JP2887634B2 - Hydraulic equipment for cargo handling vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic device for a cargo handling vehicle, and more particularly, to a hydraulic device capable of saving energy and the like.

[0002]

2. Description of the Related Art Conventionally, in a cargo-handling vehicle that performs various cargo-handling operations using the output of a hydraulic cylinder, for example, a battery-powered forklift, generally, as shown in FIG.
When the cargo handling lever 3 is operated, the cargo handling switch 4 detects the tilting operation of the cargo handling lever 3, and the controller 20 rotates the electric motor 8 connected to the hydraulic pump 7 at a constant voltage.

However, when the load W is raised, if the cargo handling lever 3 is continuously operated even after the piston rod 1A of the hydraulic cylinder 1 reaches the stroke end, the pressure in the pipelines 12, 13 increases. The relief valve 5 is usually connected to the pipe 12 because the hydraulic equipment is damaged or the pipe ruptures. When the pressure in the pipeline 12 exceeds a predetermined relief set pressure, the relief valve 5 communicates the pipeline 12 with the drain pipeline 14 to return the hydraulic oil to the tank T and prevent the pressure from rising. doing.

When the cargo handling lever 3 is tilted upward to raise the piston rod 1A, the cargo handling switch 4 is first turned on to rotate the electric motor so that the load W does not drop. The control valve 2 is configured to mechanically open the connection between the control valve 2 and the pipe 13. Conversely, when the loading lever 3 is returned to the neutral position while the piston rod 1A is being lifted, first, the load W is not dropped so that the load W does not fall.
The control valve 2 mechanically shuts off the pipeline 12 and the pipeline 13, and then the loading switch 4 linked to the loading lever 3 is turned off and the electric motor 8 stops. As described above, when the control valve 2 is closed in spite of the rotation of the electric motor 8, the pressure in the pipeline 12 increases, and the relief valve 5 is opened as described above.

[0005]

However, such a conventional configuration has the following problems. That is,
Even after the piston rod 1A reaches the stroke end, if the cargo handling lever 3 is operated, the electric motor is driven to rotate at a constant voltage. Loss.

Further, as described above, every time the cargo handling lever 3 is returned to the neutral position from the state during the cargo handling operation, the same problem as described above occurs.

Further, when it is desired to slightly raise the piston rod 1A, the loading / unloading lever 3 is slightly moved to reduce the flow passage area of the control valve 2. That is, since the pressure in the pipeline 12 (on the hydraulic pump side) increases, the flow rate of the hydraulic oil passing through the flow path of the control valve 2 increases, and as a result, the fine adjustment operation of the piston rod 1A is difficult. There is.

In addition, when the hydraulic oil passes through the relief valve 5, there is a problem that heat is generated due to mechanical loss and decompression loss, thereby changing the viscosity characteristics of the hydraulic oil.

The present invention has been made in view of the above circumstances, and has as its object to reduce energy consumption by reducing useless rotation of an electric motor, and to reduce the pressure of a relief valve set by a relief valve. It is an object of the present invention to provide a hydraulic device for a cargo handling vehicle capable of controlling pressure in a road and preventing heat generation of hydraulic oil.

[0010]

SUMMARY OF THE INVENTION The present invention provides a hydraulic cylinder for moving a cargo handling device capable of performing a cargo handling operation, an electric motor connected to a hydraulic pump, a switching unit for rotating the electric motor, and a hydraulic pipeline. A pressure sensor capable of detecting the pressure inside the pressure sensor, and a control unit which receives a hydraulic signal of the pressure sensor as an input. The control unit includes a target pressure at which the pressure in the hydraulic line does not exceed the relief set pressure of the relief valve. And a gate signal corresponding to the chopper conductivity is output to the switching unit.

[0011]

According to the present invention, when an arbitrary reference pressure lower than the relief set pressure of the relief valve 5 (hereinafter simply referred to as "relief pressure") is set as the target pressure and the cargo handling lever 3 is operated, The electric motor 8 connected to the hydraulic pump 7 is servo-controlled so that the pressure in the hydraulic circuit becomes equal to the target pressure.

Accordingly, the pressure in the hydraulic circuit is maintained at the target pressure, does not exceed the relief pressure, it is possible to prevent unnecessary pressure increase in the pipeline, and energy saving can be achieved. Moreover, because the hydraulic oil does not pass through the relief valve,
It can also prevent an increase in oil temperature.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a conceptual diagram of the present invention,
The hydraulic cylinder 1 that moves the load W up and down is connected to the hydraulic pump 7 via the pipe 13, the control valve 2, and the pipe 12.

The hydraulic pump 7 has an electric motor 8 as a drive source.
Are connected, and in this example, the motor 8 is a DC series motor. Further, the motor 8 is provided with a rotation speed detector 9 including an encoder or the like capable of detecting the rotation speed.

A pressure sensor 6 capable of detecting the pressure in the pipe 12 is inserted and connected to the pipe 12, and a relief valve 5 is connected thereto. When the pressure in the pipe 12 exceeds a preset relief pressure, the relief valve 5 opens the passage between the pipe 12 and the pipe 14 and returns the hydraulic oil to the tank T.

Normally, the control valve 2 is maintained at a neutral position by a spring. However, when the operator operates the operation lever 3, the control oil is delivered to the hydraulic cylinder 1.
Also, it can be discharged from the hydraulic cylinder 1. In this example, a loading / unloading switch 4 is provided which can detect an operation of supplying hydraulic oil to the hydraulic cylinder 1, that is, an operation of the operation lever 3 for switching the control valve 2 to the port A.

The detection signal of the cargo handling switch 4, the rotation speed signal of the rotation speed detector 9 and the pressure signal of the pressure sensor 6 are
Each is input to the control unit 10. The control unit 10 includes a calculation unit and a storage unit (both not shown),
Based on each of the input signals, a predetermined chopper conductivity is determined in accordance with a predetermined procedure, and a gate signal corresponding to the chopper conductivity is output to a switching unit 11 composed of a transistor or the like. Is driven to rotate.

The processing procedure of the present invention configured as described above will be described with reference to the flow chart shown in FIG. 2. First, the rotational speed of the electric motor 8 is read from the rotational speed detector 9 (S1). The actual angular acceleration of the electric motor 8 is calculated by second-order differentiation (S2).

Next, it is determined whether the cargo handling switch 4 is in the ON state, that is, whether the operating lever 3 is currently operated by the operator (S3). If the determination is negative, the chopper conductivity is reduced. All are turned off (S7), and this is output to the switching unit 11 (S6).

When the cargo handling switch 4 is on, the pressure in the pipe 12 is input from the pressure sensor 6 (S
4) The chopper conductivity is determined as follows based on the actual angular acceleration of the electric motor 8 obtained in step 2 and the pressure in the pipeline 12, and a gate signal corresponding to the chopper conductivity is converted to a switching unit 11 as follows. (S5, S6).

The relationship shown in FIGS. 3 and 4 is stored in the control unit 10 in advance. First, in the graph shown in FIG. 3, the vertical axis represents the target angular acceleration of the electric motor 8, and the horizontal axis represents the pressure in the pipeline 12. Here, the value "PS" on the horizontal axis is the relief pressure of the relief valve 5, "P1".
Indicates a target pressure in the pipeline 12, and the target pressure "P1" is lower than the relief pressure and can be arbitrarily set within a range in which the maximum load of the hydraulic cylinder 1 can be handled. It is.

The target angular acceleration increases as the pressure in the pipeline 12 decreases, and becomes zero at the target pressure "P1".
Exceeding this range, the range up to the relief pressure is negative angular acceleration.

Further, in the graph shown in FIG. 4, the vertical axis represents the amount of change in the chopper conductivity, and the horizontal axis represents the deviation between the target angular acceleration and the angular acceleration actually calculated from the rotation speed of the motor 8. I have. Also, this graph shows that the larger the deviation is, the larger the change amount of the current chopper conductivity is.
If the deviation is zero, the amount of change in the chopper conductivity is zero, so that the chopper conductivity remains unchanged and does not change.

First, a target angular acceleration of the motor 8 is calculated from the current pressure in the pipeline 12 based on each of the above graphs. Next, a deviation between the target angular acceleration and the angular acceleration actually calculated is calculated, a change amount of the chopper conductivity according to the deviation is obtained, and the change amount is added to the current chopper conductivity, The final chopper conductivity is set, and a gate signal corresponding to the chopper conductivity is output to the switching unit 11 (S6).

Therefore, if the deviation is large, the amount of change in the chopper conductivity is also large, and if the deviation is zero, the chopper conductivity is maintained as it is, as described above, and does not change.

Although described in detail above, it is needless to say that the present invention is not limited to the above-described embodiment, but can be variously modified without departing from the gist of the present invention.

[0027]

According to the present invention, as a result of employing the above configuration,
The pressure in the hydraulic line is controlled so that it is always maintained at a target pressure smaller than the relief pressure.Therefore, the pressure in the hydraulic line does not exceed the relief pressure. obtain. In particular, even when the cargo handling operation lever is operated after the piston rod has reached the stroke end, or when the cargo handling operation lever is returned to neutral from the state during the cargo handling operation, the pressure in the pipeline is not increased. As a result, the pressure in the pipeline is not unnecessarily increased to open the relief valve as in the related art.

Further, when it is desired to slightly raise the piston rod, the pressure in the pipe upstream of the control valve increases even if the cargo handling operation lever is slightly moved to narrow the flow passage area of the control valve. Therefore, the flow rate of the hydraulic oil passing through the flow path of the control valve does not increase, and the fine adjustment of the piston rod can be facilitated.

Further, since the hydraulic oil does not pass through the relief valve, it is possible to prevent the hydraulic oil from generating heat due to mechanical loss and pressure reduction loss, and to solve the problem of changing the viscosity characteristics of the hydraulic oil.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing one embodiment of the present invention.

FIG. 2 is a flowchart showing an embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a pipe pressure and a target angular acceleration.

FIG. 4 is a graph showing a relationship between a deviation between a target angular acceleration and an actual angular acceleration and a change amount of a chopper conductivity.

FIG. 5 is a conceptual diagram for explaining a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hydraulic cylinder 2 Control valve 3 Operation lever 4 Cargo handling switch 5 Relief valve 6 Pressure sensor 7 Hydraulic pump 8 Electric motor 9 Revolution detector 10 Control part 11 Switching part 12 Pipe line 13 Pipe line 14 Drain pipe

Claims (1)

(57) [Claims] 1. A hydraulic cylinder for moving a cargo handling implement capable of performing a cargo handling operation, an electric motor connected to a hydraulic pump, a switching unit for rotating the electric motor, and a pressure capable of detecting a pressure in a hydraulic pipeline. And a control unit that receives a hydraulic signal of the pressure sensor as an input. The control unit determines the chopper conduction rate so that the pressure in the hydraulic pipeline does not exceed the relief set pressure of the relief valve. And a gate signal corresponding to the chopper conductivity is output to the switching unit.