U.S. patent application number 15/818277 was filed with the patent office on 2018-05-24 for open hydraulic fluid flow circuit arrangement and method of controlling the hydraulic circuit.
The applicant listed for this patent is Danfoss Power Solutions G.m.b.H & Co. OHG. Invention is credited to Sven Fink, Florian Lindinger.
Application Number | 20180142782 15/818277 |
Document ID | / |
Family ID | 60452406 |
Filed Date | 2018-05-24 |
United States Patent
Application |
20180142782 |
Kind Code |
A1 |
Lindinger; Florian ; et
al. |
May 24, 2018 |
OPEN HYDRAULIC FLUID FLOW CIRCUIT ARRANGEMENT AND METHOD OF
CONTROLLING THE HYDRAULIC CIRCUIT
Abstract
The invention relates to a fluid flow arrangement (1, 15) with
an adjustable fluid pumping device (2) and a fluid working machine
(12). The fluid working machine (12) is connected to the fluid
pumping device (2) and a re-circulating loop is provided for the
fluid working machine (12). The re-circulating loop is fluidly
connecting a first fluid port (A) and a second fluid port (B) of
the fluid working machine (12), where the first (A) and the second
fluid port (B) are at times at a different pressure level. The
re-circulating loop comprises a controllable fluid throttling
device (21, 22), and a switchable fluid conduit device (23, 24), so
that a defined decelerating force can be generated for the fluid
working machine (12).
Inventors: |
Lindinger; Florian;
(Padenstedt, DE) ; Fink; Sven; (Linden,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Danfoss Power Solutions G.m.b.H & Co. OHG |
Neumunster |
|
DE |
|
|
Family ID: |
60452406 |
Appl. No.: |
15/818277 |
Filed: |
November 20, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16H 61/4017 20130101;
F16H 61/46 20130101; F16H 61/4157 20130101; F16H 61/4061 20130101;
F16H 39/02 20130101; F16H 61/4035 20130101; F16H 61/42 20130101;
F16H 61/44 20130101; F16H 61/4148 20130101 |
International
Class: |
F16H 61/46 20060101
F16H061/46; F16H 61/4035 20060101 F16H061/4035; F16H 61/4061
20060101 F16H061/4061; F16H 61/4157 20060101 F16H061/4157; F16H
61/4017 20060101 F16H061/4017 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2016 |
DE |
102016122535.5 |
Claims
1. A fluid flow arrangement, comprising a preferably adjustable
fluid pumping device, a fluid working machine fluidly connected to
said fluid pumping device and a re-circulating loop, fluidly
connecting a first fluid port (A) and a second fluid port (B) of
said fluid working machine, where said first (A) and said second
fluid port (B) are preferably at times at a different pressure
level, wherein the re-circulating loop comprises a controllable
fluid throttling device, and a switchable fluid conduit device.
2. The fluid flow arrangement according to claim 1, wherein said
re-circulating loop can be circulated in opposing directions, in
particular in that it comprises at least two controllable fluid
throttling devices and/or at least two switchable fluid conduit
devices.
3. The fluid flow arrangement according to claim 1, wherein said
adjustable fluid pumping device and said fluid working machine are
connected using at least one fluid switching means in particular in
a way that the output of said fluid pumping device can be
selectively connected to at least one of said at least two
different fluid ports (A, B) of said fluid working machine, in
particular to one of said first (A) and said second fluid port (B)
of said fluid working machine.
4. The fluid flow arrangement according to claim 1, wherein said
fluid flow arrangement is an open hydraulic fluid flow circuit, in
particular for propelling purposes.
5. The fluid flow arrangement according to claim 1, wherein at
least one of said controllable fluid throttling devices is a
pressure relief valve with a preferably adjustable set point.
6. The fluid flow arrangement according to claim 5, in particular
according to claim 5, wherein said controllable fluid throttling
device is an electrically controllable device and/or in that said
controllable fluid throttling device is controlled by an electronic
controlling device, in particular a programmable electronic
controlling device.
7. The fluid flow arrangement according to claim 1, wherein said at
least one of said controllable fluid conduit devices is a
directional valve, in particular a check valve and/or in that at
least one of said controllable fluid conduit devices shows a
defined pressure loss behaviour over said fluid conduit device that
is dependent on the fluid flow rate through said fluid conduit
device.
8. The fluid flow arrangement according to claim 1, characterized
by wherein at least one pressure measuring device, in particular a
plurality of pressure measuring devices that are preferably
arranged at the re-circulating loop, more preferably between a
fluid port (A, B) of said fluid working machine and at least one of
said controllable fluid throttling devices and/or between at least
two of said controllable fluid throttling devices and/or at the
fluid output line of said preferably adjustable fluid pumping
device.
9. An electronic controlling device for controlling a fluid flow
arrangement, in particular for controlling a fluid flow arrangement
according to claim 1, wherein said fluid flow arrangement comprises
at least one fluid working machine, at least a re-circulating loop,
fluidly connecting a first fluid port (A) and a second fluid port
(B) of a fluid working machine, and at least one controllable fluid
throttling device that is arranged in said re-circulating loop,
characterized in that said electronic controlling device generates
a control signal for said at least one controllable fluid
throttling device in a way to generate a defined decelerating force
for said fluid working machine.
10. The electronic controlling device according to claim 9, wherein
at least one sensor signal, describing the current state of the
fluid flow arrangement, is used for generating said control signal,
in particular in that pressure data is used for generating said
control signal.
11. The electronic controlling device according to claim 9, wherein
said control signal is generated in a way that the fluid flow
arrangement can be operated in at least one mode, taken from the
group comprising: a method, in which the speed of the fluid working
machine is controlled by outputting an appropriate control signal
to control the pressure at an outlet port of the fluid working
machine, while the fluid working machine is not driven by a fluid
pumping device; a method, in which the speed of the fluid working
machine is controlled by outputting an appropriate control signal
to control the pressure at the outlet port of the fluid working
machine, while the fluid working machine is driven, at least in
part, by a fluid pumping device; and a method, where the turning
direction of the fluid working machine is reversed by first slowing
down the speed of the fluid working machine and then switching a
fluid switching means in a way that the output of a fluid pumping
device is selectively connected to a different fluid port of said
fluid working machine.
12. A fluid flow arrangement comprising a preferably adjustable
fluid pumping device, a fluid working machine fluidly connected to
said fluid pumping device and a re-circulating loop, fluidly
connecting a first fluid port (A) and a second fluid port (B) of
said fluid working machine, where said first (A) and said second
fluid port (B) are preferably at times at a different pressure
level, wherein the re-circulating loop comprises a controllable
fluid throttling device, wherein an electronic controlling device
according to claim 9.
13. The fluid flow arrangement according to claim 11 that is used
as a propelling means for a vehicle, in particular for a land
vehicle.
14. The fluid flow arrangement according to claim 2, wherein said
adjustable fluid pumping device and said fluid working machine are
connected using at least one fluid switching means, in particular
in a way that the output of said fluid pumping device can be
selectively connected to at least one of said at least two
different fluid ports (A, B) of said fluid working machine, in
particular to one of said first (A) and said second fluid port (B)
of said fluid working machine.
15. The fluid flow arrangement according to claim 2, wherein said
fluid flow arrangement is an open hydraulic fluid flow circuit, in
particular for propelling purposes.
16. The fluid flow arrangement according to claim 3, wherein said
fluid flow arrangement is an open hydraulic fluid flow circuit, in
particular for propelling purposes.
17. The fluid flow arrangement according to claim 2, wherein at
least one of said controllable fluid throttling devices is a
pressure relief valve with a preferably adjustable set point.
18. The fluid flow arrangement according to claim 3, wherein at
least one of said controllable fluid throttling devices is a
pressure relief valve with a preferably adjustable set point.
19. The fluid flow arrangement according to claim 4, wherein at
least one of said controllable fluid throttling devices is a
pressure relief valve with a preferably adjustable set point.
20. The fluid flow arrangement according to claim 1, wherein said
controllable fluid throttling device is an electrically
controllable device and/or in that said controllable fluid
throttling device is controlled by an electronic controlling
device, in particular a programmable electronic controlling device.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims foreign priority benefits under
U.S.C. .sctn. 119 to German Patent Application No. DE102016122535.5
filed on Nov. 22, 2016, the content of which is hereby incorporated
by reference in its entirety.
TECHNICAL FIELD
[0002] The invention relates to a fluid flow arrangement that
comprises an adjustable fluid pumping device and a fluid working
machine that is fluidly connected to the fluid pumping device and
that further comprises a re-circulating loop, fluidly connecting a
first fluid port and a second fluid port of the fluid working
machine, where said first and said second fluid port are at times
at a different pressure level. The invention also relates to an
electronic controlling device for such a fluid flow arrangement (or
a similar one).
BACKGROUND
[0003] Hydraulic transmissions for transferring mechanical energy
from one place to the other (usually including the possibility to
change some characteristics of the mechanical energy involved, like
rotating speed, possible torque and the like) are used in several
technical fields in the meantime. An example for this is the field
of wind generators, where, due to varying wind speed, an input
force, coming from the propeller and showing varying turning speed
and/or driving torque has to be transmitted to an electric
generator. At the electric generator, however, usually a constant
turning speed is required. Therefore, not only the location where
the mechanical torque is present is shifted, but also some
characteristics of the mechanical energy (for example the turning
speed) are translated.
[0004] Another technical field for hydraulic circuits is used for
propelling vehicles, in particular land vehicles. Although already
some cars or trucks are propelled using a hydraulic transmission
their use is still somewhat limited, although some characteristics
of hydraulic circuits are promising. However, the use of hydraulic
circuits for driving a vehicle is the standard approach for special
vehicles that are using hydraulics for fulfilling their main duty.
Since a hydraulic pump of a considerable size is thus present
already, it is quite common to use hydraulic energy for propelling
the respective vehicle as some kind of a spin-off as well. Examples
for such machines are forklift trucks, excavators, shovel dozers
and the like.
[0005] From a technical viewpoint, closed hydraulic fluid flow
circuits are preferred for propelling a vehicle due to their
intrinsic properties. On the other hand, open fluid flow circuits
are preferred for other devices, like hydraulic pistons, where such
hydraulic pistons are used for fulfilling the main task of forklift
trucks, excavators, shovel dozers and so on. Although it is of
course possible from a technical viewpoint that for a machinery
that needs to employ an open hydraulic fluid flow circuit, a closed
hydraulic fluid flow circuit is arranged additionally, such an
approach is of course disadvantageous from an economic viewpoint.
Not only more components have to be foreseen and maintained for the
respective machine, but also the energy efficiency drops because of
the necessarily higher weight of the respective machine. Therefore,
there is a desire to use a propelling arrangement in combination
with an open hydraulic fluid flow circuit, albeit this is not
necessarily the best starting point.
[0006] The main problem when using an open hydraulic fluid flow
circuit is surprisingly not the propelling task, but instead the
main problem is when it comes to braking and/or to enable a
coasting of the vehicle. Here, one is not only confronted with the
problem of how to generate a braking force for the combined
hydraulic pump/hydraulic motor that is connected to the wheels of
the vehicle, but one is also confronted with the problem of how to
avoid cavitation on the suction side of the combined hydraulic
pump/hydraulic motor in these modes of operation.
[0007] The situation becomes even more problematic if the vehicle
has to be able to move in different directions (i.e. forward and
backward) and has to be able to be slowed down in these directions
as well (braking capability), which is a standard requirement.
[0008] Although some suggestions were already made in the state of
the art, so far they were not necessarily satisfying.
[0009] One suggestion was to sort of "circumvent the problems" by
simply providing a braking force with standard mechanical brakes
and to avoid cavitation by simply continuing to supply pressurized
fluid by the standard hydraulic pump. However, it is quite obvious
that this is disadvantageous, not only due to the wear of the
mechanical brakes, but also due to the lower energy efficiency of
the vehicle.
SUMMARY
[0010] Therefore, there is a need for a fluid flow arrangement with
which a vehicle can be propelled and slowed down although an open
hydraulic fluid flow circuit is employed.
[0011] It is therefore the object of the invention to suggest a
fluid flow arrangement that comprises an adjustable fluid pumping
device and a fluid working machine that is fluidly connected to
said fluid pumping device and that further comprises a
re-circulating loop, fluidly connecting a first fluid port and a
second fluid port of said fluid working machine, where said first
and said second fluid port are preferably at times at a different
pressure level that is improved over similar fluid flow
arrangements that are known in the state of the art. Another object
of the invention is to suggest an electronic controlling device for
controlling a fluid flow arrangement that is improved over
electronic controlling devices that are known in the state of the
art.
[0012] The invention solves this object.
[0013] It is suggested to design a fluid flow arrangement,
comprising a preferably adjustable fluid pumping device, a fluid
working machine that is fluidly connected to said fluid pumping
device and a re-circulating loop that is fluidly connecting a first
fluid port and a second fluid port of said fluid working machine,
where said first and said second fluid port of said fluid working
machine are preferably at times at a different pressure level in a
way that the re-circulating loop comprises a controllable fluid
throttling device and a switchable fluid conduit device. Although
in principle the fluid pumping device and particularly the fluid
working machine can be of a fixed type (so that one revolution of
the respective machine will pump/input essentially the same fluid
volume; minor variations can of course occur due to some effects
like pressurization effects, viscosity effects and the like) it is
preferred if at least the fluid pumping device or the fluid working
machine, preferably both the fluid pumping device and the fluid
working machine are of an adjustable type, so that those machines
can be varied in a way that one revolution will pump/input a
variable amount of fluid (within certain limits, of course). How
this adjustment is done is arbitrary. In particular, fluid pumps
and/or fluid working machines can be of a type were the adjustment
is performed by mechanical means. As an example: wobble plate
pumps/wobble plate fluid working machines are of such a
mechanically adjustable type that is well known in the state of the
art. However, it is also possible (and even preferred), if such
fluid pumping device and/or such fluid working machine is of an
electrically adjustable type. Such an electrically adjustable type
is also well known in the state of the art under the name digital
displacement Pump.RTM. (DDP) or synthetically commutated hydraulic
pump and/or motor (depending on the exact design). Fluid pumping
devices and/or fluid working machines of the electrically
adjustable type have the advantage that they can be varied much
quicker and/or in broader ranges, both is advantageous in
particular if it comes to propelling a vehicle. In a typical
application of the presently suggested fluid flow arrangement, the
fluid pumping device is usually of a design that it can only pump
hydraulic fluid, i.e. increasing the pressure of a hydraulic fluid
while consuming mechanical energy (typically applied in form of a
rotation, i.e. a torque). Of course, it is also possible that the
fluid pumping device is of a combined pumping/motoring design
(albeit the motoring mode will usually be used only rarely, if at
all). The fluid pumping device will usually be connected to a
driving device, such as a combustion engine, an electric motor or
the like. It is to be noted that if the fluid pumping device
(and/or the fluid working machine) is of an adjustable type, it is
possible that an electric motor or a combustion engine can be
running at a certain, constant speed, like the speed of maximum
power, the speed of maximum torque or the speed of maximum energy
efficiency (where it is of course possible that a different speed
regime is chosen from time to time, depending on the current
operating requirements). Due to the adjustability of the fluid
pumping device it is nevertheless possible to vary the amount of
hydraulic fluid that is pumped by the fluid pumping device. The
fluid working machine is typically of a design that it can be
switched between a motoring mode and a pumping mode (where a
partial motoring and pumping mode can be envisaged as well, in a
way that the fluid working machine comprises different services
that are fluidly separated from each other, and wherein some (at
least one) of the services are operated in a motoring mode, while
at the same time some (at least one) of the services are operated
in a pumping mode). Additionally, the fluid working machine can be
of a fixed displacement type or of a variable displacement type
(where the variable displacement type typically shows some
advantages with respect to controllability of the fluid flow
arrangement). In the motoring mode, it is able to actively propel a
vehicle, if used in this context. If the vehicle has to be
decelerated, the fluid working machine will be switched to a
pumping mode so that pressurized fluid will be "consumed" by other
consumers, in particular by the controllable fluid throttling
device which will be elucidated later on. This way wear-free
braking action can be realised. Typically, the fluid working
machine will be connected to one or several devices (either
directly or with any mechanical transmission system in-between
(including a gear or the like)). Only for the sake of completeness,
it should be mentioned that it is of course possible to use two or
even more (adjustable) fluid pumping devices and/or two or more
fluid working machines within the fluid flow arrangement. Depending
on the mode the fluid flow arrangement is currently operated in,
the first fluid port will be the high pressure port and the second
fluid port will be the low pressure port, or vice versa. Typically,
in case the fluid working machine is operating in a motoring mode,
the high pressure port will be the fluid input port, while the low
pressure port will be the fluid output port. If, however, the fluid
working machine will be driven in a pumping mode, usually the high
pressure port will be the fluid output port, while the low pressure
port will be the fluid input port. It should be noted that from a
mechanical viewpoint, the first fluid port can comprise several
"mechanical fluid ports", although the various "mechanical fluid
ports" from a single "logic fluid port" (the same applies mutatis
mutandis to the second fluid port). Such a plurality of "mechanical
fluid ports" can be connected together using a manifold or the
like. However, it is also possible that the fluid working machine
shows several internal fluid circuits that are separated from each
other, for example for generating various pressure levels or the
like. Again, for the sake of completeness it should be mentioned
that the first fluid port and the second fluid port can show the
same pressure level at certain times. The most obvious case for
this is if the machine is shut down (for example a forklift truck
that is parked overnight). With the help of the re-circulating loop
the first fluid port and the second fluid port can be selectively
"sort of short-circuited" at times. Thanks to this feature, a
cavitation at the low pressure side can be effectively avoided. In
particular, such cavitation could otherwise occur especially at the
fluid input port if the fluid working machine is operated in a
pumping mode (which happens if a vehicle is operated in a coasting
mode or in a braking mode). Of course, this "sort of
short-circuiting" should not always be present, because otherwise
quite some losses of pressurized hydraulic fluid would occur if the
fluid working machine is operated in a motoring mode when driving a
vehicle. Then, huge energy losses would occur, or the vehicle would
not be driveable anymore, at all. This selective switching of the
re-circulating loop can be realised by the presently suggested
switchable fluid conduit device. This switchable fluid conduit
device can be chosen from a huge variety of devices. In particular,
both active and passive switchable fluid conduit devices are
possible. An active switchable fluid conduit device could be a
solenoid valve, where the solenoid valve will be actuated by an
electric (electronic) controller, for example. However, it is also
possible that the switchable fluid conduit device is of a passive
type so that no "active actuation signal" has to be generated. A
possible design for such a passive switchable fluid conduit device
would be a check valve or the like. It is easily understandable
that the switchable fluid conduit device should be designed,
arranged and/or actuated in a way that the re-circulating loop is
not closed during intervals (i.e. a fluid flow throughput is
possible, where the fluid working machine is operated in a motoring
mode, while the re-circulating loop should be "sort of
short-circuited" during intervals when the fluid working machine is
operated in a pumping mode (during coasting and/or braking of a
vehicle, for example). By the notion "sort of short-circuited",
usually a closed fluid loop is meant, where the "sort of" stands
for a possible fluid obstruction device, where the obstruction to
the fluid flow can be even considerably large. However, it should
be low enough that cavitation effects for the fluid working machine
can be avoided. A "sort of short-circuiting" on the "low fluid flow
resistance" side (i.e. essentially fluidly short-circuiting the
re-circulation loop) will essentially result in little (if at all)
braking performance. This mode can nevertheless be advantageous for
realising a coasting mode for a vehicle, as an example. In case the
"sort of short-circuiting" is on the "high fluid flow resistance"
side, a "real braking" mode for a vehicle can be realised. This is
because the pressure loss over the fluid flow obstruction device
(where the mechanical energy stored in the pressure level of the
fluid will be converted to thermal energy) will operate as a
non-wearing brake for the fluid working machine. The fluid
obstruction device is realised as a controllable fluid throttling
device. The controllability of the controllable fluid throttling
device can be chosen from a wide range. In particular, it is
possible that the controllable fluid throttling device can be
switched between (essentially) two modes only, namely a first mode,
where essentially no fluid flow resistance will be generated
(during coasting or during active propelling of a vehicle, for
example), and a second mode, where a certain fluid flow resistance
will be generated (for realising a "real braking mode" for a
vehicle, for example). However, it is preferred if a plurality of
different states, in particular a continuous range of "fluid
obstruction strengths" can be realised by the controllable fluid
throttling device. This way, various braking strengths, preferably
a continuous range of braking performance can be realised. Once
again for the sake of completeness: a mode, where the controllable
fluid throttling device exerts essentially no fluid flow resistance
on the hydraulic fluid flowing through it, is important because
otherwise such a fluid flow resistance would be present during a
motoring mode of the fluid working machine, as well. Otherwise,
huge energy losses would occur if a vehicle is propelled, as an
example. In particular, the controllability of the controllable
fluid throttling device can be realised by a throttling device that
has an orifice of a variable size. However, different designs are
possible as well. As an example, a device could be used where a
tube of a certain diameter is employed and where the "effective"
length of the tube (as seen by the circulating fluid) can be
changed by "adding or removing" additional loops using switchable
valves. However, other designs are possible as well.
[0014] It is suggested to design the fluid flow arrangement in a
way that said re-circulating loop can be circulated in opposing
directions, in particular in a way that it comprises at least two
controllable fluid throttling devices and/or at least two
switchable fluid conduit devices. This way, it is possible to
operate the fluid working machine in opposite directions (where the
fluid pumping device is normally used only in one direction;
however, it might occur as well that even the fluid pumping device
can be operated in alternating directions, at least at times).
Using this design, a vehicle that is propelled by the presently
suggested fluid flow arrangement (in particular if the wheels are
mechanically connected to the fluid working machine) can be driven
in different directions, i.e. in a forward direction, as well as in
a rearward direction. Such a design thus yields an increased
operability of the respective machinery. A fluid flow circulation
in opposing directions in the re-circulating loop can be very
effectively realised with the presently suggested design of at
least two controllable fluid throttling devices and/or at least two
switchable fluid conduit devices. In particular, when such a design
is used, the functionality of a coasting and/or braking mode can be
easily realised in both driving directions of the respective
vehicle.
[0015] Another preferred embodiment of the fluid flow arrangement
can be achieved if said adjustable fluid pumping device and said
fluid working machine are connected using at least one fluid
switching means, in particular in a way that the output of said
fluid pumping device can be selectively connected to at least one
of said at least two different fluid ports of said fluid working
machine, in particular to one of said first and said second fluid
port of said fluid working machine. Using this embodiment, it is
particularly simple to realise an operation of the fluid working
machine in two different directions. If used in connection with
propelling a vehicle, a forward and a rearward movement of the
vehicle can be easily achieved. Furthermore, using the proposed
design it is particularly simple to split the fluid flow generated
by the fluid pumping device and the return flow from the fluid
working machine from each other, if the fluid flow arrangement is
operated in a propelling mode.
[0016] It is further suggested to design the fluid flow arrangement
in a way that said fluid flow arrangement is an open hydraulic
fluid flow circuit. In particular, it is suggested to use the fluid
flow arrangement for propelling purposes, especially for propelling
land vehicles. Using the proposed design, the presently proposed
fluid flow arrangement can show its intrinsic advantages and
features particularly well.
[0017] Another preferred design of the fluid flow arrangement can
be achieved if at least one of said controllable fluid throttling
devices is designed as a pressure relief valve with a preferably
adjustable set point. As already stated above, the adjustability of
the set point can be in a way that two, three, four or even more,
i.e. a plurality of different discrete states can be realised.
However, it is also possible (and usually preferred), if the set
point can be adjusted continuously (within a certain interval).
Usually, the adjustability of the set point (control of the fluid
throttling device in general) is done in an automated way. How the
input signal is applied is generally without relevance. As an
example, the adjustment signal could be applied by mechanical
means, by electrical means and/or by fluid means (pneumatics,
hydraulics). Usually, an electric control signal is preferred,
since such a signal can be easily generated by an electric control
device (in particular an electronic controlling device). It should
be stated that it is of course possible as well to apply two or
even more control signals, where each individual control signal has
a certain influence on the setting of the controllable fluid
throttling device/the adjustable set point. By a concurrence of the
individual control signals, the "final setting"/"final set point"
will be realised.
[0018] Yet another preferred design can be realised if said
controllable fluid throttling device is an electrically
controllable device and/or if said controllable fluid throttling
device is controlled by an electronic controlling device, in
particular by a programmable electronic controlling device. As
already mentioned above, the generated control signal can be a
singular one. However, a plurality of control signals can act on
the fluid throttling device as well. If the fluid throttling device
is an electrically controllable fluid device, it is usually very
easy to realise a fast and precise actuation of the controllable
fluid throttling device, resulting in the typically good
controlling behaviour of the fluid flow arrangement. Furthermore,
the generation of an electric control signal is typically quite
easy to achieve. As proposed, the control can be performed (in
part) by an electronic controlling device, in particular by a
programmable electronic controlling device. A preferred design for
this is an electronic microcontroller. In particular, a controlling
device that is designed as a single printed circuit board device is
preferred. Such devices are easily and cheaply available in the
state of the art. Just to name an example, a Raspberry Pi .COPYRGT.
or an Arduino controller .COPYRGT. are available for little money
and show a remarkable computing power in the meantime. The electric
control of an electrically controllable fluid throttling device can
be realised as an electric coil, generating a magnetic force on
some kind of a spool or the like. Also, it is possible to use a
stepper motor or an electric motor (including rotational motors as
well as linear motors) to create a movement of an appropriate
device. In particular, the size of an orifice could be changed
within the controllable fluid throttling device.
[0019] Yet another preferred fluid flow arrangement can be realised
if at least one of said controllable fluid conduit devices is a
directional valve, in particular a check valve and/or if at least
one of said controllable fluid conduit devices shows a defined
pressure loss behaviour over said fluid conduit device that is
dependent on the fluid flow rate through said fluid conduit device.
Using such a design, a reliable and cheap fluid flow arrangement
can be realised. If the connection between pressure loss and fluid
flow rate through the device is known, it is possible to measure
(or at least to estimate sufficiently well) the fluid flow rate by
performing pressure measurements. Pressure sensors for this are
comparatively cheap, need little building space and are quite
reliable, even with respect to deteriorated hydraulic oil due to
alteration effects. Furthermore, since the controllable fluid
conduit device is needed anyhow and it is essentially impossible to
avoid a pressure loss over it, this pressure loss can be used for a
sensible purpose. In particular no additional fluid flow resistance
has to be introduced for the fluid flow arrangement which result in
a higher energy efficiency and generally a better performance of
the fluid flow arrangement.
[0020] A further preferred embodiment can be realised, if the fluid
flow arrangement comprises at least one pressure measuring device,
in particular a plurality of pressure measuring devices that are
preferably arranged at the re-circulating loop, more preferably
between a fluid port of said fluid working machine and at least one
of said controllable fluid throttling devices and/or between at
least two of said controllable fluid throttling devices and/or at
the fluid output line of a preferably adjustable fluid pumping
device. Using such pressure measuring devices, it is possible to
gain sufficient knowledge for controlling the behaviour of the
fluid flow arrangement in a sufficiently precise way. In
particular, using pressure measuring devices one can obtain more
information about the amount of fluid that is pumped by the fluid
working machine in a coasting operation or a braking operation.
Using this additional input, the operation of the fluid flow
arrangement, in particular of the braking behaviour of the fluid
flow arrangement, can be controlled more precisely. Thus, it is
even easily possible to mimic the behaviour of a standard
mechanical brake or the braking behaviour of a dedicated closed
hydraulic fluid flow circuit. When talking about placing (one of)
the pressure measuring device(s) at the fluid output line of a
preferably adjustable fluid pumping device, this should be mainly
understood in a logical sense. Therefore, placing the pressure
measuring device near and/or in the vicinity of the fluid working
machine is of course possible (and quite often even advantageous,
since due to the position near the fluid working machine the
measured pressure will usually better reflect the pressure level
near the fluid working machine). However, sometimes it might be
advantageous as well to place the pressure measuring device (or
possibly even an additional one) close to the fluid output port of
the preferably adjustable fluid pumping device.
[0021] According to another aspect of the invention, it is proposed
to design an electronic controlling device for controlling a fluid
flow arrangement, in particular for controlling a fluid flow
arrangement of the previously described design, wherein the fluid
flow arrangement comprises at least one fluid working machine, at
least a re-circulating loop, fluidly connecting a first fluid port
and a second fluid port of a fluid working machine and at least one
controllable fluid throttling device that is arranged in said
re-circulating loop in a way that said electronic controlling
device generates a control signal for said at least one
controllable fluid throttling device in a way to generate a defined
decelerating force for said fluid working machine. The electronic
controlling device can be particularly a microprocessor and/or a
single printed circuit board controller. As already mentioned, an
Arduino .COPYRGT. controller or a Raspberry Pi .COPYRGT. could be
used for this purpose. Using such an electronic controlling device
it is possible to mimic the behaviour of a standard mechanical
brake for a vehicle with a hydraulic circuit, in particular even
with an open hydraulic fluid flow circuit. In particular, a variety
of different operating modes can be easily implemented using the
electronic controlling device. The electronic controlling device
can be a dedicated electronic controlling device that is more or
less solely used for operating the fluid flow arrangement. However,
the electronic controlling device can be likewise a device that
implements more functionality of the machinery, the fluid flow
arrangement is used for. In this case, a sufficient amount of
computing power has to be provided for fulfilling the computations,
necessary for operating the fluid flow arrangement.
[0022] In particular, it is possible that the electronic
controlling device is designed in a way that at least one sensor
signal, describing the current state of the fluid flow arrangement,
is used for generating said control signal. In particular, it is
possible that pressure data is used for generating said control
signal. Of course, other sensor signals can be used additionally
and/or alternatively for generating said control signal. Pressure
data can be particularly obtained from pressure measuring devices.
The use of such data (with which even a fluid flow can be
determined "indirectly") was previously suggested. Furthermore, not
only sensor signals can be used that come from sensors that are
more or less only provided for the purpose of operating the fluid
flow arrangement, but instead sensor signals that come from sensors
that are provided for a different purpose (for example for
operating a combustion engine that drives the fluid pumping device)
can be used as well. Even more, other data that is present anyhow
(for example some values that come from the present electronic
controlling device or from another electronic controlling device
for any purpose whatsoever) can be used as an input signal as
well.
[0023] It is further suggested to design the electronic controlling
device in a way that said control signal is generated in a way that
the fluid flow arrangement can be operated in at least one mode,
taken from the group comprising: a method, in which the speed of
the fluid working machine is controlled by outputting an
appropriate control signal to control the pressure at an outlet
port of the fluid working machine, while the fluid working machine
is not driven by a fluid pumping device; a method, in which the
speed of the fluid working machine is controlled by outputting an
appropriate control signal to control the pressure at the outlet
port of the fluid working machine, while the fluid working machine
is driven, at least in part, by a fluid pumping device; and a
method where the turning direction of the fluid working machine is
reversed by first slowing down the speed of the fluid working
machine and then switching a fluid switching means in a way that
the output of a fluid pumping device is selectively connected to a
different fluid port of said fluid working machine. Using such an
embodiment (or a combination thereof) a particularly versatile
device can be realised. In particular, a coasting and braking
operation can be realised that shows various possibly advantageous
embodiments. As an example, if the fluid working machine is not
driven by a fluid pumping device and the speed of the fluid working
machine is controlled by outputting an appropriate control signal
to control the pressure at the outlet port (i.e. where usually the
control of the speed of the fluid working machine is done by
setting an appropriate pressure level at the fluid outlet port of
the fluid working machine, which in turn is usually done by setting
an appropriate pressure difference over a fluid throttling device
that is arranged aft of the fluid outlet port of the fluid working
machine), a non-wearing braking system can be realised that is
highly energy-efficient (no mechanical work is needed during the
operation of the arrangement). If, however, the fluid working
machine is controlled by outputting an appropriate control signal
to control the pressure at the outlet port while the fluid working
machine is driven, it is possible to determine the speed of the
fluid working machine by the speed of the fluid pumping device, and
hence by the combustion engine (to give an example). This might be
advantageous if only a short braking impulse is needed to avoid a
rapid deceleration and acceleration of the turning speed of the
combustion engine, which might be a nuisance to the operator of the
device. Furthermore, it might be desired by the operator to have an
"audible feedback" of the driving speed by means of the turning
speed of the combustion engine. When employing a method, where the
turning direction of the fluid working machine is reversed by first
slowing down the speed of the fluid working machine and then
switching a fluid switching means in a way that the output of a
fluid pumping device is selectively connected to a different fluid
port of the fluid working machine, a behaviour of the vehicle (as
an example) is achievable which is very comfortable (and even safe,
for example in the case of a forklift truck, where goods could fall
off the fork in the case of a rapid deceleration/acceleration of
the forklift truck). In particular, a very strong braking behaviour
can be avoided when the reverse gear is selected, while the vehicle
is still moving forward. If the fluid switching means would be
operated so that the output of the fluid pumping device is
connected to the respective different fluid port while the vehicle
is still in motion, this would essentially unavoidably lead to the
effect that a very strong braking force is applied until the
vehicle comes to a complete stop. It is easily understandable that
such a behaviour is not necessarily what is desired.
[0024] A further proposal is to design a fluid flow arrangement, in
particular a fluid flow arrangement according to the previous
description in a way that it shows an electronic controlling device
according to the previous description.
[0025] Yet another advantageous embodiment can be obtained, if the
fluid flow arrangement is used as a propelling means for a vehicle,
in particular for a land vehicle. In this case, the fluid flow
arrangement can show its intrinsic advantages and features
particularly well.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Further advantages, features, and objects of the invention
will be apparent from the following detailed description of the
invention in conjunction with the associated drawings, wherein the
drawings show:
[0027] FIG. 1: the schematic circuitry of a first embodiment of a
hydraulic propelling circuit, employing an open hydraulic fluid
flow circuit;
[0028] FIG. 2: the first embodiment of a hydraulic propelling
circuit in a driving mode;
[0029] FIG. 3: the first embodiment of a hydraulic propelling
circuit in a runaway prevention mode, in which the turning speed of
the driving engine is independent from the turning speed of the
fluid working machine;
[0030] FIG. 4: a possible control schematic for implementing a
runaway prevention mode;
[0031] FIG. 5: the first embodiment of a hydraulic propelling
circuit in a metering mode, in which a braking is effectuated
wherein the turning speed of the fluid working machine depends on
the turning speed of the driving engine;
[0032] FIG. 6: a possible control schematic for implementing a
metering mode;
[0033] FIG. 7: the first embodiment of a hydraulic propelling
circuit in an ingressive reversal mode that is to be avoided;
[0034] FIG. 8: the schematic circuitry a second embodiment of a
hydraulic propelling circuit.
DETAILED DESCRIPTION
[0035] In FIG. 1, a first embodiment of a hydraulic propelling
circuit 1 that can be used for moving a vehicle (in particular a
vehicle that uses a hydraulic system anyhow, for example a forklift
truck, a shovel loader, an excavator or the like) is shown as a
fluid flow schematic. The presently shown hydraulic propelling
circuit 1 is set up in a way that the vehicle can be moved in two
different (opposing) directions, i.e. in a forward and in a
backward direction. Since the schematic is set up in a symmetric
way, the propelling characteristics (maximum speed, torque etc.)
are essentially identical in both directions. This is actually a
preferred behaviour for machinery such as excavators or forklift
trucks. Furthermore, it can be seen that the hydraulic propelling
circuit 1 is of an open hydraulic fluid flow circuit type.
[0036] In "reality", the output of the main hydraulic pump 2 could
be used for different purposes as well, like for hydraulic pistons
for raising the fork of a forklift truck, for moving the shovel of
a shovel loader or the like. Of course, it is also possible that a
dedicated pump for such "other hydraulic services" is used (or
presumably a main hydraulic pump 2 is used that comprises different
independent services, where different services are used for
different hydraulic sub-circuits).
[0037] The main hydraulic pump 2 is driven by a driving engine,
which is presently designed as a combustion engine 3 (for example a
diesel motor or a natural gas motor). The torque that is generated
by the combustion engine 3 is transmitted by a driving shaft 4 to
the main hydraulic pump 2.
[0038] As can be seen as well, an auxiliary hydraulic pump 5 is
provided. The auxiliary hydraulic pump 5 pumps hydraulic fluid from
an oil reservoir 6 (typically at ambient pressure) to the low
pressure side 8 of the hydraulic propelling circuit 1. Furthermore,
the auxiliary hydraulic pump 5 can additionally serve as a source
of fluid for other tasks/devices (presently not shown). In
particular, throttling valves can be used to provide different
pressure levels for such additional tasks/devices and/or for the
elevated pressure in the low pressure side 8 of the hydraulic
propelling circuit 1, in particular in case a single auxiliary
hydraulic pump 5 is used.
[0039] Both the main hydraulic pump 2 and the auxiliary hydraulic
pump 5 (or possibly other additional hydraulic pumps that are not
shown, as well) take in hydraulic oil from the fluid reservoir
6.
[0040] A minimum pressure is guaranteed by means of the auxiliary
hydraulic pump 5, so that the respective fluid lines 26 do not run
dry. On the other hand, the pressure within the low pressure side 8
of the hydraulic propelling circuit 1 is limited to a comparatively
low pressure by means of a low pressure relief valve 9, that can be
designed as a (slightly) pre-loaded check valve (where the
preloading can be realised by a helical spring or the like) as it
is well known in the state of the art.
[0041] With "realistic set-ups", the same combustion engine 3 is
used for both the main hydraulic pump 2 and auxiliary hydraulic
pump 5 (typically, both hydraulic pumps 2, 5 are connected to the
main driving shaft 4). While it is possible that two separate
hydraulic pumps 2, 5 are used, the hydraulic pumps 2, 5 can also be
of a "type separated by employing different services", i.e. they
can be designed as several independent services of common pump
housing.
[0042] In the presently shown example, the auxiliary hydraulic pump
5 is of a fixed displacement type (where the pumping rate of the
auxiliary hydraulic pump 5 is rather limited; the pressure the
auxiliary hydraulic pump 5 has to be able to reach is rather
limited as well, since only a pressure level that is typical for
the low pressure side 8 of the hydraulic propelling circuit 1 has
to be reached or (slightly) exceeded).
[0043] The main hydraulic pump 2 is of an adjustable type, for
example a variable displacement hydraulic pump type (a wobble plate
pump, for example). Another (typically preferred) design of the
adjustable main hydraulic pump 2, and that is chosen for the
presently shown embodiment, is a so-called digital displacement
pump (DDP.RTM.), that is also known as a synthetically commutated
hydraulic pump in the state of the art.
[0044] The pressurized fluid that is pressurized by the main
hydraulic pump 2 is fed to the high pressure side 7 of the
hydraulic propelling circuit 1. Using an appropriate switching of
the switchable fluid valves 10, 11 (both of an on-off-type), the
pressurized fluid can be fed to either port "A" (via fluid valve
10) or to fluid port "B" (via fluid valve 11) of the fluid working
machine 12. The fluid working machine 12 is a combined fluid
motor/fluid pump. It can be of a purely mechanical nature, or it
can be controlled by appropriate controlling signals and/or can
send sensor signals to an electronic controller 13 via electric
signal lines 14. The electronic controller 13 is not only connected
to the fluid working machine 12 by means of electric signal lines
14, but also other components of the hydraulic propelling circuit 1
are connected to the electronic controller 13 by means of electric
signal lines 14 for obtaining control signals and/or for feeding
sensor signals (or other feedback signals) to the electronic
controller 13. In particular, the already described combustion
engine 3, main hydraulic pump 2, fluid valves 10, 11 and fluid
working machine 12 are connected to the electronic controller
13.
[0045] As can be seen from the schematic as well, pressure sensors
16, 17 are fluidly connected to appropriate fluid lines 26 for
monitoring the pressure in the respective part of the hydraulic
propelling circuit 1. The pressure values that are measured by the
respective pressure sensors 16, 17 are fed to the electronic
controller 13. Namely, pressure sensor 16 is located aft of fluid
valve 10 in the vicinity of Port "A" of the fluid working machine
12, while pressure sensor 17 is located aft of fluid valve 11 in
the vicinity of Port "B" of the fluid working machine 12.
[0046] The middle part 18 of the hydraulic propelling circuit 1
(where the fluid working machine 12 is located) is connected to the
low pressure side 8 by means of a valve combination 19, 20 that is
arranged either on the "A" side (right side) or the "B" side (left
side) of the hydraulic propelling circuit 1. Namely, the valve
combination 19 on the right side comprises an adjustable pressure
relief valve 21 that allows a fluid flow from middle part 18 to low
pressure side 8 of the hydraulic propelling circuit 1, in case an
appropriate pressure difference is present. The cracking pressure
of adjustable pressure relief valve 21 can be adjusted by
electronic controller 13 by applying an appropriate actuation
signal via the appropriate electrical signal line 14. Thus, the
pressure difference between pressure sensor 16 (hydraulic pressure
in the middle part 18 in the proximity of Port "A" of the fluid
working machine 12) and pressure sensor 25 (hydraulic pressure in
the low pressure side 8 of hydraulic propelling circuit 1) can be
set to a defined value (of course, typically only if the pressure
at pressure sensor 16 is higher than the pressure at pressure
sensor 25).
[0047] If the pressure difference reverses (i.e. pressure at
pressure sensor 25 is higher than pressure at pressure sensor 16) a
check valve 23 opens and a fluid flow is permitted from the low
pressure side 8 to the middle part 18 of the hydraulic propelling
circuit 1.
[0048] The valve combination 20 of the arrangement on the "left
side" of the hydraulic propelling circuit 1 (near port "B" of the
fluid working machine 12) is done in a similar way as on the "right
side". In particular, the valve combination 20 comprises an
adjustable pressure relief valve 22 and a check valve 24 whose
operation and functionality is similar to the valve combination 19
on the "right side" and detailed description is omitted for
brevity.
[0049] Of course, the pressure level on the low pressure side 8 of
the hydraulic propelling circuit 1 that is measured by pressure
sensor 25 is fed to the electronic controller 13 by an appropriate
electric signal line 14 as well.
[0050] In FIG. 2, a "standard driving situation" of the hydraulic
propelling circuit 1 is shown. In particular, the direction of the
fluid flow is indicated by arrows 27 near the respective hydraulic
fluid line 26. In the presently shown example, the fluid working
machine 12 is rotating in one direction (for example a forward
direction of a forklift truck, if the hydraulic propelling circuit
1 is used for such a forklift truck). If the moving direction of
the fluid working machine 12 (and thence of the forklift truck) has
to be reversed, the fluid flow will be changed by establishing a
fluid flow in a way that essentially the left side ("B") and the
right side ("A") of the hydraulic propelling circuit 1 near fluid
working machine 12 are interchanged.
[0051] In the "standard driving mode", hydraulic fluid is sucked in
from the fluid reservoir 6 by the main hydraulic pump 2,
pressurized and ejected toward the high pressure side 7 of the
hydraulic propelling circuit 1. The fluid valves 10, 11 are
switched in a way that a fluid connection is established between
high pressure side 7 and Port "A" of fluid working machine 12 in
the middle part 18 of hydraulic propelling circuit 1. The fluid
connection between the high pressure side 7 and the side of the
middle part 18 near fluid port "B" of the fluid working machine 12,
however, is disconnected. Therefore, fluid valve 10 is switched
"on" (permitting a fluid flow there through), while fluid valve 11
is "off" (no fluid flow permitted through the valve).
[0052] Since no braking performance is needed, the adjustable
pressure relief valve 22 of the valve combination 20 on the "left
side" ("B"-side) is set to a mode that the pressure difference
across the valve is 0 (apart from unavoidable residual effects). In
effect, setting the pressure difference to essentially 0 is
advantageous from an energetic viewpoint, since any pressure
difference over adjustable pressure relief valve 22 would result in
a fluid obstruction resulting in reduced energy efficiency of the
system.
[0053] Of course, to avoid some kind of "short-circuiting", the
adjustable pressure relief valve 21 of the valve combination 19 on
the "right side" ("A"-side) is set to its maximum value, so that as
a consequence any fluid flow through adjustable pressure relief
valve 21 is hindered (apart from the possibility of any "emergency
depressurization" due to a defect of the arrangement).
[0054] As can be seen by the appropriate arrows 27 near the
hydraulic fluid lines 26, the hydraulic fluid is therefore directed
via fluid valve 10 (right side), through the fluid working machine
12 (direction port "A".fwdarw."B"), adjustable pressure relief
valve 22 (left side), low pressure relief valve 9 back to the fluid
reservoir 6.
[0055] Therefore, mechanical energy that comes from the combustion
engine 3 is converted to pressurization energy by the main
hydraulic pump 2, which is converted back to mechanical energy at
the fluid working machine 12 (operating as a hydraulic motor in
this mode of operation).
[0056] This will result in a positive torque which accelerates the
fluid working machine 12 and the attached load (for example for
propelling a vehicle).
[0057] Apart from small amounts of a leakage in the hydraulic
propelling circuit 1 and its components, the hydraulic fluid flow
across the fluid working machine 12 can be assumed to be identical
to the hydraulic fluid flow through the main hydraulic pump 2.
Hence, with a known displacement of the fluid working machine 12,
the speed of the fluid working machine 12 (and hence of the load,
for example the speed of a vehicle) can be controlled by
controlling the fluid output flow of the main hydraulic pump 2.
[0058] Now, if the amount of fluid that is pumped by the main
hydraulic pump 2 is reduced to (approximately) 0, the fluid flow
behaviour according to FIG. 3 will be established.
[0059] Due to the switching-off of main hydraulic pump 2, no fluid
flow is delivered to the fluid working machine 12 (by the main
hydraulic pump 2) anymore. In effect, fluid valve 10 could be
switched off as well.
[0060] Now the problem would arise that cavitation occurs in part
of the "A"-side of the hydraulic propelling circuit 1. Such a
cavitation has to be avoided, since it could seriously damage the
respective components, in particular the fluid working machine 12.
Therefore, the hydraulic propelling circuit 1 is designed in a way
that a fluid back flow to port "A" of the fluid working machine 12
is possible. Please note that right at the moment the (actuated)
fluid valves 10, 11 and/or the adjustable pressure relief valves 21
and 22 are still at the setting according to the situation shown in
FIG. 2.
[0061] In consequence, a "short-circuited" fluid flow is
established, starting from port "B" (the fluid output port of fluid
working machine 12, which now works as a hydraulic fluid pump)
through "left" adjustable pressure relief valve 22 (pressure
difference set to 0), through "right" check valve 23 (pressure
difference across the check valve 23 is 0 as well) and back to port
"A" (fluid intake port) of the fluid working machine 12.
[0062] Now, obviously, the connection between the turning speed of
the combustion engine 3 and/or the main hydraulic pump 2 and the
turning speed of the fluid working machine 12 is lost. In
particular, the combustion engine 3 and/or the main hydraulic pump
2 could be idling, while the fluid working machine 12 is still
running at an elevated speed (in case the hydraulic propelling
circuit 1 is used for propelling a vehicle, the vehicle would still
move).
[0063] This situation can be voluntarily (desired mode of
operation), as in the case of idling the main hydraulic pump 2
while coasting the fluid working machine 12 (coasting a vehicle).
However, the situation could also be involuntarily, as in the case
of "running away" downhill of a vehicle.
[0064] Now, some kind of a braking capability has to be
implemented. This is done by setting the "left" adjustable pressure
relief valve 22 to a certain pressure differential that corresponds
to a certain, desired braking behaviour ("runaway prevention
mode"). Typically, the "right" adjustable pressure relief valve 21
will remain at a setting (will be set to a setting) of a maximum
pressure difference (effectively, a switched off-condition).
[0065] From a controlling side, the situation according to FIG. 3
("runaway prevention mode") can be identified by the electronic
controller 13 by the first condition that P.sub.B>P.sub.A
(pressure P.sub.B=pressure at "left" pressure sensor 17; "B"-side,
while pressure P.sub.A=pressure at the "right" pressure sensor 16
at the "A"-side). This can be easily understood because the
pressure at the "A"-port of the fluid working machine 12 drops to 0
(hopefully not below 0 because of possible cavitation), while due
to the pumping behaviour of the fluid working machine 12, the
"B"-port will be at a certain pressure level (because there will
always be some pressure due to fluid obstructions and fluid
viscosity).
[0066] Another condition for detecting the situation according to
FIG. 3 is the absence of a fluid flow (fluid flux) through the main
hydraulic pump 2 (Q.sub.MHP=0). This can be seen by the actuating
signal to the main hydraulic pump 2.
[0067] To establish a defined braking behaviour for the hydraulic
propelling circuit 1 ("runaway prevention mode"), "left" adjustable
pressure relief valve 22 has to be set to a certain point, so that
the pressure at fluid port "B" of the fluid working machine 12
reaches a certain point. Then, the fluid working machine 12 has to
work against a pressure difference P.sub.B-P.sub.A, so that the
fluid working machine 12 has to perform some mechanical work
against the difference in pressure level; which is equivalent to a
braking power performed on the fluid working machine 12 (and
possibly the vehicle's movement, if employed for this use).
[0068] A possible control schematic for this is shown in FIG.
4.
[0069] The input value P.sub.C-.DELTA.P.sub.maximum allowable 28 is
the allowable pressure difference over "right" check valve 23.
Since the check valve 23 (likewise the "other check valve" 24) is
chosen in a way that the connection between the fluid flow through
the respective valve and the pressure difference occurring between
both sides of the valve is known, it is possible to determine from
this pressure difference over the valve the fluid flow through the
valve (at least in good approximation). This, however, is an
indication of the vehicle's speed (if the hydraulic propelling
circuit 1 is used for propelling a vehicle).
[0070] This value is fed (at the negative input line) to a
comparator 29, where it is compared with the measured pressure
P.sub.C at pressure sensor 25 that is connected to the low pressure
side 8 of the hydraulic propelling system 1 (and which is fed into
the positive input line of comparator 29). The output of the
comparator 29 is a value P.sub.A, set point 30, namely the
"theoretical value" of pressure P.sub.A, how it should be. This is
compared to the real value of P.sub.A 31 (measured value), i.e. the
value that is actually measured by "right" pressure sensor 16. This
is done by feeding the respective values into another comparator
32, whose output signal is one of the input signals for the
electronic controller 13. The electronic controller 13 finally
calculates the value P.sub.PRV 33, which is the pressure set point
for the pressure relief valve, currently the "left" pressure relief
valve 22. This again is the "main input value" determining the
braking performance of the arrangement.
[0071] This way, a wear-free brake can be realised in a simple and
efficient way.
[0072] Only for completeness it should be noted that a mechanical
brake should still be provided for safety reasons, of course.
[0073] Another mode that can be realised with the present
arrangement (being different from the previously described "runaway
prevention mode") is the so-called "metering mode" that is
indicated in FIG. 5. Again, the setting of the fluid valves 10, 11
and pressure relief valves 21, 22 is initially done in the same way
as it is done in FIG. 2.
[0074] Now, however, the idea is to realise a braking performance
of the hydraulic propelling circuit 1, while maintaining a direct
connection between the turning speed of the main hydraulic pump 2
(and hence of the combustion engine 3 due to the mechanical
connection by driving shaft 4). Hence, the control of the vehicle's
speed is done through an appropriate setting of the adjustable main
hydraulic pump 2.
[0075] The condition when "metering" can be used (and how it can be
identified) is in one respect identical to the previously described
"runaway prevention mode", namely in that P.sub.B>P.sub.A (fluid
working machine 12 is operating as a fluid pump, thus performing
mechanical work against the pressure difference and thus slowing
down the vehicle). Different to the "runaway prevention mode" as
previously described, the fluid flow rate of the main hydraulic
pump 2 is different from 0 (QMHP.noteq.0).
[0076] In order to establish the direct correspondence between
fluid flow through the fluid working machine 12 (and hence
rotational speed of the fluid working machine 12) and the fluid
flow, generated by the main hydraulic pump 2, the pressure upstream
of the fluid working machine 12 (which is the pressure at pressure
port "A", i.e. P.sub.A) must be maintained at a sufficiently high
level to not only avoid cavitation, but also to avoid
re-circulating fluid flow, presently through "right" check valve
23. This translates to the requirement for pressure P.sub.A
upstream of the fluid working machine 12 to be higher than the
pressure P.sub.C in the low pressure side 8 (measured by pressure
sensor 25), i.e. higher than P.sub.C. ("Right" adjustable pressure
relief valve 21 is kept at a "closed" condition, i.e. at maximum
pressure difference setting).
[0077] An appropriate control scheme schematic for this is shown in
FIG. 6. Now one of the input values of first comparator 29 is
changed to A P no circulation 34, i.e. to a setting so that
pressure P.sub.A near inlet port "A" of the fluid working machine
12 is maintained at a level that is higher than P.sub.C in the low
pressure side 8 of the hydraulic propelling circuit 1. This is
compared to P.sub.C 35, as measured by pressure sensor 25. Contrary
to the previous case, however, comparator 29 uses both values 34,
35 as a positive input signal. The output 36 of first comparator 29
is now P.sub.C+.DELTA.P.sub.no circulation as a set point. This is
compared as in the previous case with measured value of P.sub.A 31,
as measured by presently "right" pressure sensor 16 by comparator
32. This is the input signal for electronic controller 13, which
calculates as an output signal the pressure set point P.sub.PRV 33
for the presently "left" pressure relief valve 22 (therefore, the
set point for this pressure relief valve will change from the
initial "0-setting").
[0078] Although in the examples of FIGS. 2, 3 and FIG. 5 a (let's
say) forward motion of the vehicle was shown, it is obvious how to
realise a backward motion by sort of interchanging the fluid flow
between the left side and the right side of fluid working machine
12 and the respective hydraulic fluid lines 26 serving fluid ports
A and B.
[0079] Nevertheless, a potential problem that still has to be
discussed is a problem that occurs if the hydraulic propelling
circuit 1 is switched to a backward moving mode, while the vehicle
is still moving forward (or vice versa). This is the problem of
"aggressive reversal" which is shown in FIG. 7.
[0080] If switching "normally" from a forward to a backward mode of
the fluid working machine 12, this would mean that "right" fluid
valve 10 would be switched from "on" to "off", while "left" fluid
valve 11 would be switched from "off" to "on". Furthermore, the
initial settings for the adjustment pressure relief valves 21, 22
would be realised, namely a setting that "right" adjustable
pressure relief valve 21 would be set to 0-pressure difference
(from "max"), while "left" pressure relief valve 22 would be set to
maximum pressure difference setting (from a 0-pressure difference;
essentially to a shut-off of the respective valve with the
exception of the "emergency function" if the maximum allowable
pressure is exceeded). As it is easily understandable, in
particular the setting of "left" adjustable pressure relief valve
22 will lead to a maximum braking power of the hydraulic propelling
circuit 1. This would result in an at least uncomfortable behaviour
of the vehicle; quite often even in a dangerous behaviour, since in
the case of a forklift truck, heavy goods might fall off the fork,
resulting in a damage or destruction of the goods and possibly even
in injuries or fatalities of a person standing nearby. This, of
course, is to be avoided.
[0081] The idea for solving this problem is to program the
electronic controller 13 in a way that in case a reversal of
direction is commanded, the electronic controller 13 will at first
switch to either "runaway prevention mode" according to FIG. 3, or
to "metering mode" according to FIG. 5 and perform a braking
action. As soon as a complete stop is detected (which can be
determined by an equality of pressures P.sub.A and P.sub.B at the
fluid ports "A" and "B" of fluid working machine 12), the "runaway
prevention mode" or the "metering mode" will be stopped and the
"standard driving mode" as shown and described with respect to FIG.
2 will be established (in the opposite direction). This way, a
smooth transition can be made. In particular, it is possible to use
a moderate braking power for the "slowing down phase" before a
reversal of movement is established.
[0082] Of course, it should be mentioned that (some of) the
pressure sensors 16, 17, 25 can be arranged at a different position
and/or that some additional pressure sensors can be provided in the
hydraulic propelling circuit 1 as well. In such a case, the control
schematic has to be adapted appropriately (in particular some
variations from the embodiment of a control schematic as shown in
FIG. 4 and/or in FIG. 6 have to be employed).
[0083] Finally, with respect to FIG. 8, a second embodiment of a
hydraulic propelling circuit 15 is shown as fluid flow schematic.
Contrary to the previously described embodiment, which enables
reversal of motion, the presently shown embodiment of a hydraulic
propelling circuit 15 can only be used in one direction (a backward
movement has to be realised by some other devices, if needed). As
an example, a mechanical gearbox could be introduced between fluid
working machine 12 and the wheels, or a small electric helper motor
could be used for realising a backward movement. The presently
shown embodiment might prove to be useful if no backward movement
is needed at all, or if a backward movement is used only rarely, so
that some additional components with very small dimensions can be
used for such a backward movement. This could be the case for a
normal car, where a backward movement is used only rarely.
[0084] As can be seen from the circuitry scheme, no switchable
fluid valves are needed anymore between the high pressure side 7
and the middle part 18. On the contrary, a simple hydraulic fluid
line 26 between main hydraulic pump 2 and fluid working machine 12
is sufficient. Nevertheless, all three pressure sensors 16, 17, 25
are still used.
[0085] Between middle part 18 and low pressure side 8 of the
hydraulic propelling circuit 15, only one pressure relief valve 22,
namely the former "left" pressure relief valve 22 is used, while on
the "right side" only a check valve 23, namely the former "right"
check valve 23 is used. The other former "right" pressure relief
valve 21 and the former "left" check valve 24 can be omitted,
however.
[0086] As can be seen, all of the normal driving mode, runaway
prevention mode and metering mode can be realised with a simplified
circuitry according to the second embodiment of a hydraulic
propelling circuit 15, if only one direction of movement has to be
realised. It is understandable, that due to the reduced amount of
components needed, this hydraulic propelling circuit 15 is cheaper
to implement.
[0087] Due to the close similarity of both embodiments of a
hydraulic propelling circuit 1, 15, similar reference numbers have
been used for similar parts. This does not mean that in real
embodiments, the respective components had to be exactly the
same.
[0088] In particular in the presently described embodiment
according to FIG. 8, a sufficient supply of hydraulic oil at the
fluid input port A of fluid working machine 12 during coasting (or
breaking) in a way so that no cavitation occurs, can be realised as
well by moving the "right" check valve 23 in parallel to the main
hydraulic pump 2 (with an appropriate opening direction of the
check valve). Of course, an additional check valve "on top of right
check valve 23" can be used as well at the position of the main
hydraulic pump 2.
[0089] The same idea can be applied mutatis mutandis to the first
embodiment of a hydraulic propelling circuit 1 as shown and
described with reference to FIGS. 1 to 7 (and likewise to other
embodiments as well).
[0090] While the present disclosure has been illustrated and
described with respect to a particular embodiment thereof, it
should be appreciated by those of ordinary skill in the art that
various modifications to this disclosure may be made without
departing from the spirit and scope of the present disclosure.
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