U.S. patent application number 12/669796 was filed with the patent office on 2010-07-22 for stroke-regulated linear compressor.
This patent application is currently assigned to BSH BOSCH UND SIEMENS HAUSGERATE GMBH. Invention is credited to Heinz Schmidt.
Application Number | 20100183450 12/669796 |
Document ID | / |
Family ID | 39847066 |
Filed Date | 2010-07-22 |
United States Patent
Application |
20100183450 |
Kind Code |
A1 |
Schmidt; Heinz |
July 22, 2010 |
STROKE-REGULATED LINEAR COMPRESSOR
Abstract
A linear compressor having an electromagnet; an oscillating body
movably guided in an oscillating fashion in the alternating field
of the electromagnet; a cylinder; a piston connected to the
oscillating body and movable back and forth inside the cylinder; a
power supply circuit to supply the electromagnet with an
alternating current; a proximity sensor to detect whether a
distance between the piston and the end face of the cylinder falls
below a predetermined threshold value; and a control circuit to
detect a time period in which the distance between the piston and
the end face of the cylinder falls below the threshold value and to
regulate an amplitude and/or a phase of the alternating current if
the time period deviates from a positive setpoint value.
Inventors: |
Schmidt; Heinz; (Mohrendorf,
DE) |
Correspondence
Address: |
BSH HOME APPLIANCES CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
100 BOSCH BOULEVARD
NEW BERN
NC
28562
US
|
Assignee: |
BSH BOSCH UND SIEMENS HAUSGERATE
GMBH
Munich
DE
|
Family ID: |
39847066 |
Appl. No.: |
12/669796 |
Filed: |
July 9, 2008 |
PCT Filed: |
July 9, 2008 |
PCT NO: |
PCT/EP2008/058904 |
371 Date: |
January 20, 2010 |
Current U.S.
Class: |
417/212 ;
417/417 |
Current CPC
Class: |
F04B 2201/0201 20130101;
F04B 39/0016 20130101; F04B 35/045 20130101 |
Class at
Publication: |
417/212 ;
417/417 |
International
Class: |
F04B 49/00 20060101
F04B049/00; F04B 17/04 20060101 F04B017/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 24, 2007 |
DE |
10 2007 034 293.6 |
Claims
1-8. (canceled)
9. A linear compressor, comprising: an electromagnet having an
alternating field; an oscillating body movably guided in an
oscillating fashion in the alternating field of the electromagnet;
a cylinder having an end face; a piston connected to the
oscillating body and movable back and forth inside the cylinder; a
power supply circuit to supply the electromagnet with an
alternating current; a proximity sensor to detect whether a
distance between the piston and the end face of the cylinder falls
below a predetermined threshold value; and a control circuit to
detect a time period in which the distance between the piston and
the end face of the cylinder falls below the predetermined
threshold value and to regulate at least one of an amplitude and a
phase of the alternating current if the time period deviates from a
positive setpoint value.
10. The linear compressor of claim 9, wherein the setpoint value is
smaller than T .pi. cos - 1 2 ( L - ) L , ##EQU00004## wherein
.epsilon. is the predetermined threshold value, T is an oscillation
period of the piston and L is the distance between the end face of
the cylinder and the piston in a rest position of the piston.
11. The linear compressor of claim 10, wherein the setpoint value
is smaller than 0.15 T.
12. The linear compressor of claim 10, wherein the setpoint value
is greater than 0.02 T.
13. The linear compressor of claim 9, wherein the predetermined
threshold value is smaller than a tenth of the distance between the
end face of the cylinder and the piston in a rest position of the
piston.
14. The linear compressor of claim 9, wherein the predetermined
threshold value is greater than a fiftieth of the distance between
the end face and the piston in a rest position of the piston.
15. The linear compressor of claim 9, wherein the proximity sensor
is a contactless sensor.
16. The linear compressor as claimed in claim 15, wherein the
proximity sensor is an inductive switch.
Description
[0001] The present invention relates to a linear compressor, in
particular for compressing refrigerant in a refrigeration
appliance. Such a linear compressor conventionally comprises an
electromagnet for generating a magnetic alternating field, an
oscillating body, which is guided in such a manner that it can be
moved back and forth in the field of the electromagnet and a piston
that is coupled to the oscillating body and can be moved back and
forth in a cylinder.
[0002] With a compressor with a piston driven by the rotation of a
crankshaft the stroke of the piston movement is determined by the
path diameter of a point, at which a piston rod engages on the
crankshaft. The dead volume of the compressor can thus be made
extremely small without any fear of the piston striking an opposing
end side of the pump chamber. Minimizing the dead volume is
important to achieve a high level of reliability of the
compressor.
[0003] In the case of a linear compressor there is no such limiting
of the piston stroke due to structure. The piston stroke can vary
depending on the operating conditions of the compressor.
[0004] In order to operate a linear compressor with a small dead
volume and in the process prevent the piston striking the opposing
side of the pump chamber, which over time would lead to the
destruction of the compressor, active regulation of the piston
stroke is necessary. In the simplest instance it is possible to
detect whether in the course of its movement the piston is less
than a predetermined minimum distance from the opposing side at any
time and if so, to regulate down the amplitude of the piston
movement. The problem then arises that no information can be
obtained about the amplitude of the piston movement, if it does not
fall below the minimum distance from the opposing side and that
although this minimum distance has to be small to allow operation
with a small dead volume, the risk of the piston striking the
opposing side of the cylinder when it is at less than the minimum
distance is greater, the smaller the minimum distance is set to
be.
[0005] It is also possible to monitor the position of the piston
continuously during the course of its movement, in order to know
the amplitude of the oscillating movement at all times, regardless
of whether or not it falls below a minimum distance. Such
continuous monitoring and the processing of the monitoring results
require a high apparatus outlay however, making such a compressor
expensive.
[0006] The object of the present invention is to create a linear
compressor, which makes it possible with simple, economical means
to operate the compressor with a high level of efficiency and to
prevent the piston striking an opposing end side in a reliable
manner.
[0007] The object is achieved in that in the case of a linear
compressor having at least one electromagnet, at least one
oscillating body movably guided in an oscillating fashion in an
alternating field of the electromagnet, at least one piston that is
connected to the oscillating body and movable back and forth inside
a cylinder and a power supply circuit for supplying the
electromagnet with an alternating current, a proximity sensor
detects whether or not the distance between the piston and an end
face of the cylinder falls below a threshold value and a control
circuit detects a time period, in which the distance between the
piston and the end face falls below the threshold value and
regulates the amplitude and/or phase of the alternating current if
this time period deviates from a positive setpoint value.
[0008] This invention is based on the knowledge that the time
period in which the distance is below the threshold value is
uniquely related to the amplitude of the piston movement. In other
words it is sufficient to know this time period in order to be able
to calculate the amplitude. Conversely, if the maximum possible
amplitude of the piston, in other words the distance between the
piston and the end face of the cylinder in an equilibrium position
of the piston, the threshold value for the distance between the
piston and the end face and the oscillation period of the piston
are predetermined, it is possible to specify a setpoint value for
the time period for which the distance falls below the distance
threshold value, which corresponds to a desired amplitude of the
piston movement. In other words a suitable selection of the time
period allows the piston movement to be regulated so that it may
fall below the threshold value of the distance but the piston is
however certain not to strike the end face.
[0009] To prevent the piston striking the end face of the cylinder,
the setpoint value .DELTA.t.sub.soll should be less than
T .pi. cos - 1 2 ( L - ) L ##EQU00001##
where .epsilon. is the threshold value 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.
[0010] The smaller the setpoint value .DELTA.t.sub.soll, the
greater the degree to which the time period .DELTA.t, in which the
distance falls below the threshold value .epsilon., reacts to a
change in the oscillation amplitude, i.e. the more precisely it is
possible to regulate the oscillation amplitude. The setpoint value
.DELTA.t.sub.soll is therefore preferably less than 0.15 T.
[0011] On the other hand the setpoint value Dtsoll should also not
be too near to 0, as otherwise if there is a minor reduction of the
oscillation amplitude, a drop below the threshold value .epsilon.
is no longer detected and it is therefore no longer possible to
measure the amplitude. The setpoint value .DELTA.t.sub.soll should
therefore be preferably selected to be greater than 0.02 T.
[0012] Corresponding considerations apply to the threshold value
.epsilon. itself. On the one hand this should be small, to allow a
precise conclusion to be drawn about the amplitude of the piston
movement. The threshold value is therefore preferably selected to
be smaller than 1/10 of the distance between the end face and the
piston in a rest position of the piston.
[0013] On the other hand too small a value of .epsilon. means that
in some circumstances an increase in the oscillation amplitude
cannot be countered promptly and the piston strikes the end face.
The threshold value .epsilon. is therefore preferably greater than
1/50 of the abovementioned distance.
[0014] In order not to influence the piston movement a contactless
sensor is preferably used as the proximity sensor, in particular an
inductive switch.
[0015] Further features of the invention will emerge from the
description which follows of exemplary embodiments with reference
to the accompanying figures, in which:
[0016] FIG. 1 shows a schematic section through a linear compressor
according to a first embodiment of the invention;
[0017] FIG. 2 shows the temporal profile of the piston movement and
a proximity sensor signal derived therefrom;
[0018] FIG. 3 shows the relationship between the duty factor of the
proximity sensor signal and amplitude of the piston movement;
and
[0019] FIG. 4 shows a similar section to the one in FIG. 1 through
a linear compressor according to a second embodiment of the
invention.
[0020] The linear compressor shown in FIG. 1 comprises a
cylindrical pipe 1, which is closed off at one end by an end face
15, and a piston 2 held movably in an oscillating fashion in the
pipe 1. The piston 2 is configured as beaker-shaped, with a base of
the beaker forming an end side 4 of the piston facing the end face
15. A wall 6 of the beaker is formed at least partially by a
permanent magnet, which interacts with a magnetic alternating field
generated by a coil 7 to drive the back and forth movement of the
piston 2. The coil 7 is shown here by way of example as an annular
coil extending around the pipe 1; various other coil arrangements
are known in the field of the linear compressor and are also
suitable within the context of the present invention. Coil
arrangements are also possible, which can drive the piston 2 even
if it is only made of a ferromagnetic and not permanently
magnetized material.
[0021] Extending through the end face 15 and provided respectively
with nonreturn valves 10 are an inlet 14 and an outlet 13 for a gas
to be compressed, e.g. a refrigerant, if the compressor is employed
in a refrigeration unit, in particular a domestic refrigeration
appliance.
[0022] An inductive proximity switch 17 is formed here by a coil
positioned tightly around the pipe 1 which is made of a
non-ferromagnetic material. The proximity switch 17 is disposed a
short distance from the end face 15, in order to detect the end
side 4 of the piston 2 as soon and as long as its distance from the
end face 15 falls below a threshold value .epsilon. determined by
the positioning of the proximity switch 17. The output signal of
the proximity switch 17 is thus a sequence of rectangular pulses,
the period of which corresponds to the period of the piston
movement, the duration .DELTA.t.sub.ON of each pulse representing
the time period in which the distance falls below the threshold
value .epsilon..
[0023] Other types of proximity switch can also be used in the
context of the invention; for example in particular if the piston
of the compressor of an oscillating body interacting with the
magnetic alternating field of the coil is not fused in a component,
as shown in FIG. 1, but the oscillating body is disposed outside
the pipe 1 and connected to the piston, a light barrier, which
detects part of the oscillating body, can serve as the proximity
switch.
[0024] A control circuit 19 receives the output signal of the
proximity switch 17 and uses this output signal, as described in
more detail below, to regulate an alternating current, which it
applies to the coil 7.
[0025] FIG. 2 shows the temporal profile of the movement of the
piston 2 and the resulting output signal of the proximity switch
17. Time is plotted on the abscissa of the diagram with the
deflection of the piston in relation to an equilibrium position
shown as 0 on the left ordinate and the output signal level of the
proximity switch 17 on the right ordinate. 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; in other words the maximum amplitude of the piston
movement is 2 cm. A broken line at a distance x.sub.S of 0.95 cm
corresponds to the detection threshold of the proximity switch 17;
if the piston 2 is beyond this threshold, the output signal of the
proximity switch 17 has the value 1; otherwise it is 0. It can be
seen that the following applies for the amplitude 1.sub.hub of a
harmonic oscillation:
l Hub = 2 x S cos ( .pi. t Ein T ) ( 1 ) ##EQU00002##
where t.sub.ON is the duration of a pulse of the output signal of
the proximity switch 17 and T is the period of the piston
movement.
[0026] If we assume that 1.sub.hub should 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, the following requirement results from the above formula
for the pulse duration t.sub.ON of the output signal of the
proximity switch 17
t Ein < T .pi. cos - 1 2 ( L - ) L . ( 2 ) ##EQU00003##
[0027] The relationship between the duty factor t.sub.ON/T of the
proximity switch output signal and the associated oscillation
amplitude of the piston 2 is shown in FIG. 3. An upper region of
the diagram above an amplitude of 2 cm is shown hatched, to
indicate that this region in practice must not be reached, as
otherwise the piston 2 would strike the end face 15. If the
amplitude of the oscillation is smaller than 2x.sub.S=1.9 cm, the
proximity switch 17 does not respond and the duty factor is 0.
Permissible values of the duty factor are thus in an range from 0
to 0.1.
[0028] It can be seen that for an oscillation amplitude just over
2x.sub.S the duty factor t.sub.ON/T varies very significantly with
amplitude, while the dependency of the duty factor t.sub.ON/T on
amplitude decreases toward larger amplitudes. In other words the
most precise amplitude measurement is possible, if it is just above
the detection threshold of 2x.sub.S. It is therefore expedient to
make the distance .epsilon. between the detection threshold of the
proximity switch 17 and the end face 15 small, in the present
instance 0.05 cm. The duty factor can then as a maximum reach the
value 0.1; the closer to this value the compressor is operated, the
higher its level of efficiency but the higher also the risk of the
piston 2 striking the end face 15 due to an unforeseen amplitude
fluctuation. To avoid this, the control circuit 19 regulates the
amplitude and/or period of an alternating current fed into the coil
7 based on the output signal of the proximity switch 17 and a
predetermined setpoint value for the duty factor of this output
signal, which is between 0 and 0.1, for example around 0.05 here.
If the control circuit 19 determines that the duty factor exceeds
the setpoint value, it reduces the amplitude of the alternating
current fed into the coil 7 or pulls its frequency toward the
resonant frequency of the piston 2, in order thus to reduce its
movement amplitude. If the duty factor is 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, to produce more efficient oscillation excitation.
[0029] As shown in FIG. 4, the principle of the invention can also
be applied to a linear compressor with two pistons 2.sub.1, 2.sub.r
moved in a counter-rotating manner. With the arrangement shown here
the longitudinal ends of the cylindrical pipe 1 respectively form
inlets 14 for gas to be compressed and gas passes through valves 9
formed in the end faces 4 of the opposing pistons 2.sub.1, 2.sub.r
into the pump chamber 5 bounded by the pipe 1 and the pistons
2.sub.1, 2.sub.r. Holes 11 run in a center plane, shown as a broken
line, through the wall of the pipe 1 and lead to an outlet 13.
[0030] With this embodiment the end side 4 of one of the pistons
2.sub.1, 2.sub.r corresponds respectively to the end face 15 of the
compressor in FIG. 1, which the end side 4 of the respective other
piston 2.sub.r, 2.sub.1 must not strike. To monitor piston movement
proximity switches 17.sub.1, 17.sub.r are disposed on both sides of
the center plane at a distance .epsilon. from it. A control circuit
19 applies alternating currents I.sub.1, I.sub.r with mutually
identical phases to each coil 7.sub.1, 7.sub.r. In this process it
regulates the amplitude of each alternating current I.sub.1,
I.sub.r as described above based on the duty factor t.sub.ON/T of
the output signal of the respectively assigned proximity switch
17.sub.1, 17.sub.r. Regulating the oscillation amplitudes of both
pistons 2.sub.1, 2.sub.r such that they just fail to reach the
center plane allows reliable operation with a high level of
efficiency.
* * * * *