JPH06191800A - Cargo shock absorber for forklift - Google Patents

Abstract

PURPOSE:To provide a cargo shock absorber for a forklift wherein giving a shock to a cargo is avoided by providing a shock absorbing relief circuit in a lift cylinder. CONSTITUTION:A relief valve 15 is connected to a lift cylinder 1 through a shock absorbing hydraulic cylinder 10. At the time of inputting a shock, pressure oil in a cylinder chamber of the lift cylinder 1 flows into the first oil chamber 12 of the shock absorbing hydraulic cylinder 10, to move a piston 11 to a side of the second oil chamber 13, and by flowing out pressure oil in the second oil chamber into a tank 6 via the relief valve 15, a pressure of the lift cylinder 1 is suppressed from rising to a preset pressure or more of the relief valve 15, to absorb the shock. When a pressure according to the shock is returned to the original condition, pressure oil of the relief amount is supplied from an oil hydraulic pump 14 to the shock absorbing hydraulic cylinder 10 via a flow control valve 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load cushioning device for a forklift, and more particularly to a device for cushioning a shock applied to a load via a lift cylinder.

[0002]

2. Description of the Related Art In a conventional general forklift, as shown in FIG. 6, by operating an oil control valve 51 with a cargo handling lever, the amount of oil sent from a hydraulic pump 52 to a lift cylinder 53 and from the lift cylinder 53 to a tank 54. The lift amount of the lift cylinder 53 is raised and lowered by controlling the amount of return to each.

[0003]

By the way, in the case of a forklift, a suspension device as found in general passenger cars and trucks is not provided, and the lift cylinder of the forklift is fixed to the frame. ing. In other words, when traveling, the impact from the tire is directly transmitted from the frame to the load through the lift cylinder and the cargo handling device moved up and down by the lift cylinder. Therefore, when traveling on a rough road, there is a possibility that the load may bounce and be damaged or the load may collapse.

In view of the above problems, the present invention provides a load buffering device for a forklift in which a relief circuit for absorbing shock is provided in a lift cylinder to prevent the load from being shocked. This is a technical issue that should be addressed.

[0005]

In order to solve the above problems, the present invention is configured as follows. That is, a load cushioning device for a forklift according to the invention of claim 1 includes a lift cylinder, a hydraulic pump, and a buffering hydraulic cylinder partitioned by a piston into two oil chambers, a first oil chamber and a second oil chamber. A branch line that branches from the middle of the main line from the hydraulic pump to the lift cylinder through the control valve to the first oil chamber of the buffer hydraulic cylinder, and a second oil chamber of the buffer hydraulic cylinder. A relief valve connected via a relief conduit, an oil supply conduit for guiding pressure oil from the hydraulic pump or a separately provided hydraulic pump to the relief conduit, and the hydraulic pump provided in the middle of the oil supply conduit. A flow control valve to control the amount of oil sent from
When the pressure oil in the second oil chamber flows out from the relief valve, an operating means for operating the flow rate control valve to increase the amount of pressure oil to replenish the pressure relief oil to the relief conduit. It is characterized by.

Further, the load cushioning device for a forklift according to the invention of claim 2 is the variable type in which the relief pressure can be adjusted according to the magnitude of the current supplied to the solenoid. And moreover,
A load detection sensor that detects the load acting on the lift cylinder, and a detection signal from the load detection sensor are input, and a solenoid current for adjusting the relief pressure of the relief valve is set so that the relief pressure increases as the load increases. It has a controller for controlling.

Further, a load cushioning device for a forklift according to a third aspect of the present invention is a cushioning device which is partitioned into two oil chambers, a first oil chamber and a second oil chamber, by a lift cylinder, a hydraulic pump and a piston. A hydraulic cylinder, a branch line from the hydraulic pump through a control valve to the lift cylinder, and a branch line that branches from the middle of the main line to the first oil chamber of the buffer hydraulic cylinder, and the magnitude of the current supplied to the solenoid. A relief valve whose relief pressure can be adjusted according to the pressure, a relief pipe line connecting the second oil chamber of the buffer hydraulic cylinder and the relief valve, and pressure oil from the hydraulic pump or a hydraulic pump provided separately. To the relief pipeline, a flow control valve that is provided in the middle of the pipeline to control the amount of oil sent from the hydraulic pump, and pressure oil in the second oil chamber. When flowing out from the relief valve, operating means for operating the flow rate control valve to the increasing side so as to replenish the pressure oil of the outflow to the relief pipe line, and load detection for detecting the load acting on the lift cylinder. A sensor, a speed sensor that detects the traveling speed of the vehicle, and a detection signal from the load detection sensor and the speed sensor are input, and the relief pressure determined in accordance with the magnitude of the load, when the vehicle is stopped. In addition, a controller for controlling a solenoid current for adjusting the relief pressure of the relief valve is provided so as to be low during traveling.

[0008]

In the load cushioning device according to the invention of claim 1 configured as described above, for example, a shock is input from the tire, the pressure in the cylinder chamber of the lift cylinder rises,
When the relief pressure of the relief valve is exceeded, the pressure oil in the cylinder chamber of the lift cylinder flows into the first oil chamber of the buffer hydraulic cylinder to move the piston to the second oil chamber side.
The pressure oil in the second oil chamber flows out to the tank through the relief valve. As a result, the pressure in the cylinder chamber of the lift cylinder is prevented from rising above the relief pressure of the relief valve, and the impact is absorbed.

On the other hand, when the pressure oil in the second oil chamber flows out from the relief valve, the flow control valve is operated to the increasing side by the action of the operating means. Then, the pressure increase due to the impact returns to the original state in a short time, and the relief from the relief valve also stops, so the pressure oil from the hydraulic pump is pumped to the second oil chamber of the buffer hydraulic cylinder via the flow control valve. Then, the piston is moved to the first oil chamber side and returned to the initial position. Therefore, the flow control valve is operated toward the amount reduction side and returns to the original state.

In addition, in the load cushioning device for a forklift according to the invention of claim 2, in addition to the function of absorbing the impact as in the invention of claim 1, the relief pressure of the relief valve is changed at each loading operation. Adjust according to the size of the load acting on the lift cylinder. That is, the pressure in the cylinder chamber of the lift cylinder also changes due to load fluctuations acting on the piston rod during cargo handling work. Therefore, at this time, basically, the same operation as the invention of the above-mentioned claim 1 is performed, but at the time of cargo handling work, the pressure in the cylinder chamber once rises or falls and then stabilizes at that pressure. It is different from temporary pressure fluctuation. Therefore,
Based on the detection signal input from the load detection sensor, the controller determines whether the pressure fluctuation is due to impact or cargo handling work.If it is determined that the pressure fluctuation is due to cargo handling work, the relief pressure of the relief valve is set. The solenoid current of the relief valve is controlled so as to have a value according to the load, that is, the relief pressure increases as the load increases.

Further, in the load cushioning device for a forklift according to the third aspect of the invention, the relief pressure of the relief valve while the vehicle is stopped is based on the relief pressure determined by the detection signal input from the load detection sensor. , And is controlled to a value obtained by adding a high offset value determined based on the detection signal input from the vehicle speed sensor. That is, when the vehicle is stopped, the relief pressure is set to a value sufficiently higher than the pressure in the lift cylinder.
Therefore, during the cargo handling work that is performed while the vehicle is stopped, the excessive effect of the shock absorbing action is avoided.

On the other hand, the relief pressure of the relief valve while the vehicle is traveling is based on the relief pressure determined by the detection signal input from the load detection sensor, and based on the detection signal input from the vehicle speed sensor. It is controlled to a value with the low offset value determined. That is, at this time, since the relief pressure is set to a value close to the pressure in the lift cylinder (higher than the pressure in the cylinder), the shock absorbing action is performed as in the case of the invention of claim 1 described above.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, a first embodiment of the present invention will be described based on FIG. As shown in the figure, a cylinder chamber 1a of a lift cylinder 1 of a forklift is connected to a control valve 2 operated by an operator by a main pipe 3, and the control valve 2 and a hydraulic pump 4 for cargo handling.
Are connected by a discharge line 5, and a control valve 2
And the tank 6 are connected by a return line 7. In FIG. 1, reference numeral 8 denotes a cargo handling device including a fork, a lift bracket, and the like, and a mounting mode of the lift cylinder 1 to the piston rod 1b is schematically shown.
Further, 9 indicates a cargo.

Next, the cargo shock absorber according to this embodiment will be described. The load buffer is a hydraulic cylinder 10 for buffering.
Is provided as a main member, and the buffer hydraulic cylinder 10 is partitioned into two oil chambers, a first oil chamber 12 and a second oil chamber 13, by a piston 11 slidably accommodated in the axial direction. . The first oil chamber 12 is connected to a branch pipe line 14 branched from the main pipe line 3, and the second oil chamber 13 is connected to a relief valve 15 by a relief pipe line 16.

The relief valve 15 is of a variable type in which the relief pressure is adjusted according to the current flowing through the solenoid, and acts on the lift cylinder 1 in the middle of the return pipe 17 from the relief valve 15 to the tank 6. A flow rate sensor 18 as a load detection sensor for detecting a load is provided. The flow rate sensor 18 uses the amount of oil relieved from the relief valve 15 (the lift cylinder 1
(In proportion to the load acting on the valve), the controller 19 outputs an electric signal corresponding to the electric pressure to the controller 19, and the controller 19 responds to the electric signal so that the relief pressure increases as the oil amount increases. It is designed to control the solenoid current for adjustment.

On the other hand, the second of the buffer hydraulic cylinder 10
An oil supply line 20 for introducing pressure oil from the hydraulic pump 4 is connected to a relief line 16 connecting the oil chamber 13 and the relief valve 15, and an external pilot operation is provided in the middle of the oil supply line 20. A formal flow control valve 21 is provided. The flow rate control valve 21 is set so that the flow rate is controlled by the balance between the pilot pressure and the spring 21a, that is, the flow rate is increased as the pilot pressure is lower.

A pilot pressure take-out port 22 is set on the second hydraulic chamber 13 side of the buffer hydraulic cylinder 10 in order to obtain a pilot pressure as an operating means for operating the flow control valve 21. The pilot pressure take-out port 22 is specifically set to a position where the piston 11 is fully opened with the piston 11 moved to the first oil chamber 12 side, and the pilot pressure from the pilot pressure take-out port 22 passes through the pilot conduit 23. After that, it acts on the flow rate control valve 21. A drain pipe 25 having an orifice 24 inserted therein is connected to the pilot pipe 23.

The cargo shock absorber of this embodiment is constructed as described above, and its operation will be described below. Now, when an impact is input from the tire, the pressure in the cylinder chamber 1a of the lift cylinder 1 rises, and along with that, the pressure in the first oil chamber 12 and the second oil chamber 12 of the buffer hydraulic cylinder 10 communicating with it. The pressure in the chamber 13 also increases. And
When the pressure in the second oil chamber 13 exceeds the relief pressure of the relief valve 15, the pressure oil in the second oil chamber 13 flows out to the tank 6 through the relief valve 15, so that the piston 11
Moves to the second oil chamber 13 side. As a result, the pressure in the cylinder chamber 1a of the lift cylinder 1 is suppressed to the relief pressure of the riff valve 15. That is, the lift cylinder 1
The impact exerted on is absorbed by relieving the pressure from the relief valve 15, so that the impact on the cargo 9 loaded on the cargo handling device 8 is avoided.

When the piston 11 is moved to the second oil chamber 13 side and the pilot pressure take-out port 22 is closed, the pilot pressure acting on the flow control valve 21 is reduced,
Since the flow rate control valve 21 is operated to increase the flow rate, the amount of pressure oil sent from the hydraulic pump 4 to the relief pipe 16 is increased. Since the rise of the hydraulic pressure due to the impact ends in a short time, the pressure returns to the original pressure after the piston 11 moves to the second oil chamber 13 side, and the relief from the relief valve 15 also stops. Therefore, the piston 11 is moved to the first oil chamber 12 side by the pressure oil flowing from the hydraulic pump 4 to the second oil chamber 13 side via the flow control valve 21 and the relief pipe line 16, and the pilot pressure take-out port 22 is opened. It
As a result, the pilot pressure acts on the flow rate control valve 21, the flow rate control valve 21 is operated toward the amount reduction side, and the state before the impact is input is restored.

In the above description, the impact is input from the tire. However, when the impact is input from the cargo handling device 8 side, for example, during the cargo handling work, the lift cylinder 1
Although the pressure in the cylinder chamber 1a rises even when the pressure is stopped in the middle of the lowering operation of the load, the shock absorbing action is performed in the same manner as above, and the load 9 can be prevented from being shocked. is there.

On the other hand, the cylinder chamber 1a of the lift cylinder 1
The internal pressure also changes depending on the load (weight of the load 9 and presence / absence of the load 9) acting on the piston rod 1b of the lift cylinder 1 due to the normal cargo handling work. In this case, the pressure in the cylinder chamber 1a of the lift cylinder 1 once rises or falls and then becomes stable at a pressure corresponding to the load, which is different from a temporary hydraulic pressure fluctuation due to an impact. This difference in pressure change appears as a difference in relief flow rate from the relief valve 15. That is, when the pressure temporarily increases due to impact, the relief flow rate temporarily increases and then decreases, but when the pressure increases or decreases due to the load, the relief flow rate keeps increasing or decreases. Will remain.

Since the flow rate sensor 18 detects the relief flow rate and inputs the detection signal to the controller 19, whether or not the pressure fluctuation is temporary, that is, the controller 19 receives the detection signal, that is, the impact. It is determined whether the relief is due to the load fluctuation due to the cargo handling work. When it is determined that the relief is caused by an impact, the relief pressure of the relief valve 15 is not changed, but when it is determined that the relief is caused by a load change, the relief pressure of the relief valve 15 corresponds to the magnitude of the load. The solenoid current is controlled so as to be adjusted to an appropriate value, that is, a larger value as the load increases.

That is, the controller 19 controls the solenoid current of the relief valve 15 each time the load of the lift cylinder 1 changes so that the outflow amount from the relief valve 15 becomes a predetermined constant flow rate. Adjust the relief pressure of 15 to a value according to the load. Thus, according to the cargo shock absorber of this embodiment,
It is possible to absorb the impact input from the tire or the like under the relief pressure corresponding to the load and prevent the impact from affecting the load.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the flow sensor 1 is used as a load detection sensor for detecting the load acting on the lift cylinder 1.
The pressure sensor 26 is used instead of 8. That is, the pressure in the cylinder chamber 1a of the lift cylinder 1 is detected by the pressure sensor 26.
When the detection signal of the pressure sensor 26 is input to the controller 19, the controller 19 responds to the pressure of the cylinder chamber 1a only when it determines that the pressure of the cylinder chamber 1a is stable based on the detection signal. Then, the solenoid current of the relief valve 15 is controlled.

Since the other structures are the same as those of the above-mentioned embodiment, the same reference numerals are given and the description thereof will be omitted. Therefore, in the load cushioning device of the present embodiment configured as described above, only the load detecting action for adjusting the relief pressure of the relief valve 15 is different, and the relief pressure adjusting action and impact input of the relief valve 15 are different. The shock absorbing action at that time is performed in exactly the same manner as in the first embodiment.

Next, a third embodiment of the present invention will be described with reference to FIG. In the load buffering device of the above-described first and second embodiments, the shock absorbing action is sufficiently performed while the vehicle is stopped because the shock absorbing action is performed in both the stopped state and the running state of the vehicle. When the tuning is performed, the shock absorbing effect is exerted more than necessary even during the cargo handling operation, and it may be rather difficult to perform the cargo handling operation during the detailed cargo handling work.

Therefore, in the third embodiment, in consideration of the operability during the above-described cargo handling work, the shock absorbing action is prevented from being overly effective during the cargo handling work. Therefore, in this embodiment, the load acting on the lift cylinder 1 is detected by a load sensor (the pressure sensor 26 is shown in this embodiment, but the flow sensor 18 shown in the first embodiment may be used). In addition to doing, the vehicle speed sensor 27
The traveling speed of the vehicle is detected by the two sensors 2
The detection signals 6 and 27 are input to the controller 19. As the vehicle speed sensor 27, for example, a rotation detector that detects rotation of a differential or a gear of a transmission is used.

The controller 19 presets the relief pressure corresponding to the signal from the pressure sensor 26, that is, the relief pressure corresponding to the magnitude of the load, corresponding to the vehicle speed calculated based on the signal from the vehicle speed sensor 27. The solenoid current of the relief valve 15 is controlled so that the relief value of the relief valve 15 is applied with the offset value thus obtained. That is, the control is performed such that the relief pressure of the relief valve 15 becomes high while the vehicle is stopped (including low speed traveling) and becomes low while the vehicle is traveling. Therefore, the offset value is shown in FIG. Thus, it is set to a high value when the vehicle is stopped and a low value when the vehicle is running.

Therefore, in this embodiment, since the offset value is high while the vehicle is stopped, the relief pressure of the relief valve 15 is the cylinder chamber 1a of the lift cylinder 1.
It will be controlled to a value sufficiently higher than the pressure inside,
Excessive effect of shock absorption during cargo handling work is avoided and operability is improved. On the other hand, since the offset value is set low while the vehicle is traveling, the relief pressure is controlled to a value close to the pressure in the cylinder chamber 1a,
At this time, the same operation as in the above-described first embodiment can be performed to sufficiently absorb the shock generated during traveling.

As shown in FIG. 5, the offset value described in the third embodiment is set to be high when the vehicle is stopped and low in the low-speed traveling range. By setting it so that it is slightly higher than the low-speed range when it exceeds the range, for example, about 10 km / h, it absorbs only comparatively large impacts during high-speed running, and stabilizes the load. It is also possible to make an important setting.

In the illustrated embodiment, a case where the cargo handling hydraulic pump 4 is used as a hydraulic pump for replenishing the second oil chamber 13 of the buffer hydraulic cylinder 10 with pressurized oil is explained. Instead of this, it is possible to change to a configuration using a separately provided dedicated pump (small pump). Also,
The operation means of the flow rate control valve 21 is not limited to the operation method by the pilot pressure shown in the figure. For example, the operation method of the flow rate control valve 21 is electromagnetic, while the piston 11 is provided with a rod protruding outside the cylinder body. It is also possible to mount the sensor and appropriately detect the movement of the rod to the second oil chamber 13 side by a sensor, and to operate the flow rate solenoid valve 21 to increase the amount at the time of detection. Any means can be used as long as it can be operated so as to replenish the pressure oil flowing out from the relief valve 15 when the shock absorbing hydraulic cylinder 10 absorbs the shock.

[0032]

As described in detail above, according to the load cushioning device of the present invention, when a shock is input during traveling, the shock is absorbed by relieving the pressure in the cylinder chamber of the lift cylinder, and the shock is absorbed. It is possible to prevent the cargo from collapsing and prevent the cargo from collapsing or breaking. Therefore, the safety and workability are improved and the occupant's fatigue is greatly reduced.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing a cargo shock absorber according to a first embodiment of the present invention.

FIG. 2 is a hydraulic circuit diagram showing a cargo shock absorber according to a second embodiment of the present invention.

FIG. 3 is a hydraulic circuit diagram showing a cargo shock absorber according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of an offset value according to the third embodiment.

FIG. 5 is an explanatory diagram showing an example of changing an offset value setting according to a third embodiment.

FIG. 6 is a hydraulic circuit diagram of a conventional lift cylinder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Lift cylinder 2 ... Control valve 3 ... Main line 4 ... Hydraulic pump 8 ... Cargo handling device 10 ... Buffer hydraulic cylinder 11 ... Piston 12 ... First oil chamber 13 ... Second oil chamber 14 ... Branch line 15 ... Relief valve 16 ... Relief pipeline 18 ... Flow rate sensor 19 ... Controller 21 ... Flow rate control valve 22 ... Pilot pressure extraction port 23 ... Pilot pipeline 26 ... Pressure sensor 27 ... Vehicle speed sensor

Claims (3)

[Claims] 1. A lift cylinder, a hydraulic pump, a buffer hydraulic cylinder partitioned by a piston into two oil chambers, a first oil chamber and a second oil chamber, and a lift from the hydraulic pump via a control valve. A branch pipe branching from the middle of the main pipe leading to the cylinder and communicating with the first oil chamber of the buffer hydraulic cylinder, and a relief valve connected to the second oil chamber of the buffer hydraulic cylinder via a relief pipe. An oil supply conduit for guiding pressure oil from the hydraulic pump or a separately provided hydraulic pump to the relief conduit, and a flow control valve provided in the middle of the oil supply conduit for controlling the amount of oil sent from the hydraulic pump And, when the pressure oil in the second oil chamber flows out from the relief valve, operating means for operating the flow rate control valve to the increasing side so as to replenish the relief pipe with the pressure oil that flows out. Ta pho Clift load buffer device. 2. A load detection sensor, wherein the relief valve is a variable type whose relief pressure can be adjusted according to the amount of current supplied to a solenoid, and which detects a load acting on the lift cylinder. The load buffer for a forklift according to claim 1, further comprising a controller that receives a detection signal from a load detection sensor and controls a solenoid current for adjusting a relief pressure of the relief valve so that a relief pressure increases as a load increases. apparatus. 3. A lift cylinder, a hydraulic pump, a buffer hydraulic cylinder partitioned by a piston into two oil chambers, a first oil chamber and a second oil chamber, and a lift from the hydraulic pump via a control valve. A branch line that branches from the middle of the main pipe leading to the cylinder and communicates with the first oil chamber of the buffer hydraulic cylinder; and a relief valve whose relief pressure can be adjusted according to the amount of current supplied to the solenoid.
A relief pipe line connecting the second oil chamber of the buffer hydraulic cylinder and the relief valve, an oil supply pipe line for guiding pressure oil from the hydraulic pump or a separately provided hydraulic pump to the relief pipe line, and this oil supply line A flow rate control valve that is provided in the middle of the pipeline to control the amount of oil sent from the hydraulic pump, and when the pressure oil in the second oil chamber flows out from the relief valve, the pressure oil that flows out is An operating means for operating the flow rate control valve toward the increasing side to replenish the relief pipeline, and a load detection sensor for detecting a load acting on the lift cylinder,
A speed sensor for detecting the traveling speed of the vehicle, the detection signal from the load detection sensor and the speed sensor is input, and the relief pressure determined corresponding to the magnitude of the load is
A load shock absorber for a forklift, comprising: a controller that controls a solenoid current for adjusting the relief pressure of the relief valve so that the pressure is high when the vehicle is stopped and low when the vehicle is running.