JP2003083447A - Slow-speed traveling controller for work vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform slow-speed traveling control to a work vehicle in a state of large work ability wherein an engine speed is increased. SOLUTION: The work vehicle has a charging pump 5, a working hydraulic pump 4 and a traveling hydraulic pump 3 driven by an engine 2; a hydraulic motor 6 for driving a traveling device, closed-circuit-connected to the traveling hydraulic pump 2; and a pilot valve 8 controlling a discharge oil amount of the traveling hydraulic pump 3. In the work vehicle, an orifice 15 generating differential pressure according to a flow rate is provided halfway along a control circuit 14 connected to the pilot valve 8 from the charging pump 5, pilot conduits 16, 17 are connected to the pilot valve 8 from the primary side and the secondary side of the orifice 15, the secondary side of the orifice 15 is connected to a low-pressure leaf valve 19, and the primary side of the orifice 15 is connected to the suction side of the charging pump 5 through a needle valve 21 whose opening can be finely adjusted.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a traveling vehicle having a hydrostatic power transmission (hereinafter, referred to as HST) -driven traveling device and a hydraulically-driven working device. It relates to a control device. 2. Description of the Related Art Conventionally, in a work vehicle equipped with a traveling device driven by HST and a working device driven by hydraulic pressure, as shown in FIG. 34 and the charging pump 35 are directly connected. The traveling hydraulic pump 33 includes a pair of main pipelines 41 and 42.
Is connected to the hydraulic motor 36 for driving the traveling device in a closed circuit. An engine 32 is an accelerator pedal (not shown).
The traveling hydraulic pump 33 driven by the engine 32 supplies pressure oil to the hydraulic motor 36 via the main pipelines 41 and 42 to apply rotation to drive the traveling device 37. . The working hydraulic pump 34 driven by the engine 32 supplies pressure oil to a working circuit 43 for driving a working device (not shown), and the charging pump 35 driven by the engine 32 is connected to the main pipelines 41 and 42. Pressure oil is supplied to the control circuit 44 while replenishing the pressure oil. The traveling hydraulic pump 33 is a variable displacement hydraulic pump whose discharge oil amount is controlled by switching a pilot valve 38. A control circuit 44 is connected to a pump port of the pilot valve 38. I have. In the middle of the control circuit 44, the sequence valve 5
An orifice line 53 having an orifice 52 and an orifice 52;
An inching line 56 provided with a relief valve 54 and an inching valve 55 is connected in parallel. The left and right pressure chambers 39A and 39B of the piston 39 for performing the switching operation of the oil path of the pilot valve 38 are provided with solenoid valves 40A and 39B.
A and 40B are connected to the primary and secondary sides of the orifice 52. The solenoid valves 40A and 40B are turned on and off so that the left and right pressure chambers 39A and 39B of the piston 39 are communicated with either the primary side or the secondary side of the orifice 52. Select reverse or stop. The relief valve 54 includes the sequence valve 51
Since the set pressure is lower, when the rotation speed of the engine 32 is small and the amount of oil discharged from the charging pump 35 is small, the entire amount of oil flows through the inching pipe 56. At this time, since there is no pressure difference between the primary side and the secondary side of the orifice 52, even if one of the solenoid valves 40A and 40B is turned on, the piston 39 is maintained at the neutral position. The traveling hydraulic pump 33 is discharged and the amount of oil discharged is zero. That is, even if forward or reverse is selected, if the engine 32 is idling, the work vehicle is stopped. [0006] The rotation speed of the engine 32 increases and the amount of oil discharged from the charging pump 35 increases, and the inching line 56
When the resistance of the orifice 52 reaches the set pressure of the sequence valve 51, the pressure oil discharged from the charging pump 35 also flows through the orifice line 53, and the differential pressure proportional to the flow rate of the oil flows between the primary and secondary sides of the orifice 52. Occurs between and. When this differential pressure reaches a predetermined value, the piston 39 is displaced in accordance with the differential pressure and switches the pilot valve 38, so that the traveling hydraulic pump 33 discharges pressure oil and the work vehicle starts traveling. [0007] The inching valve 55 is connected to the inching pedal 48, and is normally used at the most narrowed position. When the inching pedal 48 is depressed, the inching valve 55 is opened, and the entire amount of the pressurized oil from the charging pump 35 flows through the inching line 56 and the pressure between the primary side and the secondary side of the orifice 52 is reduced. Since no difference is generated, the discharge oil amount of the traveling hydraulic pump 33 becomes zero. Therefore, the driving force is released simultaneously with the braking. The control of the working capacity (speed) of the working device is performed by controlling the rotation speed of the engine 32 by operating the accelerator pedal and adjusting the discharge oil amount of the working hydraulic pump 34. When the rotation speed of the engine 32 is increased in order to increase the working capacity of the working device, the amount of oil discharged from the working hydraulic pump 34 increases and the amount of oil discharged from the traveling hydraulic pump 33 also increases. And the traveling speed of the work vehicle also increases. If the work speed is reduced, the traveling speed of the work vehicle is reduced. Therefore, in a conventional work vehicle equipped with a traveling device driven by HST and a working device driven by hydraulic pressure, there is no problem in performing high-speed work at high speed. (About 2 km / h), when the rotation speed of the engine 32 is reduced and the amount of oil discharged from the traveling hydraulic pump 33 is reduced to reduce the traveling speed, the oil discharged from the working hydraulic pump 34 is reduced. Since the amount also decreases,
The working capacity of the working device is also reduced. In order to suppress the rotation speed of the engine 32 and secure a high working capacity, it is necessary to provide a large-capacity working hydraulic pump 34 or separately mount an engine dedicated to the working device, which significantly increases the cost. Therefore, in order to secure a high working capacity, the rotation speed of the engine 32 is fixed at a maximum, and the inching valve 48 is depressed to control the inching valve 55, so that the discharge oil amount of the traveling hydraulic pump 33 is controlled. An operation of reducing the speed of the work vehicle and reducing the traveling speed of the work vehicle is also performed. However, since the inching pedal 48 is operated by foot, it is difficult to make fine adjustments, and it is difficult to keep the traveling speed of the work vehicle constant at a low speed.
There was a problem that operator's fatigue increased when the operator operated No. 8. Therefore, when the rotational speed of the engine 32 is increased in order to secure a high working capacity, the primary side of the orifice 52 and the secondary
There has been proposed a speed control device for a working vehicle provided with a variable valve 50 between the work side and the next side (see Japanese Patent Application Laid-Open No. 9-209410). In this work vehicle, when it is desired to secure a high work capacity at low speed traveling, the accelerator pedal is depressed to increase the rotation speed of the engine 32 and increase the discharge oil amount of the work hydraulic pump 34. At this time, since the amount of oil discharged from the charging pump 35 also increases, the differential pressure between the primary side and the secondary side of the orifice 52 increases, and the amount of oil discharged from the traveling hydraulic pump 33 also increases. The running speed is also high. Then, when the variable valve 50 is opened by turning the operation lever, the orifice 5
2, the pressure difference between the primary side and the secondary side of the hydraulic pump 2 decreases, the discharge oil amount of the traveling hydraulic pump 33 decreases, and the traveling speed also decreases. Since the rotation speed of the engine 32 is not related to the opening and closing of the variable valve 50, opening the variable valve 50 does not reduce the working capacity. Therefore, a large work capacity can be ensured even at low speed traveling. However, in this working vehicle speed control device, a ball valve having an opening adjustment range of 0 to 90 degrees is used as the variable valve 50. As shown in FIG. 4, the variable valve 20 has a great change in pressure due to a slight change in the opening adjustment, so that it is difficult to finely adjust the pressure, and the traveling speed during operation is 1-2 km / h.
If the vehicle travels at a low speed, there is no problem in performing the speed control. However, when the vehicle travels at a very low speed of about 1 m / min, the speed control cannot be performed properly. SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem in controlling the speed of a work vehicle. The present invention relates to a method of controlling a work vehicle so that the work vehicle can run at a very low speed while the engine speed is increased. It is an object to provide a control device. According to the present invention, there is provided a work vehicle traveling speed control apparatus, comprising: a traveling hydraulic pump, a working hydraulic pump, and a charging pump driven by a common engine; In a working vehicle equipped with a hydraulic motor for driving a traveling device connected to a pump through a pair of main lines in a closed circuit, and a pilot valve for controlling an amount of oil discharged from the hydraulic pump for traveling, a pilot vehicle is provided from the discharge side of the charging pump. An orifice for generating a differential pressure according to the flow rate between the primary side and the secondary side is provided in the middle of a control circuit connected to the valve, and the primary side and the secondary side of the orifice are connected to the pilot valve. Connect the pilot line, connect the secondary side of the orifice to the low pressure relief valve, and connect the primary side of the orifice through a needle valve whose opening can be finely adjusted. The above problem is solved by connecting to the suction side of the charging pump. When it is desired to ensure a high working capacity at a low speed, the accelerator pedal is depressed to increase the number of revolutions of the engine, thereby increasing the discharge oil amount of the working hydraulic pump.
At this time, the pressure difference between the primary side and the secondary side of the orifice becomes large, the amount of oil discharged from the traveling hydraulic pump increases, and the traveling speed becomes high. Therefore, when the needle valve is opened, the pressure difference between the primary side and the secondary side of the orifice decreases, the discharge oil amount of the traveling hydraulic pump decreases, and the traveling speed decreases. Since this needle valve has a large opening adjustment range and can perform fine pressure adjustment, it is possible to appropriately control the speed at a low speed. Since the engine speed is independent of the opening and closing of the needle valve, the opening of the needle valve does not reduce the working capacity. Therefore, a large working capacity can be ensured even at a low speed. FIG. 1 is a circuit diagram showing the configuration of a working vehicle slow-speed traveling control apparatus according to an embodiment of the present invention, and FIG. 2 shows the relationship between the opening of a needle valve and pressure. It is a graph. The basic configuration of this work vehicle traveling speed control device is the same as that of a work vehicle equipped with a conventional HST drive traveling device and a hydraulic drive device shown in FIG.
The engine 2 has a traveling hydraulic pump 3 and a working hydraulic pump 4.
And the charging pump 5 are directly connected. The traveling hydraulic pump 3 is connected to the traveling device driving hydraulic motor 6 through a pair of main pipelines 11 and 12 in a closed circuit. The rotation speed of the engine 2 is controlled by the operation of an accelerator pedal (not shown), and the traveling hydraulic pump 3 driven by the engine 2 supplies pressure oil to the hydraulic motor 6 through the main pipelines 11 and 12. Then, the traveling device 7 is driven. The working hydraulic pump 4 driven by the engine 2 supplies pressure oil to a working circuit 13 for driving a working device (not shown), and the charging pump 5 driven by the engine 2 is connected to the main pipelines 11 and 12. Pressure oil is supplied to the control circuit 14 while replenishing the pressure oil. The traveling hydraulic pump 3 is a variable displacement hydraulic pump whose discharge oil amount is controlled by a pilot valve 8. A control circuit 14 is connected to a pump port of the pilot valve 8. Between the pilot valve 8 and the control piston 9 of the traveling hydraulic pump 3, there is provided a solenoid valve 10 for selecting and switching between forward, backward and stop of the work vehicle. In the middle of the control circuit 14, an orifice 15 for generating a differential pressure corresponding to the flow rate between the primary side and the secondary side is provided.
A pilot line 16, 17 is connected to the pilot valve 8 from the primary side and the secondary side of the orifice 15.
Is connected, and the secondary side of the orifice 15 is connected to the orifice 18.
Is connected to the low-pressure relief valve 19 via the. An inching valve 20 is provided between the primary side and the secondary side of the orifice 15 in parallel with the orifice 15. Further, the primary side of the orifice 15 is connected via a needle valve 21 to the suction side of the charging pump 5. The needle valve 21 is normally closed, and can be opened to an arbitrary opening by turning the handle. As shown in FIG. 2, the needle valve 21 has a large adjustment range of the opening degree of 0 to 900 degrees, and can perform fine pressure adjustment. High pressure relief valves 22 and 23 for regulating the pressure in the main lines 11 and 12 are provided between the main lines 11 and 12 and the low pressure relief valve 19. The rotation speed of the engine 2 is small, the amount of oil discharged from the charging pump 5 is small, and the pressure of the control circuit 14 is low.
Since the pressure difference is not generated between the primary side and the secondary side of the orifice 15 while the pressure is lower than the set pressure, the pilot valve 8 is not shown even if the solenoid valve 10 is switched to forward or reverse. , And no pressure oil is supplied to the control piston 9, so that the discharge oil amount of the traveling hydraulic pump 3 is zero. That is, even if forward or reverse is selected, if the engine 2 is in the idling state, the work vehicle is stopped. When the rotation speed of the engine 2 increases and the amount of oil discharged from the charging pump 5 increases, and the pressure of the control circuit 14 reaches the set pressure of the low-pressure relief valve 19, the pressure oil discharged from the charging pump 5 Flows through the orifice 15 to the low-pressure relief valve 19 side, and a differential pressure proportional to the flow rate is generated between the primary side and the secondary side of the orifice 15. Due to this differential pressure, the pressure on the pilot line 16 side becomes higher than the pressure on the pilot line 17 side, and the pilot valve 8 is displaced to the open side according to the differential pressure to supply the control piston 9 with pressurized oil. The working hydraulic pump 3 discharges pressure oil, and the work vehicle starts running. The inching valve 20 is connected to an inching pedal and is usually used at the most narrowed position. When the inching pedal is depressed, the inching valve 20 opens, and the pressure oil from the charging pump 5
The entire oil volume flows through the inching valve 20 and the orifice 1
No pressure difference is generated between the primary side and the secondary side of No. 5, so that the amount of oil discharged from the traveling hydraulic pump 3 becomes zero. Therefore, the driving force is released simultaneously with the braking. The working speed of the working device is controlled by controlling the rotation speed of the engine 2 by operating the accelerator pedal and adjusting the amount of oil discharged from the working hydraulic pump 4. When the rotational speed of the engine 2 is increased to increase the working speed of the working device, the amount of oil discharged from the working hydraulic pump 4 increases and the amount of oil discharged from the traveling hydraulic pump 3 also increases. And the traveling speed of the work vehicle also increases. If the work speed is reduced, the traveling speed of the work vehicle is reduced. To perform high-speed work at low speed, the accelerator pedal is depressed to increase the rotation speed of the engine 2 and increase the discharge oil amount of the working hydraulic pump 4. At this time, the differential pressure between the primary side and the secondary side of the orifice 15 increases, and the amount of oil discharged from the traveling hydraulic pump 3 increases, so that the traveling speed also increases. When the needle valve 21 is opened by turning the handle in the opening direction, a part of the pressure oil discharged from the charging pump 5 flows to the suction side of the charging pump 5, so that the primary side of the orifice 15 And the displacement of the pilot valve 8 decreases in accordance with the decrease in the differential pressure, the amount of oil discharged from the traveling hydraulic pump 3 decreases, and the traveling speed also decreases. If it is desired to work at a very low speed, the opening of the needle valve 21 is further increased. Then
The differential pressure between the primary side and the secondary side of the orifice 15 further decreases, the amount of oil discharged from the traveling hydraulic pump 3 decreases, and the vehicle travels at a low speed. Since the needle valve 21 has a large adjustment range of the opening degree and is capable of fine pressure adjustment, it is possible to appropriately control the speed at a low speed. Since the engine speed is not related to the opening and closing of the needle valve 21, even if the needle valve 21 is opened, the working capacity does not decrease. Therefore, a large working capacity can be ensured even at a low speed. If the needle valve 21 is arranged in the vicinity of the driver's seat, the opening and closing operation can be easily performed by an operator, so that the control of the traveling speed at the time of work becomes easy. As described above, the low-speed running control apparatus for a work vehicle according to the present invention appropriately controls the low-speed running of the work vehicle while the engine speed is increased. Can be. There is no need to provide a large-capacity working hydraulic pump or separately install an engine dedicated to the working device in order to ensure high working capacity at low speeds. Also, when the engine speed is increased for high-speed work, there is no need to control the inching valve by operating the inching pedal to make the traveling speed of the work vehicle very slow.
Operator fatigue can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a configuration of a work vehicle traveling speed control device according to an embodiment of the present invention. FIG. 2 is a graph showing a relationship between an opening degree of a needle valve and a pressure. FIG. 3 is a hydraulic circuit diagram showing a configuration of a conventional work vehicle speed control device. FIG. 4 is a graph showing a relationship between an opening degree and a pressure of a variable valve of the conventional speed control device for a work vehicle. [Description of Signs] 2 Engine 3 Traveling hydraulic pump 4 Working hydraulic pump 5 Charging pump 6 Hydraulic motor 7 Traveling device 8 Pilot valve 9 Control piston 10 Solenoid valve 11 Main line 12 Main line 13 Work circuit 14 Control circuit 15 Orifice 16 Pilot line 17 Pilot line 19 Low pressure relief valve 21 Needle valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 29/00 F02D 29/00 H F16H 39/04 F16H 39/04 F-term (Reference) 3D041 AA38 AB07 AC22 AD02 AD10 AD28 AE28 3G093 AA08 BA07 CA06 CB02 DA06 DB05 DB10 DB22 EB03 EB05 EC04 FA04 3J053 AA01 AB02 AB12 AB36 AB46 DA06 EA07 FB01 FB03

Claims (1)

Claims 1. A traveling hydraulic pump, a working hydraulic pump, and a charging pump driven by a common engine, and traveling traveling closed-circuit connected to the traveling hydraulic pump by a pair of main pipelines. In a work vehicle equipped with a hydraulic motor for driving the device and a pilot valve for controlling the amount of oil discharged from the traveling hydraulic pump, the flow rate is controlled in the control circuit connected to the pilot valve from the discharge side of the charging pump. An orifice for generating a corresponding differential pressure between the primary side and the secondary side is provided, a pilot line is connected to the pilot valve from the primary side and the secondary side of the orifice, and the secondary side of the orifice is connected. In addition to being connected to a low pressure relief valve, the primary side of the orifice is connected to the suction side of the charging pump via a needle valve whose opening can be adjusted finely. Fine speed travel control apparatus for working vehicle.