JPH09324446A - Hydraulic drive device for construction vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic drive device capable of preventing the occurrence of a sudden change in travel speed in the case of transition from an independent operation state for a travel to a composite operation state in a low-speed travel mode. SOLUTION: When arm direction selector valves 34a and 34b are changed over from an independent forward travel state, the maximum target tilting angles of hydraulic pumps 1a and 1b are taken at a maximum target tilting angle θL2 at the second low-travel state and a maximum target tilting angle θN in a normal case on the operation of a controller 300, thereby finding the minimum values of θa , and θb of target tilting angles for power control. In this case, operation signal pressure B2 is outputted, and an open/close valve 7 is selected at a communication position. The pressure oil of the hydraulic pump 1a is thereby introduced to both of a right travel direction selector valve 4b and a left travel direction selector valve 4a to drive left and right travel motors 57 and 58. The pressure oil of the hydraulic pump 1b is fed to the arm direction selector valve 34b and an arm cylinder 54 is thereby driven. According to this construction, the complex operation of a forward travel and an arm cloud can be implemented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic excavator
The present invention relates to a self-propelled construction vehicle such as a crane, and more particularly to a hydraulic drive system for a construction vehicle.

[0002]

2. Description of the Related Art For example, the following are known technologies relating to hydraulic drive systems for construction vehicles. Japanese Patent Publication No. 2-16416 SUMMARY OF THE INVENTION A known hydraulic drive system for a construction vehicle is driven by variable displacement first and second hydraulic pumps and pressure oil discharged from the first and second hydraulic pumps. A plurality of hydraulic actuators including first and second traveling actuators that drive the pair of left and right traveling mechanisms and a work machine actuator that drives the working mechanism; and a plurality of hydraulic actuators connected to the discharge pipeline of the first hydraulic pump. A first valve group including a first traveling directional control valve for controlling the flow rate of pressure oil supplied to the first traveling actuator; and a second traveling actuator connected to the discharge line of the second hydraulic pump. A second valve group including a second traveling direction switching valve for controlling the flow rate of pressure oil supplied to the work machine and a working direction switching valve for controlling the flow rate of pressure oil supplied to the work machine actuator; and a work machine. With the operation of the actuator, it has a communication line for communicating the pressure oil supply line of the first traveling direction switching valve and the pressure oil supply line of the second traveling direction switching valve, and has a working direction. The switching valve is connected so as to preferentially supply the pressure oil from the second hydraulic pump to the working machine actuator over the second traveling direction switching valve. At this time, although not described in this known technique, as a control of the pump discharge flow rate, when the discharge pressures of the first and second hydraulic pumps are low, the respective maximum discharge flow rates are set as normal flow rates, and 1
Also, there is generally known a pump flow rate control means for controlling the discharge flow rate (= horsepower control) such that the maximum discharge flow rate of each of the second hydraulic pumps decreases from the normal flow rate when the discharge pressure increases.

Japanese Patent Publication No. 4-18093 discloses a known technique in which only the traveling directional control valve of the control valve is operated, and the discharge flow rate of the variable displacement pump is adjusted according to the traveling speed at that time. It is a thing. That is, when the traveling directional control valve is ON and the operation valves other than traveling are OFF, when the high speed mode is selected by the speed selection switch, the pump maximum discharge flow rate is limited to the normal flow rate and the low speed mode is selected. In this case, by limiting the pump maximum discharge flow rate to a flow rate lower than the normal flow rate (hereinafter referred to as low-speed flow rate), the traveling speed is controlled to a state suitable for work, and the running traction force in the high-speed mode is insufficient. This is to prevent damage to the vehicle body or the like in the low speed mode.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Although no specific configuration of the hydraulic circuit related to the directional control valve and the actuator is disclosed, it is considered to apply the known technology to the known hydraulic circuit. However, when the known technology is applied to the known technology as described above, the following problems occur. That is, when the speed selection switch is in the low speed mode, the flow rate is low when the traveling single operation is performed, but is the normal flow rate when the combined operation of the traveling and the work implement actuator is performed. Therefore, when the work implement actuator is operated during the traveling alone operation in the low speed mode, the pump maximum discharge flow rate is immediately switched from the low speed flow rate to the normal flow rate, and the pump flow rate increases.
If the operation amount of the work implement actuator is small and the required flow rate of the work implement actuator is small at this time, the increased flow rate will flow not only into the work implement actuator but also into the traveling device, and the traveling speed will increase rapidly. There is an inconvenience that there can be. Similarly, when the operation of the work implement actuator is stopped when the traveling and the work implement actuator are performing combined operations in the low-speed mode (at this time, the maximum pump flow rate is the normal flow rate), the opposite phenomenon occurs. As a result, there is a disadvantage that the traveling speed may drop sharply. In addition, shocks such as those that occur in the vehicle body when the traveling speed changes also pose a problem.

An object of the present invention is to provide a traveling speed in the low speed mode even when the traveling single operation is changed to the composite operation accompanied by the operation of the work implement actuator having a small operation amount, or vice versa. It is an object of the present invention to provide a hydraulic drive system for a construction vehicle that does not change rapidly.

[0006]

In order to achieve the above-mentioned object, according to the present invention, the variable displacement type first and second hydraulic pumps and the first and second hydraulic pumps are used for discharge. A plurality of hydraulic actuators including first and second traveling actuators that are driven by pressure oil and that respectively drive a pair of left and right traveling mechanisms, and a work machine actuator that drives the working mechanism; and the discharge of the first hydraulic pump. A first traveling directional control valve connected to a pipeline for controlling the flow rate of pressure oil supplied to the first traveling actuator;
And a second traveling directional control valve for controlling the flow rate of pressure oil supplied to the second traveling actuator and the working machine actuator, which are connected to the discharge pipeline of the second hydraulic pump. A second valve group including a work direction switching valve for controlling a flow rate of supplied pressure oil;
And first detection means for detecting whether or not the second traveling actuator has been operated, second detection means for detecting whether or not the work implement actuator has been operated, and first and second traveling actuators of the first and second traveling actuators. A speed selecting means for selecting one of a high speed mode and a low speed mode as a traveling mode, and a maximum discharge flow rate of each of the first and second hydraulic pumps when the discharge pressure is low, the normal flow rate, And a pump flow rate control means for controlling the discharge flow rate so that the maximum discharge flow rate of each of the second hydraulic pumps decreases from the normal flow rate when the discharge pressure of the second hydraulic pump increases. Along with the operation, the pressure oil supply pipeline of the first traveling direction switching valve and the pressure oil supply pipeline of the second traveling direction switching valve communicate with each other. The work direction switching valve further has a passage, and the working direction switching valve supplies the pressure oil from the second hydraulic pump to the working machine actuator with priority over the second traveling direction switching valve. The pump flow rate control means is connected and limits the maximum discharge flow rate of the first and second hydraulic pumps to the normal flow rate when the high speed mode is selected by the speed selection means. And the low speed mode is selected, and the first and second
When it is detected by the detection means that the first and second traveling actuators are operated and the work implement actuator is not operated, the maximum discharge flow rate of the first and second hydraulic pumps is set to the normal flow rate. Lower than the first
Of the low speed flow rate, the low speed mode is selected by the speed selecting means, the first and second traveling actuators are operated by the first and second detecting means, and the working machine actuator is operated. When it is detected that the maximum discharge flow rate of the second hydraulic pump is limited to the normal flow rate, the maximum discharge flow rate of the first hydraulic pump is smaller than the normal flow rate and smaller than the first low speed flow rate. And a flow rate limiting means for limiting the flow rate to a second low speed flow rate which is also large, there is provided a hydraulic drive system for a construction vehicle. That is, in the present invention, in the low speed mode, when it is detected by the first and second detection means that the first and second traveling actuators are operated and the work implement actuator is not operated, the flow rate control means is provided. The maximum discharge flow rate of the first and second hydraulic pumps is limited to the first low speed flow rate, and the first and second traveling actuators and the work implement actuator are operated by the first and second detection means. When it is detected, the flow rate control means sets the maximum discharge flow rate of the second hydraulic pump to the normal flow rate and the maximum discharge flow rate of the first hydraulic pump to a value larger than the first low speed flow rate and smaller than the normal flow rate. Two
Limit to low flow rate. In other words, if it is assumed that the traveling single operation is changed to the composite operation accompanied by the work machine actuator operation, the flow rate distribution is as follows. Distribution of pressure oil from the second hydraulic pump Due to the shift to the combined operation, the maximum discharge flow rate of the second hydraulic pump increases from the first low speed flow rate to the normal flow rate. Here, since the working directional switching valve connected to the second hydraulic pump is supplied with the pressure oil preferentially over the second traveling directional switching valve, the pressure oil from the second hydraulic pump is , Mainly used to operate the working machine actuator. If there is a surplus at this time, it is used for actuating the second traveling actuator. Distribution of Pressure Oil from First Hydraulic Pump Due to the shift to the combined operation, the maximum discharge flow rate of the first hydraulic pump increases from the first low speed flow rate to the second low speed flow rate. Then, the pressure oil is supplied to the first traveling direction switching valve connected to the first hydraulic pump, and at this time, the communication oil conduit further connects the pressure oil supply pipeline of the first traveling direction switching valve to the first traveling direction switching valve. 2 is connected to the pressure oil supply pipe line of the traveling direction switching valve,
The pressure oil from the first hydraulic pump passes through the communication pipe to the second hydraulic pump.
It is also supplied to the traveling actuator. That is, the first
The pressure oil from the hydraulic pump will be used for operating the first and second traveling actuators. That is, the first
Traveling actuators and the sum of the maximum flow rate of the hydraulic fluid supplied to the second traveling actuators, running alone when Q _s,
Assuming that the combined operation is Q _c , Q _s = (first low speed flow rate + first low speed flow rate) when traveling alone is changed to combined operation Q _c = (second low speed flow rate). (However, it is assumed that the operation amount of the work implement actuator is not very small, at least the normal flow rate of the pressure oil is required, and the surplus pressure oil is negligible.) Accordingly, the first traveling actuator and a second difference between the maximum flow rate of the travel actuator and the hydraulic fluid supplied to the Q _c -Q _s = (second low-speed flow rate) - (first low-speed flow + first low speed Flow rate) = second low flow rate− (first
Low flow rate x 2). Therefore, if the setting is such that the second low-speed flow rate ≈ the first low-speed flow rate × 2, Q _c −Q _s can be brought close to zero, and a sudden change in traveling speed can be alleviated as compared with the conventional case. . The second low flow rate =
If it is set so that the first low flow rate × 2, Q _c −Q _s
It is possible to set = 0 so that the traveling speed does not change. As described above, when the traveling single operation is changed to the combined operation in the low speed mode, only the pressure oil from the second hydraulic pump is supplied to the working machine actuator, while the first and second traveling actuators are supplied. Is mainly supplied with the pressure oil from the first hydraulic pump, and the maximum discharge flow rate of the pressure oil from the first hydraulic pump is limited to the second low-speed flow rate, so that the traveling speed rapidly increases. Never be. On the contrary, when the composite operation shifts to the traveling only operation, the same thing as the above is established and the traveling speed does not suddenly decrease.

Preferably, in the hydraulic drive system for the construction vehicle, the traveling directional switching valve and the working directional switching valve are pilot operated valves driven by pilot pressure, and the first detecting means is for the traveling vehicle. A hydraulic drive system for a construction vehicle, which is means for detecting a pilot pressure applied to the direction switching valve, and the second detection means is means for detecting a pilot pressure applied to the working direction switching valve. Will be provided.

Further preferably, the hydraulic drive system for the construction vehicle further comprises third detecting means for detecting an operation amount of the work direction switching valve, and the pump flow rate controlling means is the speed selecting means. When the low speed mode is selected and the first and second traveling actuators are operated and the work machine actuator is operated, the maximum discharge flow rate of the second hydraulic pump is set to the first low speed flow rate. Provided is a hydraulic drive system for a construction vehicle, further comprising setting means for setting a value according to the operation amount detected by the third detection means in a range larger than the normal flow rate. That is, at the time of transition to the composite operation described above, the second operation as described above is performed.
Since the surplus pressure oil is supplied to the traveling actuator, the traveling speed may increase when the operation amount of the work implement actuator is smaller and minute. However, in the present invention, the operation direction switching valve detected by the operation amount detection means is operated by the setting means within a range in which the maximum discharge flow rate of the second hydraulic pump is larger than the first low speed flow rate and smaller than the normal flow rate. By setting the value according to the amount, the maximum discharge flow rate of the second hydraulic pump is reduced and the surplus pressure oil is reduced when the operation amount of the work implement actuator is very small. It is possible to minimize the speed change of the traveling actuator. Therefore, it is possible to more reliably prevent a sudden change in traveling speed.

More preferably, in the hydraulic drive system for the construction vehicle, the traveling directional switching valve and the working directional switching valve are pilot operated valves driven by pilot pressure, and the first detecting means is the traveling vehicle. A construction vehicle, which is means for detecting a pilot pressure applied to the working direction switching valve, and the second and third detection means are means for detecting a pilot pressure applied to the working direction switching valve. A hydraulic drive system is provided.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
This will be described with reference to FIG. 1 shows a first embodiment of the present invention.
~ It demonstrates by FIG. A circuit diagram of a hydraulic drive system for a construction vehicle according to the present embodiment is shown in FIG. In FIG. 1, the hydraulic drive system of the present embodiment is a variable displacement first hydraulic pump 1
a and a second hydraulic pump 1b. These hydraulic pumps 1a and 1b are driven by a common prime mover 2. Further, these hydraulic pumps 1a and 1b are swash plate pumps that adjust the pump discharge flow rate by changing the tilt angle (displacement volume) of the swash plate, and these hydraulic pumps 1a and 1b are known regulators 9a and 9b. Is provided. The discharge pressure of the hydraulic pumps 1a, 1b is measured by the pressure sensors 150, 1
The pressure sensors 150 and 151 detected by 51 transmit pressure signals P ₁ and P ₂ corresponding to the detected pressures to the controller 300. Then, the controller 300 transmits a drive signal to the regulators 9a and 9b according to these pressure signals, and when the pump discharge pressure rises above a predetermined value, the swash plate tilt angle is reduced to reduce the pump discharge flow rate. The horsepower control is performed so that the input horsepower of the hydraulic pumps 1a and 1b does not exceed the output horsepower of the prime mover 2. Further, preferably, the regulators 9a and 9b are interlocked with each other to perform a known total horsepower control.

The discharge line 5a of the first hydraulic pump 1a is
It is connected to the first valve group 50a. The first valve group 50a includes a left traveling directional switching valve 4a, which is a first traveling directional switching valve provided at an upstream position, and a first boom directional switching valve 14a provided downstream thereof. It has a first bucket directional control valve 24a and a first arm directional control valve 34a. The left traveling direction switching valve 4a is connected to the left traveling motor 57 that drives the left crawler belt 204 of the hydraulic excavator shown in FIGS. 2 and 3, and the first boom direction switching valve 14a is the boom cylinder 55 that drives the boom 202. Connected to the first bucket directional control valve 24a
Is connected to a bucket cylinder 56 that drives the bucket 203, and the first arm directional control valve 34a is connected to the arm 20.
It is connected to an arm cylinder 54 that drives the No. 1.

The discharge line 5b of the second hydraulic pump 1b is
It is connected to the second valve group 50b. The second valve group 50b includes a right traveling direction switching valve 4b, which is a second traveling direction switching valve provided at the downstream position, a turning direction switching valve 44 provided upstream of the right traveling direction switching valve 4b, and a second traveling direction switching valve 4b. It has an arm directional control valve 34b, a second boom directional control valve 14b, and a second bucket directional control valve 24b.
The right travel direction switching valve 4b is connected to a right travel motor 58 that drives the right crawler belt 205 of the hydraulic excavator shown in FIGS. 2 and 3. The second arm directional control valve 34b is connected to the arm cylinder 54 that drives the arm 201, and the second boom directional control valve 14b is connected to the boom cylinder 55 that drives the boom 202 to provide a second bucket direction. The switching valve 24b is connected to a bucket cylinder 56 that drives the bucket 203, and the swing direction switching valve 44 is connected to a swing motor 53 that drives the upper swing body 200 of the hydraulic excavator.

The swing body 20 shown in FIGS. 2 and 3 described above.
0, the boom 202, the arm 201, and the bucket 203 constitute a working machine for a hydraulic excavator.
2, the arm 201 and the bucket 203 constitute a front mechanism of the hydraulic excavator, and the swing motor 53, the arm cylinder 54, the boom cylinder 55 and the bucket cylinder 56 described above constitute a working machine actuator. Turning direction switching valve 44, boom direction switching valves 14a, b, bucket direction switching valves 24a, b, arm direction switching valve 34a,
b controls the flow rate of the pressure oil supplied to these working machine actuators. The left traveling direction switching valve 4a controls the flow rate of pressure oil supplied to the left traveling motor 57, and the right traveling direction switching valve 4b controls the flow rate of pressure oil supplied to the right traveling motor 58.

In the first valve group 50a, the left traveling directional control valve 4a is the first boom directional control valve 14a.
a, the first bucket directional control valve 24a, and the first arm directional control valve 34a are connected in tandem so as to supply pressure oil from the first hydraulic pump 1a to the left travel motor 57 with priority. ing. At this time, the first boom direction switching valve 14a and the first bucket direction switching valve 2
4a are connected to each other in parallel, and the first boom direction switching valve 14a and the first bucket direction switching valve 2 are connected to each other.
4a and the first arm directional control valve 34a are connected in tandem so that the pressure oil is preferentially supplied in this order. In the second valve group 50b, the second arm directional control valve 34b and the second boom directional control valve 1 are provided.
4b, the second bucket directional control valve 24b, and the turning directional control valve 44 are working machine actuators related to the pressure oil from the second hydraulic pump 1b in preference to the right travel directional control valve 4b. It is connected in tandem so as to supply to a swing motor 53, an arm cylinder 54, a boom cylinder 55, and a bucket cylinder 56. Then, at this time, in the second valve group 50b, the second arm direction switching valve 34b and the turning direction switching valve 44 are connected in parallel to each other, and the second arm direction switching valve 34b.
The turning direction switching valve 44, the second boom direction switching valve 14b, and the second bucket direction switching valve 24b are connected in tandem so that the pressure oil is preferentially supplied in this order.

A discharge passage 5a of the first hydraulic pump and an input port of the right traveling directional control valve 4b are connected by a branch passage 6. The branch passage 6 is provided with an on-off valve 7 that opens and closes the branch passage 6, and a check valve 61 that is provided on the downstream side of the on-off valve 7 and that prevents backflow of pressure oil in the direction of the discharge pipeline 5a. There is. The on-off valve 7 is a directional control valve for working, which is a directional control valve for turning 44, a directional control valve for boom 14a, a directional control valve for bucket 24a, and a directional control valve for arm 34a.
Alternatively, the boom directional control valve 14b, the bucket directional control valve 24b, and the arm directional control valve 34b are kept in the closed position shown in the figure when they are inactive, and when at least one of these directional control valves is activated, they are in the open position. It can be switched. That is, the branch passage 6, the on-off valve 7, and the check valve 61 described above are the turning direction switching valve 44, the arm direction switching valves 34a and 34b, the boom direction switching valve 14a, and the boom direction switching valve 14a.
b, the pressure oil supply line 65a of the left traveling direction switching valve 4a and the pressure oil supply line 6 of the right traveling direction switching valve 4b with the operation of at least one of the bucket direction switching valves 24a, 24b.
A communication conduit 66 for communicating with 5b is formed. It should be noted that the tank 6 is disposed on the most downstream side of the discharge pipeline 5a of the first hydraulic pump 1a and the discharge pipeline 5b of the second hydraulic pump 1b.
7 are provided.

A left traveling direction switching valve 4a and a left traveling motor 5
7, a counter balance valve 91 is provided, and a counter balance valve 90 is provided between the right traveling direction switching valve 4b and the right traveling motor 58.

Left traveling direction switching valve 4a, right traveling direction switching valve 4b, turning direction switching valve 44, boom direction switching valves 14a, 14b, bucket direction switching valves 24a, 24b, arm direction switching valve 34a. , b are hydraulic pilot operated valves, and operating lever devices 161, 162, 163, 164, 165, 166 shown in FIG. 4 as operating means for operating these directional control valves to drive corresponding actuators.
Is provided.

The operating lever device 161 is for turning, and generates pilot pressures A1 and A2 according to the operating direction and operating amount of the operating lever 161a, and these pilot pressures A1 and A2 are generated.
2 is sent to the pilot operating portion of the turning direction switching valve 44. The operation lever device 162 is for an arm, and generates pilot pressures B1 and B2 according to the operation direction and operation amount of the operation lever 162a. These pilot pressures B1 and B2 are pilot operations of the arm direction switching valves 34a and 34b. Sent to the department. The operation lever device 163 is for a boom, generates pilot pressures C1 and C2 according to the operation direction and operation amount of the operation lever 163a, and these pilot pressures C1 and C2 are pilot operations for the boom direction switching valves 14a and 14b. Sent to the department. The operation lever device 164 is for a bucket, generates pilot pressures D1 and D2 according to the operation direction and operation amount of the operation lever 164a, and generates the pilot pressures D1 and D2.
2 is sent to the pilot operation part of the bucket directional control valves 24a, 24b.

The operating lever device 165 is for left running,
The pilot pressures X1 and X2 are generated according to the operation direction and the operation amount of the operation lever 165a, and the pilot pressures X1 and X2 are generated.
X2 is sent to the pilot operating portion of the left traveling directional control valve 4a. Further, the left traveling direction switching valve 4a is provided with the operation lever 16
It has a variable throttle (not shown) that controls the flow rate of the pressure oil supplied to the left traveling motor 57 by changing the opening area according to the operation amount of 5a. The operation lever device 166 is for right traveling, and generates pilot pressures Y1 and Y2 according to the operation direction and operation amount of the operation lever 166a, and these pilot pressures Y1 and Y2 are pilot operations of the right traveling direction switching valve 4b. Sent to the department. The right travel direction switching valve 4b has a variable throttle (not shown) that controls the flow rate of the pressure oil supplied to the right travel motor 58 by changing the opening area according to the operation amount of the operation lever 166a. The other directional control valves also have the same variable throttle.

Further, the on-off valve 7 is also a hydraulic pilot operated valve, and when the operation signal pressures A, B, C and D are detected by the operation detecting device 170 shown in FIG. It is sent to the section 7a, and the on-off valve 7 is switched from the closed position to the open position. That is, the operation detecting device 170 detects the shuttle valve 171 that detects the pilot pressure A1 or A2 as the operation signal pressure A, the shuttle valve 172 that detects the pilot pressure B1 or B2 as the operation signal pressure B, and the pilot pressure C1 or C2. A shuttle valve 173 for detecting the operation signal pressure C, a shuttle valve 174 for detecting the pilot pressure D1 or D2 as the operation signal pressure D, a shuttle valve 175 for detecting the higher one of the operation signal pressures A and B, and an operation. It has a shuttle valve 176 for detecting the higher of the signal pressures C and D, and a shuttle valve 177 for detecting the higher of the operation signal pressures A or B and the operation signal pressures C or D. At this time, the pilot pressure guided from the shuttle valve 177 is detected by the pressure sensor 152, and the pressure sensor 152 operates to indicate whether or not the pilot pressure is detected, that is, whether or not the operation levers 161a to 164a related to the working machine actuator are operated. The detection signal P _ABCD is output to the controller 300. The pressure sensor 152 includes a swing direction switching valve 44, a boom direction switching valve 14a, 14b, and a bucket direction switching valve 24a, which are working machine actuators.
b, a part of the second detection means for detecting whether at least one of the arm directional control valves 34a, 34b has been operated, and the third detection for detecting the operation amount of these working directional control valves. It also constitutes part of the means.

1 and 4, the shuttle valve 178 for detecting the pilot pressure X1 or X2 as the operation signal pressure X, the shuttle valve 179 for detecting the pilot pressure Y1 or Y2 as the operation signal pressure Y, and the operation signal pressure Shuttle valve 180 for detecting the higher pressure of X and Y
And the pilot pressure introduced from the shuttle valve 180 is detected by the pressure sensor 153. The pressure sensor 153 detects whether the pilot pressure is detected or not.
That is, the controller 300 outputs the operation detection signal P _XY indicating whether the operation lever 165a related to the left traveling motor or the operation lever 166a related to the right traveling motor is operated.
Output to

Further, in FIGS. 1 and 4, there is provided a traveling speed indicating device 8 for selecting one of a high speed mode and a low speed mode as a traveling mode of the right traveling motor 58 and the left traveling motor 57. The pointing device 8 outputs a selection signal S indicating which mode is selected to the controller 300 based on this selection.

The operation of the present embodiment configured as described above will be described with reference to the flowcharts of the processing procedure in the controller 300 shown in FIGS. First, as shown in step 100, the pressure sensor 15
0, 151 output pressure signals P ₁ and P ₂ and pressure sensors 152 and 153 output operation detection signals P _ABCD and P
_XY and the selection signal S output from the traveling speed instruction device 8 are read. Next, in step 110, the maximum target tilt angle θ _amax of the first hydraulic pump 1a and the maximum target tilt angle θ _bmax of the second hydraulic pump 1b are obtained. Details of this procedure 110 are shown in FIG.

First, in step 111, it is determined whether the selection signal S is in the low speed mode or the high speed mode. Now, assuming that the operator selects the high speed mode in the traveling speed instruction device 8, the selection signal S is in the high speed mode, and therefore the procedure proceeds to step 114. In step 114, the hydraulic pump 1
The maximum target tilt angles θ _amax and θ _bmax of a and 1b are set as the maximum target tilt angles θ _{N in} normal times. That is, at this time, no limitation is imposed on the maximum flow rates of the first and second hydraulic pumps 1a and 1b. After that, returning to FIG. 5 and proceeding to step 120, the target tilt angles θ _ao and θ _bo by horsepower control are obtained in step 120, and further in step 130, among θ _N and θ _ao , and θ _N and θ _bo. The minimum values θ _a and θ _b are selected. Then, in step 140, the regulator 9
Drive signals corresponding to these θ _a and θ _b are output to a and 9 _b , and this flow ends.

At this time, the operator operates the operating lever 162a with the intention of individually performing the arm crowd, and operates the arm directional control valves 34a and 34b respectively.
If it is switched to the right position of, the operation lever device 162
The operation signal pressure B2 (see FIG. 4) from the operation detection device 1
It is given to the pilot operation part 7a of the on-off valve 7 via the shuttle valves 175 and 177 of 70, the on-off valve 7 is switched to the open position, and the communication pipe line 66 communicates. However, since the branch passage 6 is connected to the downstream side of the check valve of the pressure oil supply pipeline 65b, and the right traveling directional control valve 4b is maintained in the neutral position, the communication pipeline 66 is eventually closed. . Therefore, from the first hydraulic pump 1a to the arm directional control valve 34.
The total amount of the pressure oil supplied via a and the pressure oil supplied from the second hydraulic pump 1b via the arm directional control valve 34b is supplied to the arm cylinder 54, whereby the arm 201 is clouded. The same applies when performing an arm dump or when performing an independent operation of another work machine.

At this time, it is assumed that the operator operates the operating levers 165a and 166a to move the left and right traveling direction switching valves 4a and 4b to the right position in FIG. In this case, since none of the operation levers 161a to 164a is operated, none of the operation signal pressures A, B, C, D is output (see FIG. 4), and the open / close valve 7 is kept in the closed position. Therefore,
The entire amount of pressure oil from the first hydraulic pump 1a is supplied to the left traveling motor 57 via the left traveling direction switching valve 4a, and the entire amount of pressure oil from the second hydraulic pump 1b is transmitted to the right traveling direction switching valve. It is supplied to the right traveling motor 58 via 4b, whereby the left crawler belt 204 and the right crawler belt 205 are driven to travel. The same applies to the case where the vehicle is traveling and retracting independently.

Here, from the above-described traveling forward and forward independent operation state, the operator operates the operation lever 162a, for example, for the purpose of a combined operation of traveling forward and arm cloud operation, and the arm directional control valves 34a, 34b. 1 are switched to the right position in FIG. 1, the operation signal pressure B2 is output from the operation lever device 162, and this pressure is detected by the operation detection device 1
70 is provided to the pilot operating portion 7a of the opening / closing valve 7 via the shuttle valve 172, the shuttle valve 175, and the shuttle valve 177, so that the opening / closing valve 7 is switched to the communication position.
By this switching, a part of the pressure oil of the first hydraulic pump 1a is guided to the right travel direction switching valve 4b via the branch passage 6, the opening / closing valve 7, and the check valve 61. The other part of the pressure oil from the first hydraulic pump 1a is located upstream of the first arm directional control valve 34a, the first bucket directional control valve 24a, and the first boom directional control valve 14a. It is preferentially supplied to the left traveling directional control valve 4a. As a result, the pressure oil from the first hydraulic pump 1a is transferred to the right traveling directional control valve 4
It is possible to drive the left and right traveling motors 57 and 58 by being guided to both the left and right traveling directional control valves 4a. That is, the pressure oil from the first hydraulic pump 1a is substantially supplied only to the left and right traveling motors 57 and 58. On the other hand, the pressure oil of the second hydraulic pump 1b is supplied to the second arm directional control valve 34b through the discharge conduit 5b to drive the arm cylinder 54.

As described above, it is possible to carry out the combined operation of the forward traveling and the arm crowd. The same applies to the case of traveling backward and backward, and the same applies to the combined operation with the operation of the arm dump or another working machine.

On the other hand, if the operator selects the low speed mode in the traveling speed instruction device 8, the selection signal S is in the low speed mode, and therefore the procedure proceeds to step 112, and the operation detection signal P is detected.
Determine if _XY was detected. Here, the operator operates the operation lever 162a for the purpose of, for example, performing the arm crowd independently, and the arm direction switching valve 34
If a and b are switched to the right position in FIG. 1, respectively,
Since the operation levers 165a and 166a are not operated and the operation detection signal P _XY is not detected, the routine _proceeds to step 114, where the maximum target tilt angles θ _amax and θ _bmax of the hydraulic pumps 1a and 1b are set to the maximum target tilt angles θ _N at the normal time. And The control and operation thereafter are the same as the independent operation in the high speed mode.

Further, the operator operates the operation levers 165a and 166a for the purpose of, for example, traveling forward alone, and operates the left lever.
When the right traveling directional control valves 4a, 4b are respectively switched to the right position in FIG. 1, the operation detection signal P _XY is detected in step 112, and therefore the process proceeds to step 113. In step 113, since none of the operation levers 161a to 164a are operated and the operation detection signal P _ABCD is not detected, the process proceeds to step 116. At this time, the on-off valve 7 is maintained in the closed position. Then, in step 116, the hydraulic pump 1a,
The maximum target tilt angles θ _amax and θ _bmax of 1b are set to a first target tilt angle θ _L1 at a low speed which is smaller than the maximum target tilt angle θ _N at normal times. Then, returning to FIG. 5, the minimum values θ _a and θ _b of the target tilt angles θ _ao and θ _bo by the horsepower control are obtained in step 120 and thereafter as described above, and the corresponding drive signals are output. The maximum discharge flow rate characteristic of the hydraulic pumps 1a and 1b at the first low speed at this time is shown in FIG. 7 in comparison with the maximum discharge flow rate characteristic at the normal time. FIG. 7 shows the discharge pressure P on the horizontal axis and the tilt angle θ on the vertical axis when the rotational speeds of the hydraulic pumps 1a and 1b are constant. At this time, since the rotation speed is constant, the vertical axis may be expressed in place of the discharge flow rate Q. The maximum discharge flow rate characteristic at the second low speed in the figure will be described later.

As a result, the traveling speed can be adjusted to the intention of the operator when traveling only at a low speed. The same applies to the case of traveling backward only.

Here, from the above-described traveling forward alone state, the operator operates the operation lever 162a to operate the arm directional control valves 34a, 34b, for the purpose of, for example, a combined operation of traveling forward and arm crowding. If the respective positions are switched to the right position in FIG. 1, the operation detection signal P _XY is obtained in step 112.
Is detected and the procedure moves to step 113, and in step 113, the operation detection signal P _ABCD is detected, so the procedure moves to step 115.

In step 115, the maximum target tilt angle θ _amax of the hydraulic pump 1a is set to the normal maximum target tilt angle θ _N.
Smaller than the maximum target tilt angle θ _L1 at the first low speed and larger than the maximum target tilt angle θ _L2 at the second low speed, and
The maximum target tilt angle θ _bmax of the hydraulic pump 1b is set as the maximum target tilt angle θ _N under normal conditions. Then, returning to FIG. 5, step 120
After that, the minimum values θ _a and θ _b with the target tilt angles θ _ao and θ _bo are _calculated by the horsepower control, and the corresponding drive signals are output.
As a result, the discharge flow rate characteristic of the hydraulic pump 1b at the second low speed at this time is, as shown in FIG.
It is located between the first low-speed discharge flow rate characteristic curve and the maximum discharge flow rate characteristic curve.

At this time, the operation signal pressure B2 is output from the operation lever device 162, and this pressure is detected by the operation detecting device 17
No. 0 shuttle valve 172, shuttle valve 175, and shuttle valve 177 are applied to the pilot operating portion 7a of the opening / closing valve 7. As a result, the opening / closing valve 7 is switched to the communication position, and a part of the pressure oil of the first hydraulic pump 1a is divided into the branch passage 6,
Right travel direction switching valve 4b via the on-off valve 7 and the check valve 61
Be led to. The other parts of the pressure oil of the first hydraulic pump 1a include the first arm directional switching valve 34a, the first bucket directional switching valve 24a, and the first boom directional switching valve 1a.
It is preferentially supplied to the left traveling directional control valve 4a located upstream of 4a. As a result, the pressure oil from the first hydraulic pump 1a is guided to both the right traveling direction switching valve 4b and the left traveling direction switching valve 4a, and the left / right traveling motors 57 and 58 are driven.
Can be driven. That is, the pressure oil from the first hydraulic pump 1a is substantially the left and right traveling motors 57,
Only supplied to 58. On the other hand, since the pressure oil of the second hydraulic pump 1b is mainly supplied to the second arm directional control valve 34b through the discharge conduit 5b, the arm cylinder 54 can be driven.

As described above, it is possible to carry out the combined operation of the forward traveling and the arm crowd. The same applies to the case of traveling backward and backward, and the same applies to the combined operation with the operation of the arm dump or another working machine.

In the above structure and operation, the present embodiment prevents the traveling speed from abruptly changing in the low speed mode when the traveling single operation shifts to the composite operation involving the operation of the working machine actuator. Is. Hereinafter, the operation of this embodiment will be described in detail.

For example, as described above, considering the case of shifting from the state of traveling forward alone to the combined operation of traveling forward and arm cloud, the flow rate distribution of the pressure oil is as follows. Of the two directional control valves for work, the arm directional control valves 34a and 34b, the boom directional control valves 14a and 14b, and the bucket directional control valves 24a and 24b are frequently used in advance. What to do is the second valve group 50b
In this combined operation, the work direction switching valve, that is, the arm direction switching valve 34b,
The boom directional control valve 14b and the bucket directional control valve 24b are operated, or the second valve group 5 is also operated.
It is assumed that the turning direction switching valve 44 arranged at 0b is operated.

(1) Distribution of pressure oil from the second hydraulic pump 1b By shifting to the combined operation, the maximum target tilt angle of the second hydraulic pump 1b becomes the maximum target tilt angle at the first low speed. Increase from θ _L1 to the normal maximum target tilt angle θ _N. Where the second
The second arm directional control valve 34b connected to the second hydraulic pump 1b is supplied with pressure oil more preferentially than the downstream right directional control valve 4b. The pressure oil is used mainly for operating the arm cylinder 54 via the second arm directional control valve 34b. If there is a surplus at this time, it is supplied to the right traveling motor 58 via the right traveling direction switching valve 4b.

(2) Distribution of pressure oil from the first hydraulic pump 1a By shifting to the complex operation, the maximum target tilt angle θ of the first hydraulic pump 1a is the maximum target tilt angle θ at the first low speed. The maximum target tilt angle θ _L2 at the second low speed is increased from _L1 . Here, the left traveling direction switching valve 4a connected to the first hydraulic pump 1a is supplied with pressure oil more preferentially than the downstream first arm direction switching valve 34a, whereby the left traveling motor 5 is driven.
7 is driven. Further, at this time, as described above, the opening / closing valve 7 of the communication conduit 66 is in the communication position, and the pressure oil supply conduit 65a of the left traveling directional switching valve 4a and the pressure oil supply conduit 65b of the right traveling directional switching valve 4b. By communicating with
The pressure oil from the first hydraulic pump 1a is supplied to the communication line 6
It is also supplied to the right traveling direction switching valve 4b via 6 and the right traveling motor 58 is operated accordingly.

From the above (1) and (2), the maximum target tilt angle θ _L1 at the first low speed, the maximum target tilt angle θ _L2 at the second low speed, and the maximum target tilt angle θ _N at the normal time Corresponding to the maximum discharge flow rate of the second hydraulic pump is _QL1 (hereinafter appropriately referred to as the first maximum discharge flow rate at low speed), _QL2 (hereinafter appropriately,
Second maximum discharge flow rate at low speed), Q _N (hereinafter referred to as appropriate)
The maximum discharge flow rate during normal operation)
Assuming that the upper limit of the total amount of the pressure oil flow supplied to the right traveling motor 58 and the right traveling motor 58 when traveling alone is Q _s , and the upper limit of the combined operation is Q _c , the transition to the combined operation as described above causes Q _s = From Q _L1 + Q _L1 to Q _c = Q _L2 (however, the arm directional control valve 4
It is assumed that the operation amount of b is not small and the arm cylinder 54 requires at least the normal flow rate of pressure oil, and the surplus pressure oil is negligible.

Therefore, the left and right traveling motors 57, 58
Difference between the upper of the hydraulic fluid flow rate to be supplied, Q _c -Q _s = Q _L2 to - a _{(Q L1 + Q L1) =} Q L2 -2Q L1.

Therefore, if Q _L2 ≈2Q _N is set, Q _c -Q _s can be brought close to zero, and a sharp change in the traveling speed of the left traveling motor 57 and the right traveling motor 58 can be achieved compared to the conventional case. Can also be relaxed. Furthermore, Q _L2 = 2
If it is set to Q _N , it is possible to set Q _c −Q _s = 0 and keep the traveling speeds of the left traveling motor 57 and the right traveling motor 58 unchanged.

As described above, in the low speed mode, when shifting from the independent operation of traveling forward to the combined operation involving the arm cloud, only the pressure oil from the second hydraulic pump 1b is supplied to the arm cylinder 34b. On the other hand, the left and right traveling motors 57, 58 are mainly supplied with the pressure oil from the first hydraulic pump 1a, and the maximum discharge flow rate of the pressure oil from the first hydraulic pump 1a is set to the value at the second low speed. Maximum discharge flow rate Q
_By being limited to _L2 , the traveling speed does not suddenly increase. On the contrary, when the composite operation shifts to the traveling only operation, the same thing as above is established and the traveling speed does not suddenly decrease. The same applies to the case of traveling backwards, the case of arm dumping, and the combined operation of the turning motor 53, the boom cylinder 55, and the bucket cylinder 56. The relationship between the operation mode of the operator and the pump discharge flow rate described so far is summarized in FIG.

As described above, according to this embodiment, the left / right traveling direction switching valve 4 is operated in the low speed mode.
A combined operation in which at least one of the turning directional control valve 44, the arm directional control valve 34b, the boom directional control valve 14b, and the bucket directional control valve 24b is operated from a traveling independent operation in which only a and 4b are operated. When the work machine actuators 14b, 24b, 34
b and 44 are supplied with only the pressure oil from the second hydraulic pump 1b, while the left and right traveling motors 57 and 58 are mainly supplied with the pressure oil from the first hydraulic pump 1a, and because of the hydraulic fluid maximum discharge flow rate from the hydraulic pump 1a is limited to a maximum discharge flow rate Q _L2 when the second low speed, the traveling speed is not abruptly increased, sharply even running speed when moving in the opposite Does not get smaller. That is, since it is possible to prevent the traveling speed from changing abruptly, it is possible to prevent the vehicle body from being shocked by such a sudden change.

In the above embodiment, the first valve group 50a includes the first traveling direction switching valve 14a, which is a working direction switching valve, in addition to the left traveling direction switching valve 4a.
A first bucket directional control valve 24a and a first arm directional control valve 34a are provided, and the left traveling directional control valve has priority over the working directional control valve in the first hydraulic pump 1.
Although the pressure oil from a is supplied, the invention is not limited to this, and a structure without a work direction switching valve may be used. Also in this case, the same effect is obtained.

In the above embodiment, the left / right traveling direction switching valves 4a, 4b, the arm direction switching valves 34a, b,
The boom directional control valves 14a, 14b, the bucket directional control valves 24a, 24b, and the turning directional control valve 44 are pilot operated valves, and the left / right traveling motors 57, 57 are detected by detecting the pilot pressure applied to them. 58, arm cylinder 54, boom cylinder 55, bucket cylinder 5
6 has been operated, but the invention is not limited to this. For example, the operation lever devices 161 to 166 are provided with electric levers and the electric signals are detected, or the left / right traveling motors 57, 58 are detected. , Arm cylinder 5
4, the position change of the boom cylinder 55, the bucket cylinder 56, and the like may be directly detected by a position sensor or the like. In this case, the same effect can be obtained.

A second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the maximum target tilt angle control function of the second hydraulic pump 1b by the controller 300 is partially different in the combined operation in the low speed mode, and other than that, the construction vehicle of the first embodiment is different. The structure is almost the same as the hydraulic drive device.

Of the control processing of the controller 300 of the present embodiment, the procedure corresponding to the procedure shown in FIG. 5 of the first embodiment is almost the same, but part of the procedure shown in FIG. 6 is different. 9 shows the procedure corresponding to FIG. The same code | symbol is attached | subjected to the thing equivalent to the procedure shown in FIG. 6 of 1st Embodiment. 9 is different from FIG. 6 in that
The low speed mode is selected in step 111, the operation detection signal P _XY is detected in step 112, and the operation detection signal P _XY is detected in step 113.
_{If ABCD} is detected, in step 117, the hydraulic pump 1b is
The maximum target tilt angle θ _bmax of the first target speed in accordance with the magnitude of the operation detection signal P _{ABCD in} a range larger than the maximum target tilt angle θ _L1 at the low speed and smaller than θ _{N in the} normal time. Set to θ _LV . FIG. 10 shows the relationship between the operation detection signal P _ABCD and the maximum target tilt angle θ _LV .

As shown in FIG. 10, the operation detection signal P _ABCD
, That is, the operation amount of the turning direction switching valve 44, the arm direction switching valves 34a and 34b, the boom direction switching valves 14a and 14b, and the bucket direction switching valves 24a and 24b, which are working machine actuators, and the maximum. The target tilt angle θ _LV is substantially proportional to the target tilt angle θ _LV , so that one maximum target tilt angle θ _LV corresponding to a certain operation amount is calculated in step 117.
Further, FIG. 11 shows the relationship between the maximum target tilt angle θ _N of the hydraulic pump 1b at the normal time and the maximum target tilt angle θ _L1 at the first low speed and the pump discharge pressure at this time.

The other procedures are almost the same as those in the first embodiment.

The operation of the present embodiment configured as described above will be described below. That is, as described in the first embodiment, in the low speed mode, for example, in the case of shifting from the state of traveling forward only to the combined operation of traveling forward and arm cloud, as described in (1), the right traveling motor is used. 58
Since the excess pressure oil from the arm cylinder 54 is supplied to, the amount of excess pressure oil increases when the operation amount of the arm direction switching valve 34b is extremely small and minute.
The traveling speed of the right traveling motor 58 may increase.
However, in step 117 of FIG. 9, the controller 300 of the present embodiment sets the operation detection signal P _ABCD of the maximum target tilt angle θ _bmax of the second hydraulic pump 1b in a range larger than θ _{L1 and} smaller than θ _N. Θ _LV according to size
When the operation amount of the arm directional control valve 34b is small, the maximum discharge flow rate of the second hydraulic pump 1b is reduced to reduce the surplus pressure oil. The speed change of 58 can be minimized. Therefore, in the low speed mode, the traveling speed rapidly increases even when the traveling forward movement is changed to the combined operation of the traveling forward movement and the arm cloud that minutely operates the arm direction switching valve 34b. There is no. Further, even when shifting to the opposite, it is possible to prevent the traveling speed from changing abruptly. Therefore, the sudden change does not cause a shock to the vehicle body.

In the second embodiment described above, the case of traveling forward and arm crowding has been described, but in the case of traveling backward, control by the same procedure is also performed in the combined operation with the operation of the arm dump or another working machine. The same effect is obtained in this case as well. The relationship between the operation mode of the operator and the pump discharge flow rate in the present embodiment described above is shown collectively in FIG.

[0053]

According to the present invention, only the pressure oil from the second hydraulic pump is supplied to the working machine actuator when the traveling single operation is transited to the composite operation in the low speed mode, while the first and the second hydraulic pumps are supplied. The second traveling actuator is mainly supplied with the pressure oil from the first hydraulic pump, and the maximum discharge flow rate of the pressure oil from the first hydraulic pump is limited to the second low speed flow rate. Does not suddenly increase, and the traveling speed does not suddenly decrease even when shifting to the opposite. That is, since it is possible to prevent the traveling speed from changing abruptly, shock does not occur in the vehicle body due to such abrupt change.

Further, at this time, the setting means sets the maximum discharge flow rate of the second hydraulic pump to a value corresponding to the operation amount of the work direction switching valve within a range larger than the first low speed flow rate and smaller than the normal flow rate. The speed change of the second traveling actuator can be minimized. Therefore, it is possible to more reliably prevent a sudden change in traveling speed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a hydraulic drive system for a construction vehicle according to a first embodiment of the present invention.

FIG. 2 is a side view of a hydraulic excavator in which the hydraulic device shown in FIG. 1 is mounted.

FIG. 3 is a top view of a hydraulic excavator in which the hydraulic device shown in FIG. 1 is mounted.

4 is a circuit diagram showing a configuration of an operation lever device for operating the directional control valves of the valve group shown in FIG. 1 and an operation detection device for detecting the operation of the directional control valves.

5 is a flowchart showing a control processing procedure in the controller shown in FIG.

6 is a flowchart showing details of a control processing procedure in the controller shown in FIG.

FIG. 7 is a diagram showing discharge flow rate characteristics of the hydraulic pump shown in FIG.

FIG. 8 is a diagram showing a relationship between an operation mode of an operator and a pump discharge flow rate.

FIG. 9 is a flowchart showing details of a control processing procedure in a controller included in the hydraulic drive system for a construction vehicle according to the second embodiment of the present invention.

10 is a diagram showing the relationship between the maximum target tilt angle of the hydraulic pump set in the control procedure shown in FIG. 9 and the operation detection signal of the directional control valve.

FIG. 11 is a maximum target tilt angle at normal time which is an upper limit of the maximum target tilt angle set in the control procedure shown in FIG. 9 and a maximum target tilt angle at a first low speed which is a lower limit, and a pump discharge pressure. It is a figure which shows the relationship with.

FIG. 12 is a diagram showing a relationship between an operation mode of an operator and a pump discharge flow rate.

[Explanation of symbols]

1a Hydraulic pump 1b Hydraulic pump 4a Left traveling direction switching valve 4b Right traveling direction switching valve 5a Discharge pipe line 5b Discharge pipe line 7 Open / close valve 8 Travel speed instruction device (speed selection means) 9a Regulator 9b Regulator 14a Boom direction switch Valve 14b Boom directional control valve 24a Bucket directional control valve 24b Bucket directional control valve 34a Arm directional control valve 34b Arm directional control valve 44 Slewing directional control valve 50a First valve group 50b Second valve group 53 Swing motor 54 Arm cylinder 55 Boom cylinder 56 Bucket cylinder 57 Left traveling motor 58 Right traveling motor 65a Pressure oil supply line 65b Pressure oil supply line 66 Communication line 150 Pressure sensor 151 Pressure sensor 152 Pressure sensor 153 Pressure sensor 161 Operation lever Device 161 Control lever 162 Control lever device 162a Control lever 163 Control lever device 163a Control lever 164 Control lever device 164a Control lever 165 Control lever device 165a Control lever 166 Control lever device 166a Control lever 170 Actuation detector 171 Shuttle valve 172 Shuttle valve 173 Shuttle valve 174 Shuttle valve 175 Shuttle valve 176 Shuttle valve 177 Shuttle valve 178 Shuttle valve 179 Shuttle valve 180 Shuttle valve 200 Upper revolving structure 201 Arm 202 Boom 203 Bucket 204 Left track 205 Right track 300 Controller P ₁ Pressure signal P ₂ Pressure signal P _ABCD operation detection signal P _XY operation detecting signal S selection signal theta _L1 first maximum target tilting angle theta _L2 second maximum target tilting angle theta _LV operation detection signal of the low speed at low speed P _ABCD of the maximum target tilting angle theta _N a hydraulic pump according to the magnitude usual maximum target tilting angle Q _L1 first maximum discharge flow rate at a low speed at the time (the first slow the flow rate) Q _L2 second low speed Maximum discharge flow rate (second low-speed flow rate) Q _N Maximum discharge flow rate of hydraulic pump at normal time

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsukasa Toyooka 650 Jinrachi-cho, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. Tsuchiura factory (72) Inventor Yoichi Furuwato 650 Kintate-cho, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Inside the Engineering Co., Ltd. (72) Inventor Takeshi Nakamura 650 Kannaricho, Tsuchiura City, Ibaraki Prefecture Hitachi Construction Machinery Co., Ltd. Tsuchiura Factory

Claims (4)

[Claims] 1. A first and a second variable displacement hydraulic pumps and a first hydraulic pump driven by pressure oil discharged from the first and second hydraulic pumps respectively driving a pair of left and right traveling mechanisms. And a plurality of hydraulic actuators including a second traveling actuator and a working machine actuator that drives the working mechanism, and pressure oil supplied to the first traveling actuator and connected to the discharge pipeline of the first hydraulic pump. A first valve group including a first traveling directional control valve for controlling the flow rate of the second hydraulic pump, and a flow rate of pressure oil connected to the discharge pipeline of the second hydraulic pump and supplied to the second traveling actuator. A second valve group including a second traveling directional control valve for controlling the flow rate and a working directional control valve for controlling the flow rate of the pressure oil supplied to the working machine actuator, and the first and second traveling actuators. First detecting means for detecting whether or not the actuator has been operated, second detecting means for detecting whether or not the work implement actuator has been operated, and high speed as a traveling mode of the first and second traveling actuators. A speed selecting means for selecting one of a low speed mode and a low speed mode, and when the discharge pressures of the first and second hydraulic pumps are low, the respective maximum discharge flow rates are set as normal flow rates, and the first and second A hydraulic drive system for a construction vehicle, comprising: a pump flow rate control means for controlling the discharge flow rate so that the maximum discharge flow rate of the hydraulic pump decreases from the normal flow rate when the discharge pressure of the hydraulic pump increases. The first
Further has a communication conduit communicating the pressure oil supply conduit of the traveling direction switching valve and the pressure oil supply conduit of the second traveling direction switching valve, wherein the working direction switching valve is the first 2 is connected so as to supply the pressure oil from the second hydraulic pump to the working machine actuator with priority over the second traveling directional control valve, and the pump flow rate control means is configured to operate at high speed by the speed selection means. When the mode is selected, the maximum discharge flow rate of the first and second hydraulic pumps is limited to the normal flow rate, and the low speed mode is selected by the speed selection means.
When it is detected by the first and second detection means that the first and second traveling actuators are operated and the work implement actuator is not operated, the maximum of the first and second hydraulic pumps The discharge flow rate is limited to a first low speed flow rate lower than the normal flow rate, the low speed mode is selected by the speed selection means, and the first and second traveling actuators are selected by the first and second detection means. Is detected and it is detected that the work implement actuator is operated, the maximum discharge flow rate of the second hydraulic pump is limited to the normal flow rate, and the maximum discharge flow rate of the first hydraulic pump is changed to the normal flow rate. A hydraulic drive device for a construction vehicle, comprising: a second flow rate limiting unit that limits the flow rate to a second low flow rate that is smaller than the flow rate and is larger than the first low flow rate. 2. The hydraulic drive system for a construction vehicle according to claim 1, wherein the traveling directional control valve and the working directional control valve are pilot operated valves driven by pilot pressure, and the first detecting means is A construction vehicle characterized in that it is means for detecting a pilot pressure applied to the traveling direction switching valve, and the second detection means is means for detecting a pilot pressure applied to the working direction switching valve. Hydraulic drive. 3. The hydraulic drive system for a construction vehicle according to claim 1, further comprising third detection means for detecting an operation amount of the work direction switching valve, wherein the pump flow rate control means comprises the speed selection means. When the low speed mode is selected by the means, the first and second traveling actuators are operated, and the work machine actuator is operated, the maximum discharge flow rate of the second hydraulic pump is set to the first
The hydraulic drive system for a construction vehicle, further comprising setting means for setting a value according to the operation amount detected by the third detection means in a range larger than the low flow rate and smaller than the normal flow rate. 4. The hydraulic drive system for a construction vehicle according to claim 3, wherein the traveling directional control valve and the working directional control valve are pilot operated valves driven by pilot pressure, and the first detecting means is provided. It is means for detecting a pilot pressure applied to the traveling direction switching valve, and the second and third detection means are means for detecting a pilot pressure applied to the working direction switching valve. Hydraulic drive for construction vehicles.