JP2000190858A - Hydraulic controller for working vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic controller for a working vehicle that, for high-geared high-speed travel, improves the high-speed travel stability by reducing the power loss to prevent increases in the oil temperature and reducing the steering fluid flow rate to slow down the steering wheel operation, and for high-geared low-speed travel in work, reduces the turning circle by preventing drops in the steering fluid flow rate. SOLUTION: The oil pressure control system for working vehicles comprises a speed detecting means 23 for detecting the travel speed of a working vehicle, a shift gear detecting means 3a for detecting a selected gear, unloader valves 16 and 24 for unloading pressure oil in an assist circuit 13 and a second pump 5, and a controller 17 for receiving detection signals from the speed detecting means 23 and shift gear detecting means 3a and, when they indicate a preset or higher speed and gear, outputting commands for the unloader valves 16 and 24 to unload pressure oil in the assist circuit 13 and the second pump 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device for a work vehicle such as a wheel loader, and more particularly to a hydraulic control device for a work vehicle having improved energy efficiency and improved operability.

[0002]

2. Description of the Related Art As shown in FIG.
No. 407575, the prime mover 1 drives the transmission 3 via the torque converter 2 and the first pump 4 and the second pump
The pump 5 is driven. The discharge port of the first pump 4 is connected to a steering cylinder 10 via a first steering circuit 7, a steering priority valve 8, and a steering switching valve 9. The discharge port of the second pump 5 is a work machine circuit 11,
a is connected to the work implement switching valve 12 via a. A support circuit 13 for diverting the discharge oil of the first pump 4 from the steering priority valve 8 is connected to the working machine circuits 11 and 11a. The work implement switching valve 12 is a boom cylinder 14 or a bucket cylinder 1
5 etc. are connected to the working machine actuator. An unload valve 16a for unloading the discharge oil of the second pump 5 is connected to the work machine circuits 11, 11a. When the ON signal of the shift down switch 18 is input, the controller 17 shifts down the transmission 3 from the second speed to the first speed and outputs a signal for switching the unload valve 16a from on-load to unload.

[0003] In a work vehicle such as a wheel loader described in the official gazette having the above-described configuration, the shift-down switch 18 is turned on during low-speed work such as excavation work in which soil is excavated with a bucket and soil is loaded into the bucket. Then, the controller 17 shifts down the transmission 3 from the second speed to the first speed, and unloads the discharge oil of the second pump 5 by the unload valve 16a in conjunction with the ON operation of the downshift switch 18. In this state, only the pressure oil (black arrow) discharged from the first pump 4 is supplied to the work implement switching valve 12 via the first steering circuit 7, the steering priority valve 8, the support circuit 13 and the work implement circuit 11a. At this time, the pressure oil of the support circuit 13 and the work machine circuit 11a is supplied to the check valve 1
9 does not flow to the unload valve 16a. In this manner, the power of the prime mover 1 corresponding to the unloading of the second pump 5 is used for the traction force of the work vehicle to increase the work capacity for excavating the soil with the bucket.

[0004]

However, the conventional technique has the following problems. (1) When the work vehicle only transports the soil piled up in the bucket to a distance and does not operate the work machine, the transmission is switched to a high speed stage to run at high speed. At this time, since the shift-down switch 18 is not turned on, the second pump 5 is not unloaded by the unload valve 16a,
The discharge oil of the second pump 5 passes through the neutral position of the work implement switching valve 12 and is drained. At this time, the work implement switching valve 12
The higher the speed, the greater the flow resistance through the unload valve 16a, the greater the power loss and the higher the oil temperature due to the power loss. Therefore, not only power loss but also power for cooling hydraulic oil is required, so that energy loss increases. (2) Even when the operator is troublesome to shift to a low gear, there is a case where a small site is moved by running at a low speed while excavating soil with a bucket even at a high gear, and in this case, It is necessary to turn the steering largely, but since the rotation speed of the prime mover is low, the steering flow rate is insufficient and the small turning cannot be effected. On the other hand, if the speed is high, the reduction ratio is small, so that the driving force of the tire is reduced and the traveling speed is reduced, so that the work efficiency is reduced. On the other hand, when the work vehicle only travels at a high speed at a high speed without operating the work implement, the steering is frequently turned largely, but in rare cases, the steering is suddenly largely operated. At this time, if the steering flow rate is set to a value necessary for low-speed running, the steering flow rate is the same for high-speed running as for low-speed running, and there is a danger of the work vehicle being steered suddenly and falling over. Driving stability is reduced.

The present invention has been made in view of the above problems, and reduces power loss when a work vehicle such as a wheel loader travels at a high speed at a high speed without operating a work machine. In addition to preventing the oil temperature from rising, the steering flow rate is reduced by reducing the steering flow rate to improve running stability, and the steering flow rate is not reduced when traveling at low speeds while working at a high gear. It is an object of the present invention to provide a hydraulic control device for a working vehicle that can be turned easily.

A hydraulic control device for a work vehicle according to a first aspect of the present invention includes a transmission that can be switched to a plurality of speed stages, a first pump and a second pump that are driven to rotate by a prime mover together with the transmission, and a first pump. First and second steering circuits for supplying pump discharge oil to a steering switching valve via a steering priority valve preferentially; a working machine circuit for supplying second pump discharge oil to a working machine switching valve; In a hydraulic control device for a work vehicle having a support circuit for connecting a branch port of a valve to a work machine circuit, a vehicle speed detection means for detecting a traveling speed of the work vehicle, and a speed gear detection means for detecting a switched speed gear An unload valve for unloading the pressure oil of the support circuit and the second pump, and inputting each detection signal from the vehicle speed detecting means and the speed gear detecting means, and at a predetermined speed gear or higher, and at a predetermined vehicle speed or higher It can and having a controller for outputting a command to unload the pressurized fluid and a second pump assist circuit to unload valve.

According to the first aspect, when the vehicle travels at a high speed without working at a high speed stage, the unload valve receives the command from the controller and supplies the pressure oil of the support circuit and the discharge oil of the second pump to the unload valve. Drain. Accordingly, since the pressure oil of the support circuit and the discharge oil of the second pump do not pass through the neutral position of the work equipment switching valve having a larger flow resistance than the unload valve, the power loss due to the flow resistance of the work equipment switching valve is lost. And the rise in oil temperature is reduced. In addition, since the traction force is increased to the driving force of the unloaded second pump,
The driving force of the tire, which has decreased due to the shift to the high speed gear, can be increased to increase the climbing force and the horizontal excavation force, etc., thereby improving work efficiency. When traveling at a low speed while working even at a high speed stage, the pressure oil of the support circuit and the discharge oil of the second pump are:
The work machine switching valve passes through the neutral position without being drained from the unload valve. However, the pressure oil of the support circuit and the discharge oil of the second pump are reduced due to the low speed, the flow path resistance passing through the neutral position of the work machine switching valve is small, and the work machine can be operated.

A hydraulic control device for a work vehicle according to a second invention of the present application includes a transmission that can be switched to a plurality of speed stages, and a first pump, a second pump, and a third pump that are rotationally driven by a prime mover together with the transmission. Pump, first and second steering circuits for supplying discharge oil of the first pump to the steering switching valve via a steering priority valve, and a work machine for supplying discharge oil of the second pump to the work machine switching valve A hydraulic control device for a work vehicle, comprising: a circuit, a support circuit for connecting a branch port of a steering priority valve to a work machine circuit, and a second steering dedicated circuit for joining discharge oil of a third pump to a second steering circuit. Vehicle speed detecting means for detecting the traveling speed of the work vehicle, speed gear detecting means for detecting the switched speed gear, and an unload valve for unloading the first pump and the second pump; And a check valve in which the first, the pressure oil of the second steering dedicated circuit is prevented from flowing back to the unloading valve,
A controller which receives each detection signal from the vehicle speed detecting means and the speed gear detecting means and outputs a command to unload the first pump and the second pump to the unload valve when the speed is equal to or higher than a predetermined speed gear and equal to or higher than the predetermined vehicle speed. And characterized in that:

According to the second aspect, when the vehicle travels at high speed without working at the high speed stage, the unload valve receives a command from the controller and drains the discharge oil of the first pump and the second pump from the unload valve. Let it. Therefore, the pressure oil of the support circuit and the discharge oil of the second pump do not pass through the neutral position of the work equipment switching valve having a larger flow resistance than the unload valve, and therefore, the power generated by the flow resistance of the work equipment switching valve is reduced. Loss is eliminated and the rise in oil temperature is reduced. At this time, the pressure oil in the second steering-dedicated circuit does not flow backward to the unload valve by the check valve provided in the second steering circuit.
Further, since the traction force is increased to the driving force of the unloaded first pump and the second pump, the driving force of the tire, which has been reduced due to the high-speed gear, is increased to increase the climbing force and horizontal excavation force. And the work efficiency is improved.
In addition, since the steering flow rate is reduced by the discharge amount of the first pump that has been diverted from the steering priority valve to the second steering circuit, sudden steering cannot be performed, and the traveling stability of the work vehicle is improved.

When the vehicle travels at a low speed while working even at a high speed stage, the discharge oil of the first pump and the second pump is not drained from the unload valve.
The oil discharged from the pump passes through the neutral position of the work implement switching valve.
However, the pressure oil of the support circuit and the discharge oil of the second pump are reduced due to the low speed, the flow path resistance passing through the neutral position of the work machine switching valve is small, and the work machine can be operated. or,
The oil discharged from the first pump, which has been diverted from the steering priority valve to the second steering circuit, merges with the oil discharged from the third pump, which has been discharged to the circuit dedicated to the second steering, so that the conventional amount of hydraulic oil is supplied to the steering switching valve. Supplied. Therefore, even in a narrow work site, the work efficiency can be improved because a sharp turning operation enables a work with a small turn and a high mobility.

A hydraulic control device for a work vehicle according to a third aspect of the present invention includes a transmission that can be switched to a plurality of speed stages, a first pump and a second pump that are rotationally driven by a prime mover together with the transmission.
A pump and a third pump, first and second steering circuits for supplying discharge oil of the first pump to the steering switching valve via a steering priority valve preferentially, and discharging oil of the second pump to a work implement switching valve. Hydraulic pressure of a work vehicle having a work machine circuit for supplying, a support circuit for connecting a branch port of the steering priority valve to the work machine circuit, and a second steering dedicated circuit for joining the discharge oil of the third pump to the second steering circuit. In the control device, a vehicle speed detecting means for detecting a traveling speed of the work vehicle, a speed gear detecting means for detecting a changed speed gear, an unload valve for unloading the second pump and the third pump, Each detection signal is input from a check valve for preventing the pressure oil of the second steering circuit from flowing back to the unload valve, and vehicle speed detecting means and speed gear detecting means, and is supplied with a predetermined speed gear. In, and characterized by having a controller for outputting a command to unload the second pump and the third pump to the unloading valve when more than a predetermined vehicle speed.

According to the third aspect, when the vehicle travels at high speed without working at the high speed stage, the unload valve receives a command from the controller and drains the discharge oil of the second pump and the third pump from the unload valve. Let it. Therefore, the pressure oil of the support circuit and the discharge oil of the second pump do not pass through the neutral position of the work equipment switching valve having a larger flow resistance than the unload valve, and therefore, the power generated by the flow resistance of the work equipment switching valve is reduced. Loss is eliminated and the rise in oil temperature is reduced. At this time, the pressure oil of the second steering circuit does not flow back to the unload valve by the check valve provided in the second steering dedicated circuit.
In addition, the second pump and the third
By increasing the traction force up to the power of the pump and increasing the driving force of the tires reduced due to the high speed gear to increase the climbing force and horizontal excavation force, etc., the work efficiency is improved. Further, since the steering flow rate is reduced by the amount of the pressure oil that has been diverted from the third pump to the second steering dedicated circuit via the steering priority valve, sudden steering cannot be performed, and the traveling stability of the work vehicle is improved.

When the vehicle travels at a low speed while working even at a high speed stage, the pressure oil of the support circuit and the discharge oil of the second pump are not drained from the pilot pressure type unload valve.
It passes through the neutral position of the work implement switching valve. However, the pressure oil of the support circuit and the discharge oil of the second pump are reduced due to the low speed, the flow path resistance passing through the neutral position of the work machine switching valve is small, and the work machine can be operated. Also, the discharge oil of the third pump, which is diverted from the steering priority valve to the second steering circuit, merges with the discharge oil of the first pump discharged to the second steering circuit, and the amount of pressurized oil is changed as in the conventional case. Supplied to the valve. Therefore, even in a narrow work site, a sharp steering operation enables a work with a small turn and a high degree of mobility, thereby improving work efficiency.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments in which a hydraulic control device for a work vehicle according to the present invention is applied to a wheel loader will be described below in detail with reference to FIGS. Elements similar to those in the related art shown in FIG. 7 are denoted by the same reference numerals, and redundant description of the configuration, operation, and effect will be omitted. The first embodiment shown in FIG. 1 will be described. In the following, the working machine actuator is represented by a bucket cylinder 15 that drives the bucket of the wheel loader, and the bucket switching valve (hereinafter referred to as the bucket switching valve 12) is represented by the working machine switching valve 12. In detail, the bucket switching valve 12 is connected in parallel with the bucket switching valve 12, or another work machine switching valve such as a boom switching valve is connected in series with the bucket switching valve 12 in series with the bucket switching valve 12. The description is omitted because it is the same as 12. The forward / reverse lever 21 outputs a signal for switching the transmission 3 to forward, reverse, and neutral via the controller 17, and the speed lever 22 transmits a signal for switching the transmission 3 to the first to fourth gears via the controller 17. Is output. The running speed of the vehicle is detected by the vehicle speed detecting means 23 and output to the controller 17. Also, the first
The discharge port of the pump 4 is connected to a steering switching valve 9 via a first steering circuit 7, a steering priority valve 8, and a second steering circuit 7a downstream of the steering priority valve 8.

Here, the configuration and operation of the steering priority valve 8 will be described. A flow control throttle 25 is interposed at the pilot port of the steering switching valve 9, an upstream of the flow control throttle 25 is connected to a pilot pressure receiving portion on the left side of the steering priority valve 8 in the drawing, and a downstream of the flow control throttle 25 is steering priority. The valve 8 is connected to a pilot pressure receiving portion on the right side in the drawing. The right side of the steering priority valve 8 has a spring 8a.
Urged by the spring force of For this reason, the steering priority valve 8 is controlled such that the differential pressure between the upstream and downstream of the flow control throttle 25 is balanced with the spring force of the spring 8a. The pressure, ie, the flow rate through the flow control throttle 25, is constant. That is, when the amount of pressure oil supplied to the flow control throttle 25 (the steering switching valve 9) decreases, the differential pressure upstream and downstream of the flow control throttle 25 decreases. Then, the amount of pressure oil supplied to the steering switching valve 9 increases. As a result, the differential pressure upstream and downstream of the flow control throttle 25 increases, so that the steering priority valve 8
Moves rightward from the position shifted to the left to the position above the flow control throttle 25 and to a position where the downstream differential pressure balances the spring force. Thus, the steering priority valve 8 is connected to the first pump 4
Is supplied to the steering switching valve 9 by a fixed amount,
The surplus is diverted to the work machine circuit 11a via the support circuit 13.

The work machine circuit 11 is connected to a pilot pressure type unload valve 16 which can be switched between on-load and unload depending on the presence or absence of a pilot pressure. The pilot line of the pilot pressure type unload valve 16 is connected to a tank. An electromagnetic switching valve 24, which can be switched between a position for interrupting communication and a position b for communicating with the tank, is connected to form an unload valve. When the solenoid-operated switching valve 24 is demagnetized, it moves to the position a,
When it is excited in response to a command from the controller 16, it switches to the position b. In the working machine circuit 11, the pressure oil of the working machine circuit 11 and the support circuit 13 flows to the pilot pressure type unload valve 16 between the connection portion with the support circuit 13 and the connection portion with the pilot pressure type unload valve 16. Check valve 19 to prevent
Is interposed.

The controller 1 of the first embodiment shown in FIG.
7 will be described. Step S
When the speed gear lever 22 is at or above the third gear, the process proceeds to step S2. At step S2, when the vehicle speed is equal to or more than 12 km / H, the process proceeds to step S3. While maintaining, the electromagnetic switching valve 24
Is output, and the second pump 5 is unloaded by the pilot pressure type unload valve 16, and the flow proceeds to step S1.
Return to When the speed gear lever 22 is in the second gear or the first gear in step S1, or when the vehicle speed is 12 in step S2.
When the speed is lower than km / H, the process proceeds to step S4.
If the downshift switch 18 is OFF in step S4, the process proceeds to step S5, in which the electromagnetic switching valve 24 is demagnetized and the pilot pressure unload valve 16 is on-loaded. , Step S
Return to 1. If the downshift switch 18 is ON in step S4, the process proceeds to step S6 to shift down the transmission to the first speed stage, output a signal for exciting the electromagnetic switching valve 24, and output the signal to the pilot pressure type unload valve 16 through the pilot pressure type unloading valve 16. 2 Unload the pump 5 and return to step S1.

The operation of the first embodiment will be described. The forward / reverse lever 21 is switched to forward and the speed lever 2
2, the transmission 3 is switched to a high speed stage of three or more speed stages,
When traveling at high speed without performing work with a work machine,
The controller 17 inputs a switching signal of a predetermined speed gear (for example, three speed gears) or more from the speed gear detecting means 3a, and changes the traveling speed from the vehicle speed detecting means 23 to a predetermined vehicle speed (for example, 1).
When a signal of 2 km / H or more is input, an excitation signal is output to the electromagnetic switching valve 24. Therefore, the electromagnetic switching valve 24 is set to the position b and the pilot pressure is drained, and the pressure oil of the support circuit 13 and the discharge oil of the second pump 5 are unloaded via the pilot pressure unload valve 16. At this time, the discharge oil of the first pump 4 diverted from the steering priority valve 8 to the support circuit 13 does not flow backward to the unload valve 16 by the check valve 19. Since the flow path resistance draining from the unload valve 16 is smaller than the flow path resistance when draining from the neutral position of the bucket switching valve 12, energy saving of the prime mover 1 can be achieved. In particular, since the discharge amount of the second pump 5 is usually larger than that of the first pump 4, the effect of energy saving is remarkable. Also, by increasing the traction force of the prime mover up to the driving force of the unloaded second pump 5, and increasing the driving force of the tire, which is reduced due to a reduction in the reduction ratio due to the high speed stage, the climbing force and Since the horizontal excavation force increases, the work efficiency is improved. The first
The unloading valve may be unloaded at the speed stage to increase the tractive force even at low speed excavation.

When the vehicle travels at a low speed below the predetermined vehicle speed while working at the high speed stage, the pressure oil of the support circuit 13 and the discharge oil of the second pump 5 do not drain from the unload valve 16 and the bucket switching valve 12 Pass the neutral position of. However, since the pressure oil of the support circuit 13 and the discharge oil amount of the second pump 5 are reduced due to the low speed, the bucket switching valve 12
The resistance of the passage passing through the neutral position is small, and the working machine can be operated. When the check valve 19 is provided in the work machine circuit 11, the pressure oil in the support circuit 13 is supplied from the pilot pressure type unload valve 16 to the bucket switching valve 12 without draining. For this reason, the bucket cylinder 15 can be operated by the pressure oil of the support circuit 13, but the flow path resistance that passes through the neutral position of the bucket switching valve 12 increases by that much. Further, according to the present invention, since the existing unload valve 16a as shown in FIG. 7 can be used, the manufacturing cost can be reduced as compared with the case where a new one is provided.

A second embodiment shown in FIG. 3 will be described. FIG.
The third pump 6 is added in addition to the first pump 4 and the second pump 5 of the first embodiment, and the discharge port of the third pump 6 is formed in the first steering dedicated circuit 26 and the steering priority valve 8. The second steering circuit 7 is connected via a circuit different from the first and second steering circuits 7 and 7a and a second dedicated steering circuit 26a downstream of the steering priority valve 8.
Connect to a. In the second steering circuit 7a, a check valve 7b for preventing a reverse flow to the steering priority valve 8 is provided upstream of a connection with the second steering dedicated circuit 26a. In the first embodiment, the pilot pressure type unload valve 16 is connected to the work machine circuit 11, but in the second embodiment,
The pilot pressure type unload valve 16 is connected not only to the work machine circuit 11 but also to the first steering circuit 7 upstream of the steering priority valve 8. The other configurations are the same as those of the first embodiment, and thus the same reference numerals are given and the duplicate description will be omitted.

Next, the operation of the second embodiment will be described. The control flowchart of the controller 17 of the second embodiment is the same as S1 to S3 in FIG. The discharge oil of the third pump 6 supports the pressure oil of the second steering circuit 7a via the first steering dedicated circuit 26, the steering priority valve 8, and the second steering dedicated circuit 26a, and is controlled by the steering priority valve 8 to generate excess oil. The third pump 6 that became
Is discharged. When traveling at a high speed without working at the high gear, the controller 17 inputs a switching signal of a predetermined speed gear (for example, three speed gears) or more from the speed gear detecting means 3a, and the traveling speed is detected from the vehicle speed detecting means 23. When a signal that is equal to or higher than a predetermined vehicle speed (for example, 12 km / H) is input, an excitation signal is output to the electromagnetic switching valve 24. Therefore, the solenoid-operated switching valve 24 is set to the position b, the pilot pressure is drained, and the pilot-pressure unloading valve 16 is moved to the first position.
The oil discharged from the pump 4 and the second pump 5 is drained from the pilot pressure type unload valve 16. Therefore, the support circuit 1
The pressure oil of No. 3 and the discharge oil of the second pump 5 do not pass through the neutral position of the bucket switching valve 12 having a larger passage resistance than the pilot pressure unload valve 16, There is no power loss and the rise in oil temperature is reduced. At this time, the pressure oil in the second steering circuit 26a does not flow back to the pilot pressure type unload valve 16 by the check valve 7b provided in the second steering circuit 7a.

Further, since the traction force is increased to the driving force of the unloaded first pump 4 and the second pump 5, the driving force of the tire, which has been reduced by the shift to the high speed stage, is increased to increase the climbing force. In addition, the horizontal digging force can be increased, and work efficiency is improved. Also, the steering priority valve 8 to the second
Since the steering flow rate is reduced by the discharge amount of the first pump 4 that has been diverted to the steering circuit 7a, sudden steering cannot be performed, and the running stability of the work vehicle is improved.

When the vehicle travels at a low speed while working even at a high speed stage, the oil discharged from the first pump 4 and the second pump 5 is not drained from the pilot pressure type unload valve 16.
The pressure oil of the support circuit 13 and the discharge oil of the second pump 5 pass through the neutral position of the bucket switching valve 12. However, the pressure oil of the support circuit 13 and the discharge oil of the second pump 5 are reduced due to the low speed, the flow path resistance passing through the neutral position of the bucket switching valve 12 is small, and the working machine can be operated. Further, the discharge oil of the first pump 4 diverted from the steering priority valve 8 to the second steering circuit 7a merges with the discharge oil of the third pump 6 discharged to the second steering-dedicated circuit 26a, and the conventional pressure The oil amount is supplied to the steering switching valve 9. Therefore, even in a narrow work site, the work efficiency can be improved because a sharp turning operation enables a work with a small turn and a high mobility.

Further, according to the present invention, since the existing unload valve 16a as shown in FIG. 7 can be used, the manufacturing cost can be reduced as compared with the case where a new one is provided. Further, similarly to the second embodiment, the first steering dedicated circuit 26 and the second steering dedicated circuit 26a may be directly connected without the intervention of the steering priority valve 8. Other functions and effects are the same as those of the first embodiment, and thus redundant description will be omitted.

As described above, the operation of the pilot type unload valve 16 improves the running stability at high speed running and the steering mobility at low speed running. This will be described in detail below. Referring to FIG. 4, the relationship between the rotation speed of the first and third pumps (that is, the rotation speed of the prime mover, which is proportional to the vehicle speed) and the discharge amount according to the second embodiment shown in FIG. 3 will be described. The total discharge amount Q of the first pump 4 and the third pump 6 driven by the prime mover 1 is the steering priority valve 8
As a result, only the required steering flow Q1 that is constant at the rotation speed N1 is preferentially supplied to the steering switching valve 9, and the extra discharge amount of the first pump 4 is supplied to the bucket switching valve 12 via the support circuit 13. . When the first pump 4 is unloaded, the discharge amount of the first pump 4 runs out, so that the double hatched portion is subtracted and the discharge amount of the third pump 6 (hatched portion).
And only the required steering flow Q1 that is constant at the rotational speed N2 is supplied to the steering switching valve 9 with priority.
The extra discharge amount of the third pump 6 is drained. For this reason, at the pump rotation speed N3, only the oil amount of Q3 is supplied to the steering switching valve 9, so that the oil amount supplied to the steering switching valve 9 decreases by (Q1-Q3). For this reason, the steering speed is reduced, and the high-speed running stability is improved. In addition, when the vehicle travels at a low speed while working even at the high speed stage, the first pump 4 is not unloaded by the unload valve, so that the steering flow becomes the total discharge amount of the first pump 4 and the third pump 6 and does not decrease. Therefore, even in a narrow work site, the work efficiency can be improved because a sharp turning operation enables a highly flexible work with a small turn.

A third embodiment shown in FIG. 5 will be described. In the second embodiment shown in FIG. 3, the pilot pressure type unload valve 1 is provided in the first steering circuit 7 and the work machine circuit 11.
In the third embodiment, the pilot pressure type unload valve 16 is connected to the first steering dedicated circuit 26 and the work implement circuit 11 upstream of the steering priority valve 8 in the third embodiment. In addition, a check valve 26b for preventing a backflow to the steering priority valve 8 is provided upstream of the connection with the second steering circuit 7a in the second steering circuit 26a. Other configurations are the same as those of the first embodiment, and therefore, the same reference numerals are given and duplicate explanations are omitted.

Next, the operation of the third embodiment will be described. Note that the control flowchart of the controller 17 of the third embodiment is the same as that of the first embodiment, and a description thereof will be omitted.
When the vehicle travels at a high speed without working at the high gear, the controller 17 inputs a switching signal of a predetermined gear (for example, three gears) or more from the speed gear detecting means 3a, and outputs a switching signal from the vehicle speed detecting means 23 to the predetermined vehicle speed ( (For example, 12 km / H)
When the above signal is input, an excitation signal is output to the electromagnetic switching valve 24. Therefore, the electromagnetic switching valve 24 is set to the position b and the pilot pressure is drained, and the pilot pressure unload valve 16 drains the discharge oil of the second pump 5 and the third pump 6 from the pilot pressure unload valve 16. Therefore, the pressure oil of the support circuit 13 and the discharge oil of the second pump 5 do not pass through the neutral position of the bucket switching valve 12 having a larger flow path resistance than that of the pilot pressure type unload valve 16. Power loss due to flow path resistance is eliminated, and rise in oil temperature is reduced. At this time, the pressure oil of the second steering circuit 7a does not flow back to the pilot pressure type unload valve 16 by the check valve 26b provided in the second steering dedicated circuit 26a. Further, the traction force is increased to the power of the second pump 5 and the third pump 6 which are no longer required after being unloaded, and the driving force of the tire, which has been reduced due to the shift to the high speed stage, is increased to increase the climbing force and Increasing the horizontal digging force etc. will improve the work efficiency.
In addition, since the steering flow rate is reduced by the amount of the pressurized oil that has been diverted from the third pump 6 to the second steering dedicated circuit 26a via the steering priority valve 8, sudden steering cannot be performed, and the traveling stability of the work vehicle is reduced. improves.

When the vehicle travels at a low speed below the predetermined vehicle speed while working at the high speed stage, the pressure oil of the support circuit 13 and the second
The pump 5 discharges oil from the pilot pressure type unload valve 16.
, And passes through the neutral position of the bucket switching valve 12 without being drained. However, the pressure oil of the support circuit 13 and the second
The discharge oil of the pump 5 decreases due to the low speed, and the flow path resistance passing through the neutral position of the bucket switching valve 12 is small,
Work machine operation is also possible. Further, the discharge oil of the third pump 6 that has been diverted from the steering priority valve 8 to the second steering circuit 26a merges with the discharge oil of the first pump 4 that has been discharged to the second steering circuit 7a, and a conventional pressure. The oil amount is supplied to the steering switching valve 9. Therefore, even in a narrow work site, the work efficiency can be improved because a sharp turning operation enables a work with a small turn and a high mobility.

When the check valve 19 is provided in the work machine circuit 11, the pressure oil in the support circuit 13 is supplied from the pilot pressure type unload valve 16 to the bucket switching valve 12 without draining. For this reason, the bucket cylinder 15 can be operated by the pressure oil of the support circuit 13, but the flow path resistance that passes through the neutral position of the bucket switching valve 12 increases by that much. Further, since the present invention can utilize the existing unload valve 16a as shown in FIG. 7, the manufacturing cost is greatly reduced. Further, similarly to the second embodiment, the first steering dedicated circuit 26 and the second steering dedicated circuit 26a may be directly connected without the intervention of the steering priority valve 8. Other functions and effects are the same as those of the first embodiment, and thus redundant description will be omitted.

As described above, the operation of the pilot type unload valve 16 improves running stability at high speed running and steering mobility at low speed running. This will be described in detail below. With reference to FIG. 6, the relationship between the rotation speed of the first and third pumps (that is, the rotation speed of the prime mover and proportional to the vehicle speed) and the discharge amount of the third embodiment shown in FIG. 5 will be described. The same parts as those in FIG. 4 will not be described repeatedly. When the third pump 6 is unloaded, the discharge amount of the third pump 6 disappears, so that the double hatched portion is subtracted and only the discharge amount (hatched portion) of the first pump 4 is obtained. Is supplied to the steering switching valve 9 in priority, and the excess discharge amount of the first pump 4 is supplied to the bucket switching valve 12 via the support circuit 13. Therefore, similarly to FIG. 4, the steering speed is reduced, and the high-speed running stability is improved. In addition, when the vehicle travels at a low speed while working even at the high speed stage, the third pump 6 is not unloaded by the unload valve, so that the steering flow becomes the total discharge amount of the first pump 4 and the third pump 6 and does not decrease. Therefore, similarly to the first embodiment,
Even in a narrow work site, a sharp steering operation enables a work with a small turn and a high degree of mobility, thus improving work efficiency.

As described above, according to the present invention, when the vehicle travels at high speed without working at the high speed stage, the vehicle is unloaded and the discharge oil of the pump is drained from the unload valve,
It does not pass through the neutral position of the work implement switching valve having a larger flow path resistance than the unload valve. Therefore, there is no power loss due to the flow path resistance of the work implement switching valve, and the rise in oil temperature is reduced. In addition, the traction force is increased up to the driving force of the pump that is no longer needed after unloading, and the reduction gear ratio is reduced due to the high speed stage. The work efficiency is improved because the force and the like increase. In the case of the second and third embodiments, the steering flow rate is reduced by the amount of the unloading pressure oil, so that it is not possible to perform abrupt steering and the traveling stability of the work vehicle during high-speed traveling is improved.

When the vehicle travels at a low speed while working even at the high speed stage, the discharge oil of the pump is not unloaded by the unload valve, so that the pump is supplied to the work machine switching valve to operate the work machine at a required speed. On the other hand, since the discharge oil of the pump is not unloaded, the steering flow rate does not decrease, and even in a narrow work site, a sharp steering operation enables a work with a small turn and a high degree of mobility, thereby improving work efficiency. Further, according to the present invention, since an existing unload valve or the like as shown in FIG. 7 can be used, the manufacturing cost can be reduced as compared with the case where a new one is provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a flowchart of the first embodiment.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a relationship between a pump rotation speed and a discharge amount according to a second embodiment.

FIG. 5 is a diagram showing a third embodiment of the present invention.

FIG. 6 is a diagram illustrating a relationship between a pump rotation speed and a discharge amount according to a third embodiment.

FIG. 7 is a diagram showing a conventional technique.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 prime mover 2 torque converter 3 transmission 3a speed stage detecting means 4 first pump 5 second pump 6 third pump 7 first steering circuit 7a second steering circuit 7b, 19, 26b check valve 8 steering priority valve 9 stearin switching Valve 10 Steering cylinder 11, 11a Work machine circuit 12 Bucket switching valve (representing working machine switching valve) 13 Support circuit 15 Bucket cylinder (representing working machine actuator) 16 Pilot pressure type unload valve 17 Controller 21 Forward / reverse lever 22 Speed stage Lever 23 Vehicle speed detecting means 24 Electromagnetic switching valve 25 Flow control throttle 26 First steering dedicated circuit 26a Second steering dedicated circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3D032 CC01 CC13 CC48 CC49 DA23 DB02 DB03 DC33 EC02 GG04 3D033 EC05 EC08 EC09 EC10

Claims (3)

[Claims] 1. A transmission that can be switched to a plurality of speed stages, a first pump and a second pump that are driven by a prime mover together with the transmission, and a discharge oil of the first pump is steered through a steering priority valve. First and second steering circuits for supplying the switching valve with priority, a working machine circuit for supplying the discharge oil of the second pump to the working machine switching valve, and support for connecting a branch port of the steering priority valve to the working machine circuit. A hydraulic speed control device for a working vehicle having a circuit, a vehicle speed detecting means (23) for detecting a traveling speed of the working vehicle, a speed speed detecting means (3a) for detecting a switched speed speed, and a support circuit (13). The unload valves (16, 24) for unloading the pressure oil of the second pump (5), the vehicle speed detecting means (23) and the speed gear detecting means (3a) are inputted with respective detection signals, and the predetermined speed gear is inputted. Above, and when the vehicle speed is higher than the specified speed, the unload valve (16 , 24) and a controller (17) for outputting a command to unload the pressure oil of the support circuit (13) and the second pump (5). 2. A transmission that can be switched to a plurality of speed stages, and a first pump that is rotationally driven by a prime mover together with the transmission.
A second pump, a third pump, first and second steering circuits for supplying discharge oil of the first pump to a steering switching valve via a steering priority valve by priority, and switching of a discharge oil of the second pump to a work machine; A work vehicle having a work machine circuit for supplying a valve, a support circuit for connecting a branch port of a steering priority valve to the work machine circuit, and a second steering-dedicated circuit for joining discharge oil of a third pump to a second steering circuit. In the hydraulic control device, the vehicle speed detecting means (23) for detecting the traveling speed of the work vehicle, the speed gear detecting means (3a) for detecting the switched speed gear, a first pump (4) and a second pump ( 5) Unload valves (16, 24) for unloading the first and second steering circuits (2,
(6, 26a) to check the flow back to the unload valves (16, 24), the check valve (7b), the vehicle speed detecting means (23) and the speed gear detecting means (3a). Input, and at a predetermined speed gear or higher,
When the vehicle speed is higher than the specified speed, the unload valve (16, 24)
A hydraulic control device for a working vehicle, comprising: a controller (17) for outputting a command for unloading a pump (4) and a second pump (5). 3. A transmission that can be switched to a plurality of speed stages, and a first pump that is rotationally driven by a prime mover together with the transmission.
A second pump, a third pump, first and second steering circuits for supplying discharge oil of the first pump to a steering switching valve via a steering priority valve by priority, and switching of a discharge oil of the second pump to a work machine; A work vehicle having a work machine circuit for supplying a valve, a support circuit for connecting a branch port of a steering priority valve to the work machine circuit, and a second steering-dedicated circuit for joining discharge oil of a third pump to a second steering circuit. In the hydraulic control device, the vehicle speed detecting means (23) for detecting the traveling speed of the work vehicle, the speed gear detecting means (3a) for detecting the changed speed gear, the second pump (5) and the third pump ( 6) unloading valves (16, 24) for unloading the first and second steering circuits (7, 7a)
Check valve (26b) for preventing the pressure oil from flowing back to the unload valves (16, 24), vehicle speed detecting means (23) and speed gear detecting means (3
a), the second pump (5) and the third pump (6) are unloaded into the unload valves (16, 24) when the vehicle speed is equal to or higher than the predetermined speed and the vehicle speed is higher than the predetermined speed. And a controller (17) for outputting a command to execute the operation.