U.S. patent application number 10/846572 was filed with the patent office on 2004-11-18 for method for limiting power of a multi-stage compressor and a compressor for carrying out the method.
Invention is credited to Folchert, Uwe.
Application Number | 20040228737 10/846572 |
Document ID | / |
Family ID | 33305209 |
Filed Date | 2004-11-18 |
United States Patent
Application |
20040228737 |
Kind Code |
A1 |
Folchert, Uwe |
November 18, 2004 |
Method for limiting power of a multi-stage compressor and a
compressor for carrying out the method
Abstract
Known compressors are matched to a predetermined power range and
therefore cannot supply consumers of a closed air supply system as
well as an external consumer with an adequate quantity of air. The
invention is directed to a method for limiting the power of a
multi-stage compressor wherein at least one compressor stage is
switched off when a predetermined power limit is reached. In this
way, the lowest compressor stage can be so selected that the
external consumer obtains an adequate volume flow. The compressor
for the method includes a bypass line (22) which bypasses the inlet
valve (19) of a low-pressure chamber (11) and thereby connects the
low-pressure chamber (11) to its upstream intake space (16). A
controllable control valve (23) is disposed in the bypass line (22)
and realizes the connection of the low-pressure chamber (11) to the
intake space (16) at a predetermined opening pressure.
Inventors: |
Folchert, Uwe; (Lauenau,
DE) |
Correspondence
Address: |
Walter Ottesen
Patent Attorney
P.O. Box 4026
Gaithersburg
MD
20885-4026
US
|
Family ID: |
33305209 |
Appl. No.: |
10/846572 |
Filed: |
May 17, 2004 |
Current U.S.
Class: |
417/53 ; 417/415;
417/440 |
Current CPC
Class: |
F04B 49/24 20130101;
F04B 25/02 20130101; F04B 25/005 20130101 |
Class at
Publication: |
417/053 ;
417/415; 417/440 |
International
Class: |
F04B 001/00; F04B
017/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2003 |
DE |
103 21 771.1 |
Claims
What is claimed is:
1. A method for limiting power of a compressor which compresses an
air flow in at least two compression stages, the method comprising
the step of causing the pressure in one of said compression stages
to be adapted or equalized to the pressure in the other one of said
compression stages when a predetermined power limit of said
compressor is reached.
2. The method of claim 1, wherein the equalization of pressures in
said compression stages is initiated: pneumatically by the pressure
in an intake space; by loading pressure of a consumer supplied by
said compressor; or, electrically because of the loading of the
on-board electrical system; or, a requirement of the control
speed.
3. The method of claim 1, wherein the pressure in said two
compression stages is continuously equalized.
4. The method of claim 1, wherein the piston displacement of the
one compression stage is designed for the required volume flow of a
consumer and the power of all non-pressure-compensated compression
stages is matched to the power limit of the electric drive.
5. A multi-stage compressor comprising: a compressor housing; a
stepped piston disposed in said housing; said compressor housing
and said stepped piston conjointly defining a first low-pressure
chamber, a high-pressure chamber and a second low-pressure chamber;
drive means for driving said stepped piston in oscillation; an
inlet valve for connecting said first low-pressure chamber to said
second low-pressure chamber; an outlet valve for connecting said
high-pressure chamber to a consumer; an overflow valve for
connecting said first low-pressure chamber and said high-pressure
chamber to each other; a bypass line connecting said first
low-pressure chamber to said second low-pressure chamber so as to
bypass said inlet valve; and, a controllable control valve disposed
in said bypass line and said control valve opening in a direction
toward said second low-pressure chamber.
6. The multi-stage compressor of claim 5, wherein said second
low-pressure chamber is an intake space in said compressor housing;
and, said first low-pressure chamber and said high-pressure chamber
are part of respective first and second compression stages,
respectively.
7. The multi-stage compressor of claim 6, wherein said driver means
is an electric drive; and, said control valve is set at an opening
pressure which adjusts the power capacity of said compressor to the
maximum power limit of said electric drive.
8. The multi-stage compressor of claim 6, further comprising an
outlet connection leading to said consumer; and, wherein said
control valve includes a pneumatic control unit connected to either
said intake space or said outlet connection.
9. The multi-stage compressor of claim 6, wherein said drive means
is an electric drive; and, said control valve includes an electric
control unit which is connected to the power control of said
electric drive.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority of German patent
application no. 103 21 771.1, filed May 15, 2003, the entire
content of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a method for limiting the power of
a compressor which compresses an airflow in at least two
compression stages.
BACKGROUND OF THE INVENTION
[0003] As a rule, a corresponding air supply system is designed as
a closed loop and comprises primarily the following: several air
spring damping units, for example, for supporting the bodywork; one
or several pressurized air stores; several control units assembled
to a valve block; and, a multi-stage compressor having an air
drying unit. The multi-stage compressor has the task of moving
compressed air from individual air spring damping units into other
air spring damping units and moving air out of the air spring
damping units into the pressurized-air store or in the opposite
direction from the pressurized-air store to the air spring damping
units or even filling the pressurized-air stores with fresh air
from the atmosphere. This multi-stage compressor is often also
utilized to supply one or several consumers with pressurized air.
The consumers lie outside of the closed loop. For example, tires
can be filled with air or a driver's seat can be adjusted. For this
purpose, fresh air from the atmosphere is utilized and not the
already compressed and dried air from the pressurized-air
store.
[0004] One such multi-stage compressor with two compressor stages
is disclosed in German patent publication 197 15 291. This
compressor comprises a compressor housing wherein a cylindrical
low-pressure chamber having a larger diameter and a high-pressure
chamber having a smaller diameter are configured. A piston unit
having a larger low-pressure piston and a smaller high-pressure
piston is mounted in the compressor housing. The low-pressure
piston and the high-pressure piston are configured as one piece via
a piston rod. The low-pressure chamber has an inlet valve and the
high-pressure chamber has an outlet valve and both pressure
chambers are connected to each other via an overflow channel. A
shut-off valve is mounted in the overflow channel and opens in the
direction toward the high-pressure chamber. The compressor housing
is configured as a crankcase in the region of the piston rod. In
this region, an electrically-operated crank gearing is disposed
which engages the piston unit. The crankcase is, however, also
equipped with an intake space which is connected at the input end
to a feed connection for connecting to the pressurized-air store of
the air supply system or to the atmosphere and, on the other hand,
has a connection to the low-pressure chamber via the inlet
valve.
[0005] The two-stage compressor is so configured that the power
take-up of both compressor stages is matched to the power output of
the electric drive unit so that the two-stage compressor has only a
limited piston displacement. This limited piston displacement,
however, leads to the situation that the compressor, at a low
prepressure, produces only a small compressor flow which, as a
rule, is not sufficient for supplying an external consumer. This is
always the case when the compressor inducts its air from the
atmosphere. This greatly limits the area of application of the
compressor.
SUMMARY OF THE INVENTION
[0006] It is an object of the invention to limit the power of a
multi-stage compressor in its upper power range to a predetermined
power limit. It is also an object of the invention to provide a
multi-stage compressor which is suitable for supplying different
consumers.
[0007] The method of the invention is for limiting power of a
compressor which compresses an air flow in at least two compression
stages. The method includes the step of causing the pressure in one
of the compression stages to be adapted or equalized to the
pressure in the other one of the compression stages when a
predetermined power limit of the compressor is reached.
[0008] The method and compressor of the invention eliminate the
above-mentioned disadvantages of the state of the art.
[0009] The method of the invention especially affords the advantage
that now a compressor can be utilized with any desired power
capacity without exceeding the power limit of the electric drive.
This same advantage is afforded by the compressor of the invention.
This saves a complex matching of the power ranges of the electric
drive and of the compressor.
[0010] Now there is the possibility to intentionally select a
compressor which, for example, is over dimensioned relative to the
power limit of an electric drive so that, in the lower power range
of the compressor, a volume flow adequate for the supply of an
external consumer can be generated and without the danger that the
power is exceeded. This expands the area of use of the compressor
because now, with the same compressor, all consumers of a closed
air supply system as well as consumers, which lie outside of the
closed air loop, can be supplied.
[0011] These advantages are realized with a relatively low level of
technical complexity. Only a bypass line is needed between the
compressor stage, which is to be switched off, and the upstream
low-pressure chamber in which a simple controllable pressure valve
is mounted.
[0012] It is also an advantage that the pressure valve is
controllable in dependence upon different parameters because, in
this way, the area of application is expanded. It is also an
advantage when the pressure valve is designed as a control valve
because then, the pressure valve opens continuously and the
transition from the two-stage or multi-stage to a single-stage
operation takes place continuously.
[0013] It is also an advantage that the multi-stage compressor can
have two and more compressor stages which, in turn, makes possible
a wide area of application.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention will now be described with reference to the
drawings wherein:
[0015] FIG. 1 shows a schematic of a two-stage compressor;
[0016] FIG. 2 is a schematic of a control valve mounted in the
compressor;
[0017] FIG. 3 is a schematic showing the compressor equipped with
an electrically controlled control valve; and,
[0018] FIG. 4 is a schematic showing the compressor equipped with a
pneumatically controlled control valve.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0019] The two-stage compressor comprises a compressor housing 1
which is closed pressure-tight at its ends with a larger housing
cover 2 and a smaller housing cover 3. A through interior space 4
is formed within the compressor housing 1 and this space is stepped
with respect to its diameter and, in this way, defines a
cylindrical hollow space 5 and a cylindrical hollow space 6. The
hollow space 5 is greater in diameter and the hollow space 6 is
smaller in diameter. Both cylindrical hollow spaces 5 and 6 are
arranged along a common axis. A stepped piston 7 with a larger
low-pressure piston 8, a smaller high-pressure piston 9 and a
common piston rod 10 is disposed in the through inner space 4 of
the compressor housing 1. The larger cylindrical hollow space 5 and
the low-pressure piston 8 form a low-pressure chamber 11 having a
greater piston displacement and the smaller cylindrical hollow
space 6 and the high-pressure piston 9 form a high-pressure chamber
12 having a smaller piston displacement. The low-pressure chamber
11 is configured as a first compressor stage and the high-pressure
chamber 12 is configured as a second compressor stage. Both
pressure chambers 11 and 12 are functionally connected via an axial
overflow channel 13 which is disposed in the stepped piston 7 and
extends completely through the piston rod 10.
[0020] The stepped piston 7 in combination with the inner space 4
of the compressor housing 1 forms a free space between the
low-pressure piston 8 and the high-pressure piston 9. This free
space accommodates a crank gear 14. The stepped piston 7 is
connected to an electric drive unit 15 via this crank gear 14 so
that the stepped piston 7 is configured to be axially displaceable
in the low-pressure chamber 11 and, in the same manner, in the
high-pressure chamber 12. In this way, the low-pressure chamber 11
and the high-pressure chamber 12 are changeable with respect to
their volumes.
[0021] The free space, which is disposed between the low-pressure
piston 9 and the high-pressure piston 10, is configured as an
intake space 16 closeable pressure-tight to the outside. The intake
space 16 can be connected at the input end via a directional valve
(not shown) either to a pressurized-air store or to the atmosphere.
The intake space 16, the low-pressure chamber 11 and the
high-pressure chamber 12 are connected to each other in a special
way. For this purpose, the compressor has an inlet connection 17
which leads to the intake space 16. The intake space 16 is
connected via an inlet valve 19 to the low-pressure chamber 11. The
inlet valve 19 is mounted in the low-pressure piston 8 and opens in
flow direction to the low-pressure chamber 11 and closes
pressure-tight in the opposite flow direction. The inlet valve 19
is so designed that it already opens in response to a low opening
pressure.
[0022] The overflow channel 13 is disposed between the low-pressure
chamber 11 and the high-pressure chamber 12. An overflow valve 20
is mounted in the overflow channel 13 and this valve opens in flow
direction toward the high-pressure chamber 12 at a slight pressure
difference and closes pressure-tight in the opposite direction.
Furthermore, a spring-biased outlet valve 21 is disposed in the
high-pressure chamber 12. The outlet valve 21 is accommodated in
the smaller housing cover 3 and connects the high-pressure chamber
12 and therefore the second compressor stage to the outlet
connection 18 leading to the consumer 48. The outlet valve 21 opens
at a predetermined opening pressure in the flow direction toward
the outlet connection 18 and closes pressure-tight in the opposite
direction.
[0023] According to the invention, the low-pressure chamber 11 and
the intake space 16 are connected to each other via a bypass line
22 which bypasses the inlet valve 19 of the low-pressure chamber
11. A pressure valve 23 is disposed in this bypass line 22 and is
controlled by the pressure in the intake space 16. Correspondingly,
the pressure valve 23 has a spring-biased valve element 24 and a
pressure spring 25. The pressure spring 25 is so pretensioned that
the valve element 24 continuously or intermittently clears an
opening cross section in response to a predetermined pressure in
the intake space 16 and thereby connects the low-pressure chamber
11 and the intake space 16 to each other and leads to a pressure
equalization. To relieve pressure on the pressure valve 23, the
valve element 24 is connected to the atmosphere via a leakage
connection 26 at its spring-biased end. The compressor is designed
with respect to power so that the first compressor stage with its
low-pressure chamber 11 has a largest possible piston displacement
which is adequate, for example, for filling a tire. In contrast,
the second compressor stage has a piston displacement which, by
itself, is adequate with a single-stage compression to supply the
consumers of a closed air supply system with pressurized air. With
this division of power of the two compressor stages, the power
take-up capacity of the compressor lies above the maximum power
limit of the electric drive 15.
[0024] For the purpose of compressing an airflow, the rotating
movement of the electric drive unit 15 is converted by the crank
gear 14 into an oscillating movement of the stepped piston 7. In
this way, volume changes in the low-pressure chamber 11 and in the
high-pressure chamber 12 result which cause a lower pressure to
adjust in the low-pressure chamber 11 compared to the intake space
16 with an enlargement of the low-pressure chamber 11. This
underpressure causes the inlet valve 19 to open and air to flow
from the intake space 16 to the low-pressure chamber 11. Because of
the subsequent reversal of the direction of movement of the stepped
piston 7, there is a reduction of the volume in the low-pressure
chamber 11 and therefore there is a pressure increase of the air
enclosed therein. This pressure increase causes the inlet valve 19
of the low-pressure chamber 11 to close so that there is a first
stage of the compression of the enclosed air. For a predetermined
pressure, the overflow valve 20, which leads to the high-pressure
chamber 12, opens and the compressed pressurized air is displaced
from the low-pressure chamber 11 into the high-pressure chamber 12
with the continuing movement of the stepped piston 7. With the
reversal of the direction of movement of the stepped piston 7,
there is a pressure increase in the high-pressure chamber 12 at
which the overflow valve 20 closes and a second stage of the
compression of the compressed air is initiated. The outlet valve 21
opens at a predetermined pressure in the high-pressure chamber 12
and the compressed pressurized air reaches the consumer 48 via the
outlet connection 18.
[0025] For the supply of an external consumer, for example, of a
tire with air from the atmosphere or from a low-pressure
pressurized-air store, the pressure valve 23 in the bypass line 22
remains closed because the force, which originates from the
pressure in the intake space 16 and acts on one end of the valve
element 24, is less than the force of the pretensioned pressure
spring 25 which acts on the other end of the valve element 24. The
compression of the inducted air then takes place in the manner
described in two compression stages. The relatively high piston
displacement in the first compressor stage makes a volume flow
possible which is adequate for filling the tire, and the low
pressure in both compressor stages keeps the power take-up of the
compressor within the power range of the electric drive.
[0026] For supplying the consumers with pressurized air from a
pressurized-air store, an intake pressure adjusts in the intake
space 16, which corresponds to the pressure in the pressurized-air
store and is higher than the atmospheric pressure. This intake
pressure propagates likewise via the bypass line 22 and loads the
valve element 24 of the pressure valve 23 against the force of the
pressure spring 25. The pressure valve 23 is adjusted with a
predetermined opening pressure. If the intake pressure in the
intake space 16 remains below the opening pressure adjusted at the
pressure valve 23, then the pressure valve 23 remains closed and
the compressor operates with both compressor stages as described
above. If the intake pressure reaches the opening pressure adjusted
at the pressure valve 23, then the pressure valve 23 opens
continuously or intermittently and connects both line connections
at the pressure valve 23 and thereby the low-pressure chamber 11
and the intake space 16. For this reason, there is a continuous or
intermittent pressure equalization between both chambers which is
maintained over the entire movement of the stepped piston 7. In
this way, the compression power in the low-pressure chamber 11
reduces continuously or intermittently until the first compression
stage is no longer participating in the compression power of the
compressor. For a fully opened pressure valve 23, the trapped air
quantity is displaced without a further increase in pressure from
the low-pressure chamber 11 into the high-pressure chamber 12, so
that the compressor now operates exclusively with the second
compressor stage. With the transition from the multi-stage to the
single-stage compression, the power capacity of the compressor is
throttled to a power value which does not exceed the power limit of
the electric drive 15.
[0027] Referring to FIG. 1, the equalization of pressures in the
compression stage can be initiated by the pressure in the intake
space or the load pressure of a consumer 48 supplied by the
compressor; or, electrically because of the loading of the on-board
electrical system 46; or, a requirement of the control speed as
detected in the ECU 44. Reference numeral 42 identifies an
operator-controlled element connected to the ECU 44.
[0028] According to another feature of the invention and referring
to FIG. 3, the control valve can be an electrically operated valve
32 which is connected via electric line 34 to the power control
(ECU) 30 of the electric drive 15.
[0029] According to still another feature of the invention and
referring to FIG. 4, the control valve can include a pneumatic
control unit 36 which is connected to the outlet connection 18 via
air line 38. Alternatively, the pneumatic control unit 36 can be
connected as shown by the broken line 40.
[0030] It is understood that the foregoing description is that of
the preferred embodiments of the invention and that various changes
and modifications may be made thereto without departing from the
spirit and scope of the invention as defined in the appended
claims.
* * * * *