JPH0386684A - Hydraulic system for industrial vehicle - Google Patents

Abstract

PURPOSE:To eliminate wasteful circulation of pressurized oil by sensing the fluctuation in rotation of a pump driven by an engine and the presence or absence of cargo handling operations, and controlling the pump capacity in accordance with the detected results. CONSTITUTION:Since the pressure from a pilot pipeline 50 does not act on a flow change-over valve 20 when there is no cargo handling operation, the position of a throttling passage (b) is preserved, and the differential pressure across the change-over valve 20 produced by a throttle 23 is loaded as a pilot pressure against a capacity control valve 30. The capacity control valve 30 is thus also maintained by the counteracting pressure and spring tension. Since the flow rate after throttling is set to a degree that the flow rate exceeds slightly the required flow rate in a power steering circuit 13, the increase or decrease in delivery of a pump 11 due to fluctuation in the rotation of an engine acts on a variable capacity mechanism 40 from the capacity control valve 30 in accordance with the change in the differential pressure, and the flow rate after throttling is stably maintained. When a valve-lift is operated, the delivery pressure is loaded on the direct control valve 30, a pilot check valve 22 is opened to eliminate the differential pressure, and the mechanism 40 is thus greatly operated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic system for an industrial vehicle such as a forklift, and more particularly to a hydraulic system that controls the capacity of a hydraulic pump for cargo handling and power steering.

[Conventional technology] A typical hydraulic system equipped on a forklift truck is
As illustrated in FIG. 3, a flow divider valve 4 is provided in the discharge pipe line 3 of the constant displacement hydraulic pump 2 driven by the engine 1, and the pressure oil is adjusted to the required flow rate of the power steering circuit 5 through the flow divider valve 4. The pressure oil that is divided into the remaining flow rate for the cargo handling circuit and supplied to the cargo handling circuit 6 is supplied to the lift cylinder 8 or the tilt cylinder 9 through the operation of the cargo handling control valve 7 as needed.

[Problems to be Solved by the Invention] As described above, the conventional hydraulic system has a fixed displacement hydraulic pump 2.
Of the pressure oil discharged from the cargo handling circuit 6, all of the pressure oil discharged from the cargo handling circuit 6 except for the required flow rate secured for the power steering circuit 5.
Therefore, when no cargo handling operation is actually performed, this pressure oil simply flows back to the oil tank as surplus oil via the cargo handling control valve 7. Moreover, the amount of oil discharged from the hydraulic pump 2 increases proportionally as the engine speed increases, and the circulation of unnecessary surplus oil is further promoted. Therefore, such repeated wasteful circulation of pressure oil causes a rise in oil temperature in addition to power loss, leading to early deterioration of sealing members and the like, and causing serious defects in the hydraulic system.

A technical problem to be solved by the present invention is to detect rotational fluctuations of a pump driven by an engine and the presence or absence and type of cargo handling operations to control the pump capacity according to the machine.

[Means for Solving the Problems] In order to solve the above problems, the present invention includes a variable displacement hydraulic pump driven by an engine, and a variable displacement hydraulic pump that is installed in the discharge pipe of the pump and supplies pressure oil to the required flow rate of the power steering circuit. A diverter valve that divides the flow into the remaining flow rate for the cargo handling circuit, a cargo handling control valve equipped with a lift and tilt spool that supplies pressure oil from the cargo handling circuit to the cargo handling actuator, and a discharge pipe that leads to the diverter valve. and a flow rate switching valve with a throttle operated by pilot pressure via the operating position of each of the spools, and a pressure after the throttle of the flow rate switching valve that opposes the discharge pressure or a discharge pressure via the operating position of each of the spools. or a capacity control valve that is pilot-operated by the differential pressure with the adjustment pressure and controls the variable capacity mechanism of the pump, and the flow rate after throttling by the flow rate switching valve is slightly higher than the required flow rate of the power steering circuit. A new configuration has been adopted.

[Operation] In the apparatus of the present invention, when no cargo handling operation is being performed, the flow rate switching valve is maintained at the throttle flow path position without any pilot pressure acting on it. Therefore, the differential pressure across the flow rate switching valve generated by this restriction is applied as pilot pressure to the capacity control valve in opposition to it, and the position of the capacity control valve is also maintained by the balance between the counter pressure and the spring force. . At this time, the flow rate after throttling by the flow rate switching valve is set to a level that slightly exceeds the required flow rate of the power steering circuit, and the increase or decrease in the amount of oil discharged from the pump based on engine rotational fluctuations is accompanied by changes in the differential pressure mentioned above. Immediately, the capacity control valve acts on the variable capacity mechanism, and the amount of oil discharged per revolution of the pump is automatically adjusted to maintain the above-mentioned flow rate after throttling stably.

When a cargo handling operation, such as a lift operation, is performed in such a state, the discharge pressure introduced from the discharge pipe to the operating position of the lift spool built into the cargo handling control valve directly increases the capacity in place of the previous counterpressure. Loaded on the control valve,
At the same time, the discharge pressure also opens the pilot check valve in the flow rate switching valve, so the variable displacement mechanism operates greatly through the displacement of the displacement control valve due to the elimination of the differential pressure, and the amount of oil discharged per revolution of the pump is maximized. At the same time, the circuit resistance caused by the aperture is also eliminated.

In addition, when the cargo handling operation is a tilt operation, the discharge pressure introduced from the discharge pipe to the operating position of the tilt spool is reduced to the adjusted pressure via the throttle channel at that position, and the above-mentioned The adjusted pressure, which is set higher than the throttled pressure of the flow rate switching valve, is applied to the capacity control valve in place of the previous counterpressure. Therefore, the decrease in the differential pressure when pilot operating the capacity control valve acts on the variable capacity mechanism through the displacement of the capacity control valve, and the pump 1 has a medium capacity that can supply the amount of oil necessary for the tilt operation to the cargo handling circuit. Increase the amount of oil discharged per revolution. In addition,
In this case as well, the adjusted pressure opens the pilot check valve in the flow rate switching valve to eliminate the circuit resistance caused by the throttle.

[Embodiments] Hereinafter, embodiments of the present invention will be explained in detail based on the drawings.

1 and 2 show the main parts of a hydraulic system in which the present invention is applied to a forklift. A variable displacement hydraulic pump 11 driven by an engine 10 includes a well-known swash plate type axial piston pump (hereinafter referred to as Simply called a pump
The discharge pipe 12 connected to the pump 11 is provided with a flow divider valve 14 that divides the pressure oil into the required flow rate of the power steering circuit 13 and the remaining flow rate for the cargo handling circuit. 15 is connected to cargo handling actuators such as a lift cylinder 17 and a tilt cylinder 18 via a cargo handling control valve 16.

A flow rate switching valve 20 with a throttle is provided in the discharge pipe 12 leading to the above-mentioned flow dividing valve 14, and the detailed structure of the flow rate switching valve 20 is clearly shown in FIG. That is, the valve main body 21 is formed with a passage a passing through the pilot check valve 22 and a passage passing through the fixed throttle 23.
Since the check valve 22 remains closed unless pilot pressure is applied, a pressure difference is generated between the discharge pressure, that is, the inlet pressure P1, and the outlet pressure P2 via the fixed throttle 23.
The outlet pressure P2 is also communicated to the pilot line 26.

Reference numeral 30 denotes a capacity control valve which is operated by the differential pressure between the inlet pressure P1 via the pilot line 28 and the outlet pressure P2 via the pilot line 26 and shuttle valve 27 during non-loading. The detailed configuration of 30 is also shown in FIG.

That is, the valve body 31 is equipped with a spool 33 that is controlled by the balance between the differential pressure via the pilot line 28 and the biasing force of the spring 32, and the spool 33 has an inlet via the pilot line 28. A notch 34a for guiding the pressure P1 to the control cylinder 41 of the variable displacement mechanism 40 via the boat 35, and a notch 34b for connecting the boat 35 to the drain boat 36 are provided. In the variable displacement mechanism 40, the piston rod 42 is operated by the inlet pressure P1 introduced into the control cylinder 41, and the tilt angle of the swash plate of the pump 11 is changed in balance with the biasing force of the return spring 11a. The opening degree of the fixed throttle 23, which influences the feed flow rate during non-load handling, is determined by the differential pressure (Pl) before and after the throttle.
-P2> reaches the set pressure, the throttled flow rate obtained based on the capacity control of the pump 11 via the capacity control valve 3o is set to be slightly higher than the required flow rate of the power steering circuit 13.

Reference numeral 50 denotes a pilot pipe for applying the discharge pressure P1 of the discharge pipe 12 to the capacity control valve 30 via the cargo handling control valve 16, and a lift spool 16 installed in the cargo handling control valve 16.
A pipe line 50a, which is connected to the shuttle valve 27 via the operating (ascending) position of the tilt spool 16b and branched from the pipe line 50, similarly communicates with the shuttle valve 27 via a throttle passage provided at the operating position of the tilt spool 16b. It is merged into the shuttle valve 27. Note that the discharge pressure P1 or the adjusted pressure P3 that has passed through the operating positions of the spools 16a and 16b is roughly transmitted to the pilot check valve 2 through a branch pipe 50b.
It also acts as a pilot pressure to open 2. Also,
The adjusted pressure P3 via the throttle flow path is adjusted to match the flow rate required during tilt operation, which will be described later.
It may be set higher than 2.

In the above configuration, when the load IQ operation is not performed, the pilot check valve 22 is in a closed state, and the pressure oil flows from the discharge pipe 12 to the passage via the fixed throttle 23, and the throttle action causes the pressure oil to flow into the passage. The flow rate on the outlet side of the flow rate switching valve 20 is regulated, and at the same time, a pressure difference is generated between the inlet pressure P1 and the outlet pressure P2. In addition, the flow rate on the outlet side at this time is set to be slightly higher than the required flow rate of the power steering circuit 13 secured by the flow dividing valve 14, so that the amount of excess pressure oil supplied to the cargo handling circuit 15 is extremely small! 1
Limited to 1.

However, the rotation of the pump 11 is controlled by the engine 10 and varies from time to time. For example, when the rotation of the engine 10 increases, the flow rate of the discharge pipe 12 increases, and at the same time, the inlet pressure P1 increases.
, the outlet pressure P2 and the outlet flow rate both increase. However, the increase in inlet pressure P1
Since the pressure is immediately reflected in the flilJ control cylinder 41 via the boat 35 of the capacity control valve 30, which is maintained in an equilibrium state by the above-mentioned differential pressure, the piston rod 42 resists the biasing force of the return spring 11a. to change the swash plate inclination to the reduction side. Of course, when the rotation of the engine 10 decreases, the amount of oil discharged per revolution of the pump 11 is adjusted through an operation that is completely opposite to the above explanation, so that the flow rate on the outlet side of the flow rate control valve 20 is adjusted. remains almost constant.

From this state, for example, lift operation (lift spool 16
When displacement a> is performed, the discharge pressure P1 introduced from the discharge pipe 12 to the raised position of the lift spool 16a via the pilot pipe 50 is directly applied to the shuttle valve 27.
guided by. Until then, the discharge pressure P1 is
Since the pressure is higher than the outlet pressure P2 that has passed through the shuttle valve 27, the pressure passes through the shuttle valve 27 preferentially and is applied to the capacity control valve 30 as an alternative pressure. Therefore, the same discharge pressure (inlet pressure>Pl) acts on the spool 33 in opposite directions, and the spool 33 moves significantly to the right in the drawing due to the biasing force of the spring 32.

Therefore, the control cylinder 41 has the port 35 and the notch 34a.
The piston rod 42, which is in full communication with the drain port 36 through the piston rod and loses the support of hydraulic pressure, succumbs to the biasing force of the return spring 11a and quickly withdraws, so that the pump 11, the amount of oil discharged per revolution is maximized. Then, the discharge pressure P1 via the pilot pipe 50 simultaneously opens the pilot 1 to the check valve 22 via the pipe 50b and opens the passage a, so that the pump 11 is fully operated and the circuit resistance via the fixed throttle 23 is reduced. When the engine 10 is operated to increase the rotation of the engine 10, a sufficient amount of pressure oil is supplied to the cargo handling circuit 15 to carry out the lift operation.
will be promptly sent to.

In addition, when the cargo handling operation is a tilt operation that requires about half the amount of oil as in a lift operation, the oil is introduced from the discharge pipe 12 through the pilot pipe 50 and the branch pipe 50a to the operating position of the tilt spool 16b. discharge pressure P
1 is reduced in pressure to the adjusted pressure P3 by the throttle flow path at the position, and is similarly guided to the shuttle valve 27. At this time, the adjusted pressure P3 is also set higher than the outlet pressure P2 which has passed through the shuttle valve 27 up to that point, so it is loaded on the capacity control valve 30 in a manner that takes priority over and replaces the outlet pressure P2. Therefore, the spool 33 moves to the right in the figure due to the decrease in differential pressure, and temporarily connects the port 35 communicating with the control cylinder 41 to the drain port 3 through the notch 34b.
Connect to 6.

and the pressure drop in the control cylinder 41 and the return spring 11a.
The piston rod 42 is retracted due to the biasing force of
moves to the left, and the port 35 is insulated from the drain port 36 and at the same time receives the inlet pressure P1 again, so that the recovery pressure in the control cylinder 41 increases to the return spring 11a.
The piston rod 42 is advanced against the urging force of , and the swash plate inclination angle is changed to the reduction side. In addition, in this case as well, the conduit 50
Since the adjustment pressure P3 via b opens the pilot check valve 22 and opens the passage a, the amount of oil sent to the cargo handling circuit 15 through this series of adjustment operations is sufficient to substantially cover the tilt operation. The amount of oil discharged per revolution of the pump is adjusted so as to achieve the desired amount.

[Effects of the Invention] As described in detail above, according to the present invention, the amount of surplus oil fed to the cargo handling circuit during non-cargo handling is limited as much as possible by the flow rate switching valve with a throttle provided in the discharge pipe, and the engine rotation is In response to fluctuations in the flow rate, the flow rate of the variable displacement hydraulic pump is adjusted in cooperation with the capacity control valve to maintain a stable circuit flow rate. On the other hand, during cargo handling, the lift spool or The type of cargo handling is determined based on the pilot pressure that passes through the operating position of the tilt spool, and by adjusting the amount of pump discharged oil through displacement of each valve and eliminating circuit resistance, the amount of pressure oil suitable for each cargo handling operation is delivered. Since it is sent to the cargo handling circuit, it not only skillfully responds to fluctuations in engine speed and reduces the amount of excess oil in all situations in a very rational manner, but also extremely effectively suppresses increases in oil temperature. As a result, each sealing member is freed from thermal deterioration and significantly contributes to long-term stability of the hydraulic system.

[Brief explanation of drawings]

Fig. 1 is a hydraulic circuit diagram showing an embodiment of a hydraulic system according to the present invention, Fig. 2 is a sectional view showing a flow rate switching valve and a capacity control valve of the same embodiment, and Fig. 3 is a conventional hydraulic system. It is a hydraulic circuit diagram. 10...Engine 11...Variable displacement hydraulic pump 12...Discharge pipe line 13...Power steering circuit 14...Diversion valve 15...Cargo handling circuit 16...
・Cargo handling control valve 16a...lift spool 16b・
...Tilt spool 20...Flow rate switching valve 27...Shuttle valve 30...
・Capacity control valve

Claims (1)

[Claims] A variable displacement hydraulic pump driven by an engine; a diversion valve installed in the discharge line of the pump to divide pressure oil into the required flow rate for the power steering circuit and the remaining flow rate for the cargo handling circuit; The cargo handling control valve is equipped with a lift and tail spool that supplies pressure oil to the cargo handling actuator, and is installed in the discharge pipe leading to the above-mentioned diverter valve, and is operated by pilot pressure via the operating position of each spool. The flow rate switching valve with a throttle is pilot-operated by the differential pressure between the throttled flow rate switching valve and the throttled pressure of the flow rate switching valve opposing the discharge pressure, or the discharge pressure or adjustment pressure via the operating position of each of the spools. A hydraulic system for an industrial vehicle, comprising a capacity control valve that controls a variable capacity mechanism of a pump, and wherein the flow rate after throttling by the flow rate switching valve is set to a level that slightly exceeds the required flow rate of the power steering circuit. .