EP2171274A1

EP2171274A1 - Stroke-regulated linear compressor

Info

Publication number: EP2171274A1
Application number: EP08774910A
Authority: EP
Inventors: Heinz Schmidt
Original assignee: BSH Bosch und Siemens Hausgeraete GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 2007-07-24
Filing date: 2008-07-09
Publication date: 2010-04-07
Also published as: WO2009013131A1; US20100183450A1; DE102007034293A1; CN101755124A; RU2010103529A

Abstract

A linear compressor having at least one electromagnet (7), at least one oscillating body (2) movably guided in an oscillating fashion in an alternating field of the electromagnet (7), at least one piston (2) that is connected to the oscillating body (2) and movable back and forth inside a cylinder (1), and a power supply circuit (19) for supplying the electromagnet (7) with an alternating current, characterized by a proximity sensor (14) for detecting whether or not the distance between the piston (2) and a face (15) of the cylinder (1) falls below a threshold value (e), and a control circuit (19) for detecting a period of time (?te?n) in which the distance between the piston (2) and the face (15) falls below the threshold value (e) and for regulating the amplitude and/or phase of the alternating current in the event of a deviation of the period of time (?te?n) from a positive target value.

Description

Lift-controlled linear compressor

The present invention relates to a linear compressor, in particular for compressing refrigerant in a refrigerator. Such a linear compressor conventionally comprises an electromagnet for generating an alternating magnetic field, a vibrating body reciprocated in the field of the electromagnet, and a piston reciprocally coupled to the vibrating body in a cylinder.

In a compressor having a piston driven by the rotation of a crankshaft, the stroke of the piston movement is determined by the orbit diameter of a point at which a piston rod engages the crankshaft. The dead volume of the compressor can therefore be made extremely small, without a striking of the piston is to be feared at an opposite end face of the pumping chamber. Minimizing the dead volume is important to achieve high efficiency of the compressor.

In a linear compressor is missing such a design-related limitation of the piston stroke. The piston stroke may vary depending on the working conditions of the compressor.

In order to operate a linear compressor with low dead volume and thereby avoid striking the piston to the opposite side of the pumping chamber, which would lead to the destruction of the compressor in the long run, an active control of the piston stroke is required. In the simplest case, it is possible to detect whether, in the course of its movement, the piston eventually falls below a predetermined minimum distance to the opposite side and, if so, downshifts the amplitude of the piston movement. However, the problem arises that no information about the amplitude of the piston movement can be obtained if it does not fall below the minimum distance to the opposite side, and that on the one hand, this minimum distance must be chosen small in order to allow operation with low dead volume, that on the other hand, the risk of abutment of the piston to the opposite side of the cylinder in case of Below the minimum distance, the greater the smaller the minimum distance is set.

Although it is also conceivable to continuously monitor the position of the piston in the course of its movement, so as to know at any time the amplitude of the oscillatory motion, regardless of whether this falls below a minimum distance or not. However, such continuous monitoring and the processing of the monitoring results requires a high expenditure on equipment, which would make such a compressor expensive.

Object of the present invention is to provide a linear compressor, which makes it possible with simple, inexpensive means to operate the compressor both with high efficiency and to prevent a striking of the piston to a front side opposite him reliably.

The object is achieved in that in a linear compressor with at least one electromagnet, at least one vibrating body oscillating in an alternating field of the electromagnet, at least one connected to the oscillating body, in a cylinder reciprocally movable piston and a power supply circuit for supplying the electromagnet with detects an AC sensor, a proximity sensor, whether the distance between the piston and an end face of the cylinder falls below a limit or not, and a control circuit detects a time interval in which the distance between the piston and the end face of the limit below the limit, and in case of deviation of these Period of a positive setpoint amplitude and / or phase of the alternating current regulates.

This invention is based on the recognition that the time period in which the limit value is undershot, in a clear relationship to the amplitude of the movement of the piston. In other words, it is sufficient to know this period of time in order to be able to calculate the amplitude. Conversely, if the maximum possible amplitude of the piston, that is, the distance between the piston and face of the cylinder in an equilibrium position of the piston, the limit for the distance between the piston and face and the oscillation period of the piston are set, one setpoint for the Time interval of falling below the distance limit value set, which corresponds to a desired amplitude of the piston movement. That is, by a suitable choice of the period of time, the piston movement can be controlled so that it falls below the limit of the distance, but the piston still does not hit with certainty on the end face.

To prevent an abutment of the piston to the end face of the cylinder, the setpoint .DELTA.t _SO ιι should be less than

T _Λ 2 (L - ε)

-Cos - - π L, where ε is the limit of the distance between the piston and the end face, T is the oscillation period of the oscillating body or the piston and L is the distance between the end face and the piston in a rest position of the piston.

The smaller the target value At is _selected n, the more responsive the period .DELTA.t, in which the limit value is below the distance ε, to a change in the oscillation amplitude, ie the more exact, the oscillation amplitude can be regulated. Therefore, preferably, the target value At _{80N is} smaller than _0.15T .

On the other hand, the nominal value Dtsoll should also not be too close to 0, since otherwise, in the event of a slight decrease in the oscillation amplitude, no drop below the limit value ε more will be detected at all and thus no measurement of the amplitude will be possible. Therefore, the setpoint At _{80H is} preferably selected larger than _0.02T .

Corresponding considerations apply to the limit value ε itself. On the one hand, this should be small in order to allow a precise inference to the amplitude of the piston movement. Therefore, preferably, the limit is set smaller than 1/10 of the distance between the end face and the piston in a rest position of the piston.

On the other hand, too small a value of ε causes an increase in the oscillation amplitude under certain circumstances can not be countered in time and it comes to hitting the piston to the face. Therefore, the threshold ε is preferably set greater than 1/50 of said distance. - A -

In order not to influence the piston movement, a non-contact sensor is preferably used as the proximity sensor, in particular an inductive switch.

Further features of the invention will become apparent from the following description of embodiments with reference to the accompanying figures. Show it:

1 shows a schematic section through a linear compressor according to a first

Embodiment of the invention;

FIG. 2 shows the time profile of the piston movement and of a proximity sensor signal derived therefrom; FIG.

3 shows the relationship between the duty cycle of the proximity sensor signal and the amplitude of the piston movement. and

Fig. 4 is an analogous to Fig. 1 section through a linear compressor according to a second embodiment of the invention.

The illustrated in Fig. 1 linear compressor comprises a cylindrical tube 1, which is closed at one end by an end face 15, and an oscillatingly received in the tube 1 movably piston 2. The piston 2 is cup-shaped, wherein a bottom of the cup of the End face 15 facing end face 4 of the piston forms. A wall 6 of the cup is at least partially formed by a permanent magnet which interacts with an alternating magnetic field generated by a coil 7 to drive a reciprocating motion of the piston 2. The coil 7 is shown here by way of example as an annular coil extending around the tube 1; Various other coil arrangements are known in the field of linear compressors and also suitable in the context of the present invention. There are also coil arrangements possible, which can also drive the piston 2, if it consists only of a ferromagnetic, but not permanently magnetized material.

Through the end face 15 extend, each provided with check valves 10, an inlet 14 and an outlet 13 for a gas to be compressed, for example a refrigerant, if the Compressor is used in a refrigerator, in particular a household refrigerator.

An inductive proximity switch 17 is here formed by a tightly around the made of non-ferromagnetic material existing tube 1 around coil. The proximity switch 17 is arranged at a small distance from the end face 15 to detect the end face 4 of the piston 2, as soon as and as long as their distance from the end face 15 falls below a specified by the placement of the proximity switch 17 limit ε. The output signal of the proximity switch 17 is thus a sequence of rectangular pulses whose period enstspricht the period of piston movement, wherein the duration of each pulse _eιn .DELTA.t is the time interval in which the limit value is exceeded ε.

Other types of proximity switches are also useful in the invention; such as e.g. In particular, when the piston of the compressor of a interacting with the alternating magnetic field of the coil 7 oscillating body not shown in Fig. 1, are fused in a component, but the vibrating body is arranged outside of the tube 1 and connected to the piston, a light barrier, the detects a part of the oscillating body, serve as a proximity switch.

A control circuit 19 receives the output of the proximity switch 17 and controls based on this output signal, as will be described in more detail later, an alternating current, with which it acts on the coil 7.

Fig. 2 illustrates the time course of the movement of the piston 2 and the resulting output signal of the proximity switch 17. The abscissa of the graph, the time is plotted on the left ordinate, the displacement of the piston with respect to an equilibrium position denoted by 0 and at the right ordinate the output signal level of the proximity switch 17. The movement of the piston follows a cosine curve 18. When the piston 2 is in the equilibrium position, the distance between the piston 2 and the end face 15 is 1 cm; that is, the maximum amplitude of the piston movement is 2 cm. A dashed line at a distance x _s of 0.95 cm corresponds to the detection threshold of the proximity switch 17; If the piston 2 is beyond this limit, then the output signal of the proximity switch has 17 the value 1; otherwise it is O. It can be shown that for the amplitude 1 _{stroke of} a harmonic oscillation applies:

where tei _n the duration of a pulse of the output signal of the proximity switch 17 and T is the period of piston movement.

If one assumes that 1 _{hUb is to be} smaller than the maximum amplitude L (here L = 2 cm) of the piston movement, at which the piston 2 touches the end face 15 at the reversal point of its movement, then the above formula results for the pulse duration t _ein the output signal of the proximity switch 17 the request

The relationship between the duty cycle t _eιn / T of the proximity _switch output signal and the associated oscillation amplitude of the piston 2 is shown in Fig. 3. An upper area of the diagram above an amplitude of 2 cm is shown hatched to indicate that this area may not be reached in practice, otherwise the piston 2 would strike the end face 15. If the amplitude of the oscillation is smaller than 2x _s = 1, 9 cm, the proximity switch 17 does not respond, and the duty cycle is 0. Therefore, permissible values of the duty ratio are in an interval of 0 to 0.1.

It can be seen that with an amplitude of the oscillation just over 2x _s, the duty cycle t _eιn / T varies very greatly with the amplitude, while the amplitude of the dependence of the duty cycle t _eιn / T decreases towards greater amplitudes. This means that the most accurate amplitude measurement is possible if it is just above the detection limit of 2x _s . Therefore, it makes sense to make the distance ε between the detection limit of the proximity switch 17 and the end face 15 small, in the present case 0.05 cm. The duty cycle can then reach a maximum value of 0.1; The closer to this value the compressor is operated, the higher is its efficiency, but the higher is the risk that due to a Unexpected amplitude fluctuation of the piston 2 abuts the end face 15. In order to avoid this, the control circuit 19 regulates the amplitude and / or period of an alternating current fed into the coil 7 on the basis of the output signal of the proximity switch 17 and a predetermined desired value for the duty cycle of this output signal, here between 0 and 0.1, for example 0 , 05, lies. If the control circuit 19 determines that the duty cycle exceeds the setpoint value, it reduces the amplitude of the alternating current fed into the coil 7, or detunes its frequency against the resonant frequency of the piston 2 so as to reduce its amplitude of movement. If it falls below the setpoint value, it increases the amplitude of the alternating current or reduces the deviation between its frequency and the resonant frequency of the piston 2, in order to bring about more efficient vibration excitation.

As shown in Fig. 4, the principle of the invention is also applicable to a linear compressor with two counter-rotating pistons 2 |, 2 _r transferable. In the arrangement shown here, the longitudinal ends of the cylindrical tube 1 each form inlets 14 for gas to be compressed, and through valves 9 formed in the end faces 4 of the opposing pistons 2, 2 _r , the gas passes into that of the tube 1 and the piston 2 |, 2 _r limited pumping chamber 5. In a center plane shown as a dashed line through the wall of the tube 1 extending holes 11 lead to an outlet 13th

In this embodiment, in each case the end face 4 of one of the pistons 2 _h 2 _r corresponds to the end face 15 of the compressor of FIG. 1, to which the end face 4 of the respective other piston 2 _r can not strike. To monitor the piston movement are on both sides of the median plane at a distance ε from this proximity switch 17 _h 17 _r arranged. A control circuit 19 acts on each coil 7 _h 7 _r with mutually in-phase AC currents I ₁ , I ₁ -. In this case, it regulates the amplitude of each alternating current I ₁ , I ₁ -as described above on the basis of the pulse duty factor t _e I _n / T of the output signal of the respectively assigned proximity switch 17 ₁ , 17 _r . By controlling the vibration amplitudes of both pistons 2 |, 2 _r so that they barely reach the center plane, safe operation with high efficiency is possible.

Claims

claims

1. Linear compressor with at least one electromagnet (7), at least one in an alternating field of the electromagnet (7) oscillating movably guided oscillating body (2), at least one with the oscillating body (2) connected in a cylinder (1) reciprocally movable piston (2) and a power supply circuit (19) for supplying the electromagnet (7) with an alternating current, characterized by a proximity sensor (14) for detecting whether the distance between the piston (2) and an end face (15) of the cylinder (1) a limit (ε) falls below or not, and a

_{Control circuit} (19) for detecting a period of time (Δt _eιn ), in which the distance between the piston (2) and the end face (15) below the limit (ε) and for regulating the amplitude and / or phase of the alternating current in the event of a deviation the period (.DELTA.t _ein ) of a positive setpoint.

2. A linear compressor according to claim 1, characterized in that the setpoint is less than -cos ^"1 -, wherein ε the limit, T the oscillation period π L of the piston (2) and L, the distance between the end face (15) and the piston (2) is in a rest position of the piston (2).

3. A linear compressor according to claim 1 or 2, characterized in that the desired value is less than 0.15 T.

4. A linear compressor according to one of the preceding claims, characterized in that the desired value is greater than 0.02 T.

5. A linear compressor according to one of the preceding claims, characterized in that the limit value (ε) is less than one tenth of the distance between the end face (15) and the piston (2) in a rest position of

Piston (2) is.

6. A linear compressor according to one of the preceding claims, characterized in that the limit value (ε) is greater than one fiftieth of the distance between the end face (15) and the piston (2) in a rest position of the piston (2).

7. A linear compressor according to one of the preceding claims, characterized in that the proximity sensor (17) is a non-contact sensor.

8. A linear compressor according to claim 7, characterized in that the sensor is an inductive switch (17).