U.S. patent application number 14/114394 was filed with the patent office on 2015-08-06 for crawler work vehicle.
This patent application is currently assigned to KOMATSU LTD.. The applicant listed for this patent is KOMATSU LTD.. Invention is credited to Taneaki Fujino, Takeshi Yoshikawa.
Application Number | 20150217805 14/114394 |
Document ID | / |
Family ID | 48189369 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150217805 |
Kind Code |
A1 |
Yoshikawa; Takeshi ; et
al. |
August 6, 2015 |
CRAWLER WORK VEHICLE
Abstract
A crawler work vehicle includes an engine, left and right travel
devices, a power transmission device, left and right steering
clutches, left and right steering brakes, a rotation speed
detecting device, a brake hydraulic pressure obtaining device, and
a brake protecting device. The rotation speed detecting device
detects an output rotation speed of the steering brakes. The brake
hydraulic pressure obtaining device obtains a brake hydraulic
pressure supplied to the steering brakes. The brake protecting
device refers to the output rotation speed and the brake hydraulic
pressure to compute a heat rate of the steering brakes, and
executes a protection process of the steering brakes by reducing
the engine output upon determining the heat rate that was computed
is equal to or greater than a preset first threshold.
Inventors: |
Yoshikawa; Takeshi;
(Komatsu-shi, JP) ; Fujino; Taneaki; (Komatsu-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOMATSU LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
KOMATSU LTD.
Tokyo
JP
|
Family ID: |
48189369 |
Appl. No.: |
14/114394 |
Filed: |
October 1, 2012 |
PCT Filed: |
October 1, 2012 |
PCT NO: |
PCT/JP2012/075293 |
371 Date: |
October 28, 2013 |
Current U.S.
Class: |
180/9.42 |
Current CPC
Class: |
B60W 10/18 20130101;
E02F 9/2062 20130101; B62D 11/08 20130101; E02F 9/02 20130101; B60W
10/06 20130101; E02F 9/268 20130101; B60W 10/02 20130101; F02D
41/021 20130101; E02F 9/226 20130101; E02F 9/26 20130101; F02D
29/04 20130101; E02F 9/2066 20130101; E02F 9/202 20130101 |
International
Class: |
B62D 11/08 20060101
B62D011/08; E02F 9/20 20060101 E02F009/20; E02F 9/26 20060101
E02F009/26; E02F 9/02 20060101 E02F009/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 1, 2012 |
JP |
2012-104519 |
Claims
1. A crawler work vehicle comprising: an engine; left and right
travel devices that respectively have a crawler and a drive wheel
for driving the crawler; a power transmission device that transmits
power from the engine to the drive wheels of the left and right
travel devices; left and right steering clutches that are disposed
between the power transmission device and the left and right drive
wheels and transmit or block power; left and right steering brakes
that are respectively disposed between the left and right steering
clutches and the left and right drive wheels, and that brake
rotation of the left and right drive wheels; a rotation speed
detecting device that detects an output rotation speed of the
steering brakes; a brake hydraulic pressure obtaining means device
that obtains a brake hydraulic pressure supplied to the steering
brakes; and a brake protecting device that refers to the output
rotation speed and the brake hydraulic pressure to compute a heat
rate of the steering brakes, and that executes a protection process
of the steering brakes by reducing the engine output upon
determining the heat rate that was computed is equal to or greater
than a preset first threshold.
2. The crawler work vehicle according to claim 1, wherein the brake
protecting device conducts a heat rate computation and a protecting
process repeatedly in a fixed cycle, and increases the engine
output upon determining the heat rate is equal to or less than a
second threshold that is smaller than the first threshold.
3. The crawler work vehicle according to claim 1, further
comprising: an engine rotation speed determining device that
determines whether the engine rotation speed is a previously
accepted minimum engine rotation speed; the brake protecting device
executing a warning process without reducing the engine output
while the engine rotation speed is lower than the minimum rotation
speed upon determining the heat rate is equal to or greater than
the first threshold.
4. The crawler work vehicle according to claim 1, wherein the power
transmission device includes a torque converter that transmits
power through operating fluid.
5. The crawler work vehicle according to claim 2, further
comprising: an engine rotation speed determining device that
determines whether the engine rotation speed is a previously
accepted minimum engine rotation speed; the brake protecting device
executing a warning process without reducing the engine output
while the engine rotation speed is lower than the minimum rotation
speed upon determining the heat rate is equal to or greater than
the first threshold.
6. The crawler work vehicle according to claim 5, wherein the power
transmission device includes a torque converter that transmits
power through operating fluid.
7. The crawler work vehicle according to claim 2, wherein the power
transmission device includes a torque converter that transmits
power through operating fluid.
8. The crawler work vehicle according to claim 3, wherein the power
transmission device includes a torque converter that transmits
power through operating fluid.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. National stage application of
International Application No. PCT/JP2012/075293, filed on Oct. 1,
2012. This U.S. National stage application claims priority under 35
U.S.C. .sctn.119(a) to Japanese Patent Application No. 2012-104519,
filed in Japan on May 1, 2012, the entire contents of which are
hereby incorporated herein by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to a work vehicle and in
particular to a crawler work vehicle that travels using a crawler
and is steered using a steering clutch and a steering brake.
[0004] 2. Background Information
[0005] Power from an engine in a bulldozer, which is an example of
a crawler work vehicle, is transmitted through a transmission to
left and right drive wheels so that the left and right crawlers are
driven. This type of bulldozer is provided with steering clutches
and steering brakes corresponding to the left and right drive
wheels. Left and right turning is conducted by controlling the left
and right steering clutches and steering brakes with hydraulic
pressure (see for example Japanese Patent PublicationH8-18573).
[0006] For example, when gently turning left, the left side
steering brake is set to a half-engaged condition and the left side
steering clutch is disengaged while the right side steering clutch
is engaged and the right side steering brake is disengaged.
[0007] Under such a condition, slippage occurs in the left side
steering brake since the left side steering brake is in a
half-engaged condition. Therefore, if such a condition continues
for a long time, there is a problem that a thermal load on the left
side steering brake increases and the steering brake is
scorched.
[0008] Accordingly, in a control device on the vehicle of the
Japanese Laid-open Patent 2010-144598, the engine speed is
decreased to protect the steering brake when the vehicle is
detected to be descending a slope with a certain angle of
inclination or greater in a state in which a high gear speed is
selected and when the engine rotation speed exceeds a certain
rotation speed during a turning operation.
[0009] In a control device in the vehicle of the Japanese Laid-open
Patent 2010-144816, when the vehicle is detected to be descending a
slope with a certain angle of inclination or greater during a
turning operation with a lock-up clutch in an engaged state, the
lock-up clutch is disengaged. As a result, since the power is
transmitted through a torque converter, the load is absorbed by the
torque converter and the load on the steering brake is reduced to
protect the steering brake.
SUMMARY
[0010] As described above, in a conventional steering brake
protection process, a preset fixed load condition such as a vehicle
angle of inclination or gear speed and the like is observed and the
protection process is conducted when the fixed condition is
satisfied.
[0011] However, it is difficult to set all of the overload modes
for steering brakes. Further, many man-hours are required to ensure
that the protection process is executed for all the overload modes.
Further, in Japanese Laid-open Patent 2010-144816, while the
thermal load on the steering brake is reduced, fuel consumption
deteriorates when the engagement of the lock-up clutch is released
to protect the steering brakes.
[0012] An object of the present invention is to accurately detect a
load acting on the steering brakes and effectively protect the
steering brakes.
[0013] A crawler work vehicle according to a first aspect of the
present invention includes an engine, left and right travel
devices, a power transmission device, left and right steering
clutches, left and right steering brakes, a rotation speed
detecting means, a brake hydraulic pressure obtaining means, and a
brake protecting means. The left and right travel devices each have
a crawler and drive wheels for driving the crawler. The power
transmission device transmits power from the engine to the drive
wheels of the left and right travel devices. The left and right
steering clutches are disposed between the power transmission
device and the left and right drive wheels and transmit or block
power. The left and right steering brakes are respectively disposed
between the left and right steering clutches and the left and right
drive wheels and brake rotation of the left and right drive wheels.
The rotation speed detecting means detects an output rotation speed
of the steering brakes. The brake hydraulic pressure obtaining
means obtains a brake hydraulic pressure supplied to the steering
brakes. The brake protecting means refers to the output rotation
speed and the brake hydraulic pressure to compute a heat rate of
the steering brakes, and executes a protection process of the
steering brakes by reducing the engine output when the computed
heat rate is equal to or greater than a preset first threshold.
[0014] The power from the engine is transmitted through the power
transmission device and the left and right steering clutches to the
left and right travel devices. When turning, one of the steering
clutches is engaged and one of the steering brakes is disengaged
while the other steering clutch is disengaged and the other
steering brake is engaged or set in a half-engaged condition. As a
result, the vehicle turns in one direction.
[0015] Since the steering brake is in a half-engaged condition,
slippage occurs in that steering brake especially when conducting a
gentle turn with the above conditions. If such an operation
continues for a long time, the steering brake may be damaged due to
the thermal load.
[0016] Accordingly, the output rotation speed and the brake
hydraulic pressure of the steering brakes are referenced to compute
a heat rate of the steering brakes, and the computing result is
compared to a preset first threshold. If the heat rate meets or
exceeds the first threshold, it is determined that an overload is
acting upon the steering brakes and the engine output is
reduced.
[0017] Thus the output rotation speed of the steering brake is
detected, the heat rate of the steering brake is computed, and
protection process is executed on the basis of the computing
result. Therefore, since instance of the overload acting upon the
steering brakes can be detected reliably and with high accuracy
under such conditions, the steering brakes can be effectively
protected.
[0018] The crawler work vehicle according to a second aspect of the
present invention relates to the work vehicle of the first aspect,
wherein the brake protecting means conducts a heat rate computation
and a protecting process repeatedly in a fixed cycle, and increases
the engine output when the heat rate is equal to or less than a
second threshold that is smaller than the first threshold.
[0019] If the heat rate of the steering brake drops, there is no
need to reduce the engine output and thus the engine output is
preferably increased in consideration of turning performance.
[0020] Accordingly, the engine output is increased by a certain
amount when the heat rate meets or falls below the second threshold
due to the execution of the protecting process in the vehicle of
the second aspect. As a result, the reduction of the engine output
is minimized as required to protect the steering brakes and a
deterioration of the turning performance can be suppressed when the
protecting process is executed.
[0021] Further, chattering during the control process can be
prevented since the second threshold is a value smaller than the
first threshold.
[0022] A crawler work vehicle according to a third aspect of the
present invention is related to the work vehicle of the second
aspect and further includes an engine rotation speed determining
means that determines whether the engine speed is a previously
accepted minimum engine speed. Further, when the heat rate meets or
exceeds the first threshold, the brake protecting means executes a
warning process to not reduce the engine output when the engine
speed is lower than the minimum speed.
[0023] Reducing the output by lowering the engine speed and the
like when the heat rate of the steering brakes meets or exceeds the
first threshold is an effective process for protecting the steering
brakes. However, if the engine speed is reduced too much,
satisfactory vehicle performance cannot be achieved. Accordingly,
if the engine speed falls below the minimum speed acceptable for
vehicle performance, a process to emit a warning to the operator is
executed instead of reducing the engine output.
[0024] A crawler work vehicle according to a fourth aspect of the
present invention is related to the work vehicle from any of the
first to third aspects, wherein the power transmission device
includes a torque converter that transmits power through operating
fluid.
[0025] When an overload acts on the steering brakes, the protection
of the steering brakes is simplified since a certain load can be
absorbed by the torque converter.
[0026] According to the present invention described above, a load
acting on the steering brake can be accurately detected and the
steering brakes can be effectively protected. Further, reduction in
turning performance can be suppressed and the steering brakes can
be protected by conducting control so that the heat rate of a
steering brake is held between two thresholds.
BRIEF DESCRIPTION OF DRAWINGS
[0027] FIG. 1 is an external perspective view of a bulldozer
according to an embodiment of the present invention.
[0028] FIG. 2 illustrates a schematic configuration of the
bulldozer illustrated in FIG. 1.
[0029] FIG. 3 is a flow chart of a protection process of steering
brakes.
[0030] FIG. 4 is a flow chart of a protection process of steering
brakes according to another embodiment.
DETAILED DESCRIPTION OF EMBODIMENTS
[0031] A bulldozer 1 illustrated in FIG. 1 is an example of a
crawler work vehicle. The bulldozer 1 is equipped with left and
right travel devices 4L, 4R that respectively have sprockets 2L, 2R
and crawlers 3L, 3R; a blade 5 provided at the front portion of the
vehicle; and a ripper device 6 provided at the rear portion of the
vehicle as illustrated in FIGS. 1 and 2. The bulldozer 1 is able to
do work such as pushing earth with the blade 5, and work such as
excavation and crushing and the like with the ripper device 6.
(Configuration of Power Transmission System)
[0032] As illustrated in FIG. 2, the bulldozer 1 includes an engine
10, a power transmission device 11 that transmits power from the
engine 10 to the left and right sprockets 2L, 2R, left and right
steering clutches 12L, 12R, and left and right steering brakes 13L,
13R.
[0033] Power from the engine 10 is transmitted through a damper 15
to a torque converter 16 in the power transmission device 11. An
output shaft of the torque converter 16 is coupled to an input
shaft of a transmission 17 so that power from the torque converter
16 is transmitted to the transmission 17. The power output from the
transmission 17 is transmitted through a first bevel gear 18 and a
second bevel gear 19 to a cross shaft 20.
[0034] The power transmitted to the cross shaft 20 is transmitted
through the left steering clutch 12L and a left final drive gear
22L to the left sprocket 2L. Moreover, the power transmitted to the
cross shaft 20 is transmitted through the right steering clutch 12R
and a right final drive gear 22R to the right sprocket 2R. The
crawlers 3L, 3R are wound around the sprockets 2L, 2R. As a result,
when the sprockets are rotated, the crawlers 3L, 3R are driven and
consequently the bulldozer 1 travels.
[0035] A forward-reverse shifting clutch 25 and a plurality of gear
changing clutches 26 are provided in the transmission 17. The
clutches 25, 26 are hydraulic clutches that are able to switch
hydraulically between an engaged condition and a disengaged
condition. The supply and discharge of pressure oil to the clutches
25, 26 are controlled by a transmission control valve 26a.
[0036] The left and right steering clutches 12L, 12R are
respectively provided between the power transmission device 11 and
the left and right sprockets 2L, 2R, and are hydraulic clutches
that are able to hydraulically switch between an engaged condition
and a disengaged condition. The supply and discharge of pressure
oil to the steering clutches 12L, 12R are controlled by steering
clutch control valves 27L, 27R. The left and right steering
clutches 12L, 12R are negative type hydraulic clutches and thus are
engaged when hydraulic pressure is not supplied and become
disengaged when a certain amount or more hydraulic pressure is
supplied.
[0037] In this case, power is transmitted from the second bevel
gear 19 to the left sprocket 2L when the left steering clutch 12L
is in the engaged condition. Further, power is transmitted from the
second bevel gear 19 to the right sprocket 2R when the right
steering clutch 12R is in the engaged condition.
[0038] The left and right steering brakes 13L, 13R are respectively
disposed between the left and right steering clutches 12L, 12R and
the left and right sprockets 2L, 2R. The supply and discharge of
pressure oil to the steering brakes 13L, 13R are controlled by
brake control valves 28L, 28R, and are hydraulic brakes that are
able to hydraulically switch between an braking state and a
non-braking state. The left and right steering brakes 13L, 13R are
normally braking-type hydraulic brakes, and enter the engaged
condition (normally braking) when hydraulic pressure is not
supplied, and become disengaged when a certain amount or more of
hydraulic pressure is supplied. Therefore, when the supplied brake
hydraulic pressure is lower than the certain amount, an engagement
region is entered in which complete engagement with "0" slippage
and a half-engaged condition in which slippage occurs are both
possible.
[0039] Braking of the output rotation of the left steering clutch
12L, that is, rotation of the left sprocket 2L, is possible in
accordance with the braking state of the left steering brake 13L.
Further, braking of the output rotation of the right steering
clutch 12R, that is, rotation of the right sprocket 2R is possible
in accordance with the braking state of the right steering brake
13R.
[0040] According to the above configuration, when the left steering
clutch 12L is disengaged and the left steering brake 13L is braking
or half-braking (half-engaged) while the right steering clutch 12R
is engaged and the right sprocket 2R is rotating, the bulldozer 1
turns to the left. Conversely, when the right steering clutch 12R
is disengaged and the right steering brake 13R is braking or
half-braking (half-engaged) while the left steering clutch 12L is
engaged and the left sprocket 2L is rotating, the bulldozer 1 turns
to the right.
(Configuration for Output Control)
[0041] The bulldozer 1 has a control unit 30. The control unit 30
switches velocity stages of the transmission 17, controls the
control valves 26a, 27L, 27R, 28L, 28R, and executes a protection
process of the left and right steering brakes 13L, 13R.
[0042] To carry out protection of the left and right steering
brakes 13L, 13R, the control unit 30 includes an on/off determining
function, a rotation speed detecting function, a brake hydraulic
pressure obtaining function, and a protection function.
[0043] The on/off determining function is a function that
determines whether each of the steering brakes 13L, 13R is in an
engagement region according to a hydraulic pressure command value
for the steering brakes 13L, 13R. The rotation speed detecting
function is a function that detects an output rotation speed of
each of the steering brakes 13L, 13R in accordance with rotation
speed detecting sensors 32L, 32R respectively provided on output
portions of the steering clutches 12L, 12R. The brake hydraulic
pressure obtaining function is a function that obtains the
hydraulic pressure supplied to each of the steering brakes 13L, 13R
according to the hydraulic pressure command value for the steering
brakes 13L, 13R. The protection function is a function for
referring to the output rotation speed and the brake hydraulic
pressure, computing a heat rate of a steering brake generated by
slippage, and comparing the computed heat rate with a preset
threshold to execute the steering brake protection process.
[0044] The hydraulic pressure supplied to the steering brakes 13L,
13R may be actually detected by a hydraulic pressure sensor.
(Protection Process)
[0045] An explanation of the protection process of the steering
brakes 13L, 13R will be provided according to a flowchart in FIG.
3. While the following describes the protection process of the left
steering brake 13L, the protection process of the right steering
brake 13R is exactly the same.
[0046] First, in step S1, a determination is made as to whether the
left steering brake 13L (referred to simply as "steering brake"
below) is in an engagement region according to a hydraulic pressure
command value I (current value) for the steering brake.
Specifically, a determination is made as to whether the command
current value I is less than a threshold X1. As described above,
the steering brake is a hydraulic brake that is maintained in a
braking condition when brake hydraulic pressure is not supplied,
and is disengaged when the hydraulic pressure becomes equal to or
higher than a certain value. Therefore, if the command current
value I is less than the threshold X1, the steering brake is
determined to be in the engagement region and the routine advances
to step S2. If the command current value I is not less than the
threshold X1, the steering brake is determined to be in the
disengaged state and the protection process is not executed.
[0047] In step S2, the output rotation speed of the steering brakes
is detected. Specifically, a detection value R(out) from the
rotation speed detecting sensor 32L at the output portion of the
steering clutch is made the output rotation speed of the steering
brake. A determination is then made as to whether the output
rotation speed R(out) is larger than a threshold X2. The threshold
X2 may normally be set as "0 rpm", or may be set as a low rotation
speed close to 0 rpm.
[0048] If the output rotation speed R(out) is larger than the
threshold X2, the routine moves from step S2 to step S3. In step
S3, a heat rate q that is a thermal load on the steering brake is
computed using the following equation (1).
q=.mu..times.P.times.R(out) (1) [0049] .mu.: friction coefficient
of the friction members that constitute the steering brake [0050]
P: brake pressure force at a certain time (computed from the
hydraulic pressure command value and the brake disk surface
area).
[0051] In step S4, a determination is made as to whether the heat
rate q is equal to or greater than a threshold X3. The threshold X3
is a threshold preset according to the plates that constitute the
steering brake and the durability of the friction members fixed to
the plates.
[0052] If the heat rate q is greater than the threshold X3, the
routine moves from step S4 to step S5. In step S5, a determination
is made as to whether a current engine rotation speed R(eng) is
lower than a threshold X4. The threshold X4 is the minimum engine
rotation speed allowed in the vehicle and is preset.
[0053] If the engine rotation speed is equal to or greater than the
threshold X4, the routine moves from step S5 to step S6 since a
margin exists to further reduce the engine rotation speed from the
current rotation speed. In step S6, the engine rotation speed is
reduced by a certain time (.DELTA.T) and a certain rotation speed
(.DELTA.R) to reduce the engine output. The routine then returns to
step S1 and the above processing is repeated. As a result, a
thermal load on the steering brake is reduced.
[0054] Further, in step S5, if the engine rotation speed is equal
to or less than the threshold X4, the routine moves from step S5 to
step S7 since it is not desirable to reduce the engine rotation
speed any further. A warning process is conducted in step S7.
Specifically, a warning to the operator to lower the engine
rotation speed to a low idle speed is displayed on an operating
panel and the like to reduce the thermal load on the steering
clutch.
(Characteristics)
[0055] The heat rate of the steering brake caused by slippage is
computed and the protection process is executed on the basis of the
computing result. As a result, the steering brakes can be protected
reliably with higher accuracy in comparison to a case of executing
the protection process by estimating various slippage modes as in
conventional devices.
[0056] (2) Since the output of the engine is controlled in
consideration of the thermal load on the actual steering brakes,
defects such as unnecessarily reducing the engine output or not
reducing the engine output when necessary can be prevented.
[0057] (3) When a determination is made as to whether the engine
rotation speed is the previously accepted minimum rotation speed
and the engine rotation speed is lower than the minimum rotation
speed when reducing the engine rotation speed to control the
output, a warning process is executed without reducing the engine
output. As a result, the minimum level of vehicle performance can
be maintained.
Other Embodiments
[0058] The present invention is not limited to the above
embodiments and various changes and modifications may be made
without departing from the spirit of the invention.
[0059] While a process to reduce the engine rotation speed when the
thermal load on the steering clutch has become high in the
aforementioned embodiment, raising the engine output when the
thermal load is reduced may be conducted along with the process of
the aforementioned embodiment. This case is illustrated in a flow
chart in FIG. 4.
[0060] The processing of steps S1 to S7 in FIG. 4 are the same as
the processing of steps S1 to S7 in the aforementioned embodiment.
Here, steps S8 and S9 are added.
[0061] Specifically, if the heat rate q of the steering clutch is
lower than the threshold X3 in step S4, the routine moves to step
S8. In step S8, a determination is made as to whether the heat rate
q is equal to or less than a threshold X5. The threshold X5 is set
as a value smaller than the threshold X3.
[0062] If the heat rate q is equal to or less than the threshold
X5, the routine moves from step S8 to step S9 since it is
determined that the thermal load is small enough. In step S9, the
engine rotation speed is raised by a certain time (.DELTA.T) and a
certain rotation speed (.DELTA.R) to increase the engine output.
The routine then returns to step S1 and the above processing is
repeated.
[0063] The engine output can be reduced within a required minimum
limit for the protection of the steering brakes. As a result,
deterioration of the turning performance due to the protection of
the steering brakes can be suppressed.
[0064] (b) While the heat rate q of the steering brakes is computed
to control the engine output in the aforementioned embodiment, a
total heat value Q while slippage is occurring in the steering
brakes may be derived so that the engine output is controlled
according to whether the total heat value Q is equal to or greater
than a certain threshold. In this case, "heat rate" may be replaced
by "total heat value".
[0065] (c) While an example of a bulldozer has been described as
the crawler work vehicle in the aforementioned embodiments, the
present invention may be another crawler type work vehicle and can
be applied in the same way to a vehicle including a steering
clutch.
[0066] In the crawler work vehicle of the present invention, a load
acting on the steering brakes can be accurately detected and the
steering brakes can be effectively protected. Further, a reduction
in turning performance can be suppressed and the steering brakes
can be protected by controlling the heat rate of the steering
brakes so that the heat rate is held between two thresholds.
* * * * *