JPH04371618A - Travelling controller for construction equipment - Google Patents

Abstract

PURPOSE:To enable travelling and rectilinear movement by one-good or one-hand operation by interposing changeover valves for forward movement and backward movement in a pilot duct communicating pilot valves for forward movement and backward movement and pilot pressure receiving sections on the forward movement side and the backward movement side respectively. CONSTITUTION:A solenoid valve 21 for forward movement is installed to two pilot dusts 28a-28b, 29a-29b communicating the pilot valves 7, 9 for forward movement of a pair of pedal devices 3L, 3R and the forward-movement side pilot pressure receiving sections 17, 19 of a pair of travelling valves 12L, 12R. A solenoid valve 22 for backward movement is installed to two pilot ducts 30a-30b, 31a-31b communicating pilot valves 8, 10 for backward movement and the backward-movement side pilot pressure receiving sections 18, 20 of the travelling valves 12L, 12R. When both the solenoid valves 21, 22 of the changeover valves for forward movement and backward movement are changed over to the positions (b), (d) of travelling and rectilinear movement, forward or backward rectilinear movement is conducted by working and operating either one of the pedal devices 3L, 3R forward or backward.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates primarily to a travel control system for tracked construction machines such as hydraulic excavators and work vehicles.

0002

2. Description of the Related Art FIG. 4 is a perspective view showing the vicinity of a driver's seat 1 of a hydraulic excavator (not shown) equipped with a travel control device. In the figure, 2 is a floorboard, 3L and 3R are a pair of left and right pedal devices, and 4L and 4R are pedal devices 3L and 3, respectively.
The R pedals, 5L and 5R, are driving operation levers, 6L, which are integrally fixed to the pedals 4L and 4R, respectively.
and 6R are left and right work operation levers. FIG. 5 is a main part circuit diagram showing a conventional travel control device. In the figure, 7 and 8 are forward and reverse pilot valves for the left pedal device 3L, 9 and 10 are forward and reverse pilot valves for the right pedal device 3R, 11L and 11R are left and right travel motors, and 12L and 12R are Traveling pilot switching valves for controlling the traveling motors 11L and 11R, 13 and 14 are main pumps, 15 is a pilot pump, and 16 is an oil tank.

Next, a conventional travel control device will be described with reference to FIGS. 4 and 5. By operating the pair of pedal devices 3L and 3R forward or backward from their neutral positions, pilot pressure is derived from their respective pilot valves (any one of pilot valves 7, . . . , 10). Pilot switching valve 12L for traveling
, 12R respectively pilot pressure receiving parts (17, -, 2
0 (one of the pilot pressure receiving parts),
Switch the driving pilot switching valves 12L and 12R,
The left and right travel motors 11L and 11R are activated.

0004

[Problems to be Solved by the Invention] When a construction machine equipped with a conventional travel control device travels in a straight line, the driver operates the left and right pedal devices with the left and right feet (the left and right hands operate the pedal devices, respectively). (In some cases, the driving control lever was operated.) In such cases, the timing of the operations of both feet may not match, or both feet may not move in the same way at the same time, causing the construction machine to meander or traverse diagonally, which is dangerous. In addition, if the construction machine is equipped with a pedal for another working device (not shown) and it is necessary to press the pedal while the machine is moving, it is desirable to operate the pair of driving pedal devices with one foot to move in a straight line. But it was difficult. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a travel control device that allows a vehicle to travel in a straight line by operating one foot with one hand.

[0005]

[Means for Solving the Problems] The present invention provides two pilot pipes that communicate the forward pilot valves of a pair of left and right pedal devices and the forward pilot pressure receiving portions of a pair of travel pilot switching valves. A forward switching valve is interposed with respect to the road, and two pilots communicate the respective reverse pilot valves of the pair of pedal devices and the reverse pilot pressure receiving portions of the pair of travel pilot switching valves. If a reverse switching valve is installed in the conduit, and both the forward and reverse switching valves are in the normal running operation position, the vehicle will not run when the pair of pedal devices is operated in the forward or reverse direction. When the pilot switching valve is switched to the forward position or reverse position so that the left and right travel motors rotate forward or reverse, and when both the forward and reverse switching valves are switched to the straight travel position, a pair of pedal devices The forward pilot valve of one of the pedal devices communicates with the forward pilot pressure receiving portion of each of the pair of travel pilot switching valves through the straight travel position of the forward switching valve, and The reverse pilot valve and the reverse pilot pressure receiving portions of the pair of travel pilot switching valves are configured to communicate through the straight-travel position of the reverse travel pilot switching valve. Alternatively, if the forward and reverse selector valves are both in the normal travel operation position, the case is the same as above, but when both the forward and reverse selector valves are switched to the straight travel position, the pair of pedals The forward pilot valve of one of the pedal devices and the forward pilot pressure receiving portions of the pair of travel pilot switching valves communicate through the straight travel position of the forward switching valve, and the The reverse pilot valve and the reverse pilot pressure receiving portions of the pair of travel pilot switching valves are configured to communicate through the straight-travel position of the reverse travel pilot switching valve. Or again,
If both the forward and reverse switching valves are set to the normal travel operating position, the case is the same as above, but when both the forward and reverse switching valves are switched to the straight travel position,
The forward pilot valve of one of the pair of pedal devices and the forward pilot pressure receiving portion of each of the pair of travel pilot switching valves communicate through the straight travel position of the forward switching valve, and The forward pilot valve of the pedal device and the respective reverse pilot pressure receiving portions of the pair of travel pilot switching valves are configured to communicate through the straight travel position of the reverse travel switching valve.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing a travel control device according to claim 1 of the present invention. In the figure, the same reference numerals are given to the same components as in the prior art. 21 is a forward switching valve (hereinafter referred to as forward solenoid valve); 22 is a reverse switching valve (hereinafter referred to as reverse solenoid valve); 23 and 24 are forward switching valves, respectively. solenoid for the solenoid valve 21 and the solenoid valve 22 for reverse, 25
is a pilot pressure oil pressure source (same as the pilot pump 15 in the prior art) 26 is a switch, and 27 is a power source. Next, the configuration of the travel control device according to claim 1 of the present invention will be described with reference to FIG. The forward pilot valves 7, 9 of the pair of left and right pedal devices 3L, 3R are communicated with the forward pilot pressure receiving parts 17, 19 of the pair of travel pilot switching valves (hereinafter referred to as travel valves) 12L, 12R, respectively. 2
A forward solenoid valve 21 is provided for the main pilot pipes 28a-28b, 29a-29b, and a pedal device 3L is provided.
, 3R, respectively, and the reverse pilot pressure receiving parts 18, 20 of the traveling valves 12L, 12R, respectively, are connected to two pilot pipes 30a-.
30b, 31a-31b are provided with a reverse solenoid valve 22, and when the forward and reverse solenoid valves 21, 22 are in the normal travel operation positions A and C, respectively, the pair of pedal devices When 3L and 3R are operated in the forward direction or reverse direction, the travel valves 12L and 12R are respectively switched to the forward position H, H or the reverse position H, so that the left and right travel motors 11L and 11R rotate forward or reverse. , when both the forward and reverse solenoid valves 21 and 22 are switched to the straight travel positions B and D, the pair of pedal devices 3L,
The forward pilot valve 9 of one of the pedal devices 3R, for example, the right pedal device 3R, and the forward pilot pressure receiving parts 17 and 19 of the pair of travel valves 12L and 12R, respectively, are connected to each other through the B position of the forward solenoid valve 21. At the same time, the reverse pilot valve 10 of the one pedal device 3R communicates with the reverse pilot pressure receiving parts 18 and 20 of the pair of travel valves 12L and 12R, respectively, through the two positions of the reverse solenoid valve 22. It was configured as follows. Although the electromagnetic valves 21 and 22 are used as the forward and reverse switching valves in the embodiment of the present invention, they are not electromagnetic switching valves, but are replaced with manually operated or pilot pressure operated switching valves for interlocking operation. It may be possible to do so.

Next, the operation of the travel control device according to claim 1 of the present invention will be described. When the switch 26 is in the OFF state, the forward and reverse solenoid valves 21 and 22 are both in normal travel operation positions A and C. In this case, when the pedal devices 3L, 3R are operated, the travel motors 11L, 11R perform the same operation as in the prior art. Next, the switch 26 is turned on according to the driver's needs. Solenoid 23
, 24 are energized, so that the forward and reverse solenoid valves 21,
22 are both switched to straight running positions B and D. In this state, when only the pedal device 3R is depressed forward (the same applies to forward tilting of the travel control lever 5R), the pilot pressure from the pilot pressure oil pressure source 25 is transferred to the forward pilot valve 9, the pipe line 29a, passes through the B position of the forward electromagnetic valve 21, one acts on the forward pilot pressure receiving part 19 via the conduit 29b, and the other branches at the B position,
It acts on the forward pilot pressure receiving section 17 via the pipe line 28b. Since the traveling valves 12L and 12R are switched to the forward positions H and G, respectively, the left and right traveling motors 11L and 11R both rotate in the normal direction, and the construction machine moves straight forward. Next, when the switch 26 is left on and only the pedal device 3R is depressed backwards (the same applies to the backward tilting operation of the travel control lever 5R), the pilot pressure from the pilot pressure oil pressure source 25 is pilot valve 10, pipe line 31a
, passing through two positions of the reverse solenoid valve 22, one of which is connected to the conduit 31b.
The other side branches off at the above-mentioned position 2 and acts on the reverse side pilot pressure receiving section 18 via the conduit 30b. Travel valve 12L, 12R
are switched to the reverse position, respectively, so the left and right travel motors 11L, 11R are both reversed, and the construction machine moves straight backward.

[0008] In the travel control device of claim 1, even if the other pedal device of the left and right pedal devices 3L, 3R, for example, the pedal device 3L in FIG. 1 in this case, is operated forward or backward, the forward pilot The passage from the valve 7 is blocked at the forward solenoid valve 21 at the B position, and the passage from the reverse pilot valve 8 is blocked at the reverse solenoid valve 22 at the D position. Since the travel valves 12L and 12R do not switch, even if the above-mentioned erroneous operation is made, the travel motor 11L will not switch.
, 11R are safe because they do not rotate.

FIG. 2 is a circuit diagram showing a traveling control device according to a second aspect of the present invention. In the figure, components using the same components as those of the travel control device according to claim 1 are given the same reference numerals. Next, the configuration of the travel control device according to claim 2 of the present invention will be described with reference to FIG. Pair of left and right pedal devices 3L, 3R
forward pilot pressure receiving portions 1 of the forward pilot valves 7 and 9, respectively, and the forward pilot pressure receiving portions 1 of the pair of traveling valves 12L and 12R, respectively.
Two pilot pipes 28a-2 communicating with 7 and 19
8b, 29a-29b are provided with a forward solenoid valve 21, and also reverse pilot valves 8, 10 of the pedal devices 3L, 3R, respectively, and reverse pilot pressure receiving portions 18, 18 of the traveling valves 12L, 12R, respectively. A reverse solenoid valve 22' is interposed between the two pilot pipes 30a-30b, 31a-31b that communicate with the 20, and both the forward and reverse solenoid valves 21, 22' are placed in the normal traveling position. stomach,
When set to 'C', the pair of pedal devices 3L, 3 are
Travel valve 12L when R is operated in the forward or reverse direction.
, 12R are respectively switched to forward positions H, H or reverse positions H, H, so that the left and right travel motors 11L, 11R rotate forward or reverse, and the forward and reverse solenoid valves 21
, 22' are both switched to straight-ahead travel positions B and R, the forward pilot valve 9 of one of the pair of pedal devices 3L and 3R, for example, the right pedal device 3R, and the pair of travel valves 12L and 12R, respectively. The forward pilot pressure receiving parts 17 and 19 communicate with each other through the B position of the forward solenoid valve 21, and the reverse pilot pressure of the other pedal device 3L and the reverse pilot valve 8 of the pair of travel valves 12L and 12R respectively. The pressure receiving parts 18 and 20 are configured to communicate with each other through the rear position of the reverse electromagnetic valve 22'.

Next, the operation of the travel control device according to claim 2 of the present invention will be described. When the switch 26 is in the OFF state, the forward and reverse solenoid valves 21 and 22 are both in normal travel operation positions A and C'. In this case, when the pedal devices 3L and 3R are operated, the traveling motors 11L and 11R are activated.
performs the same operation as in the prior art. Next, the switch 26 is turned on according to the driver's needs. solenoid 2
3 and 24' are energized, so the forward and reverse solenoid valves 2
1 and 22' are both switched to straight running positions B and R. In this state, when only the pedal device 3R is depressed forward, the pilot pressure from the pilot pressure hydraulic pressure source 25 is
Forward pilot valve 9, conduit 29a, forward solenoid valve 21
One passes through the conduit 29b and acts on the forward pilot pressure receiving section 19, and the other branches at the above position B, passes through the conduit 28b, and acts on the forward pilot pressure receiving section 17.
It acts on Since the travel valves 12L and 12R are switched to forward positions H and G, respectively, the left and right travel motors 11L and 11
Both R rotate forward, and the construction machine moves straight forward. Next, when the switch 26 is left on and only the pedal device 3L is depressed backward, the pilot pressure from the pilot pressure oil pressure source 25 is transferred to the reverse pilot valve 8 and the conduit 30.
a, passes through the position of the reverse solenoid valve 22', and one side is connected to the pipe 3
0b, acts on the reverse pilot pressure receiving part 18,
The other branch is branched at the above-mentioned position and acts on the reverse pilot pressure receiving section 20 via the pipe line 31b. Travel valve 12L, 1
Since the motors 2R and 2R are respectively switched to the backward movement position, the left and right travel motors 11L and 11R are both reversed, and the construction machine moves straight backward.

[0011] Furthermore, in the traveling control device of claim 2, when one of the pedal devices, for example, the right pedal device 3R, is depressed forward, the construction machine moves straight ahead, and when the left pedal device 3L is depressed backward. Since the vehicle sometimes travels straight backwards, the driver can decide, for example, to operate the vehicle with the right foot when traveling straight forward, and with the left foot when traveling straight backwards. Therefore, it is convenient and easy for the driver to operate the pedals with both feet on the pedals. Moreover, even if the pedal device 3R is pressed backward or the pedal device 3L is pressed forward, the passage of the reverse pilot valve 10 is in the reverse position of the reverse solenoid valve 22', and the forward pilot valve 7
It is safe because the travel valves 12L and 12R do not operate because the passage is blocked at the position B of the forward solenoid valve 21.

FIG. 3 is a circuit diagram showing a travel control device according to claim 3 of the present invention. In the figure, the same reference numerals are given to components using the same components as those of the travel control device according to the second aspect. 32 is a pilot passage switching solenoid valve, 33 is a solenoid for the solenoid valve 32, and 34, 35, 36, and 37 are pilot pipes, respectively. When the switch 26 is turned on, the solenoids 23, 24', and 33 are energized at the same time, so the forward solenoid valve 21 is moved from the A position to the B position, the reverse solenoid valve 22' is moved from the C' position to the R position, and the pilot The passage switching solenoid valve 32 performs a switching operation from the ``nu'' position to the ``ru'' position.

Next, the configuration of the travel control device according to claim 3 of the present invention will be described with reference to FIG. A pair of left and right pedal devices 3L,
The forward solenoid valve 21 is connected to the two pilot pipes that communicate the forward pilot valves 7 and 9 of the 3R and the forward pilot pressure receiving parts 17 and 19 of the pair of travel valves 12L and 12R, respectively. Also, the pedal devices 3L, 3
Reverse pilot valves 8 and 10 and travel valve 1 for R, respectively.
Reverse pilot pressure receiving portion 18 for 2L and 12R, respectively
, 20, a reverse electromagnetic valve 22' is interposed between the two pilot pipes that communicate with the two pilot pipes. A pilot passage switching solenoid valve 32 is provided in the pilot circuit so that when the switch 26 is turned on, the pilot passage 34 leading from the forward pilot valve 7 can be switched to the pilot pipe 37 leading from the reverse pilot valve 8. Ta. Then, by turning on the switch 26, the forward and reverse solenoid valves 21,
22' are both in the straight-ahead travel position RO and RI, and when the pilot passage switching solenoid valve 32 is switched from the N position to the R position, one of the pair of pedal devices 3L and 3R, for example, the right pedal device 3R, is switched from the N position to the R position. The forward pilot valve 9 communicates with the forward pilot pressure receiving parts 17 and 19 of the pair of travel valves 12L and 12R, respectively, through the B position of the forward solenoid valve 21, and the forward pilot of the other pedal device 3L. The valve 7 and the reverse pilot pressure receiving portions 18 and 20 of the pair of travel valves 12L and 12R, respectively, are located at the position of the pilot passage switching solenoid valve 32 and the reverse solenoid valve 22.
' configured to communicate through the relocation.

Next, the operation of the travel control device according to claim 3 of the present invention will be described. When the switch 26 is in the OFF state, the forward and reverse solenoid valves 21, 22' and the pilot passage switching solenoid valve 32 are all in the normal travel operation positions A, C', and N, respectively. In this case, when the pedal devices 3L, 3R are operated, the travel motors 11L, 11R perform the same operation as in the prior art. Next, the switch 26 is turned on according to the driver's needs. Solenoid 23
, 24', and 33 are all energized at the same time, so both the forward and reverse solenoid valves 21, 22' are in the straight traveling position R,
Then, the pilot passage switching solenoid valve 32 is switched to the passage switching position. In this state, when only the pedal device 3R is depressed forward, the pilot pressure from the pilot pressure oil pressure source 25 is transferred to the forward pilot valve 9 and the pipe 29.
a, passes through the b position of the forward solenoid valve 21, and one side is the conduit 29
b, it acts on the forward pilot pressure receiving section 19, and the other branched at the above position B, and acts on the forward pilot pressure receiving section 17 through the pipe line 28b. Travel valve 12L, 12
Since R is switched to forward positions H and G, the left and right travel motors 11L and 11R both rotate in the normal direction, and the construction machine moves straight forward. Next, when the switch 26 is left on and only the pedal device 3R is depressed forward, the pilot pressure from the pilot pressure oil pressure source 25 is transferred to the forward pilot valve 7, the conduit 34, and the pilot passage switching solenoid valve. 32
One side passes through the conduit 30b and acts on the reverse side pilot pressure receiving part 18, and the other branches at the above position, and the conduit 31
b, it acts on the reverse pilot pressure receiving section 20. Since the traveling valves 12L and 12R are respectively switched to the backward traveling position, the left and right traveling motors 11L and 11R are both reversed, and the construction machine moves straight backward.

[0015] In the travel control device according to claim 3, when one of the left and right pedal devices 3L, 3R, for example, pedal device 3R, is depressed forward, the vehicle travels straight ahead, and the other pedal device 3L is moved forward. It is designed to move straight backwards when the pedal is pressed. Since all the pedals are depressed in the forward direction, the pedal operation is very easy. Further, in the case of the above operation, even if both the pedal devices 3L and 3R are erroneously depressed backwards, or even if one of them is erroneously depressed backwards, the travel valves 12L and 12R will not operate, so it is safe.

[0016]

Effects of the Invention: When a construction machine equipped with a conventional travel control device travels in a straight line, the driver operates the left and right pedal devices with his left and right feet, respectively. ) In that case, the timing of the operations of both feet may not match, or both feet may not move in the same way at the same time.
Construction machinery was meandering and diagonally moving, which was dangerous. In addition, when a construction machine is equipped with a pedal for another working device and must depress that pedal while the machine is moving, it is desirable to operate the pair of traveling pedal devices with one foot to move in a straight line, but this may be difficult. Was that. However, in the travel control device of the present invention, the two pilot pipes that communicate the forward pilot valves of the pair of left and right pedal devices, and the forward pilot pressure receiving portions of the pair of travel pilot switching valves, For two pilot pipes in which a forward switching valve is interposed and communicates the reverse pilot valves of the pair of pedal devices and the reverse pilot pressure receiving parts of the pair of travel pilot switching valves. A reverse switching valve was installed. Therefore, when both the forward and reverse switching valves are in the normal travel operating position, the pair of pedal devices described above can be operated in the same manner as in the prior art, and the travel motor can be operated in the same manner. Furthermore, when the electromagnetic switching valve is switched from the normal travel operation position to the straight travel position by operating a switch or the like, the pedal device can be made into a pedal device exclusively for straight travel that can be operated with one foot.

[0017] Among the travel control devices of the present invention, when one pedal device is pressed forward or backward to move straight forward or backward, it is necessary to press only one pedal (including the control lever) with one foot. This is the most convenient method as all you have to do is operate it. In this case, even if the other pedal device is erroneously operated, the travel motor will not operate, so it is safe. Also, when one pedal device is pressed forward, the vehicle will move straight forward,
A device that allows the vehicle to travel straight backwards when the other pedal device is depressed backwards is convenient for the driver to operate the vehicle with both feet on the pedals. In addition, in the case of a vehicle that can travel straight forward when one pedal device is pressed forward and can travel straight backward when the other pedal device is pressed forward, all pedals are pressed in the forward direction, so the driver's It is very easy to operate. The circuit of the travel control device of the present invention is a circuit of the prior art in which a commercially available electromagnetic switching valve is provided, so that the manufacturing cost is low and the construction is simple.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a travel control device according to claim 1 of the present invention.

FIG. 2 is a circuit diagram showing a traveling control device according to claim 2 of the present invention.

FIG. 3 is a circuit diagram showing a travel control device according to claim 3 of the present invention.

FIG. 4 is a perspective view showing the vicinity of a driver's seat of a hydraulic excavator equipped with a travel control device.

FIG. 5 is a circuit diagram of a main part of a conventional travel control device.

[Explanation of symbols]

3L, 3R Pedal device 7, 9 Forward pilot valve 8, 10 Reverse pilot valve 11L, 11R Travel motor 12L, 12R Travel pilot switching valve 17, 19
Forward side pilot pressure receiving section 18, 20 Reverse side pilot pressure receiving section 21 Forward solenoid switching valve 22, 22' Reverse solenoid switching valve 25 Pilot pressure oil pressure source 26 Switch 32 Solenoid valve for pilot passage switching

Claims (3)

[Claims] Claim 1: Pilot pressure is derived from a forward pilot valve or a reverse pilot valve by operating a pair of pedal devices provided on the construction machine, and the pilot pressure is applied to a pair of pilot switching valves for traveling. This travel control device operates the left and right travel motors by controlling the travel pilot switching valve by acting on the pressure receiving part, and includes a forward pilot valve of a pair of left and right pedal devices, and a pair of forward pilot valves of a pair of left and right pedal devices. A forward switching valve is interposed between the two pilot pipes communicating with the forward pilot pressure receiving portion of each of the traveling pilot switching valves, and a pair of forward switching valves are interposed with the respective reverse pilot valves of the pair of pedal devices described above. A reverse switching valve is interposed between two pilot pipes that communicate with the reverse side pilot pressure receiving part of each of the traveling pilot switching valves, and both the forward and reverse switching valves are placed in the normal traveling operation position. , when the pair of pedal devices is operated in the forward or reverse direction, the travel pilot switching valve is switched to the forward or reverse position, causing the left and right travel motors to rotate forward or reverse, and When both the forward and reverse switching valves are switched to the straight travel position, the forward pilot pressure receiving portion of the forward pilot valve of one of the pair of pedal devices and the pair of travel pilot switching valves is is communicated via the straight-travel position of the forward switching valve, and the reverse pilot pressure receiving portion of the reverse pilot valve of one of the pedal devices and the pair of travel pilot switching valves communicates with the reverse pilot pressure receiving portion of the reverse switching valve. A travel control device for a construction machine, characterized in that the device is configured to communicate through a straight travel position. Claim 2: In the travel control device for construction machinery as claimed in claim 1, when both the forward and reverse switching valves are in the normal travel operation position, the pair of pedal devices is operated in the forward or reverse direction. When operated in the direction, the pilot switching valve for traveling is switched to the forward position or reverse position, so that the left and right traveling motors rotate forward or reverse, and both the forward and reverse switching valves are switched to the straight traveling position. Sometimes, the forward pilot valve of one of the pair of pedal devices and the forward pilot pressure receiving portion of each of the pair of travel pilot switching valves communicate via the straight travel position of the forward switching valve, and Construction characterized in that the reverse pilot valve of the other pedal device and the respective reverse pilot pressure receiving portions of the pair of travel pilot switching valves communicate with each other via the straight-travel position of the reverse travel pilot switching valve. Machine travel control device. Claim 3: In the travel control device for a construction machine as claimed in claim 1, when both the forward and reverse switching valves are in the normal travel operation position, the pair of pedal devices is operated in the forward direction or in the reverse direction. When operated in the direction, the pilot switching valve for traveling is switched to the forward position or reverse position, so that the left and right traveling motors rotate forward or reverse, and both the forward and reverse switching valves are switched to the straight traveling position. Sometimes, the forward pilot valve of one of the pair of pedal devices and the forward pilot pressure receiving portion of each of the pair of travel pilot switching valves communicate via the straight travel position of the forward switching valve, and A construction characterized in that the forward pilot valve of the other pedal device and the respective reverse pilot pressure receiving portions of the pair of travel pilot switching valves communicate with each other via the straight-travel position of the reverse travel switching valve. Machine travel control device.