U.S. patent application number 11/572327 was filed with the patent office on 2007-12-13 for arrangement and a method for controlling a work vehicle.
This patent application is currently assigned to VOLVO CONSTRUCTION EQUIPMENT HOLDING SWEDEN AB. Invention is credited to Patrik Fransson, Stefan Harald Salomonsson, Kjell Sjogren, Bo Vigholm.
Application Number | 20070283688 11/572327 |
Document ID | / |
Family ID | 35786490 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070283688 |
Kind Code |
A1 |
Vigholm; Bo ; et
al. |
December 13, 2007 |
Arrangement And A Method For Controlling A Work Vehicle
Abstract
An arrangement for controlling a work vehicle including a
hydraulic system that includes at least one pump and at least one
actuator operatively driven by hydraulic fluid delivered from the
pump is provided. At least a first pump is a variable displacement
pump. The system is of load-sensing type in that the pump
displacement is controlled by a pilot pressure representing a load
exerted on the system. The arrangement includes an arrangement for
reducing the pilot pressure delivered to the first pump so that the
first pump displacement is regulated down when there is a need for
limiting hydraulic power consumption.
Inventors: |
Vigholm; Bo; (Stora Sundby,
SE) ; Fransson; Patrik; (Kumla, SE) ; Sjogren;
Kjell; (Eskilstuna, SE) ; Salomonsson; Stefan
Harald; (Maggie Valley, NC) |
Correspondence
Address: |
WRB-IP LLP
1217 KING STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
VOLVO CONSTRUCTION EQUIPMENT
HOLDING SWEDEN AB
S-635 85
Eskilstuna
SE
|
Family ID: |
35786490 |
Appl. No.: |
11/572327 |
Filed: |
June 20, 2005 |
PCT Filed: |
June 20, 2005 |
PCT NO: |
PCT/SE05/00968 |
371 Date: |
January 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60521946 |
Jul 26, 2004 |
|
|
|
Current U.S.
Class: |
60/327 ;
60/421 |
Current CPC
Class: |
F15B 2211/253 20130101;
F15B 2211/6655 20130101; F15B 2211/6652 20130101; E02F 9/2296
20130101; F15B 2211/20576 20130101; F15B 2211/20523 20130101; F16H
61/475 20130101; F15B 2211/26 20130101; F15B 2211/654 20130101;
F04B 49/022 20130101; F15B 11/165 20130101; F15B 2211/781 20130101;
E02F 9/2253 20130101; E02F 9/2292 20130101; E02F 9/2217 20130101;
E02F 9/2221 20130101; F15B 2211/20553 20130101 |
Class at
Publication: |
060/327 ;
060/421 |
International
Class: |
E02F 9/22 20060101
E02F009/22; F16H 61/46 20060101 F16H061/46 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2004 |
SE |
0402233-1 |
Claims
1. An arrangement for controlling a work vehicle (1) comprising a
hydraulic system (22), which comprises at least one pump (18,180)
and at least one actuator (4,5,8,9,10) operatively driven by
hydraulic fluid delivered from said pump, wherein at least a first
pump (18) is a variable displacement pump, the system (22) being of
load-sensing type in that the pump displacement is controlled by a
pilot pressure representing a load exerted on the system,
characterized in that the arrangement comprises means (63) for
reducing the pilot pressure delivered to the first pump (18) so
that the first pump displacement is regulated down when there is a
need for limiting hydraulic power consumption.
2. An arrangement according to claim 1, characterized in that said
means (63) for reducing the pilot pressure to the first pump (18)
is adapted to reduce the pilot pressure to the first pump to such
an extent that the first pump does not deliver any hydraulic fluid
flow.
3. An arrangement according to claim 1 or 2, characterized in that
the hydraulic system (22) comprises at least two variable
displacement pumps (18,180) for delivering hydraulic fluid to said
actuator (4,5,8,9,10).
4. An arrangement to claim 3 characterized in that the displacement
of a second pump (180) is controlled by a pilot pressure
representing the load exerted on the system in a non-manipulated
form.
5. An arrangement to claim 3 or 4 characterized in that conduits
(48,59) for the pilot pressure are connected both to an input pilot
port (47) of the first pump (18) and to an input pilot port (45) of
a second pump (180), that a flow restrictor (66) is arranged on the
conduit (48) to the input pilot port (47) of the first pump (18)
and that the flow restrictor is arranged upstream of said means
(63) for reducing the pilot pressure to said first pump.
6. An arrangement according to any of the preceding claims,
characterized in that said means (63) for reducing the pressure to
said first pump (18) is formed by a valve, and that the valve in an
activated state is adapted to at least partly route the pilot
pressure in a conduit (65) bypassing the first pump.
7. An arrangement according to any of the preceding claims
characterized in that each pump (18,180) has an associated
hydraulically controlled arrangement (43,44) for controlling the
displacement of the pump and that the displacement control
arrangement controls the pump displacement depending on the input
pilot pressure.
8. An arrangement according to any of the preceding claims
characterized in that said pump (18,180) is operatively driven by
an engine (14) arranged for propelling the vehicle.
9. An arrangement according to claim 8 characterized in that the
arrangement comprises means (60,61,70) for detecting an operation
state of a driveline (13) of the work vehicle and means (62)
connected to the detection means for evaluating the detected
operation state and generating an operation state signal.
10. An arrangement according to claim 9 characterized in that said
evaluating means (62) is connected to said means (63) for reducing
the pilot pressure to the first pump (18) for controlling the
displacement reduction depending on the operation state of the
driveline.
11. An arrangement according to claim 9 or 10 characterized in that
said detection means comprises means (60) for detecting an engine
speed.
12. An arrangement according to any of claims 9-11 characterized in
that said detection means comprises means for detecting a
turbocharger pressure.
13. An arrangement according to any of claims 9-12 characterized in
that said detection means comprises means for detecting an engine
torque or output power.
14. An arrangement according to any of claims 9-13 characterized in
that said detection means comprises means (61) for detecting a gear
state in a vehicle gear box (15).
15. An arrangement according to any of claims 9-14 characterized in
that said detection means comprises means (70) for detecting a
position of an accelerator pedal (71).
16. An arrangement according to claim any of claims, characterized
in that at least one of said actuators is arranged to move an
implement of the work vehicle.
17. A method of controlling a work vehicle with a hydraulic system
for operating at least one actuator, comprising the steps of
sensing a load exerted on the system and controlling a displacement
of a first pump with variable displacement by means of a pilot
pressure representing the load, the pump operatively driving the
actuator by delivering hydraulic fluid to it, and reducing the
pilot pressure to the first pump in case the hydraulic power needs
to be limited.
18. A method according to claim 17, wherein the pilot pressure to
the first pump is reduced to such an extent that the first pump
does not deliver any hydraulic fluid flow.
19. A method according to claim 17 or 18, wherein said pump is
operatively driven by an engine arranged for propelling the
vehicle.
20. A method according to any of claims 17-19, wherein an operation
state of a driveline of the work vehicle is detected, the detected
operation state is evaluated and an operation state signal
generated for controlling the pump displacement reduction depending
on the operation state of the driveline.
21. A method according to claim 20, wherein an engine speed is
detected.
22. A method according to claim 20 or 21, wherein a turbocharger
pressure is detected.
23. A method according to any of claims 20-22, wherein an engine
torque or output power is detected.
24. A method according to any of claims 20-23, wherein a position
of an accelerator pedal (71) is detected.
25. A method according to any of claims 20-24, wherein a gear state
in a vehicle gear box (15) is detected.
26. A computer program comprising code means for performing all the
method steps described in any of claims 17-25 when said program is
run on a computer.
27. A computer program product comprising program code means stored
on a computer readable medium for performing the method described
in any of claims 17-25 when said program product is run on a
computer.
Description
BACKGROUND AND SUMMARY
[0001] The present invention relates to an arrangement for
controlling a work vehicle comprising a hydraulic system. The
hydraulic system comprises at least one pump and at least one
actuator operatively driven by hydraulic fluid delivered from said
pump, wherein at least a first pump is a variable displacement
pump. The system is of load-sensing type in that the pump
displacement is controlled by a pilot pressure representing a load
exerted on the system.
[0002] The pump is normally operatively driven by an internal
combustion engine arranged for propelling the work vehicle.
[0003] The term work vehicle comprises different types of material
handling vehicles like construction machines, such as a wheel
loader, a backhoe loader, a motor grader and an excavator. The
invention will be described below in a case in which it is applied
in a wheel loader. This is to be regarded only as an example of a
preferred application.
[0004] Said actuator may be a linear actuator in the form of a
hydraulic cylinder. A wheel loader comprises several such hydraulic
cylinders in order to perform certain functions. A first pair of
hydraulic cylinders are arranged for turning the wheel loader.
Further, there are hydraulic cylinders provided for lifting a load
arm unit and tilting an implement, for example a bucket, arranged
on the load arm unit.
[0005] A load sensing hydraulic system is characterized by that the
operating condition of the load is sensed and that the output
pressure of the pump is controlled so that it exceeds the load
pressure existing in the hydraulic actuator by a predetermined
differential. More specifically, the pressure (an LS signal) from
the hydraulic cylinder for the load is sensed via a shuttle valve
and via an activated control valve unit associated with the
hydraulic cylinder for the load. The pump then delivers a hydraulic
fluid flow to the hydraulic cylinder, the level of which depends on
the extent to which the activated control valve unit is
operated.
[0006] In order for the work vehicle to function well, the engine,
transmission and hydraulic system must be balanced with regard to
available power and output power. It is difficult to find an engine
that exactly manages the desired power outputs at different engine
speeds. The problem with different output power demand is
particularly pronounced at low engine speeds. If the driver
utilizes the power from the engine at low engine speeds to drive
the vehicle's half shafts at the same time as the hydraulic system
is activated, then there is a risk that the engine will cut out or
that the engine will "stick", that is it will not be able to
increase the engine speed when the driver depresses the accelerator
pedal. The driver can, of course, adjust the power consumption via
various controls, when he senses a loss of engine speed, but this
can be problematical, particularly when the engine suddenly cuts
out. Further, even skilled drivers overcompensate and therefore
unnecessarily reduce the amount of hydraulic work the hydraulic
system is truly capable of performing. As a result, machine
productivity is reduced.
[0007] There are known arrangements, which are adapted to relieve
the engine load by reducing pump displacement when there is a risk
for stalling the engine.
[0008] In U.S. Pat. No. 6,644,429, engine speed or engine torque is
sensed and the pump displacement is reduced to zero for certain
engine speed or engine torque limit values. A left and right
solenoid is controlled by a controller and adapted to position the
swash plates on the pumps.
[0009] In U.S. Pat. No. 4,335,577, engine speed is sensed and the
pump displacement is reduced to zero for a certain engine speed
limit value. The pump is short-circuited so that it regulates down,
ie the pump output pressure is conveyed directly to the
load-sensing conduit and the pressure is increased until the pump
maximum pressure limitation is reached. A disadvantage is that when
a higher flow is used for a function, the pump may stick on maximum
displacement and cannot increase the pressure to the maximum level.
The pump will then continue to pump with full flow and not maximum
pressure although it is short-circuited.
[0010] It is desirable to achieve an alternative control
arrangement for a work vehicle with a load-sensing hydraulic system
that creates conditions for limiting the hydraulic power to relieve
engine load, especially when there is a risk for stalling the
engine. Further, the arrangement should be cost-efficient in
operation and/or to install in the work vehicle.
[0011] According to an aspect of the present invention, an
arrangement comprises means for reducing the pilot pressure
delivered to the first pump so that the first pump displacement is
regulated down when there is a need for limiting hydraulic power
consumption. More specifically, the load signal delivered to the
first pump is reduced to a pressure level below the load pressure
resulting in that the displacement of the first pump is regulated
down to zero output. Thus, the load sensing signal from the
hydraulic cylinder is manipulated before reaching the first
pump.
[0012] More specifically, the pump displacement is reduced by
pressure control. This arrangement may easily be introduced in a
conventional load-sensing system.
[0013] Further, the arrangement is adapted to sense a reduction of
a value of an operation state of the vehicle's driveline, for
example a reduction in the engine speed, resulting from excessive
hydraulic loads and control the pressure reducing means based on
the detected operation state value.
[0014] According to a preferred embodiment said means for reducing
the pilot pressure to the first pump is adapted to reduce the pilot
pressure to the first pump to such an extent that the first pump
does not deliver any hydraulic fluid flow. Thus, the first pump is
completely destroked. This is particularly advantageous when there
are more than one pump delivering hydraulic fluid to the
actuator.
[0015] In the case that the hydraulic system comprises at least two
variable displacement pumps for delivering hydraulic fluid to said
actuator the displacement of a second pump is preferably controlled
by a pilot pressure representing the load exerted on the system in
a non-manipulated form. Thus, only the input pilot pressure signal
to the first pump is manipulated. Existing load-sensing hydraulic
systems may easily and cost-efficiently be amended for achieving
the limitation of the hydraulic power to relieve engine load in
this way.
[0016] According to a preferred embodiment the arrangement
comprises means for detecting an operation state of a driveline of
the work vehicle and means connected to the detection means for
evaluating the detected operation state and generating an operation
state signal. Further, said evaluating means is connected to said
means for reducing the pilot pressure to the first pump for
controlling the displacement reduction depending on the operation
state of the driveline.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention will be explained below, with reference to the
embodiments shown on the appended drawings, wherein
[0018] FIG. 1 shows a wheel loader in a side view,
[0019] FIG. 2 schematically shows an exemplary embodiment of a
driveline for the wheel loader, and
[0020] FIG. 3 illustrates diagrammatically a preferred embodiment
of an arrangement for controlling the wheel loader.
DETAILED DESCRIPTION
[0021] FIG. 1 shows a wheel loader 1. The body of the wheel loader
1 comprises a front body section 2 and a rear body section 3, which
sections each has a pair of half shafts 12, 120. The rear body
section 3 comprises a cab 101. The body sections are connected to
each other in such a way that they can pivot. The body sections 2,
3 can pivot in relation to each other around a vertical axis by
means of two actuators in the form of hydraulic cylinders 4, 5
arranged between the two sections. The hydraulic cylinders 4, 5 are
thus arranged to turn the wheel loader 1.
[0022] The wheel loader 1 comprises an equipment 11 for handling
objects or material. The equipment 11 comprises a load-arm unit 6
and an implement 7 in the form of a bucket fitted on the load-arm
unit. A first end of the load-arm unit 6 is pivotally connected to
the front vehicle section 2. The implement 7 is connected to a
second end of the load-arm unit 6.
[0023] The load-arm unit 6 can be raised and lowered relative to
the front section 2 of the vehicle by means of two second actuators
in the form of two hydraulic cylinders 8, 9, each of which is
connected at one end to the front vehicle section 2 and at the
other end to the load-arm unit 6. The bucket 7 can be tilted
relative to the load-arm unit 6 by means of a third actuator in the
form of a hydraulic cylinder 10, which is connected at one end to
the front vehicle section 2 and at the other end to the bucket 7
via a link-arm system. FIG. 2 illustrates schematically an example
of the wheel loader's 1 driveline 13. The driveline 13 comprises an
internal combustion engine 14, in the form of a diesel engine, an
automatic gearbox 15 and a hydrodynamic torque converter 16.
Advantageously, the engine comprises a turbocharger (not shown) .
The gearbox 15 consists of an electrically controlled automatic
gearbox of the power-shift type. The gearbox 15 comprises a forward
and reverse gear 17.
[0024] FIG. 2 also shows two pumps 18, 180 in the wheel loader's
hydraulic system for supplying the hydraulic cylinders 4, 5, 8, 9,
10 with hydraulic fluid. The pumps 18, 180 (like the torque
converter 16) is driven by an output shaft 19 from the engine 14.
In the illustrated embodiment, the pumps 18, 180 are drivingly
connected between the torque converter 16 and the gearbox 15. More
specifically, the pumps 18, 180 are driven by a torque converter
output shaft 19 via a transmission 24. An output shaft 20 from the
gearbox 15 leads to a differential gear 21, which is drivingly
connected to said half-shafts 12, on which the vehicle's driving
wheels 23 are arranged.
[0025] FIG. 3 illustrates an embodiment of an arrangement 25 for
controlling the wheel loader 1. The solid lines indicate main
hydraulic conduits, the dashed lines indicate pilot hydraulic
conduits and the lines with a longer dash followed by two shorter
dashes indicate lines for electric signals.
[0026] It is schematically shown in FIG. 3 that the pumps 18, 180
are drivingly connected to the engine 14. The control arrangement
25 comprises a control unit 26, or computer. A number of electric
operating levers 64 arranged in the cab are connected to the
control unit 26, and this is adapted to handle the signals from the
levers. A number of electrically controlled hydraulic valve units
27, 28 in a hydraulic system 22 are electrically connected to the
control unit 26 and hydraulically connected to the hydraulic
cylinders 4, 5, 8, 9, 10 for regulating the reciprocating work of
these. The first and second pump 18 and 180, respectively are
provided in order to supply the hydraulic cylinders 4, 5, 8, 9, 10
with hydraulic oil through the hydraulic valve units 27, 28. Each
of said valve units 27, 28 comprises a directional control valve
(not shown) . The directional control valve has a pair of service
passages being connected to opposite ends of each of the
double-acting hydraulic cylinders.
[0027] The hydraulic system 22 further comprises a valve unit 31
arranged between said pumps 18, 180 and said actuators 4, 5, 7, 8,
9 for controlling a flow of hydraulic fluid supplied to the
actuators from said pumps. Said valve unit comprises a prioritizing
valve connected between the pumps 18, 180 and the electric valves
27, 28. This prioritizing valve unit 31 is adapted for prioritizing
steering hydraulics over lifting hydraulics.
[0028] An accumulator 32 with an associated valve unit 71 is
connected to the loading cylinders 8, 9 in such a way that
spring-action characteristics are obtained when the vehicle is
driven with a loaded implement.
[0029] The signals from the electric operating levers 64 may be
converted in a characteristic way in the control unit 26 and are
then sent as output signals to the valve units 27, 28 in the form
of electric pilot hydraulic valves, which in turn control the
hydraulic cylinders 4, 5, 8, 9, 10.
[0030] Another valve unit 33 is indicated in FIG. 3. This valve
unit 33 is intended to regulate the supply of hydraulic oil to an
actuator of an implement and is coupled hydraulically to the pumps
18, 180 through the prioritizing valve unit 31 and electrically to
the control unit 26. Said actuator of the implement can consist of,
for example, a working cylinder of the gripping arms for moving
these relative to one another or a working cylinder of the fork
implement for relative movement of the two legs. The prioritizing
valve unit 31 is also adapted to prioritize the steering hydraulics
over the hydraulics for the implement concerned.
[0031] Both pumps 18, 180 have variable displacement. The hydraulic
output by the pumps can thereby be controlled. The pumps 18, 180
feed hydraulic fluid to. said actuators 4, 5, 8, 9, 10 and the
associated loads coupled thereto. The pumps 18, 180 are provided so
as to supply fluid to the control valves 27, 28 through fluid
supply conduits.
[0032] Each of the pumps 18, 180 has a main inlet 34 and 35,
respectively, connected to a sump 36 and a main outlet 37 and 38,
respectively, connected to an inlet port 39, 40 of the control
valve unit 31 through fluid supply conduits 41, 42.
[0033] A displacement control arrangement 43 and 44, respectively,
is arranged at each pump 18, 180 for controlling the displacement
thereof. The pump 18, 180 includes a swash plate being rotatable
for varying pump displacement. The displacement control arrangement
43, 44 is hydraulically activated and comprises a mechanical
element coupled to the swash plate for rotating the same and set it
in a desired position. The displacement control arrangement 43, 44
works against spring force. The displacement control arrangement
43, 44 comprises a pilot inlet port 45 and 47, respectively. The
displacement control arrangement 43, 44 is operative to increase
the displacement of the pumps 18, 180 in response to receipt of
respective increased pressure signals.
[0034] The hydraulic system 22 is load sensing and the pump
displacement is therefore automatically controlled by a pilot
pressure signal representing a load exerted on the system. In other
words, the displacement of said first pump 18 is controlled by a
load signal (pressure signal) representing an actual load. Thus,
both pumps 18, 180 have their displacements controlled
automatically in response to the requirement of various hydraulic
functions.
[0035] The first pump 18 and the second pump 180 are hydraulically
interconnected so that the pilot pressure is supplied to the input
pilot port 45 of the second pump 180. An output pilot port 46 of
the second pump 180 is connected to the input pilot port 47 of the
first pump 18 through a hydraulic fluid conduit 48.
[0036] The displacement control arrangement 43 of the second pump
180 is connected to said inlet port 45 so that it controls the pump
displacement depending on the input pilot pressure. The
displacement control arrangement 44 of the first pump 18 is
connected to said inlet port 47 so that it controls the pump
displacement depending on the input pilot pressure.
[0037] The hydraulic system 22 further comprises shuttle valve
means 49 operable for routing the larger fluid pressure existing at
the output ports of the valve units 27, 28, 33 to the pump
displacement control arrangements 43, 44 to thereby automatically
control the pumps 18, 180 to satisfy the highest demand of the
loads associated with the valve units 27, 28, 33. The pumps 18, 180
are hydraulically controlled to deliver an output pressure equal to
such highest load pressure plus the load sensing pressure drop of
the valve unit 27, 28, 33 associated with the load. For example,
the pumps may be adapted to deliver a pressure of 25 bar higher
than the load pressure.
[0038] More specifically, pilot conduits 50, 51, 52 connect the
outlet ports of the control valve units 27, 28, 33 to first and
second inlet ports 53, 54 of the shuttle valve 49. The shuttle
valve 49 comprises a ball 55, which is arranged in a central space,
and two opposite seats 56, 57 for the ball 55, each associated with
one of said first and second inlet ports 53, 54. Each seat 56, 57
is arranged so that the ball 55 will block the respective inlet
port 53, 54. The shuttle valve comprises an outlet port 58
connected to the inlet ports 53, 54 by said central space. In this
way, the greater of the pressures in the pilot conduits connected
to the inlet ports 53, 54 will act on the ball 55 and seat the ball
in the opposite seat so that the larger of the pressures in the
pilot conduits is communicated to the outlet port 58. The outlet
port 58 of the shuttle valve 49 is connected, by a further pilot
fluid conduit 59, to the displacement control arrangement 43 of the
second pump 180.
[0039] For example, when the operator wants to lift the load-arm
unit 11, he operates the specific control lever 64 associated with
this function. The valve unit 28 associated with the lift cylinders
8, 9 will then start opening. The valve unit 28 is arranged to
first open a port to the conduit 51 connected to the shuttle valve
49. The pressure of the lift cylinders 8, 9 will then be forwarded
to the second pump 180 via the conduit 59 connected to the inlet
port 45. The second pump 180 will now deliver a flow so that the
output pressure from the second pump will be a specific
differential higher, for example 25 bar, than the lift cylinder
pressure.
[0040] The pressure from the lift cylinder 8, 9 will be forwarded
from the second pump outlet port 46 to the inlet port 47 of the
first pump 18. The first pump 18 will in the same way as the second
pump 180 deliver a flow so that the output pressure from the first
pump 18 will be a specific differential higher, for example 25 bar,
than the lift cylinder pressure.
[0041] When the valve unit 28 opens further, a main inlet port 72
of the valve unit 28 will open so that hydraulic fluid flow from
the pumps 18, 180 is delivered from the pumps to the lift
cylinder.
[0042] The control arrangement 25 comprises means 60, 61, 70 for
detecting an operation state of the driveline 13 of the work
vehicle. Said detection means 60, 61, 70 (sensors) may be adapted
to sense a reduction of a value of the operation state, for example
a change in the engine speed, resulting from excessive hydraulic
loads, and producing parameter signals in response to the detected
operating state. The control unit 26 is connected to the detection
means 60, 61, 70 and comprises means 62 for evaluating the detected
operation state and generating an operation state signal. Said
evaluating means comprises software code for performing the
evaluation. Thus, it is programmed with certain algorithms.
[0043] The evaluating means 62 is connected to means 63 for
reducing the pilot pressure signal to the first pump 18 for
controlling the displacement reduction depending on the operation
state of the driveline. More specifically, the pilot pressure
signal is reduced to a pressure level below the load pressure
resulting in that the displacement of the first pump is regulated
down to zero. Said means 63 for reducing the pressure signal to the
first pump 18 is connected to said evaluation means 62 for
receiving the operation state signal and reduce said pressure
signal depending on the operation state signal.
[0044] Said detection means comprises means 60 for detecting an
engine parameter. The engine parameter detection means 60 include a
boost pressure sensor located at the inlet manifold of the engine
downstream of the turbocharger, an ambient pressure sensor and an
engine speed sensor.
[0045] The engine speed sensor may be a magnetic pick-up device
sensitive to the movement of a gear tooth in the engine, which is
proportional to crankshaft speed. The boost pressure sensor and the
ambient pressure sensor are preferably pulse-width modulated
pressure sensors of a type well known in the art producing signals
having duty-cycles proportional to sensed pressure levels.
[0046] According to a first embodiment, the engine speed is sensed.
When the engine speed falls to a predetermined minimum, the control
unit 26 will output a signal with a level as a function of the
detected engine speed. Said detection means may also comprise means
70 for detecting the position of an accelerator pedal 71.
Therefore, as an alternative, the control unit 26 will output a
signal with a level as a function of both the detected engine speed
and the detected position of an accelerator pedal 71.
[0047] According to a second embodiment, the turbocharger pressure
is sensed. When the turbocharger pressure falls to a predetermined
minimum, the control unit 26 will output a signal with a level as a
function of the detected turbocharger speed. As an alternative, the
control unit 26 will output a signal with a level as a function of
both the detected turbocharger pressure and the detected position
of an accelerator pedal 71.
[0048] According to a third embodiment, a driveline torque or
output power is sensed. In this embodiment the engine torque is
sensed. The pressure in a clutch in the gear box is used as a
measure of the engine torque. Such clutch pressure signals are
directly related to the torque being transmitted by the clutch to
the wheels and by the wheels to the ground. When the torque falls
to a predetermined minimum, the control unit 26 will output a
signal with a level as a function of accessible engine torque. As
an alternative, the control unit 26 will output a signal with a
level as a function of both accessible engine torque and the
detected position of an accelerator pedal 71.
[0049] Said detection means further comprises means 61 for
detecting a gear state in the gear box 15. More specifically, the
detection means 61 detects a neutral state in the gear box 15. If
the driver uses the hydraulic system 22 for a certain work
operation when the vehicle is standing still, the driver normally
puts the gear in the neutral state. Thus, in such a case, the
engine is not used for propelling the vehicle. Thus, when a neutral
state is detected, there is no need for destroking/disconnecting
the first pump 18. Therefor, according to a further embodiment,
when a neutral state is detected, the control unit 26 will not
initiate destroking/disconnection of the first pump 18 independent
of the engine speed.
[0050] Further, in a certain work situation, the driver may want a
higher engine speed and he therefore depresses the accelerator
pedal 71. Said means 70 detects the position of the accelerator
pedal 71 and at a certain predefined depression, suitably
substantially corresponding to a desired full gas, the control unit
26 will produce a signal to the pilot pressure reducing means 63 in
order to regulate the first pump displacement down (or
disconnecting the pump). Thus, there is no requirement for the
engine speed to be substantially decreased (close to engine cut
out) for regulating the pump displacement down. Instead, the first
pump displacement may be regulated down at a comparably low pilot
pressure (system load) in order to increase the engine speed for a
different reason.
[0051] The control unit 26 is programmed to activate the means 63
for reducing the pilot pressure signal to the first pump 18. More
specifically, the pilot pressure signal reducing means 63 is formed
by a solenoid-operated valve arranged in a branch conduit 65
connected to the pilot conduit 48 connecting the second pump outlet
port 46 and the first pump inlet port 47. Thus, the pilot pressure
signal reducing means 63 will control the hydraulic load signal to
a pressure level corresponding to the electric signal from the
control unit 26. The branch conduit 65 is connected to the sump 36.
The hydraulic pilot signal will thus be drained to the sump 36 if
the load pressure level is higher than the regulated pressure. The
first pump 18 will then be destroked (the displacement of the first
pump 18 will be reduced to zero and will not deliver any hydraulic
fluid flow).
[0052] A flow restrictor 66, or orifice, is arranged on the conduit
48 connecting the output pilot port 46 of the second pump 180 and
the input pilot port 47 of the first pump 18. The flow restrictor
66 is arranged upstream of said means 63 for reducing the pressure
signal to said first pump 18. Thanks to the flow restrictor 66, the
second pump 180 can maintain its pressure level and thereby
continue to deliver fluid flow. This is due to that a flow will
continuously be guided from the hydraulic cylinder to the pilot
pressure inlet port 45 for the second pump 180. The flow is large
enough for saturating the orifice 66.
[0053] When there is no need for reducing the power of the
hydraulic system, the control unit will send a high electric signal
to the solenoid valve 63 so that its opening pressure is higher
than the maximum pump pressure.
[0054] When the control unit 26 regulates the solenoid valve 63 to
a certain extent, the first pump 18 will be disconnected (stroked
down) if the load pressure is larger than the regulated pressure
level. The first pump 18 will be connected (and delivering fluid)
as long as the load pressure is smaller than the regulated pressure
level.
[0055] When the driveline is in a neutral state, an upper engine
speed limit boundary may be used for activating the first pump.
Thus, when the detected engine speed reaches said upper engine
speed limit boundary, the control unit 26 will send a signal to the
solenoid valve 63 for deactivating the same so that it does not
influence the load pressure from the hydraulic cylinder
independently of whether the above described methods of controlling
the solenoid valve 63 based on the operation parameter of the
driveline is in operation or not.
[0056] Further, in case the engine speed is reduced to a predefined
lower critical level, the control unit 26 sends a signal to the
solenoid valve 63 to reduce the pilot input pressure to the first
pump and thereby disconnect the pump.
[0057] The ambient atmospheric pressure may further be sensed and
used as an input for determining the level of manipulation of the
input pressure signal to the first pump.
[0058] The invention is also directed to a computer program
comprising code means for performing the method steps described
above when said program is run on a computer. Said computer program
is loaded in a memory in the control unit 26. Said computer program
may be sent to the control unit by wireless technique, for example
via the internet.
[0059] The invention is further directed to a computer program
product comprising program code means stored on a computer readable
medium for performing the method described above when said program
product is run on a computer. Said computer readable medium may be
in the form of a floppy disk or a CD-ROM.
[0060] The abovementioned control unit (ECU) 26 is also often
called a CPU (Control Power Unit) or plainly vehicle computer.
[0061] The invention has above been described for solving the
problem of limiting hydraulic power output at low engine speeds.
The invention may of course also be used for limiting hydraulic
power also at high engine speeds, which may be necessary when an
engine with "too little" power is used for an arrangement where
"too high" power outputs are demanded.
[0062] The invention is not in any way limited to the above
described embodiments, instead a number of alternatives and
modifications are possible without departing from the scope of the
following claims. For example, the driveline described above in
connection with FIG. 2 should only be regarded as an example. Any
type of transmission may be used.
[0063] As an alternative or complement to the control methods
described above, said detection means comprises means for detecting
an engine fan torque or output power and the detected value is used
to set the input pressure level to the first pump.
[0064] Further, output power may be sensed instead of torque in the
methods described above.
[0065] The specific hydraulic system for controlling the first pump
by manipulating its input pilot pressure may be solved in a number
of different ways. One conduit for guiding the pilot pressure
should be connected to an input pilot port of the first pump, one
conduit for guiding the pilot pressure should be connected to an
input pilot port of the second pump and the conduit leading to the
first pump (to be regulated down) should have an orifice and a
downstream bypass conduit to tank. Thus, the embodiment described
and showed in FIG. 3 should only be regarded as an example.
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