U.S. patent application number 14/914663 was filed with the patent office on 2016-11-10 for wheel loader.
This patent application is currently assigned to Hitachi Construction Machinery Co., Ltd.. The applicant listed for this patent is HITACHI CONSTRUCTION MACHINERY CO., LTD.. Invention is credited to Koji HYODO, Shoroku KAWAHARA, Keigo KIKUCHI, Atsushi SHIMAZU, Kohtaroh UNO.
Application Number | 20160326720 14/914663 |
Document ID | / |
Family ID | 53041328 |
Filed Date | 2016-11-10 |
United States Patent
Application |
20160326720 |
Kind Code |
A1 |
UNO; Kohtaroh ; et
al. |
November 10, 2016 |
WHEEL LOADER
Abstract
Provided is a wheel loader having an HST type driving system. In
order to make it possible to improve working efficiency in an eco
mode when a power mode and the eco mode have been set in the wheel
loader, the wheel loader is provided with a controller 18 which has
an eco mode characteristic line 31, a power mode characteristic
line 32, and a lifting operation characteristic line 34 having a
matching point C located between a matching point A between a
working device operating engine torque characteristic line 30 and
the eco mode characteristic line 31 and a matching point B between
the working device operating engine torque characteristic line 30
and the power mode characteristic line 32. The controller 18
includes a control portion which controls an HST pump 11 in
accordance with the lifting operation characteristic line 34 when
lifting operation of a lift arm 4 is detected in the condition that
the eco mode has been selected by a work mode selecting portion
22.
Inventors: |
UNO; Kohtaroh; (Ibaraki,
JP) ; KAWAHARA; Shoroku; (Ibaraki, JP) ;
KIKUCHI; Keigo; (Ibaraki, JP) ; HYODO; Koji;
(Ibaraki, JP) ; SHIMAZU; Atsushi; (Ibaraki,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HITACHI CONSTRUCTION MACHINERY CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
Hitachi Construction Machinery Co.,
Ltd.
Tokyo
JP
|
Family ID: |
53041328 |
Appl. No.: |
14/914663 |
Filed: |
October 15, 2014 |
PCT Filed: |
October 15, 2014 |
PCT NO: |
PCT/JP2014/077458 |
371 Date: |
February 26, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E02F 3/431 20130101;
E02F 9/2066 20130101; E02F 9/0841 20130101; E02F 9/2289 20130101;
E02F 3/283 20130101; E02F 9/02 20130101; E02F 9/2296 20130101; F16H
61/468 20130101; F02D 29/04 20130101; E02F 9/2253 20130101 |
International
Class: |
E02F 9/22 20060101
E02F009/22; E02F 9/02 20060101 E02F009/02; F16H 61/468 20060101
F16H061/468; E02F 3/28 20060101 E02F003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2013 |
JP |
2013-232100 |
Claims
1. A wheel loader comprising: a vehicle body frame (11); wheels (9,
10); a working device (3) which is attached to the vehicle body
frame (10) and which has a lift arm (4) capable of being rotated in
an up/down direction; an engine (17) which is attached to the
vehicle body frame (10); an HST traveling device in which a
variable displacement type HST pump (11) driven by the engine (17)
and an HST motor (14) driving the wheels (9, 10) are connected to
each other in a closed circuit, and which has an HST pump control
portion (15) controlling input torque of the HST pump (11); and a
working machine pump (13) which is driven by the engine (17) to
discharge pressure oil for operating the working device (3);
wherein: the wheel loader further comprises: a work mode selecting
device (22) which selects one from a power mode and an eco mode,
the power mode serving as a work mode when the workload is a heavy
load, the eco mode serving as a work mode when the workload is a
light load; a detecting device (23) which detects lifting operation
of the lift arm (4) of the working device (3); and a control device
(18) which makes control so that the input torque of the HST pump
(11) can be controlled in accordance with a preset eco mode
characteristic by the HST pump control portion (15) when the eco
mode is selected by the work mode selecting device (22), and the
input torque of the HST pump (11) can be controlled in accordance
with a preset power mode characteristic by the HST pump control
portion (15) when the power mode is selected by the work mode
selecting device (22), but the input torque characteristic of the
HST pump (11) can be controlled in accordance with a lifting
operation characteristic in place of the eco mode characteristic
when the lifting operation of the lift arm (4) is detected by the
detecting device (23) after the eco mode has been selected.
2. A wheel loader according to claim 1, wherein: the control device
(18) has a storage portion (28) which stores an eco mode
characteristic line (31), a power mode characteristic line (32),
and a lifting operation characteristic line (34); each of the eco
mode characteristic line (31), the power mode characteristic line
(32) and the lifting operation characteristic line (34) includes a
characteristic line expressing a relation between engine speed and
the input torque of the HST pump (11); and the lifting operation
characteristic line (34) is set as a characteristic in which a
matching point as an intersection point of the lifting operation
characteristic line (34) with a working device operating engine
torque characteristic line (30) obtained by subtracting torque of
the working machine pump (13) from torque of the engine (17) is
provided between a matching point as an intersection point between
the eco mode characteristic line (31) and the working device
operating engine torque characteristic line (30) and a matching
point as an intersection point between the power mode
characteristic line (32) and the working device operating engine
torque characteristic line (30).
3. A wheel loader according to claim 1, further comprising: a
multistage transmission which is connected to the HST motor (14)
and which has a plurality of speed stages including a high speed
stage and a low speed stage; a speed stage detecting device (20)
which detects that the multistage transmission has been changed
over to the low speed stage; and a forward movement detecting
sensor (21) which detects that the wheel loader is in a state of
forward movement; wherein: the HST motor (14) includes a variable
displacement type hydraulic motor; the HST traveling device has an
HST motor control portion (16) which controls tilting of the HST
motor (14); and when it is detected by the speed stage detection
device (20) that the multistage transmission has been changed over
to the low speed stage and it is detected by the forward movement
detecting sensor (21) that the wheel loader is in a state of
forward movement, the control device (18) makes control so that
minimum tilting of the HST motor (14) can be set as minimum tilting
larger than minimum tilting in the eco mode by the HST motor
control portion (16).
4. A wheel loader according to claim 1, wherein: the lifting
operation characteristic line (34) is provided to diverge from the
middle of the eco mode characteristic line (31).
5. A wheel loader according to claim 2, wherein: the lifting
operation characteristic line (34) is provided to diverge from the
middle of the eco mode characteristic line (31).
6. A wheel loader according to claim 2, further comprising: a
multistage transmission which is connected to the HST motor (14)
and which has a plurality of speed stages including a high speed
stage and a low speed stage; a speed stage detecting device (20)
which detects that the multistage transmission has been changed
over to the low speed stage; and a forward movement detecting
sensor (21) which detects that the wheel loader is in a state of
forward movement; wherein: the HST motor (14) includes a variable
displacement type hydraulic motor; the HST traveling device has an
HST motor control portion (16) which controls tilting of the HST
motor (14); and when it is detected by the speed stage detection
device (20) that the multistage transmission has been changed over
to the low speed stage and it is detected by the forward movement
detecting sensor (21) that the wheel loader is in a state of
forward movement, the control device (18) makes control so that
minimum tilting of the HST motor (14) can be set as minimum tilting
larger than minimum tilting in the eco mode by the HST motor
control portion (16).
7. A wheel loader according to claim 3, wherein: the lifting
operation characteristic line (34) is provided to diverge from the
middle of the eco mode characteristic line (31).
8. A wheel loader according to claim 6, wherein: the lifting
operation characteristic line (34) is provided to diverge from the
middle of the eco mode characteristic line (31).
Description
TECHNICAL FIELD
[0001] The present invention relates to a wheel loader having an
HST type driving system.
BACKGROUND ART
[0002] As this type of wheel loader, there is a wheel loader which
has been disclosed in Patent Literature 1. The wheel loader is
provided with wheels, a vehicle body frame with an operator's cab,
a working device, etc. The working device is provided with a lift
arm which moves in an up/down direction, and a bucket which is
attached to a distal end of the lift arm.
[0003] As this type of wheel loader, there is a wheel loader having
an HST type driving system. The HST type driving system is provided
with an HST pump and an HST motor which form a closed circuit, a
working machine pump which discharges pressure oil for driving the
working device, and a driving wheel system which operates in
response to an output from the HST motor.
CITATION LIST
PATENT LITERATURE
[0004] Patent Literature 1: JP-A-2008-223899
SUMMARY OF INVENTION
Technical Problem
[0005] In order to achieve an energy saving effect, it can be
considered that a power mode and an eco mode are set for control of
the HST pump and the HST motor in the aforementioned wheel loader
having the HST type driving system. The power mode supports
heavy-load excavation. In the eco mode attaching importance to a
fuel consumption reduction effect, engine speed is suppressed to be
lower than that in the power mode.
[0006] However, it can be considered that the wheel loader which
has been configured thus to have the eco mode has the following
disadvantage. That is, the working machine pump is also directly
connected to the engine and the HST pump. The discharge flow rate
of the working machine pump is determined in accordance with
rotation speed of an input shaft directly connected to the engine.
Accordingly, when soil which has been, for example, held by a
bucket of the working device is lifted up by the lift arm in the
eco mode, operation speed of the working device may become slow to
thereby lower working efficiency.
[0007] FIG. 8 is a graph showing input torque characteristics of
the HST pump relative to the engine speed, which have been
considered from the aforementioned background-art technique. In
FIG. 8, the reference sign 32 designates a power mode
characteristic; 31, an eco mode characteristic; 29, an engine
torque characteristic; and 30, an engine torque characteristic
which is obtained by subtracting input torque of the working
machine pump during driving of the working device from the engine
torque characteristic 29. The engine torque characteristic 30
expresses engine torque which can be consumed by the HST pump.
Assume that traveling operation is performed while the working
device is driven. In this case, in the power mode, the engine is
driven at a matching point B and engine speed N(B) corresponds to
higher rotation speed. On the other hand, in the eco mode, the
engine is driven at a matching point A at which the engine speed is
lower than that at the matching point B due to a larger increase
rate of the input torque of the HST pump with respect to the
increase of the engine speed. Therefore, rotation speed N(A)
corresponds to lower engine speed. Thus, the speed of the working
device becomes slower.
[0008] The invention has been accomplished in consideration of the
aforementioned real circumstances in the background-art technique.
It is an object of the invention to provide a wheel loader which
has an HST type driving system and which can improve working
efficiency in an eco mode in the case where a power mode and the
eco mode have been set in the wheel loader.
Solution to Problem
[0009] In order to achieve the object, the invention provides a
wheel loader including: a vehicle body frame; wheels; a working
device which is attached to the vehicle body frame and which has a
lift arm capable of being rotated in an up/down direction; an
engine which is attached to the vehicle body frame; an HST
traveling device in which a variable displacement type HST pump
driven by the engine and an HST motor as a driving source for
driving the wheels are connected to each other in a closed circuit,
and which has an HST pump control portion controlling input torque
of the HST pump; and a working machine pump which is driven by the
engine to discharge pressure oil for operating the working device;
wherein: the wheel loader further includes: a work mode selecting
device which selects one from a power mode and an eco mode, the
power mode serving as a work mode when the workload is a heavy
load, the eco mode serving as a work mode when the workload is a
light load; a detecting device which detects lifting operation of
the lift arm of the working device; and a control device which
makes control so that the input torque of the HST pump can be
controlled in accordance with a preset eco mode characteristic by
the pump control portion when the eco mode is selected by the work
mode selecting device, and the input torque of the HST pump can be
controlled in accordance with a preset power mode characteristic by
the pump control portion when the power mode is selected by the
work mode selecting device, but the input torque characteristic of
the HST pump can be controlled in accordance with a lifting
operation characteristic in place of the eco mode characteristic
when the lifting operation of the lift arm is detected by the
detecting device after the eco mode has been selected.
[0010] The invention also provides a wheel loader having the
aforementioned configuration, wherein: the control device has a
storage portion which stores an eco mode characteristic line, a
power mode characteristic line, and a lifting operation
characteristic line; each of the eco mode characteristic line, the
power mode characteristic line and the lifting operation
characteristic line includes a characteristic line expressing a
relation between engine speed and the input torque of the HST pump;
and the lifting operation characteristic line is set as a
characteristic in which a matching point as an intersection point
of the lifting operation characteristic line with a working device
operating engine torque characteristic line obtained by subtracting
torque of the working machine pump from torque of the engine is
provided between an eco mode matching point as an intersection
point between the eco mode characteristic line and the working
device operating engine torque characteristic line and a power mode
matching point as an intersection point between the power mode
characteristic line and the working device operating engine torque
characteristic line.
[0011] The invention also provides a wheel loader having the
aforementioned configuration, wherein: the lifting operation
characteristic line is provided to diverge from the middle of the
eco mode characteristic line.
[0012] The invention also provides a wheel loader having the
aforementioned configuration, including: a multistage transmission
which is connected to the HST motor and which has a plurality of
speed stages including a high speed stage and a low speed stage; a
speed stage detecting device which detects that the multistage
transmission has been changed over to the low speed stage; and a
forward movement detecting sensor which detects that the wheel
loader is in a state of forward movement; wherein: the HST motor
includes a variable displacement type hydraulic motor; the HST
traveling device has an HST motor control portion which controls
tilting of the HST motor; and when it is detected by the speed
stage detection device that the multistage transmission has been
changed over to the low speed stage and it is detected by the
forward movement detecting sensor that the wheel loader is in a
state of forward movement, the control device makes control so that
minimum tilting of the HST motor can be set as minimum tilting
larger than minimum tilting in the eco mode by the HST motor
control portion.
Advantageous Effects of Invention
[0013] According to the invention, when the lifting operation of
the lift arm of the working device is performed in the eco mode in
the case where the power mode and the eco mode has been set in the
wheel loader having the HST type driving system, the HST pump is
controlled in accordance with the lifting operation characteristic
line so that the engine speed can be higher than that in the eco
mode. Thus, according to the invention, it is possible to increase
operation speed of the lifting operation of the lift arm of the
working device so that it is possible to improve working efficiency
more greatly than in the background art. In addition, according to
the invention, the lifting operation characteristic line is set to
diverge from the eco mode characteristic line. Accordingly, it is
possible to carry out the lifting operation of the lift arm in the
eco mode while reducing an operator's feeling of difference from a
feeling of operation in the eco mode.
BRIEF DESCRIPTION OF DRAWINGS
[0014] [FIG. 1] A side view showing a first embodiment of a wheel
loader according to the invention.
[0015] [FIG. 2] An electric and hydraulic circuit diagram provided
in the first embodiment.
[0016] [FIG. 3] A block diagram showing a control system provided
in the first embodiment.
[0017] [FIG. 4] A flow chart showing a processing procedure of a
vehicle body controller provided in the first embodiment.
[0018] [FIG. 5] A graph showing characteristics obtained in the
first embodiment.
[0019] [FIG. 6] A block diagram showing a control system provided
in a second embodiment of the invention.
[0020] [FIG. 7] A flow chart showing a processing procedure of a
vehicle body controller provided in the second embodiment.
[0021] [FIG. 8] A graph showing characteristics considered from the
background-art technique.
DESCRIPTION OF EMBODIMENTS
[0022] Embodiments of a wheel loader according to the invention
will be described below based on the drawings.
First Embodiment
[0023] FIG. 1 is a side view showing a first embodiment of a wheel
loader according to the invention. As shown in FIG. 1, the wheel
loader according to the first embodiment is provided with a vehicle
body frame 1, an operator's cab 2, wheels, i.e. front wheels 9 and
rear wheels 10, and a working device 3. The working device 3 is
attached to the vehicle body frame 1. The working device 3 includes
a lift arm 4, a lift cylinder 6, a bucket 5, a bucket cylinder 7,
and a bellcrank 8. The lift arm 4 can be rotated in an up/down
direction. The lift cylinder 6 drives the lift arm 4. The bucket 5
is attached to a distal end of the lift arm 4 so that the bucket 5
can be loaded with soil. The bucket cylinder 7 rotates the bucket 5
in the up/down direction. The bellcrank 8 forms a link mechanism
between the bucket 5 and the bucket cylinder 7.
[0024] FIG. 2 is an electric and hydraulic circuit diagram provided
in the first embodiment.
[0025] As shown in FIG. 2, the first embodiment is provided with an
engine 17, a hydraulic closed circuit, and a working machine pump
13. The engine 17 is attached to the vehicle body frame 1. The
hydraulic closed circuit includes a variable displacement type HST
pump 11 which is driven by the engine 17, and an HST motor 14 which
is driven by pressure oil discharged from the HST pump 11. The
working machine pump 13 is driven by the engine 17 to discharge
pressure oil for operating the working device 3. Further, the first
embodiment has an HST charge pump 12 and a driving wheel system 24.
The HST charge pump 12 discharges pressure oil for controlling the
HST pump 11. The driving wheel system 24 transmits driving force
generated by the HST motor 14 to the front wheels 9 and the rear
wheels 10. The pressure oil discharged from the working machine
pump 13 is delivered to the lift cylinder 6 serving as the working
device 3 through a control valve 35.
[0026] The first embodiment is also provided with a detecting
portion, a work mode selecting portion 22 and an engine speed
sensor 25. The detecting portion detects lifting operation of the
lift arm 4 of the working device 3. For example, the detecting
portion is a working machine pressure detecting portion 23 which
detects pressure of a conduit making communication between the
control valve 35 and a bottom chamber of the lift cylinder 6. The
work mode selecting portion 22 selects one from a power mode and an
eco mode. The power mode serves as a work mode when the workload is
a heavy load. The eco mode serves as a work mode when the workload
is a light load. The engine speed sensor 25 detects real rotation
speed of the engine 17. The first embodiment is further provided
with a control device, i.e. a controller 18, to which pieces of
information are inputted from the working machine pressure
detecting portion 23, the work mode selecting portion 22 and the
engine speed sensor 25. Information outputted from the controller
18 is sent to an HST pump control portion 15 and an HST motor
control portion 16. The HST pump control portion 15 controls
tilting (pump input torque) of the HST pump 11 in accordance with a
command from the controller 18. The HST motor control portion 16
controls tilting (motor output torque) of the HST motor 14 in
accordance with a command from the controller 18.
[0027] Incidentally, the controller 18 controls the HST pump
control portion 15 so as to increase the pump tilting (pump input
torque) in accordance with the increase of the engine speed. In
addition, the controller 18 controls the HST motor control portion
16 so as to increase the motor tilting (motor output torque) more
toward maximum tilting as discharge pressure of the HST pump
(driving pressure of the HST motor 15) is higher and so as to
decrease the motor tilting more toward minimum tilting as the
discharge pressure of the HST pump is lower.
[0028] Traveling torque increases as the motor tilting is larger.
Travelling speed increases as the motor tilting is smaller. Thus,
the travelling speed can reach the highest speed at the minimum
tilting. Thus, low-speed high-torque traveling and high-speed
low-torque traveling are achieved.
[0029] FIG. 3 is a block diagram showing a control system provided
in the first embodiment. FIG. 4 is a flow chart showing a
processing procedure of the vehicle body controller provided in the
first embodiment. FIG. 5 is a graph showing characteristics
obtained by the first embodiment.
[0030] The controller 18 shown in FIG. 3 has a storage portion 28
(see FIG. 3) which stores the relation of the input torque of the
HST pump to the engine speed as a map as shown in FIG. 5. An eco
mode characteristic line 31, a power mode characteristic line 32, a
matching point A, a matching point B, and a lifting operation
characteristic line 34 are stored in advance in the map. The eco
mode characteristic line 31 expresses the relation between the eco
mode engine speed which is used when the eco mode is selected by
the work mode selecting portion 22, and the input torque of the HST
pump 11. The power mode characteristic line 32 expresses the
relation between the power mode engine speed which is used when the
power mode is selected, and the input torque of the HST pump. The
matching point A is located on a working device operating engine
torque characteristic line 30 which is obtained by subtracting the
torque of the working machine pump 13 from the torque of the engine
17 (a characteristic line 29). The matching point A is an
intersection point between the eco mode characteristic line 31 and
the working device operating engine torque characteristic line 30.
The matching point B is an intersection point between the power
mode characteristic line 32 and the working device operating engine
torque characteristic line 30. The lifting operation characteristic
line 34 has a matching point C which is an intersection point with
the working device operating engine torque characteristic line 30
and between the matching point A and the matching point B. The
lifting operation characteristic line 34 is set to diverge from the
eco mode characteristic line 31 and expresses the relation between
the engine speed during the lifting operation of the lift arm 4 and
the input torque of the HST pump.
[0031] The input torque of the HST pump during operation of the
working device matches with an intersection point on the working
device operating engine torque characteristic line 30. The engine
17 is operated at the rotation speed at the intersection point. The
eco mode characteristic line 31 is set in such a manner that the
input torque of the HST pump increases at a larger increase rate
relative to the increase of the engine speed. The engine speed at
the matching point A corresponds to lower rotation speed N(A).
Thus, the engine is operated at lower rotation speed so that fuel
consumption can be improved. The power mode characteristic line 32
is set in such a manner that the input torque of the HST pump
increases more gently relatively to the increase of the engine
speed than in the eco mode characteristic line 31. Engine speed
N(B) at the matching point B corresponds to a higher value than the
engine speed N(A) at the matching point A. Therefore, the engine
can be operated at higher rotation speed to increase the discharge
flow rate of the working machine pump 13 to thereby increase the
driving speed of the lift arm 4 etc. of the working device 3. Thus,
it is possible to improve workability. The lifting operation
characteristic line 34 diverges from the middle of the eco mode
characteristic line 31. The lifting operation characteristic line
34 is set in such a manner that, up to the divergence point, the
input torque of the HST pump increases at a larger increase rate
relative to the increase of the engine speed in the same manner as
in the eco mode characteristic line 31, but beyond the divergence
point, the input torque of the HST pump increases gently relatively
to the increase of the engine speed, for example, substantially at
the same increase rate as in the power mode characteristic line 32.
Engine speed N(C) at the matching point C is a value larger than
the engine speed N (A) but smaller than the engine speed N(B). The
characteristic of the engine speed N(C) is set so that the engine
speed N(C) can be a value close to the engine speed N(B).
[0032] In addition, as shown in FIG. 3, the controller 18 is
provided with a determination portion 26, a storage portion 28, and
a control portion 27. The determination portion 26 determines
whether the lifting operation of the lift arm 4 of the working
device 3 has been detected or not by the working machine pressure
detecting portion 23 in the condition that the eco mode has been
selected by the work mode selecting portion 22. The characteristics
shown in FIG. 5 are stored in the storage portion 28. The control
portion 27 controls the HST pump 11 in accordance with the lifting
operation characteristic line 34 in place of the eco mode
characteristic line 31 when it is determined by the determination
portion 26 that the lifting operation of the lift arm 4 has been
detected.
[0033] As shown in FIG. 4, first, the determination portion 26 of
the controller 18 determines whether the eco mode has been selected
as the work mode or not (step S1). When the eco mode has not been
selected, control of the HST pump 11 is made in accordance with the
power mode characteristic line 32 shown in FIG. 5 (step S2). When
pressure is detected by the working machine pressure detecting
portion 23 in the case where the eco mode has been selected,
determination is made as to whether the lift arm 4 has been lifted
or not (step S3). When the set working machine pressure is not
detected, determination is made that the lift arm 4 has not been
lifted yet so that control of the HST pump 11 is made in accordance
with the eco mode characteristic line 31 shown in FIG. 5 (step S4).
When the set working machine pressure is detected, determination is
made that the lift arm 4 has been lifted so that control of the HST
pump is made in accordance with the lifting operation
characteristic line 34 shown in FIG. 5 (step S5).
[0034] Incidentally, in FIG. 5, the reference sign 29 designates an
engine output torque characteristic line corresponding to torque
obtained as the sum of the input torque of the HST pump and the
input torque of the working machine pump. As described above, the
working device operating engine torque characteristic line 30 is a
torque characteristic line relevant to the engine 17 and
corresponding to torque obtained by subtracting the input torque of
the working machine pump from the output torque of the engine. The
input torque of the HST pump during acceleration from a stop state
of the vehicle body is expressed by the eco mode characteristic
line 31, the power mode characteristic line 32 and the lifting
operation characteristic line 34 in FIG. 5. In the power mode, the
engine speed N(B) corresponds to higher rotation speed as indicated
at the matching point B. On the other hand, in the eco mode, the
rotation speed N(A) corresponds to lower engine speed as indicated
at the matching point A, and the discharge flow rate of the working
machine pump 13 decreases accordingly. However, in the lifting
operation characteristic line 34, since the engine speed N(C) as
indicated at the matching point C can be set as rotation speed
higher than the engine speed N(A), the discharge flow rate of the
working machine pump 13 close to that in the power mode can be
obtained in spite of the eco mode.
[0035] According to the first embodiment configured thus, when the
lifting operation of the lift arm 4 of the working device 3 in the
wheel loader having the HST type driving system has been performed
in the eco mode, the HST pump 11 is controlled in accordance with
the lifting operation characteristic line 34 stored in the storage
portion 28 of the controller 18 so that the engine speed can be
increased to be higher than that in the eco mode. Such lifting
operation of the lift arm 4 is carried out when soil held by the
bucket 5 is loaded into a truck etc. or released to a mound of
sediment. In this manner, according to the first embodiment, it is
possible to increase the operation speed of the lifting operation
of the working device 3 so that it is possible to improve working
efficiency.
[0036] In addition, the lift operation characteristic line 34 is
set to diverge from the eco mode characteristic line 31 in the
first embodiment. Accordingly, it is possible to carry out the
lifting operation of the lift arm 4 in the eco mode while reducing
an operator's feeling of difference from a feeling of operation in
the eco mode.
Second Embodiment
[0037] FIG. 6 is a block diagram showing a control system provided
in a second embodiment of the invention. FIG. 7 is a flow chart
showing a processing procedure of a vehicle body controller
provided in the second embodiment. The fundamental configuration of
the second embodiment is equivalent to that of the first
embodiment. Only different parts will be described below.
[0038] The second embodiment is provided with a not-shown
multistage transmission, a speed stage detecting portion 20, and a
forward movement detecting sensor 21. The multistage transmission
is connected to an HST motor 14 and is formed as a constituent part
of a driving wheel system 24. The multistage transmission changes
rotation of the HST motor 14 to one of a high speed stage and a low
speed stage so as to change the speed. The speed stage detecting
portion 20 detects that the multistage transmission has been
changed over to the low speed stage as shown in FIG. 6. The forward
movement detecting sensor 21 detects that the vehicle body of the
wheel loader is in a state of forward movement.
[0039] In addition to the determination made in the first
embodiment, a determination portion 26 of a controller 18 is
configured to also determine whether or not it has been detected by
the speed stage detecting portion 20 that the multistage
transmission has been changed over to the slow speed stage and it
has been detected by the forward movement detecting sensor 21 that
the wheel loader is in the state of forward movement. A control
portion 27 is configured to also output a control signal to an HST
motor control portion 16.
[0040] In the second embodiment, as shown in the flow chart of FIG.
7, when pressure is detected by a working machine pressure
detecting portion 23 so that determination is made that a lift arm
4 has been lifted in a step S3, control of an HST pump 11 is made
in accordance with a lifting operation characteristic line 34 in a
step S5. Moreover, when it is determined by the determination
portion 26 of the controller 18 that the multistage transmission
has been changed over to the low speed stage and the wheel loader
is in the state of forward movement (step S6), the control portion
27 of the controller 18 outputs a control signal to the HST motor
control portion 15 to make control so that minimum tilting of the
HST motor 14 can be set as minimum tilting larger than minimum
tilting in an eco mode (step S8). When the condition is not
consistent with any of the low speed stage and the state of forward
movement, the control portion 27 controls the HST motor control
portion 15 to keep the minimum tilting of the HST motor 14 at the
same minimum titling as that in the eco mode (step S7).
[0041] According to the second embodiment, not only is it possible
to obtain an equivalent effect to that in the first embodiment but
it is also possible to reduce the vehicle speed to be lower than
that in the eco mode in the background art when the speed of the
vehicle body is accelerated from a stop state or a very slow speed
region during lifting operation of the lift arm 4 of the working
device 3, i.e. when soil held by a bucket 5 is loaded into a truck
etc. or released to a mound of sediment.
[0042] Here, operation speed of the working device 3 and traveling
speed in a power mode are set to be balanced with each other in
consideration of workability and operability in the wheel loader
according to the background-art technique. Therefore, there is a
fear that the balance between the operation speed of the lift arm 4
of the working device 3 and the vehicle speed in the eco mode may
be poor to lower working efficiency. That is, since the vehicle
speed is higher relatively to the operation speed of the lift arm 4
of the working device 3 in the eco mode in the wheel loader
according to the background-art technique, the traveling distance
tends to be longer, and further, there arises a difference in
operability between the power mode and the eco mode. Therefore,
when equivalent work to loading work etc. performed in the power
mode is intended to be performed in the eco mode, the traveling
distance required for the work in the eco mode becomes longer than
that in the power mode. Accordingly, it is difficult to do the work
in a narrow work site.
[0043] According to the second embodiment, the minimum tilting of
the HST motor 14 is set as the larger minimum tilting as described
above so that the vehicle speed can be reduced when soil held by
the bucket 5 is loaded into a truck etc . or released to a mound of
sediment. Accordingly, it is possible to improve the balance
between the operation speed of the lift arm 4 of the working device
3 and the vehicle speed so that it is possible to increase the
working efficiency. In addition, when the same work such as work
for loading soil held by the bucket 5 into a truck etc. or work for
releasing soil to a mound of sediment is performed, it is possible
to make the traveling distance substantially equal between the
power mode and the eco mode.
REFERENCE SIGNS LIST
[0044] 1 vehicle body frame [0045] 3 working device [0046] 4 lift
arm [0047] 5 bucket [0048] 6 lift cylinder [0049] 7 bucket cylinder
[0050] 8 bellcrank [0051] 11 HST pump [0052] 12 HST charge pump
[0053] 13 working machine pump [0054] 14 HST motor [0055] 15 HST
pump control portion [0056] 16 HST motor control portion [0057] 17
engine [0058] 18 controller (control device) [0059] 20 speed stage
detecting portion (speed stage detecting device) [0060] 21 forward
movement detecting sensor [0061] 22 work mode selecting portion
(work mode selecting device) [0062] 23 working machine pressure
detecting portion (detecting device) [0063] 24 driving wheel system
[0064] 25 engine speed sensor [0065] 26 determination portion
[0066] 27 control portion [0067] 28 storage portion [0068] 29
engine torque characteristic line [0069] 30 working device
operating engine torque characteristic line [0070] 31 eco mode
characteristic line [0071] 32 power mode characteristic line [0072]
34 lifting operation characteristic line
* * * * *