U.S. patent application number 14/055105 was filed with the patent office on 2014-02-06 for travel control device for work vehicle and work vehicle.
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 Eiji Egawa, Tsuyoshi Nakamura, Akira Nakayama, Kensuke Satou, Hideo Sorata, Makoto Sugaya, Kazuo Takiguchi, Tsukasa Toyooka, Tsutomu Udagawa.
Application Number | 20140033699 14/055105 |
Document ID | / |
Family ID | 38005845 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140033699 |
Kind Code |
A1 |
Udagawa; Tsutomu ; et
al. |
February 6, 2014 |
TRAVEL CONTROL DEVICE FOR WORK VEHICLE AND WORK VEHICLE
Abstract
A travel control device for a work vehicle includes: a hydraulic
pump; a plurality of hydraulic motors connected to the hydraulic
pump in parallel through a closed-circuit connection, that drive
different wheels with pressure oil delivered from the hydraulic
pump; a slip detection device that detects a slip occurring at each
of the wheels; and a flow control device that reduces, upon
detection of a slip occurring at any of the wheels by the slip
detection device, a quantity of pressure oil supplied to a
hydraulic motor for driving the wheel at which the slip has been
detected, among the plurality of hydraulic motors.
Inventors: |
Udagawa; Tsutomu;
(Tsukuba-shi, JP) ; Egawa; Eiji; (Tsuchiura-shi,
JP) ; Toyooka; Tsukasa; (Omitama-shi, JP) ;
Sugaya; Makoto; (Narita-shi, JP) ; Sorata; Hideo;
(Kasumigaura-shi, JP) ; Nakamura; Tsuyoshi;
(Tsuchiura-shi, JP) ; Nakayama; Akira;
(Tsuchiura-shi, JP) ; Takiguchi; Kazuo;
(Kasumigaura-shi, JP) ; Satou; Kensuke;
(Ushiku-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi Construction Machinery Co., Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Hitachi Construction Machinery Co.,
Ltd.
Tokyo
JP
|
Family ID: |
38005845 |
Appl. No.: |
14/055105 |
Filed: |
October 16, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12092370 |
May 1, 2008 |
8585156 |
|
|
PCT/JP2006/321837 |
Nov 1, 2006 |
|
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14055105 |
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Current U.S.
Class: |
60/422 |
Current CPC
Class: |
Y10T 477/619 20150115;
B66F 9/07572 20130101; B60K 17/356 20130101; B60K 17/043 20130101;
F16H 61/42 20130101; B60W 2520/263 20130101; F16H 61/4035 20130101;
B66F 9/0655 20130101; B60K 2007/0092 20130101; Y10T 477/631
20150115; B60K 17/10 20130101; F16H 61/452 20130101; B66F 9/22
20130101; B60K 7/0015 20130101 |
Class at
Publication: |
60/422 |
International
Class: |
F16H 61/42 20060101
F16H061/42; B66F 9/075 20060101 B66F009/075 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 2, 2005 |
JP |
2005-319362 |
Claims
1. A travel control device for a work vehicle, comprising: a
hydraulic pump; a hydraulic motor for driving front wheels and a
hydraulic motor for driving rear wheels with pressure oil delivered
from the hydraulic pump, connected to the hydraulic pump in
parallel through a closed-circuit connection; a slip detection
device that detects a slip occurring at any of the front wheels and
the rear wheels; and a flow control device that reduces, upon
detection of a slip occurring at any of the front wheels and the
rear wheels by the slip detection device, a quantity of pressure
oil supplied to a hydraulic motor for driving the wheel at which
the slip has been detected, among the hydraulic motor for driving
the front wheels and the hydraulic motor for driving the rear
wheels.
2. A travel control device for a work vehicle according to claim 1,
wherein: the flow control device reduces the quantity of pressure
oil supplied to the hydraulic motor by a greater extent as an
extent of slippage detected by the slip detection device becomes
larger.
3. A travel control device for a work vehicle according to claim 1,
wherein: the flow control device comprises a restoring device that
gradually restores the quantity of pressure oil supplied to the
hydraulic motor to a value before reduction as the slip detection
device determines that a slip is eliminated after the quantity of
pressure oil supplied to the hydraulic motor is reduced upon the
detection of a slip by the slip detection device.
4. A travel control device for a work vehicle according to claim 1,
wherein: the slip detection device comprises a speed detection
device that detects a rotational velocity at each of the front
wheels and the rear wheels, estimates a vehicle speed based upon
the rotational velocities detected by the speed detection device
and detects a slip based upon deviations of the rotational
velocities detected by the speed detection device relative to the
estimated vehicle speed.
5. A travel control device for a work vehicle according to claim 1,
wherein: the flow control device comprises flow control valves each
disposed in a pipeline between the hydraulic pump and one of the
hydraulic motor for driving the front wheels and the hydraulic
motor for driving the rear wheels and electromagnetic switching
valves via which a pilot pressure is applied to the flow control
valves.
6. A travel control device for a work vehicle according to claim 3,
wherein: the flow control device comprises flow control valves each
disposed in a pipeline between the hydraulic pump and one of the
hydraulic motor for driving the front wheels and the hydraulic
motor for driving the rear wheels and electromagnetic switching
valves via which a pilot pressure is applied to the flow control
valves; and the restoring device is constituted with slow return
valves that slowly restores the pilot pressure applied to the flow
control valves via the electromagnetic switching valves.
7. A travel control device for a work vehicle according to claim 3,
wherein: the flow control device comprises flow control valves each
disposed in a pipeline between the hydraulic pump and one of the
hydraulic motor for driving the front wheels and the hydraulic
motor for driving the rear wheels and electromagnetic switching
valves via which a pilot pressure is applied to the flow control
valves; and the restoring device is constituted with a delay
processing circuit that executes delay processing on control
signals provided to the electromagnetic switching valves.
8. A work vehicle comprising: a drive control device for a work
vehicle according to claim 1.
9. A travel control device for a work vehicle according to claim 2,
wherein: the flow control device comprises a restoring device that
gradually restores the quantity of pressure oil supplied to the
hydraulic motor to a value before reduction as the slip detection
device determines that a slip is eliminated after the quantity of
pressure oil supplied to the hydraulic motor is reduced upon the
detection of a slip by the slip detection device.
10. A travel control device for a work vehicle according to claim
2, wherein: the slip detection device comprises a speed detection
device that detects a rotational velocity at each of the front
wheels and the rear wheels, estimates a vehicle speed based upon
the rotational velocities detected by the speed detection device
and detects a slip based upon deviations of the rotational
velocities detected by the speed detection device relative to the
estimated vehicle speed.
11. A travel control device for a work vehicle according to claim
3, wherein: the slip detection device comprises a speed detection
device that detects a rotational velocity at each of the front
wheels and the rear wheels, estimates a vehicle speed based upon
the rotational velocities detected by the speed detection device
and detects a slip based upon deviations of the rotational
velocities detected by the speed detection device relative to the
estimated vehicle speed.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/092,370, filed May 1, 2008, the entire disclosure of
which is incorporated herein by reference, which is the U.S.
national phase of international application no. PCT/JP2006/321837,
filed Nov. 1, 2006, which in turn claims the priority of Japanese
application 2005-319362, filed Nov. 2, 2005.
TECHNICAL FIELD
[0002] The present invention relates to a travel control device for
a work vehicle such as a telescopic handler and a work vehicle.
BACKGROUND ART
[0003] The work vehicles proposed for applications in the related
field include work vehicles equipped with an HST traveling
hydraulic circuit with a hydraulic pump and a traveling hydraulic
motor connected therein through a closed circuit connection (see
patent reference literature 1). In the work vehicle disclosed in
patent reference literature 1, two traveling hydraulic motors,
disposed parallel to each other, are connected to a single
hydraulic pump through a closed circuit connection and each
hydraulic motor is connected to the front wheels or the rear wheels
so as to drive the front wheels and the rear wheels with different
hydraulic motors. A variable relief valve is connected to the
hydraulic motor for driving the front wheels and the drive torque
at the front wheels is controlled by adjusting the relief pressure
setting. [0004] Patent reference literature 1: Japanese Laid Open
Patent Publication No. 2000-1127
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0005] There is an issue yet to be effectively addressed in the
work vehicle disclosed in patent reference literature 1 in that if
either a front wheel or a rear wheel slips, the pressure oil from
the hydraulic pump cannot be efficiently distributed to the
individual hydraulic motors, resulting in a significant loss of
power.
Means for Solving the Problems
[0006] A travel control device for a work vehicle according to a
first aspect includes: a hydraulic pump; a plurality of hydraulic
motors connected to the hydraulic pump in parallel through a
closed-circuit connection, that drive different wheels with
pressure oil delivered from the hydraulic pump; a slip detection
device that detects a slip occurring at each of the wheels; and a
flow control device that reduces, upon detection of a slip
occurring at any of the wheels by the slip detection device, a
quantity of pressure oil supplied to a hydraulic motor for driving
the wheel at which the slip has been detected, among the plurality
of hydraulic motors.
[0007] In the first aspect, it is preferable that the flow control
device reduces the quantity of pressure oil supplied to the
hydraulic motor by a greater extent as an extent of slippage
detected by the slip detection device becomes larger.
[0008] In the first aspect, the flow control device may include a
restoring device that gradually restores the quantity of pressure
oil supplied to the hydraulic motor to a value before reduction as
the slip detection device determines that a slip is eliminated
after the quantity of pressure oil supplied to the hydraulic motor
is reduced upon the detection of a slip by the slip detection
device.
[0009] A travel control device for a work vehicle according to a
second aspect includes: a hydraulic pump; a plurality of hydraulic
motors connected to the hydraulic pump in parallel through a
closed-circuit connection, that drive different wheels with
pressure oil delivered from the hydraulic pump; a slip detection
device that detects a slip occurring at each of the wheels; and a
displacement reducing device that reduces, upon detection of a slip
occurring at any of the wheels by the slip detection device, a
motor displacement of a hydraulic motor for driving the wheel at
which the slip has been detected, among the plurality of hydraulic
motors.
[0010] In the second aspect, it is preferable that the displacement
reducing device reduces the motor displacement of the hydraulic
motor by a greater extent as an extent of slippage detected by the
slip detection device becomes larger.
[0011] In second aspect, the displacement reducing device may
include a restoring device that gradually restores the motor
displacement of the hydraulic motor to a value before reduction as
the slip detection device determines that a slip is eliminated
after reducing the motor displacement of the hydraulic motor upon
the detection of a slip by the slip detection device.
[0012] In the travel control device for a work vehicle according to
the first or second aspect, the slip detection device may include a
speed detection device that detects a rotational velocity at each
of the wheels, may estimate a vehicle speed based upon the
rotational velocities detected by the speed detection device and
may detect a slip based upon deviations of the rotational
velocities detected by the speed detection device relative to the
estimated vehicle speed.
[0013] In the first aspect, it is preferable that the flow control
device includes flow control valves each disposed in a pipeline
between the hydraulic pump and one of the plurality of hydraulic
motors and electromagnetic switching valves via which a pilot
pressure is applied to the flow control valves.
[0014] In the first aspect, it is preferable that the flow control
device includes flow control valves each disposed in a pipeline
between the hydraulic pump and one of the plurality of hydraulic
motors and electromagnetic switching valves via which a pilot
pressure is be applied to the flow control valves; and the
restoring device is constituted with slow return valves that slowly
restores the pilot pressure applied to the flow control valves via
the electromagnetic switching valves.
[0015] In the first aspect, the flow control device may include
flow control valves each disposed in a pipeline between the
hydraulic pump and one of the plurality of hydraulic motors and
electromagnetic switching valves via which a pilot pressure is
applied to the flow control valves; and the restoring device may be
constituted with a delay processing circuit that executes delay
processing on control signals provided to the electromagnetic
switching valves.
[0016] In the second aspect, it is preferable that the restoring
device is a delay processing circuit that executes delay processing
on a control signal used to control the motor displacement of the
hydraulic motor.
[0017] A work vehicle according to a fifth aspect of the present
invention includes the drive control device for a work vehicle
according to the first or second aspect.
Advantageous Effect of the Invention
[0018] According to the present invention, as a slip of a wheel is
detected, the quantity of pressure oil delivered to the hydraulic
motor driving the wheel detected to have slipped is reduced or the
motor displacement of the hydraulic motor driving the slipping
wheel is reduced. As a result, the extent of slippage can be
minimized and the pressure oil from the hydraulic pump can be
distributed to the hydraulic motors efficiently.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a side elevation of a telescopic handler that may
adopt the present invention;
[0020] FIG. 2 is a traveling hydraulic circuit diagram illustrating
the structure adopted in a travel control device achieved in a
first embodiment;
[0021] FIG. 3 presents an example of displacement control
characteristics that may be assumed by hydraulic motors in FIG.
2;
[0022] FIG. 4 is a block diagram showing the structure adopted in
the travel control device in the first embodiment;
[0023] FIGS. 5(a) and 5(b) show the characteristics of coefficient
generating circuits in FIG. 4;
[0024] FIG. 6 is a traveling hydraulic circuit diagram illustrating
the structure adopted in the travel control device achieved in a
second embodiment;
[0025] FIG. 7 is a block diagram showing the structure adopted in
the travel control device in a third embodiment;
[0026] FIG. 8 shows the operational characteristics of the travel
control device achieved in the third embodiment;
[0027] FIG. 9 is a traveling hydraulic circuit diagram illustrating
the structure adopted in the travel control device achieved in a
fourth embodiment;
[0028] FIG. 10 is a block diagram showing the structure adopted in
the travel control device in the fourth embodiment; and
[0029] FIG. 11 presents an example of a variation of FIG. 10.
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment
[0030] The following is an explanation of the first embodiment of a
travel control device according to the present invention, given in
reference to FIGS. 1 through 5.
[0031] FIG. 1 is a side elevation of a telescopic handler that may
adopt the first embodiment of the present invention and FIG. 2
presents a circuit diagram of the traveling hydraulic circuit of
the telescopic handler. As shown in FIG. 1, the telescopic handler
includes a body 101, an operator's cab 102 disposed on the body 101
and an extensible boom 103 which is supported at the rear of the
body in such a manner that it can be hoisted up and down. An
attachment mount unit 104 is rotatably mounted at the front end of
the boom 103 and a fork 105 used in a loading operation is attached
to the attachment mount unit 104. It is to be noted that FIG. 1
shows the boom 103 in a lowered state (solid line) and the boom 103
in both a raised, extended state and a raised contracted state
(two-point chain lines). Front wheels (front tires 10) and rear
wheels (rear tires 20) are mounted at the body 101 and the vehicle
travels as the tires 10 and 20 rotate.
[0032] As shown in FIG. 2, a traveling hydraulic circuit is an HST
traveling circuit which includes a hydraulic motor 11 connected
through a closed-circuit connection to a main hydraulic pump 1,
which is driven by an engine 2, via pipelines 3 and 4 and a
hydraulic motor 21 disposed in parallel to the hydraulic motor 11
and connected to the main hydraulic pump 1 through a closed-circuit
connection via pipelines 5 and 6.
[0033] The hydraulic motors 11 and 21 are respectively linked to
travel control devices 12 and 22. The travel control device 12
transmits a drive torque from the hydraulic motor 11 to an axle 14
via a speed reducer 13 to drive the front wheels. Likewise, the
travel control device 22 transmits a drive torque from the
hydraulic motor 21 to an axle 24 via a speed reducer 23 to drive
the rear wheels. In other words, the front wheels and the rear
wheels are driven by different hydraulic motors 11 and 21.
[0034] Flow control valves 15 and 25 are disposed in the pipelines
4 and 6 respectively, and a pilot pressure from a hydraulic source
7 is applied to the flow control valves 15 and 25 respectively via
electromagnetic switching valves 16 and 26. The electromagnetic
switching valves 16 and 26 are individually switched as detailed
later by signals provided by controller 30 and as the flow control
valves 15 and 25 are driven in response, the diameters of the
pipelines 4 and 6 change.
[0035] The motor displacements of the hydraulic motors 11 and 21,
each constituted with a variable-displacement motor, are
respectively controlled by displacement control devices 11a and
21a. The rotational speeds (peripheral velocities) of the tires 10
and 20 are detected respectively by rotation detectors 17 and 27
and the detection signals are input to the controller 30. The
controller 30 calculates the body traveling speed (vehicle speed)
based upon the detection signals provided from the rotation
detectors 17 and 27 and controls the displacement control devices
11a and 21a as detailed later based upon the vehicle speed.
[0036] The hydraulic pump 1 is a variable-displacement pump, the
pump displacement of which is controlled by a displacement control
device 1a. The displacement control device 1a includes a
displacement cylinder and a forward/reverse switching valve, which
is switched by interlocking with an operation of a forward/reverse
switching lever (not shown). As the forward/reverse switching lever
is operated to a neutral (stop) position, the forward/reverse
switching valve is switched to the neutral position and the
displacement cylinder is controlled to disallow any displacement of
the hydraulic pump 1 and thus set the pump output quantity to
0.
[0037] As the forward/reverse switching lever is operated to a
forward position or a reverse position, the forward/reverse
switching valve is switched to the forward position or the reverse
position accordingly and the direction along which the displacement
cylinder operates is controlled so as to control the displacement
direction of the hydraulic pump 1. At this time, a control pressure
is supplied to the displacement cylinder via the forward/reverse
switching valve and the pump displacement quantity is controlled
based upon the control pressure. The control pressure increases in
proportion to an increase in the engine rotation speed and, as the
control pressure rises, the pump displacement quantity, too,
increases. In other words, an increase in the engine rotation speed
results in increases in both the rotation speed of the hydraulic
pump 1 and the pump displacement quantity, which allows the pump
output quantity to increase smoothly in quick response to the
increase in the engine rotation speed so as to achieve smooth and
powerful acceleration. It is to be noted that the engine rotation
speed is adjusted through an operation of an accelerator pedal (not
shown).
[0038] FIG. 3 presents an example of displacement control
characteristics that may be assumed by the hydraulic motors 11 and
21, with the vehicle speed indicated along the horizontal axis and
the motor displacement indicated along the vertical axis. In the
figure, A represents the control characteristics of the hydraulic
motor 11 for driving the front wheels and B represents the control
characteristics of the hydraulic motor 21 for driving the rear
wheels. These characteristics A and B are stored in advance in the
controller 30 and the motor displacements of the individual
hydraulic motors 11 and 20 are controlled based upon the stored
characteristics.
[0039] The characteristics curve A indicates that the motor
displacement is sustained at a maximum level qmax as long as the
vehicle speed is equal to or less than V1, that the motor
displacement gradually decreases as the vehicle speed picks up once
the vehicle speed exceeds V1 and that the motor displacement drops
from the minimum level qmin to 0 as the vehicle speed reaches V3.
The characteristics curve B indicates that the motor displacement
is sustained at the maximum level qmax as long as the vehicle speed
is equal to or less than V2 (V1<V2<V3), that the motor
displacement gradually decreases as the vehicle speed picks up
after the vehicle speed exceeds V2 and that the motor displacement
is reduced to the minimum level qmin when the vehicle speed is
equal to or higher than V4 (>V3).
[0040] FIG. 4 is a block diagram illustrating the processing
executed by the controller 30 in the first embodiment. A vehicle
speed detector 40 calculates the vehicle speed (estimated vehicle
speed) based upon the signals provided from the rotation detectors
17 and 27. In this example, the rotational velocities vf and vr of
the front and rear wheels detected by the rotation detectors 17 and
27 respectively are added together at an adder 41, the average of
the two rotational velocities (vf+vr)/2 is calculated at an average
value calculation circuit 42 and then the average value having been
calculated undergoes low pass filter processing at a filter
processing circuit 43 so as to remove response at frequencies equal
to or greater than an estimated body response frequency (noise
removal). The estimated vehicle speed vm thus obtained is used for
substitution in a displacement calculation circuit 44 having the
characteristics shown in FIG. 3 stored therein so as to determine
through arithmetic operation a target motor displacement and
control signals are output to the displacement control devices 11a
and 21a to adjust the motor displacements to the target motor
displacement.
[0041] Flow control circuits 50 and 60 respectively control the
electromagnetic switching valves 16 and 26 in correspondence to
deviations .DELTA.vf and .DELTA.vr of the rotational velocities vf
and vr at the front and rear wheels relative to the estimated
vehicle speed vm. At this time, subtractors 51 and 61 respectively
subtract the rotational velocities vf and vr at the front and rear
wheels detected by the rotation detectors 17 and 27 from the
estimated vehicle speed vm, thereby determining the speed
deviations .DELTA.vf (=vm-vf) and .DELTA.vr (=vm-vr). As long as
the tires 10 and 20 do not slip, the speed deviations .DELTA.vf and
.DELTA.vr both remain at 0. However, if a tire slips, the
corresponding speed deviation .DELTA.vf or .DELTA.vr (the absolute
value of the speed deviation) assumes a greater value in
correspondence to the extent of slippage (slip quantity). In other
words, the extent of slippage can be detected by checking the speed
deviations .DELTA.vf and .DELTA.vr. It is to be noted that if a
front tire 10 slips while the vehicle is accelerating, vf becomes
greater than vm and, accordingly, .DELTA.vf<0 is true. If, on
the other hand, a front tire 10 slips while the vehicle is
decelerating, vf becomes less than vm and accordingly, vf>0 is
true.
[0042] Coefficient generating circuits 52 and 62 respectively
calculate coefficients Kf and Kr corresponding to the speed
deviations .DELTA.vf and .DELTA.vr based upon characteristics (see
FIGS. 5(a) and 5(b)) stored in advance. Multipliers 53 and 63
respectively multiply maximum restriction diameters (constants) of
the flow control valves 16 and 26 stored in advance by the
coefficients Kf and Kr so as to determine target restriction
diameters. Control signals are then output to the electromagnetic
switching valves 16 and 26 so as to adjust the restriction
diameters at the flow control valves 15 and 26 to the respective
target restriction diameters.
[0043] FIGS. 5(a) and 5(b) respectively show the characteristics
stored in the coefficient generating circuits 52 and 62. The
characteristics in FIG. 5(a) indicate that when the value (absolute
value) of the speed deviation .DELTA.vf is less than a
predetermined value vf1 (-vf1<.DELTA.vf<vf1) the coefficient
Kf assumes a value of 1, that when the value of the speed deviation
.DELTA.vf is equal to or greater than the predetermined value vf1
and equal to or less than a predetermined value vf2, the
coefficient Kf gradually decreases from 1 to 0 as the speed
deviation .DELTA.vf increases and that the coefficient Kf assumes
the value of 0 if the speed deviation .DELTA.vf is greater than the
predetermined value vf2 (.DELTA.vf<-vf2, .DELTA.vf>vf2).
Likewise, the characteristics in FIG. 5(b) indicate that when the
value (absolute value) of the speed deviation .DELTA.vr is less
than a predetermined value vr1 (-vr1<.DELTA.vr<vr1) the
coefficient Kr assumes a value of 1, that when the value of the
speed deviation .DELTA.vr is equal to or greater than the
predetermined value vr1 and equal to or less than a predetermined
value vr2, the coefficient Kr gradually decreases from 1 to 0 as
the speed deviation .DELTA.vr increases and that the coefficient Kr
assumes the value of 0 if the speed deviation .DELTA.vr is greater
than the predetermined value vr2 (.DELTA.vr<-vr2,
.DELTA.vr>vr2). Thus, if the extents of slip at the tires 10 and
20 are small, the flow control valves 15 and 25 assume greater
restriction diameters but if the extents of slip are significant,
the restriction diameters become smaller.
[0044] Next, the primary operations of the travel control device
achieved in the first embodiment are explained.
[0045] At the start of a vehicle traveling operation, the
forward/reverse operation lever (not shown) is switched from the
neutral position to the forward position and the accelerator pedal
(not shown) is depressed. In response, the engine rotation speed
rises and the quantity of output from the hydraulic pump 1
increases. At this point, the displacement quantities of the
hydraulic motors 11 and 21 are both at the maximum qmax level and
the vehicle thus starts traveling in a high torque four-wheel-drive
state. As the vehicle speed (estimated speed) rises, the motor
displacements decrease, as indicated by the characteristics curves
in FIG. 3. During this process, the motor displacement of the
hydraulic motor 11 decreases ahead of the motor displacement of the
hydraulic motor 21 and as the vehicle speed becomes equal to or
greater than the predetermined value V3, the motor displacement of
the hydraulic motor 11 is set to 0 and the vehicle enters a two
wheel drive (rear wheel drive) state. By controlling the motor
displacements in correspondence to the vehicle speed as described
above, the speed reduction ratio is controlled continuously, to
assure smooth traveling performance.
[0046] Assuming that no slip has occurred at the front and rear
tires 10 and 20, the deviations .DELTA.vf and .DELTA.vr of the
rotational velocities of and vr at the tires 10 and 20 relative to
the estimated vehicle speed vm are both 0 and, accordingly, the
coefficients Kf and Kr calculated at the coefficient generating
circuits 52 and 62 assume a value of 1. As a result, the maximum
restriction diameters are assumed at the flow control valves 16 and
26 and since the quantities of pressure oil supplied to the
hydraulic motors 11 and 21 are not restricted via the flow control
valves 15 and 25 in this state, the vehicle traveling performance
as indicated by the characteristics curves in FIG. 3 is
achieved.
[0047] If, on the other hand, a rear tire 20 slips (if slippage
occurs) as the accelerator pedal is depressed (as the vehicle
accelerates) the rotational velocity vr of the tire 20 becomes
greater than the estimated vehicle speed vm and thus, the speed
deviation .DELTA.vr becomes less than 0. In this situation, the
speed deviation .DELTA.vr (absolute value) assumes a greater value
if the extent of slippage of the tire 20 is greater. When .DELTA.vr
is equal to or greater than the predetermined value vr1
(.DELTA.vr.ltoreq.-vr1, .DELTA.vr.gtoreq.vr1), the coefficient Kr
assumes a value smaller than 1. As .DELTA.vr1 is equal to or
greater than the predetermined value vr2 (.DELTA.vr.ltoreq.-vr2,
.DELTA.vr.gtoreq.vr2), the coefficient Kr assumes the value of
0.
[0048] The restriction diameter at the flow control valve 25
gradually decreases as the extent of slippage increases and thus,
the quantity of oil supplied to the hydraulic motor 21 is
restricted. As a result, the rotational velocity of the rear wheels
is lowered so as to minimize the extent of slippage at the tire 20.
Consequently, the drive pressure oil from the hydraulic pump 1 can
be distributed to the front and the rear wheels efficiently and
since the drive force at the front wheels can be transmitted to the
road surface reliably, desirable traveling performance is
assured.
[0049] If a rear tire 20 slips (e.g., if a tire 20 becomes locked)
while a brake pedal is operated (while the vehicle is
decelerating), the deviation .DELTA.vr becomes greater than 0 and
the coefficient Kr assumes a value less than 1. This reduces the
restriction diameter at the flow control valve 25 and the quantity
of pressure oil supplied to the hydraulic motor 21 becomes
restricted. As a result, the braking force needed to stop the
vehicle (the braking force applied to the brake device) is reduced
to minimize the extent of slippage and the drive pressure oil from
the hydraulic pump 1 can thus be distributed to the front and rear
wheels efficiently. While an explanation is given above on the
operations executed when a rear tire 20 slips, similar operations
are executed in the event of a front tire slip.
[0050] In the first embodiment, a single hydraulic pump 1 is
connected through a closed circuit connection to two hydraulic
motors 11 and 21 disposed parallel to each other so as to drive the
front wheels and the rear wheels via the different hydraulic motors
11 and 21. As a result, differential drive of the front wheels and
the rear wheels is enabled so as to allow the vehicle to travel
smoothly around a corner by absorbing the difference between the
loci of the front wheel and the rear wheel (the difference between
the loci of the inner wheels). In addition, any occurrence of
slippage is detected by checking the deviations .DELTA.vf and
.DELTA.vr of the rotational velocities vf and vr of the tires 10
and 20 relative to the estimated vehicle speed vm and if a slip
occurs, the corresponding flow control valve 15 or 25 is
constricted to reduce the quantity of pressure oil supplied to the
hydraulic motor 11 or 21. As a result, the rotational velocity of
the slipping tire 10 or 20 is reduced to effectively minimize the
extent of slip. This, in turn, allows the drive pressure oil to be
distributed to the individual hydraulic motors 11 and 21
efficiently. Since the quantity of pressure oil supplied to the
hydraulic motor 11 or 21 is reduced to a greater extent if the
extent of the slip is more significant, the slip can be eliminated
promptly. Since the vehicle speed vm is estimated by utilizing the
rotation detectors 17 and 27, which detect the rotational
velocities vf and vr of the tires 10 and 20 and then the deviations
.DELTA.vf and .DELTA.vr of the rotational velocities vf and vr
relative to the vehicle speed vm are determined, slip detection can
be enabled while requiring a minimum member of sensors.
Second Embodiment
[0051] The second embodiment of the travel control device according
to the present invention is now explained in reference to FIG.
6.
[0052] In the second embodiment, the restriction diameters at the
flow control valves 15 and 25 assume dynamic characteristics.
Namely, the flow control valves 15 and 25 each assume
characteristics such that the restriction diameter is promptly
reduced in the event of a slip and the restriction diameter is then
slowly increased once the slip is eliminated. It is to be noted
that the following explanation focuses on the difference from the
first embodiment. FIG. 6 is a traveling hydraulic circuit diagram
of the traveling hydraulic circuit of the work vehicle achieved in
the second embodiment. In the figure, the same reference numerals
are assigned to components identical to those in FIG. 2.
[0053] As shown in FIG. 6, slow return valves 18 and 28 are
disposed respectively between the electromagnetic switching valve
16 and the flow control valve 15 and between the electromagnetic
switching valve 26 and the flow control valve 25. Thus, as soon as
a slip starts to occur at a tire 10 or 20, the pilot pressure oil
from the hydraulic source 7 is immediately supplied to the
corresponding flow control valve 15 or 25, which immediately
constricts the flow control valve 15 or 25. Consequently, the drive
force applied to the slipping tire 10 or 20 decreases quickly so as
to eliminate the slippage. Once the slip is eliminated, the pilot
pressure oil having been applied to the flow control valve 15 or 25
is caused to flow back slowly via the corresponding slow return
valve 18 or 28. As a result, a slip does not occur readily as the
flow control valve 15 or 25 is reset to the initial state so as to
prevent recurrence of a slip. It is to be noted that the slip-free
state can be detected in much the same way as the detection of the
slipping state, based on the deviations .DELTA.vf and .DELTA.vr of
the rotational velocities of and vr at the tires 10 and 20 relative
to the estimated vehicle speed vm.
Third Embodiment
[0054] In reference to FIGS. 7 and 8, the third embodiment of the
travel control device according to the present invention is
explained.
[0055] While the restriction diameters at the flow control valves
15 and 25 are reduced promptly and increased slowly via the slow
return valves 18 and 28 in the second embodiment, similar
restriction diameter control is achieved through processing
executed by the controller 30 in the third embodiment. The
following explanation focuses on the difference from the first
embodiment. FIG. 7 is a block diagram illustrating the processing
executed by the controller 30 in the third embodiment. In the
figure, the same reference numerals are assigned to components
identical to those in FIG. 4.
[0056] As shown in FIG. 7, control signals obtained through
arithmetic operations executed in the flow control circuits 50 and
60 first undergo processing at delay processing circuits 55 and 65
respectively before they are output to the electromagnetic
switching valve 16 and 26. The delay processing circuits 55 and 65
respectively include retardation processing circuits 56 and 66,
which execute first-order lag processing on the signals (indicating
the target restriction diameters) provided by the coefficient
generating circuits 53 and 63 and minimum value selection circuits
57 and 67, which select either the signals provided from the
coefficient generating circuits 53 and 63 or the signals provided
by the retardation processing circuits 56 and 66, whichever
indicate smaller values.
[0057] Operations are executed as follows in the third embodiment.
Assuming that a tire 10 slips at a time t1 in FIG. 8 and that the
slip is eliminated at a time t2, the coefficient generating circuit
53 outputs a signal that will reduce the restriction diameter at
the time t1 and outputs a signal that will reset the restriction
diameter to the initial setting at the time t2, as indicated by the
characteristics curve L1 (the solid line). During this process, the
retardation processing circuit 56 outputs a first-order lag signal
such as that indicated by the characteristics curve L2 (the dotted
line). The minimum value selection circuit 57 thus selects the
characteristics L1 at the start of the slip and selects the
characteristics L2 once the slip is eliminated. As described above,
the structure adopted in the embodiment allows the restriction
diameters at the flow control valves 15 and 25 to be reduced
quickly and increased slowly. As a result, slipping of the tires 10
and 20 can be eliminated promptly and also, recurrence of slipping
that may otherwise manifest readily as the restriction diameters at
the flow control valves 15 and 25 are reset to the initial settings
can be effectively prevented.
Fourth Embodiment
[0058] In reference to FIGS. 10 and 9, the fourth embodiment of the
travel control device according to the present invention is
explained.
[0059] While the extent of slippage is minimized by controlling the
flow control valves 15 and 25 in the first through third
embodiments, the extent of slippage is minimized by controlling the
motor displacements at the hydraulic motors 11 and 25 in the fourth
embodiment. It is to be noted that the following explanation
focuses on the difference from the first embodiment. FIG. 9 is a
traveling hydraulic circuit diagram of the traveling hydraulic
circuit of the work vehicle achieved in the fourth embodiment. In
the figure, the same reference numerals are assigned to components
identical to those in FIG. 2.
[0060] As shown in FIG. 9, the flow control valves 15 and 25 are
not disposed in the pipelines 4 and 6 in the fourth embodiment. The
controller 30 (not shown in FIG. 9) executes the following
processing based upon signals provided from the rotation detectors
17 and 27 to control the displacement control devices 11a and
21a.
[0061] FIG. 10 is a block diagrams illustrating the processing
executed by the controller 30 in the fourth embodiment. In the
figure, the same reference numerals are assigned to components
identical to those in FIG. 4. As shown in FIG. 10, the motor
displacements of the hydraulic motors 11 and 21, calculated in the
displacement calculation circuit 44, are respectively input to
multipliers 58 and 68. The multipliers 58 and 68 respectively
multiply the motor displacements by the coefficients Kf and Kr
having been determined through arithmetic operations executed at
the coefficient generating circuits 52 and 62, thereby determining
the target motor displacements. Control signals are then output to
the displacement control devices 11a and 21a so as to adjust the
motor displacements to the target motor displacements.
[0062] In the fourth embodiment, the multipliers 58 and 68 multiply
the motor displacements respectively by the coefficient Kf set to 1
and the coefficient Kr set to 1 and thus, the motor displacements
calculated at the displacement calculation circuit 44 are directly
used as the target motor displacements, as long as no slip occurs
at the tires 10 and 20. If, on the other hand, a slip occurs at a
front tire 10, the motor displacement calculated by the
displacement calculation circuit 44 is multiplied by the
coefficient Kf assuming a value less than 1, resulting in a smaller
target motor displacement. As a result, the drive torque applied to
the tires 10 is reduced so as to minimize the extent of slippage
occurring between the tires and the road surface.
[0063] As described above, if a tire 10 or 20 slips, the motor
displacement of the hydraulic motor 11 or 21 driving the slipping
tire is reduced so as to minimize the extent of the slip by
reducing the drive torque in the fourth embodiment. In addition,
since the flow control valves 15 and 25 do not need to be disposed
in the pipelines 4 and 6, a simpler structure requiring a smaller
number of parts is achieved.
[0064] It is to be noted that instead of outputting the
coefficients Kf and Kr calculated at the coefficient generating
circuits 52 and 62 directly to the multipliers 58 and 68, the
coefficients Kf and Kr may be output to the respective multipliers
58 and 68 via the delay processing circuits 55 and 65 described in
reference to the third embodiment, as shown in FIG. 11. In this
case, the motor displacement decreases promptly in the event of a
slip and the motor displacement then increases slowly as the slip
is eliminated. In other words, the slip is controlled quickly and a
recurrence of the slip while restoring the motor displacement is
prevented effectively.
[0065] It is to be noted that while any slippage of the tires 10
and 20 is detected by the rotation detectors 17 and 27 constituting
a speed detection means, a slip detection means other than those
may be utilized. For instance, a vehicle speed sensor, which is
independent of the rotation detectors 17 and 27, may be utilized to
detect a vehicle speed and a slip may be detected by calculating
the deviations of the rotational velocities detected by the
rotation detectors 17 and 27 relative to the detected vehicle
speed. While the quantity of pressure oil supplied to the hydraulic
motor 11 or 21 or the motor displacement of the hydraulic motor 11
or 21 is gradually restored via the slow return valve 18 or 28 or
the delay processing circuits 55 or 65 when the slip is eliminated,
a restoring means other than those may be utilized.
[0066] While the quantities of pressure oil supplied to the
hydraulic motors 11 and 21 are reduced via the electromagnetic
switching valves 16 and 26 and the flow control valves 15 and 25,
any flow control means other than those may be utilized as long as
the quantity of pressure oil supplied to the hydraulic motor 11 or
21 driving a slipping tire 10 or 20 is reduced upon detecting a
slip of the tire 10 or 20. In addition, while the motor
displacements are reduced by the displacement control devices 11a
and 21a, any displacement control means other than those may be
utilized as long as the motor displacement of the hydraulic motor
11 or 21 driving a slipping tire 10 or 20 is reduced upon detecting
a slip of the tire 10 or 20. This means that the controller 30 may
execute processing other than that described earlier.
[0067] While the present invention is adopted in a telescopic
handler in the embodiments described above, the present invention
may be adopted equally effectively in another type of work vehicle
(e.g., wheel loaders and wheel hydraulic excavators) as long as the
work vehicle is engaged in traveling operation via the hydraulic
motors 11 and 21 connected to the hydraulic pump 1 through a
closed-circuit connection. Namely, as long as the features and
functions of the present invention are realized, the present
invention may be embodied in a travel control device other than
those described in reference to the embodiments. It is to be noted
that the embodiments described above simply represent examples and
that the present invention may be interpreted without being in any
way restricted by the correspondence between the description of the
embodiments and the description in the scope of patent claims.
[0068] The disclosure of the following priority application is
herein incorporated by reference: [0069] Japanese Patent
Application No. 2005-319362 filed Nov. 2, 2005
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