JPH07257206A - Travel controlling circuit for construction machinery - Google Patents

Abstract

PURPOSE:To prevent unstable movement of a car body by setting a pressure switch in such a manner that it turns on when the pressure switch change-over working pressure is lower than the prescribed pilot secondary pressure and outputting a cut-off commanding signal to a maximum flow cut-off valve of a main pump when the ON-state signal is inputted into a controller. CONSTITUTION:When travel levers 28L, 28R are returned to the neutral position to stop the travelling, the pilot secondary pressure derived from pilot valves 29L, 29R becomes lower than a prescribed value and pressure switches 31L, 31R are turned on. When this signal is inputted into a controller 27, a cut-off commanding signal is outputted to a solenoid 26 of a maximum flow cut-off valve 25. Then, the pilot pressure from a pilot pump 23 acts on a pump inclination regulating pilot port 22 of a regulator 21 via pipe passages 35, 36. With this, since the maximum discharging flow rate of first and second pump 19, 20 decreases, the shock caused by the sudden stop of travel motors 17L, 17R can be relieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crawler-type construction machine such as a hydraulic excavator and a control circuit for running a work vehicle.

[0002]

2. Description of the Related Art FIG. 6 is a partially cutaway side view of a conventional hydraulic excavator. As shown in FIG. 6, in the hydraulic excavator, a revolving structure 2 is provided on the upper part of the traveling structure 1, and the center part of the traveling structure 1 is constituted by a car body frame 3. The car body frame 3 has a pair of left and right crawler frames 4L, 4R is fixedly mounted, and each of the crawler frames 4L and 4R has an idler wheel 5 at the front end, a drive wheel 6 at the rear end, an upper roller 7 at the upper surface, and a plurality of lower rollers 8 at the lower surface. An endless crawler 9 is wound around the drive wheel 6, the upper roller 7, the idler wheel 5, and the lower roller 8, and the crawler 9 is tensioned by a crawler tensioning device 10.

FIG. 7 is a side view of another embodiment of a hydraulic excavator disclosed in Japanese Utility Model Laid-Open No. 61-191982. This excavator has front and rear brackets 11,
11 'are rotatably attached to the front and rear ends of the crawler frame 12, respectively, and idle wheels 13 and drive wheels 14 are attached to the front and rear brackets 11 and 11', respectively. Also front and rear brackets 11, 1
1'denotes front and rear hydraulic cylinders 15, 15 ', respectively
Is connected to the crawler frame 1 so as to be vertically movable. Therefore, the front and rear hydraulic cylinders 15, 15 '
By reducing (in this case, the crawler 1
The contact length of 6 is A1), and the traveling performance when climbing over uneven terrain can be improved. Front and rear hydraulic cylinder 1
When 5,15 'is extended, the ground contact length of the crawler 4 increases to A2. As a result, the ground pressure of the crawler 16 can be reduced and the stability of the hydraulic excavator during excavation work can be ensured.

[0004]

Conventionally, in hydraulic excavators, in order to perform smooth crawler rotation when traveling on a solid ground, as shown in FIG. 6, horizontal planes (H, L,) on the lower front surface of the crawler 9 are provided. And an escape angle θ′2 of the rear lower side surface. Therefore, the ground contact length 1 of the lower surface of the crawler 9 is considerably shorter than the total length L of the traveling body 1. Further, in the hydraulic shovel of another embodiment shown in FIG. 7, in order to improve the overpassing traveling property, the hydraulic cylinder is contracted to displace the guide wheel and the drive wheel upward when traveling. However, if the hydraulic excavator is suddenly stopped while moving forward or backward at a fairly high speed, the inertia of the hydraulic excavator may cause the vehicle body to lean forward or backward. That is, the vehicle body was unstable when the vehicle was stopped, and the driving sensation was poor. It is an object of the present invention to provide a traveling control circuit for a crawler type construction machine that can solve the above problems.

[0005]

In the control circuit according to the first embodiment of the present invention, a secondary pilot pressure is derived from a forward / reverse pilot valve by operating a pair of traveling operation levers, and the secondary pilot pressure is derived. In the crawler type construction machine in which the pressure is applied to the pilot pressure receiving portion of the pair of pilot switching valves to control the switching of the pilot switching valves to operate the left and right traveling motors, the pilot pressure hydraulic source and the main pump A maximum flow cutoff valve for cutoff control of the maximum discharge flow of the main pump is provided between the regulator and the pilot port for adjusting the pump tilt angle, and a command signal from the controller is input to the maximum flow cutoff valve. The pilot switch for each pilot valve. And the switching operating pressure of the pressure switch is set to a predetermined pilot secondary pressure at which the construction machine starts to move, and when the predetermined pilot secondary pressure is exceeded, the pressure switch is turned off and the predetermined pilot secondary pressure is set. Adjust and set to turn on when pressure is lower than pressure,
In addition, when the on-state signal of the pressure switch is input to the controller, the pilot secondary pressure derived from the pilot valve is equal to or less than the specified pilot secondary pressure when the traveling operation lever is returned to the neutral position when the construction machine is traveling. When the ON state signal from the pressure switch is input to the controller, the controller judges based on the ON state signal, and the controller issues a maximum flow cutoff command signal to the maximum flow cutoff valve. I tried to output it.

In the control circuit of the second embodiment, instead of the travel motors 17L and 17R in the control circuit of the first embodiment, the travel motor can be switched between the low speed and high torque first speed and the high travel speed second speed.・ A second speed drive motor is installed,
By operating the electromagnetic switching valve for speed switching, the pilot pressure is applied to the speed conversion portion of the traveling motor so as to switch between the 1st and 2nd speeds, and the second speed position signal of the electromagnetic switching valve is input to the controller. When the traveling operation lever is returned to the neutral position when the construction machine is traveling, the second speed position signal from the electromagnetic switching valve is input to the controller, and the pilot secondary pressure derived from the pilot valve is the predetermined pilot. When the pressure drops below the secondary pressure and the on-state signal from the pressure switch is input to the controller, the controller determines based on that on-state signal, and the controller cuts the maximum flow rate from the maximum flow cut-off valve. The off command signal is output.

Further, in the control circuit of the third embodiment, the idler wheels and the drive wheels are supported by the left and right crawler frames of the traveling body,
An endless crawler is laid over both wheels, and means for changing the vertical position of the idler wheel and the drive wheel by hydraulic cylinder operation during traveling and excavation work, and operating a pair of traveling operation levers. Is used to derive the pilot secondary pressure from the forward / reverse pilot valve, and the pilot secondary pressure is applied to the pilot pressure receiving portions of the pair of pilot switching valves to switch the pilot switching valves to control the left and right traveling motors. In a construction machine that is made to operate, between the pilot pressure hydraulic pressure source and the pump tilt angle adjustment pilot port of the main pump regulator, the maximum discharge flow rate of the main pump is cut off and the maximum flow rate is cut off valve. Is provided so that the command signal from the controller can be input to the maximum flow cutoff valve. Further, a pressure switch for detecting the pilot secondary pressure is provided in each pilot circuit of each pilot valve, and the switching operating pressure of the pressure switch is set to a predetermined pilot secondary pressure at which the traveling movement of the construction machine is started. The pressure switch is turned off when the secondary pressure is exceeded, and is adjusted and set so that it is turned on when the pressure is lower than the predetermined pilot secondary pressure, and the on-state signal of the pressure switch is input to the controller.
A hydraulic cylinder for vertically displacing the idler wheel and the drive wheel is provided with a means for detecting the expansion / contraction state of the hydraulic cylinder, and a signal from the expansion / contraction state detection means is input to the controller. When returning to the position direction, the upward displacement signal from the expansion / contraction state detecting means is input to the controller, and the pilot secondary pressure derived from the pilot valve further falls below a predetermined pilot secondary pressure, and the pressure switch outputs When the on-state signal is input to the controller, the controller determines based on the on-state signal, and the controller outputs the maximum flow rate cutoff command signal to the maximum flow rate cutoff valve.

Further, in the control circuit of the fourth embodiment, the travel motor in the control circuit of the third embodiment is used as a travel motor, and the first and second speeds can be switched between the low speed and high torque first speed and the travel speed fast second speed. A traveling motor is arranged and the pilot pressure is applied to the speed conversion portion of the traveling motor by operating the electromagnetic switching valve for switching between the 1st and 2nd speeds so that the 1st and 2nd speeds are switched. A second speed position signal from the electromagnetic switching valve and an upward displacement signal from the expansion / contraction state detecting means are used when the traveling operation lever is returned to the neutral position when the construction machine is traveling, so that the speed position signal is input to the controller. Is input to the pilot valve and the pilot secondary pressure derived from the pilot valve drops below a predetermined pilot secondary pressure, and the on-state signal from the pressure switch is controlled. By being input to the over La, it is determined by the controller based on the on-state signal, and outputs a maximum flow cutoff command signal to the maximum flow cutoff valve from the controller.

[0009]

When the pair of traveling operation levers are tilted forward or backward from the neutral position, the pilot secondary pressure is derived from the forward or reverse pilot valve. When the pilot secondary pressure exceeds the pressure value of the predetermined pilot secondary pressure, the hydraulic excavator starts running motion. During traveling of the hydraulic excavator, the pilot secondary pressure fluctuates in proportion to the tilting operation angle of the traveling operation lever, and the rotational speed of the traveling motor also increases or decreases accordingly. When the operating lever for traveling is returned to the neutral position in order to stop traveling while the hydraulic excavator having the control circuit according to the first embodiment of the present invention is traveling at high speed, the pilot secondary pressure derived from the pilot valve is generated. Falls below a predetermined pilot secondary pressure. Since the pressure switch for detecting the pilot secondary pressure is switched to the ON state by the spring force of the built-in spring, the ON state signal of the pressure switch is input to the controller. The controller determines based on the ON state signal, and the controller outputs a maximum flow rate cutoff command signal to the solenoid of the maximum flow rate cutoff valve. Since the solenoid is energized, the maximum flow cutoff valve is switched from the tank communication oil passage position to the opening oil passage position. Pilot pressure Pilot pressure from the hydraulic source acts on the pump tilt angle adjusting pilot port of the main pump regulator through the opening oil passage position of the maximum flow rate cutoff valve. Since the maximum discharge flow rate of the main pump is cut off and the flow rate is reduced, the shock caused by the sudden stop of the rotation of the traveling motor can be alleviated.
That is, since the traveling motor makes a slow stop, the inertia of the vehicle body can be reduced when stopping the hydraulic excavator running at high speed.

Next, in the control circuit of the second embodiment, as a travel motor instead of the travel motor in the control circuit of the first embodiment, it is possible to perform a switching operation between a low speed and high torque first speed and a high travel speed second speed. A high-speed traveling motor is arranged so that the second speed position signal from the first / second speed switching electromagnetic switching valve can be input to the controller. Therefore, when the traveling operation lever is returned to the neutral position when the hydraulic excavator is traveling at the second speed, the second speed position signal from the electromagnetic switching valve is input to the controller, and the pilot secondary pressure derived from the pilot valve is predetermined. When the secondary pressure falls below the pilot secondary pressure and the on-state signal from the pressure switch is input to the controller, the controller outputs the maximum flow rate cutoff command signal to the maximum flow rate cutoff valve. The operation of the switching operation of the maximum flow rate cutoff valve in this case is the same as the operation of the maximum flow rate cutoff valve in the control circuit of the first embodiment.

Next, in the control circuit of the third embodiment, in addition to the control circuit of the first embodiment, a hydraulic cylinder for vertically displacing the idler wheel and the drive wheel and means for detecting the expansion / contraction state thereof are provided, and the expansion / contraction state detection thereof is performed. The signal from the means is input to the controller. When the traveling operation lever is returned to the neutral position during traveling of the hydraulic excavator, the upward displacement signal from the expansion / contraction state detecting means is input to the controller, and the pilot secondary pressure derived from the pilot valve is applied to the predetermined pilot secondary. When the pressure falls below the next pressure and the ON state signal from the pressure switch is input to the controller, the controller outputs a maximum flow rate cutoff command signal to the maximum flow rate cutoff valve. The operation of the switching operation of the maximum flow rate cutoff valve in this case is the same as the operation of the maximum flow rate cutoff valve in the control circuit of the first embodiment.

Next, in the control circuit of the fourth embodiment, the travel motor in place of the travel motor in the control circuit of the third embodiment can be switched between the first speed with low torque and high torque and the second speed with high travel speed. A high-speed traveling motor is arranged so that the second speed position signal from the first / second speed switching electromagnetic switching valve can be input to the controller. When the traveling operation lever is returned to the neutral position when the hydraulic excavator is traveling at the second speed, the second speed position signal from the electromagnetic switching valve and the upward displacement signal from the expansion / contraction state detecting means are input to the controller, and the pilot is further operated. When the pilot secondary pressure derived from the valve drops below the specified pilot secondary pressure and the ON state signal from the pressure switch is input to the controller, the controller cuts the maximum flow rate to the maximum flow rate cutoff valve. Outputs an off command signal. The operation of the switching operation of the maximum flow rate cutoff valve in this case is the same as the operation of the maximum flow rate cutoff valve in the control circuit of the first embodiment.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing a control circuit according to the first embodiment of the present invention. In the figure, 17L and 17R are left and right traveling motors, and 18L and 18R are traveling motors 17L and 17R.
And 20 are first and second pumps, which are main pumps, respectively, 21 is a regulator of the first pump 19 and the second pump 20, and 22
Is a pilot port for adjusting the pump tilt angle of the regulator 21, 23 is a pilot pump which is a pilot pressure hydraulic source, 24 is an oil tank, 25 is a maximum flow cutoff valve, 2
6 is a solenoid of the maximum flow cutoff valve 25, 27 is a controller, 28L and 28R are left and right traveling operation levers (hereinafter referred to as traveling levers), 29L and 29R are left and right forward pilot valves, and 30L and 30R are left and right. Reverse pilot valves, 31L and 31R are left and right forward pressure switches, 32L and 32R are left and right reverse pressure switches, and 33
Is the power supply. Symbols ai,-, and ni indicate connections of pilot circuits that connect the pilot valves 29L, 30L, 29R, and 30R with the pilot pressure receiving portions of the pilot switching valves 18L and 18R, respectively.

Next, the configuration of the control circuit according to the first embodiment of the present invention will be described with reference to FIG. In the present invention, the pilot valve 29 is operated by operating the pair of traveling levers 28L and 28R.
The pilot secondary pressure is derived from L, 29R, 30L, 30R, and the pilot secondary pressure is applied to the pilot pressure receiving portions of the pair of pilot switching valves 18L, 18R to control the switching of the pilot switching valves 18L, 18R. In the crawler type hydraulic excavator configured to operate the left and right traveling motors 17L and 17R, the maximum flow rate cutoff valve 25 is provided in a pipe line that connects the pilot pump 23 and the pilot tilt angle adjusting pilot port 22 of the regulator 21. Is provided so that the command signal from the controller 27 is input to the solenoid 26 of the maximum flow rate cutoff valve 25, and the pressure switches 31L, 31R, 32L, 32R for detecting the pilot secondary pressure are respectively provided. In the pilot circuit of pilot valves 29L, 29R, 30L, 30R Is provided, the pressure switch 31L,
The switching operating pressure of 31R, 32L, 32R is set to a predetermined pilot secondary pressure Po (for example, 7
kg / cm2), and when the specified pilot secondary pressure Po is exceeded, pressure switches 31L, 31R, 32L, 32R
Is turned off, and is adjusted and set to be in the on state when the pressure is lower than the predetermined pilot secondary pressure Po (the pressure PL is, for example, 5 kg / cm2), and the pressure switch 31L,
The on-state signals of 31R, 32L, and 32R are input to the controller 27. When the traveling levers 28L and 28R are returned to the neutral position during traveling of the hydraulic excavator, the pilot valves 29L, 29R, 30L, 30R
The pilot secondary pressure derived from is reduced to a low pressure PL below a predetermined pilot secondary pressure Po, and the pressure switch 31L
When the on-state signal from -31R or 32L-32R is input to the controller 27, the controller 27 determines based on the on-state signal, and the controller 27 causes the solenoid 2 of the maximum flow cutoff valve 25 to operate.
The maximum flow rate cutoff command signal is output to the No. 6 unit.

Next, the operation of the control circuit according to the first embodiment of the present invention will be described. The excavator travels forward and backward, but for convenience of description, the case of forward travel will be described as an example. When the pair of travel levers 28L and 28R are tilted forward from the neutral position, the pilot secondary pressure is derived from the forward pilot valves 29L and 29R. When the pilot secondary pressure exceeds a pressure value of a predetermined pilot secondary pressure Po (for example, 7 kg / cm2) (increases to 8 kg / cm2), the hydraulic excavator starts running and starts moving. When the hydraulic excavator is traveling at high speed (the pressure switches 31L and 31R are switched to the off contacts a and a, respectively), the traveling lever 28 is used to stop traveling.
When L and 28R are returned to the neutral position, the pilot valve 2
The pilot secondary pressure derived from 9L and 29R is a low pressure PL (for example, 5 kg / c, which is equal to or lower than a predetermined pilot secondary pressure Po).
m2). Since the pressure switches 31L and 31R are turned on by the spring force of the built-in springs 34 and 34 (switch to the on contacts b and b, respectively), the on state signals of the pressure switches 31L and 31R are input to the controller 27. . Controller 2 based on the ON state signal
7, the controller 27 outputs the maximum flow rate cutoff command signal to the solenoid 26 of the maximum flow rate cutoff valve 25. Since the solenoid 26 is energized, the maximum flow rate cutoff valve 25 is switched from the tank communication oil passage position E to the open oil passage position. Pilot pump 23
The pilot pressure from the above acts on the pump tilt angle adjusting pilot port 22 of the regulator 21 through the pipes 35 and 36, the positions of the maximum flow rate cutoff valve 25, and the pipe 37. Since the maximum discharge flow rates of the first pump 19 and the second pump 20 are cut off and the flow rates are reduced, it is possible to mitigate the shock of sudden rotation stop of the traveling motors 17L and 17R. That is, since the traveling motors 17L and 17R perform a slow stop, the inertia of the vehicle body can be reduced when stopping the hydraulic excavator running at high speed.

Next, FIG. 2 is a circuit diagram showing a control circuit according to a second embodiment of the present invention. In FIG. 2, components using the same components as those of the control circuit of the first embodiment shown in FIG. 1 are designated by the same reference numerals. 38L and 38R are left and right first and second speed traveling motors, and 39L and 39R are first and second speed traveling motors 38L and 3
8R each operating speed conversion unit, 40L and 40R each speed switching valve, 41 an electromagnetic switching valve for switching between first speed and second speed,
42 is a solenoid of the electromagnetic switching valve 41, 43 is a switch,
44 is a power supply. The configuration of the second embodiment control circuit of the present invention will be described with reference to FIG. In this second embodiment control circuit, the travel motors 17L and 17R in the first embodiment control circuit are used.
The first and second speed running motors 3 can be operated as a running motor instead of the first running mode and can be switched between a low speed and high torque first speed and a fast running speed second speed.
8L and 38R are placed, and switch 43 is operated to bring the
The electromagnetic switching valve 41 for speed switching is switched so that the pilot pressure is applied to the speed converting portions 39L, 39R of the traveling motors 38L, 38R to perform the 1st / 2nd speed switching. The speed position signal is input to the controller 27.

Next, the operation of the control circuit according to the second embodiment of the present invention will be described. When the switch 43 is turned on while the hydraulic excavator is traveling, the electromagnetic switching valve 41 is switched from the tank communication oil passage position G to the opening oil passage position H, so that the traveling motors 38L and 38R rotate at high speed in the second speed. At the same time, the second speed position signal of the solenoid 42, which is energized,
It is input to the controller 27. Therefore, when the traveling levers 28L and 28R are returned to the neutral position in order to stop traveling when the hydraulic excavator is traveling at the second speed, the electromagnetic switching valve 41 described above is used.
Is input to the controller 27, and the pilot secondary pressure derived from the pilot valves 29L and 29R further decreases to a low pressure PL that is equal to or lower than the predetermined pilot secondary pressure Po. Since the pressure switches 31L and 31R are turned on by the spring force of the built-in springs 34 and 34, the on-state signal is input to the controller 27. The second speed position signal and the ON state signal are the controller 2
The controller 27 makes a determination based on both of the above signals by inputting the signal to the controller 7, and outputs the maximum flow rate cutoff command signal from the controller 27 to the solenoid 26 of the maximum flow rate cutoff valve 25. The action of switching the maximum flow rate cutoff valve 25 in this case is the same as the action of the maximum flow rate cutoff valve 25 in the control circuit of the first embodiment. In the hydraulic excavator provided with the control circuit of the second embodiment, since the first speed running is low speed, the slow stop function is not activated during the first speed running.

Next, FIG. 3 is a partially cutaway side view of a traveling body 45 of a hydraulic excavator having a control circuit according to a third embodiment of the present invention. In the figure, 46L and 46R are left and right crawler frames (in the figure, the crawler frame 4) of the traveling body 45.
6R is not visible), 47 is an idle wheel, 48 is a drive wheel, 17
L and 17R are traveling motors that rotate the left and right drive wheels 48 and 48, respectively, and 49 and 50 are crawler frames 46.
Central part frame 5 of L (crawler frame 46R is symmetrical with 46L, and therefore will be described as a representative of 46L side)
Brackets fixed in the interior of the bracket 1. 52 is a pin pivotally supporting the rear end of the front frame 53 on the bracket 49; 54 is the front end of the rear frame 55;
Pins 56L and 56R pivotally supported on the front frame 5
The left and right hydraulic cylinders connecting 57 and one end of the rear frame 55, and 57 are crawler tensioning devices. By moving the hydraulic cylinders 56L and 56R to expand and contract, the idler wheel 47 and the drive wheel 48 can be rotationally displaced in the up-down direction (in the direction indicated by arrows r and n), respectively.
When the idler wheel 47 and the drive wheel 48 are displaced upward, the rising rotation angle of the front lower surface of the crawler 58 with respect to the horizontal plane (HL) is θ1, and the rising rotation angle of the rear lower surface of the crawler 58 with respect to the horizontal surface. Is θ2.

Next, FIG. 4 is a circuit diagram showing a control circuit according to a third embodiment of the present invention. In FIG. 4, components using the same components as those of the control circuit of the first embodiment shown in FIG. 1 are designated by the same reference numerals. 59L and 59R are hydraulic cylinders 56L,
Solenoid switching valve for hydraulic cylinders controlling 56R,
60 is a hydraulic power source, 61 is a switch, 62 is a power source, 63, 6
Reference numeral 4 is a stroke sensor provided in each of the hydraulic cylinders 56L and 56R. The configuration of the third embodiment control circuit of the present invention will be described with reference to FIG. In addition to the control circuit of the first embodiment, the control circuit of the third embodiment is provided with hydraulic cylinders 56L and 56R for vertically displacing the idler wheel and the drive wheel, and stroke sensors 63 and 64 for detecting the expansion / contraction state thereof. The signals from the stroke sensors 63 and 64 are input to the controller 27.

Next, the operation of the control circuit according to the third embodiment of the present invention will be described. When the switch 61 is operated to the ru contact in order to improve the ability of the crawler to get over the uneven ground when the hydraulic excavator travels, the solenoids 65 and 6 are operated.
6 is energized. Solenoid selector valve 59L, 59 for hydraulic cylinder
Since R is switched between the O position and the W position, respectively, the hydraulic cylinders 56L and 56R are reduced, and the idler wheels and the drive wheels are displaced upward. In this case, the hydraulic cylinders 56L, 56
The upward displacement signals from the stroke sensors 63 and 64 that detect the reduced state of R are input to the controller 27. Therefore, when returning the traveling levers 28L and 28R to the neutral position direction to stop traveling during traveling of the hydraulic excavator, the upward displacement signals from the stroke sensors 63 and 64 are input to the controller 27, and the pilot valve 2
The pilot secondary pressure derived from 9L and 29R decreases to a low pressure PL that is equal to or lower than a predetermined pilot secondary pressure Po. Since the pressure switches 31L and 31R are turned on by the spring force of the built-in springs 34 and 34, the on-state signal is input to the controller 27. By inputting the upward displacement signal and the ON-state signal to the controller 27, the controller 27 makes a determination based on the both signals, and the controller 27 instructs the solenoid 26 of the maximum flow cutoff valve 25 to output the maximum flow cutoff command signal. Is output. The action of switching the maximum flow rate cutoff valve 25 in this case is the same as the action of the maximum flow rate cutoff valve 25 in the control circuit of the first embodiment.

Next, FIG. 5 is a circuit diagram showing a control circuit according to a fourth embodiment of the present invention. In FIG. 5, elements using the same components as those of the control circuits of the second and third embodiments shown in FIGS. 2 and 4 are designated by the same reference numerals. The configuration of the control circuit according to the fourth embodiment of the present invention will be described with reference to FIG. In the control circuit of the fourth embodiment, the traveling motor 17L in the control circuit of the third embodiment,
Instead of the 17R, as traveling motors, first and second speed traveling motors 38L and 38R that can switch between low speed and high torque first speed and fast traveling speed second speed are arranged, and the switch 43 is operated to electromagnetically switch between the first and second speeds. The valve 41 is switched to change the pilot pressure to the speed conversion portions 39L, 3L of the traveling motors 38L, 38R.
By acting on 9R, the 1st and 2nd speeds are switched, and the 2nd speed position signal of the electromagnetic switching valve 41 is input to the controller 27.

Next, the operation of the control circuit according to the fourth embodiment of the present invention will be described. When the traveling levers 28L and 28R are returned to the neutral position in order to stop traveling during the second speed traveling of the hydraulic excavator with the switch 43 in the ON operation state,
The second speed position signal from the first / second speed switching electromagnetic switching valve 41 is input to the controller 27, and the pilot secondary pressure derived from the pilot valves 29L and 29R is a low pressure equal to or lower than the predetermined pilot secondary pressure Po. Falls to PL.
By inputting the second speed position signal and the ON-state signal of the pressure switch 31L31R to the controller 27, the controller 27 makes a determination based on both signals, and the controller 27 instructs the solenoid 26 of the maximum flow cutoff valve 25 to operate. The maximum flow rate cutoff command signal is output. The action of switching the maximum flow rate cutoff valve 25 in this case is the same as the action of the maximum flow rate cutoff valve 25 in the control circuit of the first embodiment. In the hydraulic excavator having the control circuit according to the fourth embodiment, since the first speed running is low speed, the slow stop function is not activated during the first speed running.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a control circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a control circuit according to a second embodiment of the present invention.

FIG. 3 is a partially cutaway side view of a traveling body of a hydraulic excavator having a control circuit according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a control circuit according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a control circuit according to a fourth embodiment of the present invention.

FIG. 6 is a partially cutaway side view of a conventional hydraulic excavator.

FIG. 7 is a side view of a hydraulic excavator according to another embodiment of the prior art.

[Explanation of symbols]

 1,45 Traveling body 5,13,47 Idling wheel 6,14,48 Drive wheel 9,16,58 Crawler 15,15 ', 56L, 56R Hydraulic cylinder 17L, 17R Traveling motor 19,20 1st, 2nd pump 21 Regulator 25 Maximum flow rate cut-off valve 27 Controller 28L, 28R Traveling operation lever 29L, 29R, 30L, 30R Pilot valve 31L, 31R, 32L, 32R Pressure switch 38L, 38R 1st / 2nd speed running motor 41 1st speed / 2nd speed switching Solenoid switching valve 43,61 switch 63,64 Stroke sensor

Claims (4)

[Claims] 1. A pilot secondary pressure is derived from a forward / reverse pilot valve by operating a pair of traveling operation levers, and the pilot secondary pressure is applied to a pilot pressure receiving portion of a pair of pilot switching valves. In the crawler type construction machine in which the pilot switching valve is controlled to be operated to operate the left and right traveling motors, the pilot pressure hydraulic source and the pilot tilt angle adjusting pilot port of the main pump regulator are connected to each other. A maximum flow cutoff valve for cutoff control of the maximum discharge flow of the main pump is provided so that a command signal from the controller can be input to the maximum flow cutoff valve, and a pressure switch for detecting the pilot secondary pressure. Is installed in the pilot circuit of each pilot valve, and the switching operating pressure of the pressure switch is Set to the specified pilot secondary pressure at the beginning of the running motion of the construction machine, and adjust so that the pressure switch is turned off when the specified pilot secondary pressure is exceeded and turned on when the pressure is lower than the specified pilot secondary pressure. The pilot secondary pressure that is derived from the pilot valve is set to a predetermined pilot secondary pressure when the traveling operation lever is returned to the neutral position when the construction machine is traveling, by setting the pressure switch ON signal to the controller. When the pressure drops below the pressure and the on-state signal from the pressure switch is input to the controller, the controller determines based on that on-state signal, and the controller issues a maximum flow cutoff command to the maximum flow cutoff valve. A traveling control circuit for a construction machine, which is characterized by outputting a signal. 2. The traveling control circuit for a construction machine according to claim 1, wherein the traveling motor can be switched between a low speed high torque first speed and a high traveling speed second speed.
・ A second speed traveling motor is arranged, and pilot pressure is applied to the speed conversion portion of the traveling motor by operating an electromagnetic switching valve for switching between the first and second speeds so that the first and second speeds are switched. The second speed position signal of the valve is input to the controller, and when the traveling operation lever is returned to the neutral position direction when the construction machine is running, the second speed position signal from the electromagnetic switching valve is input to the controller.
Furthermore, the pilot secondary pressure derived from the pilot valve drops below the predetermined pilot secondary pressure, and the on-state signal from the pressure switch is input to the controller, and the controller determines based on that on-state signal. A control circuit for running a construction machine, wherein a controller outputs a maximum flow cutoff command signal to a maximum flow cutoff valve. 3. The left and right crawler frames of a traveling body are supported with idler wheels and drive wheels, and endless crawlers are hung over the both wheels, so that the idler wheels and the drive wheels can be vertically moved during traveling and excavation work. The pilot secondary pressure is derived from the forward / reverse pilot valve by providing a means for changing the position by operating the hydraulic cylinder, and by operating the pair of traveling operation levers. In the construction machine in which the pilot switching valve is operated to control the pilot switching valve to operate the left and right traveling motors, the pilot pressure hydraulic source and the pilot for adjusting the pump tilt angle of the main pump regulator are used. A cutoff valve is installed between the port and the maximum flow rate that controls the maximum discharge flow rate of the main pump. A command signal from the controller is input to the flow cutoff valve, and a pressure switch for detecting the pilot secondary pressure is provided in the pilot circuit of each pilot valve, and the switching operating pressure of the pressure switch is set to the construction machine. Is set to the specified pilot secondary pressure at the beginning of the running motion of the vehicle, the pressure switch is turned off when the specified pilot secondary pressure is exceeded, and is turned on when the pressure is lower than the specified pilot secondary pressure. In addition, the hydraulic cylinder for inputting the ON state signal of the pressure switch to the controller and vertically displacing the idler wheel and the drive wheel is provided with means for detecting the expansion / contraction state, and the signal from the expansion / contraction state detecting means is supplied to the controller. Input, and when the construction machine is traveling, the travel control lever is returned to the neutral position. The upward displacement signal from the expansion / contraction state detecting means is input to the controller, and the pilot secondary pressure derived from the pilot valve further falls below a predetermined pilot secondary pressure, and the ON state signal from the pressure switch is transmitted to the controller. Is input to the controller, the controller judges based on the ON state signal, and the controller outputs a maximum flow cutoff command signal to the maximum flow cutoff valve. Control circuit. 4. The traveling control circuit for a construction machine according to claim 3, wherein the traveling motor can be switched between a low speed and high torque first speed and a high traveling speed second speed.
・ A second speed traveling motor is arranged, and pilot pressure is applied to the speed conversion portion of the traveling motor by operating an electromagnetic switching valve for switching between the first and second speeds so that the first and second speeds are switched. The second speed position signal of the valve is input to the controller, and when the traveling operation lever is returned to the neutral position direction during traveling of the construction machine, the second speed position signal from the electromagnetic switching valve and the upward displacement from the expansion / contraction state detecting means. When the signal is input to the controller, the pilot secondary pressure derived from the pilot valve further drops below the predetermined pilot secondary pressure, and the on-state signal from the pressure switch is input to the controller to turn it on. The controller judges based on the status signal and outputs the maximum flow cutoff command signal from the controller to the maximum flow cutoff valve. Travel control circuit for a construction machine is characterized in that so as to.