JP2003269607A - Maximum speed control device of work vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control the maximum speed of a work vehicle and to bring out high work ability for working device at the required traveling speed in the state of an increased engine speed. <P>SOLUTION: The device is equipped with a hydraulic pump 3 for traveling, a charging pump 5 and a hydraulic pump for working driven by the engine, and a hydraulic pump 6 for driving the traveling device connected to the hydraulic pump 3 for traveling with the closed circuit of a pair of main circuits 11, 12. In the work vehicle in which a pump control circuit 14 is connected with a motor control circuit 26 via a sequence valve 13 from a charging circuit 4, a maximum speed control circuit 29 interposing a variable reducing valve 28 is switchably connected to the motor control circuit 26 from the charging circuit 4. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a traveling device driven by a hydrostatic power transmission (hereinafter referred to as HST) and a maximum speed control device for a working vehicle including a working device. . 2. Description of the Related Art Conventionally, in a working vehicle equipped with a traveling device driven by an HST, as shown in FIG. 2, a traveling hydraulic pump 33 and a charging pump 35 are directly connected to an engine (not shown). I have. The traveling hydraulic pump 33 is connected to the traveling device driving hydraulic motor 36 by a pair of main circuits 41 and 42 in a closed circuit. The rotation speed of the engine is controlled by operating an accelerator pedal (not shown), and the traveling hydraulic pump 33 driven by the engine supplies pressure oil to the hydraulic motor 36 via the main circuits 41 and 42 to give rotation. The driving device 37 is driven. A charging pump 35 driven by the engine is connected to a main circuit 4 via a charging circuit 34.
Supply pressure oil to 1, 42 and charge circuit 3
From the pump control circuit 4 via the sequence valve 43
4 and supply the control oil to the motor control circuit 56. In the middle of the charging circuit 34, a filter 38 and an orifice 45 for generating a differential pressure according to the flow rate between the primary side and the secondary side are provided.
Pilot circuits 46 and 47 are connected to the sequence valve 43 from the secondary side and the secondary side. The traveling hydraulic pump 33 is a variable displacement hydraulic pump whose discharge oil amount is controlled by a control piston 39. To the control piston 39, a pump control circuit 44 controls the forward and backward movement of the work vehicle. , And stop is selected via a solenoid valve 40 for switching. By switching the solenoid valve 40, the pump control circuit 44 is connected to one of the left and right pressure chambers of the control piston 39 or the communication is cut off, and the forward, backward, or stop of the work vehicle is selected. [0005] A motor control circuit 56 provided with a solenoid valve 54 and an inching valve 55 is connected to the hydraulic motor 36, branching from the middle of the pump control circuit 44. Charging pump 3 with low engine speed
When the discharge oil amount of No. 5 is small, there is no pressure difference between the primary side and the secondary side of the orifice 45, so even if the solenoid valve 40 is switched to either forward or reverse, The control piston 39 is maintained at the neutral position, and the amount of oil discharged from the traveling hydraulic pump 33 is zero. That is, even if forward or reverse is selected, if the engine is in the idling state, the work vehicle is stopped. When the rotation speed of the engine increases and the amount of oil discharged from the charging pump 35 increases, the charging circuit 3
The differential pressure proportional to the flow rate of the orifice 45
Occurs between the next side. When this differential pressure reaches a predetermined value,
The sequence valve 43 is opened, the control piston 39 is displaced in accordance with the differential pressure, the traveling hydraulic pump 33 discharges pressure oil, and the work vehicle starts traveling. Since the control pressure proportional to the rotation of the engine is applied to the motor control circuit 56 to control the hydraulic motor 36, the work vehicle runs at a speed proportional to the rotation of the engine. [0007] The inching valve 55 is connected to an inching pedal, and is normally used at the most narrowed position. When the inching pedal is depressed, the inching valve 55 is opened, pressure oil flows from the motor control circuit 56 and the pump control circuit 44 to the oil tank 57, and the work vehicle is decelerated. On the other hand, the working device is usually operated by a working hydraulic pump (not shown) driven by an engine. [0008] The control of the working capacity (speed) of the working device is performed by controlling the number of revolutions of the engine by operating the accelerator pedal and adjusting the discharge oil amount of the working hydraulic pump. Therefore, when the rotation speed of the engine is increased in order to increase the working capacity of the working device, the amount of oil discharged from the working hydraulic pump increases, and the traveling hydraulic pump 33 increases.
Therefore, the rotation speed of the hydraulic motor 36 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. For this reason, in a work vehicle equipped with a conventional HST-driven traveling device and a hydraulically operated working device, there is no problem in performing high-speed work at high speed. However, in practice, there are cases where it is desired to perform high-speed work while suppressing the traveling speed.
For example, when using a wheel loader equipped with a bucket as a working device and scooping earth and sand in a bucket and throwing it into a high hopper, run the wheel loader toward the hopper while raising the bucket that has scooped the earth and sand etc. Let it. At this time, it is necessary to raise the bucket quickly. However, if the traveling speed is too high, the bucket approaches the position of the hopper before the bucket rises to a required height, which hinders the work. When the engine speed is reduced and the amount of oil discharged from the traveling hydraulic pump 33 is reduced to reduce the traveling speed, the amount of oil discharged from the working hydraulic pump is also reduced. Will drop. If an engine dedicated to the working device is separately installed to suppress the running speed and ensure high working capacity, the cost will increase significantly. In order to secure high working capacity, fix the engine speed to the maximum,
An operation is also performed to reduce the traveling speed of the work vehicle by controlling the inching valve 55 by depressing the inching pedal. However, since the inching pedal is operated with the foot, it is difficult to make fine adjustments, it is difficult to keep the working vehicle at a required speed, and there is a problem in that constantly operating the inching pedal increases operator fatigue. An object of the present invention is to solve the above-mentioned problem in controlling the speed of a work vehicle. The present invention is capable of controlling the maximum speed of a work vehicle in a state where an engine speed is increased, and a work apparatus having a required traveling speed. It is an object of the present invention to provide a maximum speed control device for a working vehicle that can exhibit high working ability. According to the maximum speed control device for a working vehicle of the present invention, a traveling hydraulic pump, a charging pump, a working hydraulic pump driven by an engine, and a traveling hydraulic pump are provided. A work vehicle having a hydraulic motor for driving the traveling device connected in a closed circuit by a pair of main circuits, and a pump control circuit and a motor control circuit connected from the charging circuit via a sequence valve; The above-mentioned problem is solved by switchingably connecting a maximum speed control circuit provided with a variable pressure reducing valve to the control circuit. When it is desired to ensure a high working capacity at low speed running, the accelerator pedal is depressed to increase the engine speed and increase the discharge oil amount of the working hydraulic pump.
At this time, the amount of oil discharged from the traveling hydraulic pump also increases, and the traveling speed also increases. Therefore, when the motor control circuit is switched to the maximum speed control circuit side and the variable pressure reducing valve is set to a required pressure, the maximum pressure of the motor control circuit is limited by the variable pressure reducing valve, so that the maximum speed of the hydraulic motor for driving the traveling device is controlled. Is restricted and the traveling speed decreases. By setting the pressure of the variable pressure reducing valve, the maximum traveling speed of the work vehicle can be arbitrarily controlled according to the work mode, so that the traveling speed control can be appropriately performed. FIG. 1 is a circuit diagram showing a configuration of a traveling device of a work vehicle provided with a maximum speed control device according to an embodiment of the present invention. In this traveling device for a work vehicle, a traveling hydraulic pump 3 and a charging pump 5 are directly connected to an engine (not shown). The traveling hydraulic pump 3
A pair of main circuits 11 and 12 are connected to the hydraulic motor 6 for driving the traveling device in a closed circuit. The rotational speed of the engine is controlled by operating an accelerator pedal (not shown), and the traveling hydraulic pump 3 driven by the engine supplies pressure oil to the hydraulic motor 6 via the main circuits 11 and 12. Rotation is applied to drive the traveling device 7. The charging pump 5 driven by the engine supplies pressure oil to the main circuits 11 and 12 via the charging circuit 4 and a pump control circuit 14 and a motor from the charging circuit 4 via the sequence valve 13. The pressure oil is supplied to the control circuit 26. The traveling hydraulic pump 3 is a variable displacement hydraulic pump whose discharge oil amount is controlled by a control piston 9. To the control piston 9, a pump control circuit 14 is used to move the work vehicle forward and backward. , And stop are connected via a solenoid valve 10 for switching. The solenoid valve 10 switches the control piston 9
The pump control circuit 14 is communicated with one of the left and right pressure chambers, or the communication is cut off, and the forward, backward, or stop of the work vehicle is selected. In the middle of the charging circuit 4, a filter 8 and an orifice 15 for generating a differential pressure corresponding to the flow rate between the primary side and the secondary side are provided. Pilot circuits 16 and 17 are connected to the sequence valve 13 from the side and the secondary side. A motor control circuit 26 provided with a solenoid valve 24 and an inching valve 25 is connected to the hydraulic motor 6 from the middle of the pump control circuit 14. Further, a maximum speed control circuit 29 provided with a variable pressure reducing valve 28 is connected to the motor control circuit 26 from the charging circuit 4 by a solenoid valve 24 so as to be switchable. When the rotation speed of the engine is small and the amount of oil discharged from the charging pump 5 is small,
Since there is no pressure difference between the secondary side and the secondary side, even if the solenoid valve 10 is switched to either forward or reverse, the control piston 9 is maintained at the neutral position, and The discharge oil amount of the hydraulic pump 3 is zero. That is, even if forward or reverse is selected,
If the engine is idling, the work vehicle has stopped. When the engine speed increases and the amount of oil discharged from the charging pump 5 increases, a differential pressure proportional to the flow rate of the charging circuit 4 is generated between the primary side and the secondary side of the orifice 15. . When the differential pressure reaches a predetermined value, the sequence valve 13 is opened, the control piston 9 is displaced according to the differential pressure, the traveling hydraulic pump 3 discharges pressure oil, and the work vehicle starts traveling. Since the control pressure proportional to the rotation of the engine is applied to the motor control circuit 26 to control the hydraulic motor 6, the work vehicle runs at a speed proportional to the rotation of the engine. The inching valve 25 is connected to an inching pedal and is usually used at the most narrowed position. When the inching pedal is depressed, the inching valve 25 opens, pressure oil flows from the motor control circuit 26 and the pump control circuit 14 to the oil tank 27, and the work vehicle is decelerated. On the other hand, the working device of the working vehicle is operated by a working hydraulic pump (not shown) driven by an engine, similarly to the conventional one, and the control of the working capacity (speed) of the working device is as follows. The operation is performed by controlling the rotation speed of the engine by operating the accelerator pedal and adjusting the discharge oil amount of the working hydraulic pump. Therefore, when the rotation speed of the engine is increased in order to increase the working capacity of the working device, the amount of oil discharged from the working hydraulic pump is increased and the amount of oil discharged from the traveling hydraulic pump 3 is also increased. The rotation speed of the hydraulic motor 6 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. When it is desired to ensure a high working capacity at low speed, the accelerator pedal is depressed to increase the number of revolutions of the engine and increase the discharge oil amount of the working hydraulic pump. Then, the amount of oil discharged from the traveling hydraulic pump is also increased, and the traveling speed is also increased. Therefore, by switching the solenoid valve 24 of the motor control circuit 26, connecting the maximum speed control circuit 29 to the motor control circuit 26, and setting the variable pressure reducing valve 28 to a required pressure, the motor control circuit 26
Is limited by the variable pressure reducing valve 28, the maximum speed of the hydraulic motor 6 for driving the traveling device is restricted, and the traveling speed is reduced. As described above, by setting the pressure of the variable pressure reducing valve 28, the maximum traveling speed of the work vehicle can be arbitrarily controlled in accordance with the work mode, so that the traveling speed can be controlled appropriately. For example, when using a wheel loader equipped with a bucket as a working device and scooping earth and sand in a bucket and throwing it into a high hopper, run the wheel loader toward the hopper while raising the bucket that has scooped the earth and sand etc. At this time, the bucket is quickly raised, and the running speed is controlled so as not to be too fast so as to reach the position of the hopper after the bucket is raised to a required height, so that work can be performed efficiently. As described above, the maximum speed control device for a work vehicle according to the present invention can control the maximum speed of the work vehicle in a state where the engine speed is increased, and the required traveling speed can be controlled. Therefore, the working device can exhibit high working ability. There is no need to separately install an engine dedicated to the working device in order to ensure high working capacity at low speeds. In addition, when the rotation speed of the engine is increased for high-speed operation, it is not necessary to control the inching valve by operating the inching pedal to reduce the traveling speed of the work vehicle, so that fatigue of the operator can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a configuration of a traveling device of a work vehicle including a maximum speed control device according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing a configuration of a traveling device of a conventional work vehicle. [Description of Signs] 2 Engine 3 Traveling hydraulic pump 4 Charging circuit 5 Charging pump 6 Hydraulic motor 7 Traveling device 9 Control piston 10 Solenoid valve 11 Main circuit 12 Main circuit 13 Sequence valve 14 Pump control circuit 15 Orifice 16 Pilot circuit 17 Pilot circuit 24 Solenoid valve 25 Inching valve 26 Motor control circuit 28 Variable pressure reducing valve 29 Maximum speed control circuit

Claims (1)

Claims: 1. A traveling hydraulic pump, a charging pump, and a working hydraulic pump driven by an engine,
A work vehicle having a traveling hydraulic pump and a traveling device driving hydraulic motor connected in a closed circuit with a pair of main circuits, and connecting a pump control circuit and a motor control circuit via a sequence valve from a charging circuit. A maximum speed control device for a work vehicle, wherein a maximum speed control circuit provided with a variable pressure reducing valve is switchably connected from a charging circuit to a motor control circuit.