JPS6315280Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a hydraulic circuit for lift cylinders in a lift truck that is equipped with two hydraulic cylinders and is operated simultaneously at all times to raise and lower an inner mast. However, it prevents variations in the operation of both cylinders,
The objective is to provide a hydraulic circuit that can control the descending speed to perform safe cargo handling operations, and can prevent the inner mast from descending suddenly even if the piping that supplies oil to the bottom chambers of both cylinders is damaged. .

An embodiment of the present invention will be explained in detail below based on the drawings.

In the figure, reference numeral 1 denotes a pair of left and right outer masts, which are installed at the front of the forklift truck's vehicle body. Both masts 1 are integrally connected on the left and right by a lower tie beam 1A, etc., and the inner mast 2 is equipped with rollers (not shown). It is attached so that it can be raised and lowered through. 3 in the figure is a lift cylinder consisting of a pair of left and right, and the inner mast 2
Or, the piston rod is located behind the rear flange of the outer mast 1, the bottom of which is supported by the lower tie beam 1A, and the tip of the piston rod that extends from this is
It is connected to an upper beam 2A that connects the tops of the inner mast 2. Although not shown in the drawings, a fork that can be raised and lowered is attached to the inner mast 3. Each of the above configurations is a well-known must-have configuration, so a detailed explanation will be omitted.

A in the figure is a flow control valve, which is removably attached to the bottom of the lift cylinder 3B (hereinafter referred to as the left cylinder 3B) located on the left side in FIG. (hereinafter referred to as right cylinder 3A)
A down control valve B is removably attached to the bottom.

Here, both control valves A and B will be explained in detail with reference to FIG.
The valve body 4 consists of a bottomed cylindrical piston 6 that fits vertically and slidably into the inner cylindrical portion 4A.
From the middle part to the lower flange part 4 on the outer peripheral surface
By tightly fitting the threaded part carved in the part leading to D into the bore 5 provided through the bottom of the right cylinder 3A to communicate the outside and the cylinder bottom chamber, It will be installed. In this state, the other end of the flow passage 4B, which is formed in the carved part of the threaded part of the valve body 4 and has one end open to the bottom wall of the inner cylinder part 4A, is bored into the bottom of the right cylinder 3A. An oil hole 4E that communicates with the port 7 and that faces the bottom chamber of the cylinder 3A from the upper part of the valve body 4, that is, the upper end of the bore 5, is penetrated through which the bottom chamber and the inner cylindrical portion 4A of the valve body 4 are constantly communicated. It is set up.

The top outer diameter of the bottomed cylindrical piston 6, which is the open end, is approximately the same diameter as the inner cylindrical portion 4A of the valve body 4, and is fitted into the inner cylindrical portion 4A to prevent the piston 6 from sliding up and down. A guide portion 6A for guiding, a small diameter portion 6B having an intermediate outer diameter smaller than that of the guide portion 6A and having a step for receiving the spring 8, and a lower portion having a shape capable of opening and closing the opening end of the flow path 4B. The small diameter part 6B has an oil hole 6D, and the axial center of the shutoff part 6C has an orifice 6.
The inner cylindrical portion 6F of the piston 6 and the flow path 4B are connected to the flow formed between the small diameter portion 6B of the piston 6 and the inner cylindrical portion 4A of the valve body 4 by the orifice 6E. The passage 4C and the inner cylindrical portion 6F are always in communication with each other through an oil hole 6D. The spring 8, which is wound around the outer periphery of the small diameter portion 6B of the piston 6, has its lower end engaged with the bottom wall of the inner cylindrical portion 4A of the valve body 4, and its upper end engaged with a stepped portion between the guide portion 6A and the small diameter portion 6B of the piston 6, When the piston rod moves up and down,
The pressure in the flow path 4B of the valve body 4 and the biasing force of the spring 8 urge the blocking portion 6C of the piston 6 to separate from the flow path 4B of the valve body 4, thereby separating the flow paths 4B from 4C. The pressure difference between the inner cylindrical portion 6F of the piston 6 and the flow path 4B is caused when the pressure inside the flow path 4B becomes equal to zero due to, for example, damage to the piping 22, which will be described later. If the flow rate of the hydraulic oil flowing out from the flow path 4C to 4B increases significantly and the piston rod descending speed of the right cylinder 3A, that is, the speed converted to the descending speed of the fork becomes, for example, 500 mm/sec or more, the piston 6 will descend. , and the piston 6 is biased to close the opening of the flow path 4B with the blocking part 6C, and the hydraulic oil in the right cylinder 3A passes only through the orifice 6E, and the descending speed is, for example, 200 mm/ Controlled to about sec. Reference numeral 9 in the figure denotes a stop member, which is attached to the upper end portion of the inner cylindrical portion 4A of the valve body 4, and prevents the piston 6 from moving excessively upward.

Next, an embodiment of the flow control valve A installed at the bottom of the left cylinder 3B will be explained in detail with reference to FIG. The valve body 12 consists of a bottomed cylindrical piston 13 that is slidably fitted into the valve body 12. The valve body 12 has a threaded portion carved in a portion of the outer circumferential surface from the middle portion to the lower flange portion 12D. It is attached to the bottom of the left cylinder 3B by tightly fitting into a bore 14 provided through the bottom to communicate the outside and the cylinder bottom chamber. In this state, of the oil holes 12B and 12C that are vertically spaced apart and penetrated through the side wall of the inner cylinder portion 12A of the valve body 12, the lower oil hole 12C communicates with the port 15 bored in the bottom of the left cylinder 3B. However, an upper oil hole 12B located in a portion of the valve body 12 facing the bottom chamber of the left cylinder 3B communicates with the bottom chamber.

The bottomed cylindrical piston 13 has an outer diameter that is approximately the same as the inner cylindrical portion 12A of the valve body 12, and has an open lower end. 12A to form a chamber, which is used as the flow path 17.

Further, an oil hole 13B is provided through the bottom wall side of the inner cylinder portion 13A of the piston 13, and is in constant communication with the oil hole 12B of the valve body 12. A check ball 19A is provided between the top cover 18 fixed to the top cover 18 and a check ball 19A for opening and closing an orifice 18A provided through the cover 18.
A regulating member 19 consisting of a return spring 19B that urges toward the 8A side, a holder member 19C that holds the ball 19A and the spring 19B, and that itself prevents excessive upward movement of the piston 13 and prevents the piston 13 from chattering. is mediated. In the figure, reference numeral 20 denotes a spring, the upper end of which engages with a step formed in the inner cylindrical portion 13A of the piston 13, and the lower end of which engages with the bottom wall of the inner cylindrical portion 12A of the valve body 12, so that when the piston rod is raised. , valve body 12
The piston 13 is raised to the highest level by the pressure in the flow path 17 and the biasing force of the spring 20, and the port 15 - oil hole 12C - flow path 17 - oil hole 13B - 12
B- Although the hydraulic oil is allowed to freely pass through to the bottom chamber of the left cylinder 3B, the flow rate of the hydraulic oil flowing out from the bottom chamber to the boat 15 becomes abnormally large, and the piston rod of the left cylinder 3B descends at a rate of, for example, 400 mm/
When it exceeds sec, the piston 13 is allowed to descend,
The lower end of the piston 13 is biased to narrow the opening area of the oil hole 12C. In the figure, reference numeral 21 denotes a port, one end of which opens facing the bottom chamber at the bottom of the left cylinder 3B, and the other end communicates with the port 7 formed at the bottom of the right cylinder 3A via a pipe 22.

Continuing to explain the function, the hydraulic pump 25
The hydraulic oil that is pumped from
5 - Oil hole 12C - Flow path 17 - Oil hole 13B of piston 13 - Hydraulic oil that is supplied to the bottom chamber of left cylinder 3B via oil hole 12B of valve body 12 and acts as power to raise the piston rod, and port 21 The hydraulic oil is divided into two. port 2
The hydraulic oil supplied to the valve body 1 enters the piping 22 - the port 7 of the right cylinder 3A - the flow path 4B - 4C, and from there passes through the oil hole 6D of the piston 6 - the inner cylinder part 6F, and is then transferred to the oil in the valve body 4. The hydraulic oil is separated from the hydraulic oil passing through the hole 4E and is supplied to the bottom chamber of the right cylinder 3A.

At this time, the flow resistance from the bottom chamber of the left cylinder 3B to the bottom chamber of the right cylinder 3A is only the pipe resistance, so the bottom chambers of the left and right cylinders 3A and 3B are in almost the same state as a direct connection state. The oil amount in the bottom chambers of left and right cylinders 3A and 3B is equal.
Moreover, since the piston rods of both cylinders 3A and 3B are interconnected at the upper part via the upper beam 2A of the inner mast, both piston rods rise simultaneously and at the same speed.

Next, when the lift switching valve 24 is operated to the lower position,
The hydraulic oil in the bottom chamber of the right cylinder 3A flows through oil hole 4.
E and the inner cylinder part 6F of the piston 6 - the oil hole 6D both enter the flow path 4C, and from this flow path 4B-
Port 7 - Piping 22 - Port 2 of left cylinder 3B
1-Flows down to the bottom chamber of the left cylinder 3B, merges with the hydraulic oil in the bottom chamber of the left cylinder 3B, and flows into oil holes 12B-13B-flow path 17-oil hole 12C-port 15-piping 23-lifting switching valve 24 It is then returned to the tank.

At this time, the piston 13 of the flow control valve A installed in the left cylinder 3B is
The pressure on the A side decreases and a pressure difference occurs between the upper and lower sides of the bottomed wall, so the hydraulic oil in the bottom chamber pushes down the check ball 19A of the regulating member 19 and flows into the upper part of the piston 13 from the orifice 18A. The hydraulic oil pushes the top of the piston 13 downward, but this pressing force is due to the biasing force of the spring 20 located on the lower side of the piston 13 and the oil in the area from the flow path 17 to the elevation switching valve 24. The piston 13 is moved downward until it balances with the sum of the pressures, and the lower end of the piston 13 throttles the oil hole 12C at the bottom of the valve body 12, and the flow rate of the hydraulic oil that returns to the tank is adjusted so that the descending speed of the piston rod is, for example, 400 mm/sec.
Control so that At this time, the flow rate of the hydraulic oil flowing down from the flow path 4B of the right cylinder 3A to the bottom chamber of the left cylinder 3B is controlled by the flow control valve A attached to the left cylinder 3B since both bottom chambers are in communication. Since the control is performed, the inner cylindrical portion 6F of the piston 6 is transferred from the bottom chamber of the right cylinder 3A.
The downward pressing force applied to the bottom wall of the inner cylindrical portion 6F by the hydraulic oil flowing down to the flow path 4B through the piston 6 reaches the point where it moves the piston 6 downward against the biasing force of the spring 8. First, the flow rate flowing down from the flow path 4C to 4B is not obstructed by the lower part of the piston 6.

Therefore, the hydraulic oil flowing down from the bottom chambers of the left and right cylinders 3A and 3B to the tank is controlled by the flow control valve A installed in the left cylinder 3B so that the descending speed of the piston rod is, for example, 400 mm/sec. Since the amount of oil in the bottom chambers of both cylinders is equal, it is possible to obtain a safe lowering speed of the inner mast.

Next, we will discuss the case where the piping 23 that communicates the lift switching valve 24 and the flow control valve A is damaged.The piping 23 is damaged and the amount of oil passing through the oil hole 12C of the valve body 12 becomes abnormally large, causing the piston rod to The descending speed is the set speed, for example 400mm/
sec, the pressure difference between the upper and lower parts of the piston 13 inside the flow control valve A becomes significant, and the only force that urges the piston 13 upwards is the urging force of the spring 20, so the balance of the piston 13 becomes large. Collapse.

Therefore, the regulating member 19 is pushed down by the hydraulic oil in the bottom chamber of the left cylinder 3B, and the piston 13 is moved against the spring 20 so that the spring 2
The piston 13 is rapidly moved downward until the biasing force of 0 and the downward pressing force on the piston 13 match, and the oil hole 12C in the lower part of the valve body 12 is narrowed at the lower end of the piston 13. Oil hole 12C
By controlling the flow rate flowing out to the mast, a sudden descent of the mast is prevented.

Next, we will discuss the case where the piping 22 that connects the left and right cylinders 3A and 3B is damaged. The hydraulic oil in the bottom chamber of the left cylinder 3B is
The hydraulic oil in the right cylinder 3A is controlled by the operation of the down control valve B installed in the right cylinder 3A.

In other words, if the amount of oil passing through the flow path 4B of the valve body 4 becomes abnormally large and the descending speed of the piston rod exceeds a set speed, for example, 500 mm/sec, the inside of the inner cylindrical portion 6F of the piston 6 in the valve B and the piston 6
The pressure difference with the outside becomes significant, and piston 6
Since the force that urges the piston 6 upward is only the urging force of the spring 8, the balance of the piston 6 is lost. This pressure difference causes the piston 6 to move downward against the spring 8, and the shutoff portion 6C of the piston 6 completely closes the flow path 4B of the valve body 4. Therefore, the hydraulic oil flowing out from the bottom chamber of the cylinder 3A has only the path of the inner cylinder part 6F of the piston 6 - the orifice 6E - the flow path 4B, and the diameter of the orifice 6E is such that the lowering speed of the piston rod is, for example, about 200 mm/sec. Since the piston rod is constricted so that the amount of piston rod flowing out from the bottom chamber is controlled, the piston rod of the right cylinder 3A is prevented from descending rapidly.

Therefore, if the lowering of the piston rod of the right cylinder 3A is controlled, all the hydraulic oil in the bottom chamber of the left cylinder 3B will be removed and even if the piston rod tries to descend rapidly, the left and right cylinder rods are connected by the tie beam 2A of the inner mast. The left and right piston rods slowly descend at the same speed in accordance with the descending control of the right cylinder.

This invention has a lift cylinder installed behind each of the left and right masts installed at the front of the vehicle.
In a forklift truck in which both piston rods of the lift cylinder are connected to an inner mast to raise and lower the mast, one of the lift cylinders has a bottom chamber that is not operated at all times, and when the passing flow rate exceeds a set value. A down control valve having an actuated piston is built in, and a flow control valve is built in the bottom chamber of the other lift cylinder, and the flow control valve is set to have a lower flow rate than the normal control flow rate of the down control valve. The bottom chambers of both lift cylinders are connected through piping, and the bottom chamber of the other lift cylinder is connected with piping from an elevation switching valve that switches the elevation of the inner mast, so that both lift cylinders are connected in series. By connecting to the cylinder, two control valves are used, and when the mast is raised or lowered, the bottom chambers of both cylinders are in direct communication even though the hydraulic oil passes through both valves, and they are also connected to the raising and lowering switching valve. Since the flow rate required for raising and lowering is controlled only by the flow control valve on the side, there is no variation in the flow rate into and out of the bottom chamber of both cylinders, and the mast always moves up and down at the same time on the left and right sides, and its flow control valve The lowering speed of the piston rod is controlled by the operation of the piston rod, and safe cargo handling operations are performed.

Furthermore, even if a pipe breakage occurs, the control valve disposed upstream of the broken pipe acts immediately to prevent the piston rod from descending suddenly, thereby avoiding the danger of sudden descent.

In particular, if the piping 22 is damaged, the cylinder 3
The hydraulic oil from the bottom side of cylinder B flows out as it is from the damaged part of the pipe 22, but the hydraulic oil from the bottom side of cylinder 3A suddenly passes through the down control valve, so the piston 6 operates. By exerting the throttling effect of the orifice 6E for the first time, the left and right piston rods can be lowered at a slower speed than normal.

In addition, the flow control valve and down control valve are built into the bottom of the cylinder, allowing for more space on the piping.
This has the effect of reducing external damage as much as possible.

[Brief explanation of the drawing]

FIG. 1 is an explanatory rear view of the mast device, FIG. 2 is an explanatory plan view thereof, FIG. 3 is an explanatory circuit diagram, and FIG. 4 is a sectional view of the main part. 1... Outer mast, 2... Inner mast, 3A... Right cylinder, 3B... Left cylinder, 4, 12... Valve body, 6, 13... Piston, 22, 23... Piping, A... Flow Control valve, B...down control valve.

Claims (1)

[Scope of Claim for Utility Model Registration] A lift cylinder is provided behind a pair of left and right masts installed at the front of the vehicle body, and both piston rods of the lift cylinders are connected to an inner mast to raise and lower the masts. In such a forklift truck, one lift cylinder has a built-in down control valve in the bottom chamber, which is equipped with a piston that does not operate all the time but operates when the passing flow rate exceeds a set value. The chamber has a built-in flow control valve that is set to have a lower flow rate than the normal control flow rate of the down control valve, and the bottom chambers of both lift cylinders are connected through piping, and the bottom chambers of the other lift cylinder are connected to each other through piping. Hydraulic circuit for the lift cylinder of a forklift truck in which both lift cylinders are connected in series by connecting the piping from the lift switching valve that performs lifting/lowering operation of the inner mast to the bottom chamber of the lift cylinder.