018] FIG. 3 shows a graphic representation of the rotational vibrations produced by the motor and the compressor according to the solution according to the invention with regard to a first embodiment, and

[0019] FIG. 4 shows a graphic representation of the speed profile in the case of the first embodiment,

[0020] FIG. 5 shows a graphic representation of the time-based profile of the phase currents of a three-phase motor as a drive according to the first embodiment,

[0021] FIG. 6 shows a graphic representation of the rotational vibrations produced by the motor and the compressor according to the solution according to the invention with regard to a second embodiment,

[0022] FIG. 7 shows a graphic representation of the speed profile in the case of the second embodiment,

[0023] FIG. 8 shows a graphic representation of the time-based profile of the phase currents of a three-phase motor as a drive according to the second embodiment.

[0024] FIG. 1 shows a piston-type compressor substantially consisting of a piston compressor 1 and a three-phase motor 2. The piston compressor 1 is formed as a two-stage compressor unit and here comprises two low-pressure cylinders 3a, 3b and a high-pressure cylinder 4. Coming from the atmosphere, the compressed air is first pre-compressed in the low-pressure cylinder 3a, 3b and then brought to an even higher pressure level by the high-pressure cylinder 4, before this compressed air that is produced is passed on for further use in the vehicle.

[0025] For actuating the piston drive of pistonsnot shown any furtherof the cylinders 3a, 3b and 4, the piston compressor 1 has a crankshaft 5, which is driven by the three-phase motor 2. The electrical three-phase motor 2 is equipped with a frequency converter 6, by way of which the connection to a three-phase system 7 is made. The frequency converter 6 is assigned an electronic control unit 8, which is structurally integrated in it. On the input side, the electronic control unit 8 receives the measurement signal of a position sensor 9, which is arranged in the region of the crankshaft 5 and prescribes the current angular position of the crankshaft 5 to the electronic control unit 8.

[0026] FIG. 2 shows in a graphic representation the torque profile with respect to a complete revolution of 0 to 360 of the crankshaft of a piston compressor of the prior art. The average torque of the drive is at approximately 50 Nm (dotted line). It can be seen in the profile of the load moment M.sub.L that, on account of a pressure peak at an angular position of the crankshaft of about 200, it has a maximum of approximately 140 Nm. The profile of the load moment M.sub.L that is shown is characteristic of two-stage piston compressors, as illustrated in FIG. 1. The motor only responds to the dominant pressure peak after a time delay and, as can be seen, only builds up the motor torque M.sub.M with a phase offset at an angular position of the crankshaft of about 0. Consequently, the maximum motor torque M.sub.M of about 75 Nm only comes into effect when the load moment M.sub.L of the piston compressor has already fallen, here has even reached its minimum. Due to this effect, depending on their type of design, three-phase motors even increase the rotational vibration excitation in interaction with the piston compressors driven by them. The dominant pressure peak of the load moment M.sub.L of about 150 Nm results from the compression of the second stage, to be specific the high-pressure cylinder. The three-phase drive responds to this pressure peak and builds up its torque M.sub.M of the profile shown. The area between the load moment M.sub.L and the torque M.sub.M of the motor is marked here by hatching and represents a measure of the vibration excitation around the crankshaft of the piston compressor. Because of the hatched area having quite a large area content, a relatively great disadvantageous vibration excitation is to be assumed.

[0027] FIG. 3 shows the torque profile of the torque M.sub.M of the motor and of the load moment M.sub.L of the piston compressor for a full revolution of the crankshaft as a consequence of the vibration compensation according to the invention. In the case of this embodiment, the control of the motor takes place in such a way that its torque M.sub.M follows the load moment M.sub.L of the piston compressor. This has the result that the area content of the area between the load moment M.sub.L and the motor torque M.sub.M is minimal as compared with the prior-art embodiment explained above, so that a very small vibration excitation takes place. This is so because, on account of the control according to the invention, the driving motor builds up its torque M.sub.M synchronously and to this extent in a requirement-controlled manner with respect to the load moment M.sub.L of the piston compressor that is to be handled. Because there are only minimal non-uniformities, there is a similarly minimal vibration excitation.

[0028] FIG. 4 illustrates as a consequence of this a uniform profile of the rotational speed n of the crankshaft over the entire revolution. This also corresponds approximately to the average profile of the rotational speed n.

[0029] FIG. 5 shows the time-based profile of the phase currents with respect to the three phases of the three-phase motor, which, on account of the almost complete control-system vibration compensation, also turns out here to be quite a uniform respective sine curve.

[0030] FIG. 6 illustrates with regard to the second embodiment the torque profile of the torque M.sub.M and of the load moment M.sub.L for a full revolution of the crankshaft, though, by contrast with the embodiment described above, here there is only a compensation with regard to the first order of the load moment profile of the piston compressor by the torque M.sub.M of the three-phase motor. This has the result that, in comparison with the prior art explained above, a much smaller and uniformly distributed area content as a hatched area between the curves of the profile of the motor torque M.sub.M of the rotational speed motor and the load moment M.sub.L of the piston converter contributes to a vibration excitation. The vibration compensation achieved in this way can be regarded as sufficient for the application that is the subject of the invention.

[0031] FIG. 7 shows as a consequence of this that the rotational speed n of the crankshaft only fluctuates slightly about the average speed n. A further uniformity of the speed profile can therefore be achieved here by the compensation of the first order of the load moment profile of the piston compressor.

[0032] FIG. 8 accordingly shows the time-based profile of the phase currents of the three phases of the three-phase motor, which, by contrast with the almost complete compensation of the invention that is discussed above, does in fact reveal a slight non-uniformity. Nevertheless, the phase current profile stays within narrow limits, which demonstrates the effect of the solution according to the invention according to the second embodiment.

[0033] The invention is not restricted to the preferred embodiments described above. Rather, modifications thereof that are included within the scope of the following claims are also conceivable. For example, instead of a two-stage piston-type compressor, it is also possible to also equip a single-stage piston-type compressor with the control-system vibration compensation according to the invention.

LIST OF DESIGNATIONS

[0034] 1 Piston compressor [0035] 2 Three-phase motor [0036] 3 Low-pressure cylinder [0037] 4 High-pressure cylinder [0038] 5 Crankshaft [0039] 6 Frequency converter [0040] 7 Three-phase source [0041] 8 Control unit [0042] 9 Position sensor [0043] M.sub.L Load moment of piston compressor [0044] M.sub.M Torque of three-phase motor [0045] n Rotational speed [0046] n Average speed