U.S. patent application number 10/524536 was filed with the patent office on 2005-11-17 for control method for controlling the gas flow in a compressor.
Invention is credited to Hedman, Mats.
Application Number | 20050254980 10/524536 |
Document ID | / |
Family ID | 20288702 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050254980 |
Kind Code |
A1 |
Hedman, Mats |
November 17, 2005 |
Control method for controlling the gas flow in a compressor
Abstract
A control method for controlling the gas flow by a compressor in
which a volume is expanded during an intake stroke and the intaken
volume of gas is compressed and taken out through a non return
valve (6) for outflow and/or an operable outlet valve (3) during an
evacuation stroke, and in which the compressor has a controllable
inlet valve (2) that is pneumatically, hydraulically or
electromagnetically operable and that is opened and closed upon
basis of a signal from a control system. The inlet valve (2) is
kept closed during at least a part of an intake stroke.
Inventors: |
Hedman, Mats; (Bavensvik,
SE) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Family ID: |
20288702 |
Appl. No.: |
10/524536 |
Filed: |
February 14, 2005 |
PCT Filed: |
August 12, 2003 |
PCT NO: |
PCT/SE03/01263 |
Current U.S.
Class: |
417/503 ;
417/283; 417/295; 417/297; 417/298; 417/439; 417/505 |
Current CPC
Class: |
F04B 49/24 20130101;
F04B 49/065 20130101 |
Class at
Publication: |
417/503 ;
417/283; 417/295; 417/297; 417/298; 417/439; 417/505 |
International
Class: |
F04B 049/00; F04B
039/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 13, 2002 |
SE |
020403-2 |
Claims
1. A control method for controlling the gas flow by a compressor in
which a volume is expanded during an intake stroke and the
introduced volume of gas is compressed and taken out through a non
return valve (6) for outflow and/or an operable outlet valve (3)
during an evacuation stroke, and in which the compressor has a
controllable inlet valve (2) that is pneumatically, hydraulically
or electromagnetically operable and that is opened and closed upon
basis of a signal from a control system, characterized in that the
inlet valve (2) is kept closed during at least a part of an intake
stroke.
2. A control method according to claim 1, characterized in that the
inlet valve (2) is kept closed during the whole intake stroke.
3. A control method according to claim 1, characterized in that the
frequency of cycles with closed intake stroke is varied between 0%
and 100% of the number of revolutions per minute in order to, at
the given number of revolutions per minute, deliver the amount of
the compressed gas required for the moment.
4. A control method according to claim 3, characterized in that,
between each cycle or each continuous series of cycles with closed
intake strokes, an equal amount of revolutions are performed.
5. A control method according to claim 1, characterized in that the
inlet valve (2) is closed upon transition, or after the transition,
from intake stroke to evacuation stroke.
6. A control method according to claim 1, characterized in that the
inlet of the compressor (1), besides the controllable inlet valve
(2), comprises a non return valve (13) for inflow, and that the
conduit for supply of gas to the latter is throttled down or closed
by means of a closure member (14) arranged by or upstream the non
return valve, by controlling the gas pressure in a tank (8)
associated to the compressor.
7. A control method according to claim 6, characterized in that the
closure member (14) is a controllable valve, which is opened and
closed upon basis of a signal from the control system.
8. A control method according to claim 1, characterized in that the
outlet of the compressor (1), apart from a non return valve (6) for
outflow, comprises a controllable outlet valve (3) which is
pneumatically, hydraulically or electro-magnetically operated, and
which opens and closes upon basis of a signal from the control
system.
9. A control method according to claim 1, characterized in that the
outlet valve (3) is opened as there is a pressure balance between
the gas to be evacuated and the gas on the opposite side of the
outlet valve (3), the latter being controlled by means of a sensor
(18) that registers the cylinder pressure that is compared to the
pressure in the tank registered by another sensor (9).
10. A control method according to claim 1, characterized in that a
conduit (7) that extends between the compressor (1) and the tank
(8) fulfills the need of pressurized gas between the compressor and
the equipment that will use the pressurized gas.
11. A control system, characterized in that it comprises a computer
program adapted for executing the control method according to claim
1.
12. A control method according to claim 2, characterized in that
the frequency of cycles with closed intake stroke is varied between
0% and 100% of the number of revolutions per minute in order to, at
the given number of revolutions per minute, deliver the amount of
the compressed gas required for the moment.
13. A control method according to claim 12, characterized in that,
between each cycle or each continuous series of cycles with closed
intake strokes, an equal amount of revolutions are performed.
Description
THE FIELD OF THE INVENTION
[0001] The present invention relates to a control method for
controlling the gas flow in a compressor in which a volume is
expanded during an intake stroke and an introduced volume of gas is
compressed and taken out through a non return valve for outflow
and/or an operable valve during an evacuation stroke, the
compressor having a controllable inlet valve that is pneumatically,
hydraulically or electromagnetically operated and that is opened
and closed upon basis of a signal from a control system.
[0002] This type of compressor, of which there are a plurality of
embodiments, but where the piston compressor is the most common
one, is often called displacement compressor. In order to take
advantage of the invention, the compressor should have a
controllable inlet valve. However, it is preferred that the
compressor also has a non return valve for inflow that can be
turned off, and a controllable outlet valve. The invention provides
for a varying need of pressurized gas with a reduced energy
consumption and environment affection in relation to known
methods.
[0003] The invention is applicable to displacement compressors for
industrial use, for vehicles and vehicle engines, for fuel cells
etc.
[0004] The invention can only be put into practice by use of a
control system. The software of the control system is decisive for
its function. The software that is used for putting the invention
into practise can be applied as a part of a larger control system,
for example a system for engine operation.
[0005] As the piston compressor is the most common displacement
compressor, the invention will be described, by way of example,
outgoing from its implementation on a piston compressor.
THE BACKGROUND OF THE INVENTION
[0006] Displacement compressors, particularly piston compressors,
are normally operated with a constant and relatively low number of
revolutions per minute. Normally, the inlet valves and the outlet
valves are non return valves that have a restraining influence on
the gas flow at higher numbers of revolutions per minute.
[0007] The flow control is normally performed by letting the
compressor start when the pressure in a tank connected thereto
falls below a certain level and letting it stop when a certain
pressure level has been obtained. Frequent starts and stops will
result in a large wear and will be energy consuming.
[0008] According to another common type of control, the gas flow to
the non return valve for inflow is cut off by means of a closure
valve when a certain pressure in a tank connected to the compressor
is obtained, while the operation of the compressor is permitted to
continue with the cycles without any gas to compress. When the
pressure in the tank falls below a certain level the gas flow is
once again permitted.
[0009] When the need of pressurized gas is not very frequent, the
first type of control is the most economical one. When the need is
more frequent, the latter type is substantially more economical.
However, the closure/opening of the gas flow is relatively slow.
This means that a plurality of cycles without compression of any
gas will be performed also by the shortest possible cut off.
Moreover, a slow closure/opening will result in substantial flow
losses. Therefore, the tank and the compressor must be of larger
dimension than if the cut off of the gas flow to the compressor
could be performed so temporarily as one single cycle. Further, a
rapid closure/opening would reduce the flow losses.
[0010] The invention results in the gas flow not being restrained
as mentioned above in the case of non return valves, and that the
flow of air can be cut off/opened rapidly and can be cut off for
such a short period as one single cycle. Thereby, the energy
consumption and the environmental affection can be reduced in
relation to prior methods, as well as the size of the compressor
and the tank.
THE OBJECT OF THE INVENTION
[0011] The object of the invention is to provide a method of
controlling the gas flow in a compressor and to avoid the above
drawbacks and to provide for varying need of pressurized gas with a
more rapid control and with a more even pressure level and, at the
same time, a reduced energy consumption and environmental affection
in relation to methods of prior art.
SUMMARY OF THE INVENTION
[0012] The object of the invention is achieved by means of a
compressor in which a volume is expanded during an intake stroke
and in which the introduced volume of gas is compressed and taken
out through a non return valve for outflow during an evacuation
stroke, the compressor having a controllable inlet valve that is
pneumatically, hydraulically or electromagnetically operable and
that is opened and closed on basis of a signal from a control
system, the control method being characterized in that the inlet
valve is kept closed during at least a part of an intake stroke.
Further features are shown in the following description and in the
patent claims.
[0013] Here, compressor is referred to as a displacement
compressor, and particularly a piston compressor.
[0014] A controllable inlet valve, a controllable outlet valve, a
non return valve for inflow, a non return valve for outflow and
similar expressions are intended to include also other possible
embodiments that uses a larger number of valves of said types of
valves.
[0015] It is also assumed that a compressor can be constituted by a
plurality of compressors, for example a plural cylinder piston
compressor by which each cylinder defines an individual piston
compressor and by which each individual compressor operates in
accordance with the description and the patent claims.
[0016] A common feature for displacement compressors is that a
volume is expanded during an intake stroke. When the volume is
expanded, it is filled with gas, such as air, that flows in through
a valve, normally a non return valve. At the end of the intake
stroke, a volume that encloses the introduced gas is compressed,
and the gas is evacuated through a valve, normally a non return
valve. The piston compressor is the most common displacement
compressor, and in the piston compressor the volume which is
expanded and the volume which is compressed is the same. There are
also, for example, rotating displacement compressors where the
volume that is expanded is not the same as the volume that is
compressed. In a piston compressor, a piston moves inside a
cylinder between two dead points, referred to as the upper dead
point and the lower dead point respectively. The movement of the
piston from the upper dead point to the lower dead point results in
a volume being expanded in an intake stroke, as expressed in the
preamble of patent claim 1. The piston movement from the lower dead
point to the upper dead point results in the introduced volume of
gas being compressed and taken out through a non return valve for
outflow during an evacuation stroke, as also expressed in the
preamble.
[0017] Normally, there is a non return valve for inflow and a non
return valve for outflow located at the upper dead point. When the
piston, during an intake stroke, moves from the upper dead point
towards the lower dead point, a volume is expanded between the
piston and the upper dead point, said volume being filled with gas
during the movement through a non return valve for the inflow. From
the lower dead point the piston moves, during an evacuation stroke,
towards the upper dead point, the volume between the piston and the
upper dead point being compressed. Initially, the enclosed gas has
nowhere to go and, accordingly, the pressure increases in the
volume that gets increasingly smaller. When the pressure in the
enclosed gas is sufficiently higher than the pressure on the other
side of the non return valve for outflow, the latter is opened and
the gas is evacuated during the continued movement of the piston
towards the upper dead point. An intake stroke followed by an
evacuation stroke is here referred to as a cycle. A complete cycle
is executed during a complete compressor shaft revolution.
[0018] With reference to the above description of the background,
important advantages are achieved if a cut off can take part for
such a brief period as one single cycle. With the aid of a
controllable valve according to the initial definition in the
description, one single intake stroke can be executed with a closed
inlet valve, and this means that no gas is introduced during the
intake stroke. This automatically results in no gas being evacuated
during the evacuation stroke. Accordingly, the gas flow is cut off
during one cycle. An intake stroke executed with a closed inlet
valve is referred to as a closed intake stroke.
[0019] In order to be able to put the invented method into
practice, controllable valves are required, primarily a
controllable inlet valve. However, it is preferred with an
embodiment with a controllable outlet valve apart from the already
present non return valve for outflow. Controllable valves permit a
substantially larger flow of air than is possible with contemporary
non return valves in compressors of today. Thereby, a substantially
higher number of revolutions per minute can be permitted, making it
possible to use smaller piston compressors than today. By also
applying a non return valve for inflow together with a gas conduit
that can be closed, for example with the aid of mechanical
technique based on the fact that a certain quantity of air of a
certain pressure has been obtained, a substantial advantage of
having an aid function is obtained. An aid function that will work
even if the controllable inlet valve and/or outlet valve would have
a breakdown. By the use of a controllable inlet valve, the latter
can be closed during a complete intake stroke, here referred to as
a closed intake stroke, but also during a part of the intake
stroke, this part being variable from cycle to cycle. Accordingly,
the method according to the present invention relies on a closure
of the inlet valve during at least a part of the intake stroke for
the purpose of controlling the outflow volume during the evacuation
stroke. Further, it is also evident that the closure takes place
during the sequence by which an ordinary intake stroke normally
would exist, and that the compressor operates with a plurality of
subsequent cycles of intake strokes and evacuation strokes.
[0020] By means of the characterizing control strategy of the
control method, namely to provide for the amount of compressed gas
that is needed at each moment by the use of a frequency of cycles
with closed intake stroke, in which the frequency varies between 0%
and 100% of the number of revolutions per minute, a significantly
economical operation is achieved. If, for example, the control
system chooses the frequency 0%, then no cycle with closed intake
stroke is performed, but the gas will be supplied each revolution,
and at the frequency of 100%, each cycle is performed with a closed
intake stroke, and at the frequency of 50% a cycle with a closed
intake stroke will be performed each second revolution, and at the
frequency of 20% a cycle with a closed intake stroke will be
performed each fifth revolution, and at the frequency of 10% a
cycle with a closed intake stroke will be performed each tenth
revolution. Accordingly, a cycle with a closed intake stroke can be
performed, for example, each second, each third, each fourth, each
fifth revolution etc. During the remaining cycles/revolutions, gas
is supplied during the intake stroke. At a frequency between 50%
and 100%, a cycle with a closed intake stroke will be directly
followed by one, two or more consecutive cycles, a series of
consecutive cycles, with closed intake stroke. At, for example, 80%
cycles with closed intake stroke, a suitable distribution would be
to have one single cycle with normal intake stroke after a
continuous series of four cycles with closed intake strokes, and
then another continuous series of four cycles with closed intake
strokes followed by another single cycle with normal intake stroke
etc. In order to keep the pressure level as even as possible in a
tank for pressurized gas that is associated to the compressor, and
in order to permit the tank to be as small as possible, the control
system should be characterized in that generally the same number of
revolutions between each cycle, or each continuous series of cycles
with closed intake strokes should be performed. The invention could
also be described as a way of providing for the immediate need of
compressed gas by using a frequency of cycles with a normal intake
stroke, resulting in the same effect.
[0021] Another characterizing control strategy of the control
method, that advantageously can be combined with the frequency
control that has been described above, is to provide for the
immediate need of compressed gas by the use of cycles where the
controllable valve is closed during a part of the intake stroke as
decided by the control system, somewhere along the piston path from
its upper dead point to its lower dead point. This part of the
intake stroke in question can be varied from cycle to cycle. This
advantageous possibility makes it possible to minimize a reservoir
for the storage of compressed gas or even to let the reservoir be
formed by the conduit that conducts the pressurized gas from the
compressor to the equipment in which the gas is to be used. The
possibility of having a minimum of storage space for the compressed
gas is a result of letting a varying consumption be followed by a
substantially simultaneously varying production of generally the
same quantity of pressurized gas as the quantity that is consumed
at a given moment.
[0022] Controllable inlet valves and, possibly, outlet valves
permit, thanks to substantially reduced flow losses, a
substantially increased flow capacity for a predetermined cubic
capacity, the latter being referred to as the inner volume of the
cylinder between the two dead points of the piston in a piston
compressor. This means that a piston compressor, for example, can
be connected to the engine shaft of a vehicle engine, and that the
number of revolutions per minute directly, or by means of gear
reduction, follow the number of revolutions per minute of the
engine. In the case of an embodiment comprising a vehicle, the term
gas should be substituted by air. The piston compressor may, for
example, be used for the production of pressurized air to the
engine combustion, for the purpose of operating controllable,
pneumatically operated valves for the engine and/or the compressor
itself, for air-assisted fuel injection, for the break system etc.
A characterizing feature is that, by high numbers of revolutions
per minute and a large need of compressed air, which is the case by
engine operation, the inlet valve can be closed after the piston
having reached the lower dead point, resulting in that a larger
amount of air to be compressed can be supplied in comparison to the
case in which the inlet valve closes before the piston reaches its
lower dead point. Another characterizing way of increasing the
capacity of the compressor upon engine operation is to connect its
conduit for air supply to an existing air conduit to the engine
with pressurized air produced by an exhaustion gas turbo or a screw
compressor. A connection downstream an existing intercooler would
be preferred. A connection to a vehicle engine conduit for air
supply, downstream the air filter and upstream any existing
throttle, is suitable, even if there is no equipment for
compressing the air, since the air has passed the air-cleaning
filter.
[0023] The aid function described above, particularly useful at
engine operation, is also a feature of the invention. It defines a
feature that results in a certain capacity for the production of
compressed air, or any other gas, always being at hand. The aid
function is, as has been mentioned, advantageous upon any breakdown
of any controllable valve. But it also results in the possibility
of immediately building up an air pressure to be used, for example,
for start up, by means of the electric start engine, of an engine
with air-assisted fuel injection if there is no remaining pressure
in the pressure reservoir or the conduit for the pressurized air.
The same applies if there, for example, are controllable valves
that are pneumatically operated. When there is a large flow
capacity in the non return valves for the inflow and the outflow
respectively and there is a controllable, pneumatically,
hydraulically or electromagnetically operated closure member
arranged by or upstream the non return valve for inflow, the aid
function principle is also a prerequisite for the execution of a
frequency of cycles with closed intake stroke, or cycles where the
controllable closure member is closed during a part of the intake
stroke in question, somewhere on the piston path from its upper
dead point to its lower dead point, said part being determined by
the control system.
[0024] As has been mentioned, the method also comprises an
embodiment in which the controllable valve for the outflow also is
pneumatically, hydraulically or electromagnetically operable. The
method is also characterized in that the controllable outlet valve
is opened in connection to a pressure balance being obtained
between the gas that is to be evacuated and the gas on the opposite
side of the outlet valve. It is important to avoid any contact
between the piston and the outlet valve, and therefore the
preferred embodiment is characterized in that the outlet valve is
opened in a direction from the cylinder, that is in the same
direction as the movement direction of the piston during
compression and evacuation. If the outlet valve is opened in the
opposite direction, that is towards the movement direction of the
piston, it has to close sufficiently early to avoid any piston
contact. In such cases, a combination of a controllable outlet
valve and a non return valve for the outflow of gas is
advantageous, and a feature, in order to be able to evacuate an
amount of compressed gas that otherwise would remain. A
sufficiently slight piston contact when a sufficiently small
distance remains to the complete closure of the outlet valve is,
however, not detrimental, but can be taken advantage of for a good
evacuation. However, this implies that the outlet valve is moved
along an access/a direction which is exactly the same as the one of
the piston.
[0025] From the above description and the following description it
is obvious that an electronically based control system with the
necessary sensors and other components, including a computer
program developed for the specific purpose, is an absolute
necessity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The invention shall now be described with reference to the
only FIG. 1, which shows an exemplifying, schematic picture of a
compressor with a piston.
DETAILED DESCRIPTION OF EN EMBODIMENT
[0027] FIG. 1 is an exemplifying, schematic picture that shows a
compressor cylinder with a-piston 1. The piston is under movement
during an intake stroke, and air (or any other gas) is flowing
through the open inlet valve 2. The inlet valve 2 and the closed
outlet valve 3 are constituted by controllable valves that are
pneumatically, hydraulically or electromagnetically operable. A
circuit 4 is used for operating the valves 2 and 3. A control unit
5 is operatively connected with the circuit 4 for signal control of
the circuit and the valves 2 and 3 that are connected to the
circuit. Air that is compressed is transported through the outlet
valve 3 and/or a non return valve for the outflow of gas 6 through
a conduit 7 to a tank 8. By means of a sensor 9 in the tank 8,
which is operatively connected to the control unit 5, the control
unit is provided with continuous information about the pressure in
the tank. A sensor 10, arranged at a graduated arc 12, mounted on
the compressor shaft 11 and operatively connected to the control
unit 5, delivers continuous information to the control unit for the
calculation of number of revolutions per minute and the piston
position in the cylinder 1. The control unit 5 determines when the
controllable valves 2 and 3 shall open or close. The compressor
shaft 11 is, for example, connected to an electric motor or to an
engine in a vehicle (connection not shown). Air supplied via the
inlet valve 2 may, preferably, be precompressed by means of, for
example, an exhaust gas turbine in a vehicle. Advantageously, air
for compression may be taken out downstream an intercooler
(connection not shown) that might be present in a vehicle. The non
return valve 6 for the outflow and a non return valve 13 for the
inflow, equipped with a closure member 14, establishes an aid
function. Through a conduit 15 the closure member 14 is connected
to the tank 8. If the pressure in the tank 8 decreases below a
predetermined level, the closure member 14 opens, for example by
the action of a mechanical spring 16, such that air to be
compressed is supplied through the non return valve 13 for the
inflow. This aid function means that pressurized air can be reduced
to a certain amount while the controllable inlet valve 2 is closed
or out of function. This is important in order to make it possible
to, at least to some extent, propel a vehicle by means of
air-assisted members for, for example, fuel injection or brake
systems. If, for example, the controllable valves 2 and 3 are
constituted by pneumatically operated valves, and the pressure in
the tank 8 is too low for the activation of said valves, the aid
function shall be provided such that the pressure in the tank will
be sufficient for the activation of the valves 2 and 3 being
obtained by means of the spring 16 before the closure member 14
associated to the non return valve 13 for the inflow closes. When
the controllable valves 2 and 3 are pneumatically operated valves,
there is a conduit for the air (not shown) between the valves and
the tank 8. Pressurized air for, for example, the aid system of a
vehicle is taken from the tank 8 through a connection 17. For the
described aid function only small non return valves 13, 6 are
required. The need of a large flow capacity is fulfilled by the
controllable valves 2, 3. During compression strokes when the non
return valve 13 for the inflow is closed through the action of the
closure member 14, the outlet valve 3 shall open upon pressure
balance between the air in the tank 8 and the air that is
compressed in the cylinder 1. A sensor 18, operatively connected to
the control unit 5, registers the cylinder pressure. This pressure
is compared, by the control unit, with the pressure in the tank for
the purpose of checking that the outlet valve 3 has been activated
at a correct angular position of the crank. According to an
alternative embodiment of the invention, the small non return valve
6 for the outflow and the controllable outlet valve 3 are replaced
by one or more non return valves for the outflow. According to a
further embodiment of the invention, the non return valve 13 for
the inflow and the controllable inlet valve 2 are replaced by a
large non return valve for the inflow, and the closure member 14 is
replaced by a rapid, controllable member that, like the valves 2
and 3, is able to cut off the flow of air to be compressed during
such a short time as one single cycle.
* * * * *