JP2000229794A - Controller for lift cylinder of fork lift truck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform the optimum control of a lift cylinder in accordance with a load condition. SOLUTION: In a controller for a lift cylinder of a fork lift truck, a load pressure of a lift cylinder 3 detected by a load detection means 10 when a lift rises in the lift cylinder 3 is stored in a controller 9 in advance, and a signal which is generated based on an operation amount of a lift operation lever 11 and is obtained by adding coefficient of load corresponding to the load pressure of the lift cylinder 3 when the lift rises which is stored in advance when the lift lowers in the lift cylinder 3 and the load pressure of the lift cylinder 3 detected by the load detection means 10 becomes a set pressure of a relief valve 12 is output to a proportional electromagnetic valve 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for controlling a lift cylinder in a forklift truck.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 1, in a lift cylinder 3 for moving a fork 1 up and down via a chain 2, a control device for controlling the lift cylinder 3 is as follows. The hydraulic circuit 4 includes a hydraulic pump 6 for discharging hydraulic oil from a hydraulic tank 5, a pump motor 7 for driving the hydraulic pump 6, and a hydraulic pump 6 for discharging hydraulic oil from the hydraulic pump 6. A proportional solenoid valve 8 is provided which regulates the flow rate and supplies a desired flow rate to the lift cylinder 3 to raise and lower the lift.

[0003] The proportional solenoid valve 8 is moved at a raised position U, a stopped position N, and a lowered position D by moving a spool by a solenoid A and a solenoid B based on an input signal. Then, the lift of the lift cylinder 3 is stopped, the lift is stopped, and the lift is lowered by changing the flow rate of the hydraulic oil. The solenoids A and B are connected to a controller 9 and are controlled by receiving signals from the controller 9.

In the hydraulic circuit 4, a load detecting means 10 is provided between the proportional solenoid valve 8 and the lift cylinder 3, and the load detecting means 10 is a pressure sensor for detecting the load pressure of the lift cylinder 3. Thus, the presence or absence of a load on the fork 1 and the load state as the weight of the load are detected from the load pressure. The load detecting means 10 is connected to the controller 9 and detects the lift cylinder 3 detected by the load detecting means 10.
Is input to the controller 9.

The controller 9 is connected to a lift operation lever 11 installed in the cab of the vehicle body,
An operation amount of the lift operation lever 11 is input, and a signal based on the input operation amount of the lift operation lever 11 and taking into account a load coefficient corresponding to the load pressure of the lift cylinder 3 detected by the load detection means 10 is proportionally calculated. The output is output to the solenoid A or the solenoid B of the solenoid valve 8, and by controlling the proportional solenoid valve 8, lift lifting, lift stop, and lift lowering of the lift cylinder 3 are controlled. In addition, as a method of taking into account the load coefficient according to the load pressure of the lift cylinder 3 in the signal, first, assuming that the maximum output value when no load is applied to the proportional solenoid valve 8 is 100%, when the rated load is applied, α% (α <100), and the maximum descent speed under load is the same as that under no load. Alternatively, β% is set so that the speed is set in advance for each load. Second,
When the lift operation lever 11 is suddenly operated, output is not performed in accordance with the operation amount of the lift operation lever 11, and control is performed so that the output rise time does not fall below a certain value. Suddenly when there is no load, and gradually when there is a rated load. In addition, the first or second,
For a load between no load and rated load, a coefficient corresponding to the load may be taken.

In the hydraulic circuit 4, a relief valve 12 is provided between the proportional solenoid valve 8 and the hydraulic pump 6.
The pressure in the hydraulic circuit 4 is maintained at a set pressure. Note that the relief valve 12 may be built in the proportional solenoid valve 8.

[0007]

In such a conventional lift cylinder control apparatus, the controller takes into account a load coefficient based on the operation amount of the lift operation lever and according to the load pressure of the lift cylinder detected by the load detection means. The output signal is output to a proportional solenoid valve to control the lift cylinder.

In such control of the lift cylinder, for example, when the lift is performed by supplying pressure oil to the lift cylinder and the lift reaches the end, that is, the upper end of the lift cylinder, the pressure increases in the hydraulic circuit. Then, the pressure is maintained at the set pressure by the relief valve. And
When the lift is lowered from this state, the load pressure of the lift cylinder does not drop suddenly, so that the load pressure of the lift cylinder remains at the pressure set by the relief valve. Therefore, an accurate load state cannot be detected from the load pressure of the lift cylinder, and when the lift is lowered from the upper end, there is a possibility that control according to the load state cannot be performed. Specifically, when the lift is lowered from the upper end when there is no load, the load pressure of the lift cylinder remains at the pressure set by the relief valve, so that it is determined that there is a load, and the control is performed in accordance with the load. When the load coefficient according to the load pressure of the lift cylinder is the first one, the problem that the maximum speed is greatly reduced occurs, and the load coefficient according to the load pressure of the lift cylinder described above occurs. If the method of adding is the second method, the problem arises that the rise time of the output is delayed and agility is deteriorated. An object of the present invention is to solve these problems.

[0009]

According to the present invention, there is provided a hydraulic pump for discharging hydraulic oil, the flow rate of hydraulic oil discharged from the hydraulic pump is regulated, and a desired flow rate is supplied to a lift cylinder to lift the hydraulic oil. A proportional solenoid valve for lowering the lift and a load detecting means for detecting the load pressure of the lift cylinder are provided, and the operation of the lift operating lever in consideration of a load coefficient corresponding to the load pressure of the lift cylinder detected by the load detecting means. In a lift cylinder control device for a forklift truck having a controller that outputs a signal based on the amount to a proportional solenoid valve and controls the operation of the proportional solenoid valve,
In the controller, the load pressure of the lift cylinder detected by the load detecting means when the lift of the lift cylinder is raised is stored in advance, and when the lift of the lift cylinder is lowered, the load pressure of the lift cylinder detected by the load detecting means is stored in the relief valve. When the value becomes equal to or more than a certain value that can be regarded as the set pressure of the lift solenoid valve, a signal based on the operation amount of the lift operation lever in consideration of the load coefficient according to the load pressure of the lift cylinder when the lift is lifted in advance is added to the proportional solenoid valve. A lift cylinder control device for a forklift truck.

[0010]

According to the present invention, when the lift in the lift cylinder is lifted and the lift is lowered from the state in which the lift cylinder reaches the upper end, for example, the pressure increases in the hydraulic circuit, and the pressure is increased to the set pressure by the relief valve. Even if it is held, the load state of the lift cylinder at the time of lift lift stored in advance can be used to accurately detect the load state,
By outputting to the proportional solenoid valve a signal that takes into account the load coefficient corresponding to the load pressure of the lift cylinder when this lift is lifted, even when the lift is lowered from the upper end of the lift cylinder, the optimum lift suitable for the load condition Control of the cylinder becomes possible.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a control apparatus for a lift cylinder of a forklift truck according to the present invention will be described. As in the prior art, as shown in FIG. 1, in a lift cylinder 3 that moves a fork 1 up and down via a chain 2, a control device for controlling the lift cylinder 3 first includes a hydraulic circuit that operates the lift cylinder 3. The hydraulic circuit 4 includes a hydraulic pump 6 that discharges hydraulic oil from a hydraulic tank 5, a pump motor 7 that drives the hydraulic pump 6, and regulates the flow rate of hydraulic oil discharged from the hydraulic pump 6. A proportional solenoid valve 8 is provided to supply a desired flow rate to the lift cylinder 3 to raise and lower the lift.

The proportional solenoid valve 8 moves a spool by a solenoid A and a solenoid B based on an input signal, so as to supply hydraulic oil to the bottom side of the lift cylinder 3, a rising position U, and a flow of hydraulic oil. At the stop position N at which the hydraulic oil flows from the bottom side of the lift cylinder 3 to the stop position N at which the hydraulic oil flows into the hydraulic tank 5, and changes the flow direction of the hydraulic oil and the flow rate of the hydraulic oil. And lift lift in the lift cylinder 3;
Stop the lift and lower the lift. The solenoids A and B are connected to a controller 9 and are controlled by receiving signals from the controller 9.

In the hydraulic circuit 4, a load detecting means 10 is provided between the proportional solenoid valve 8 and the lift cylinder 3, and the load detecting means 10 is a pressure sensor for detecting the load pressure of the lift cylinder 3. Thus, the presence or absence of a load on the fork 1 and the load state as the weight of the load are detected from the load pressure. The load detecting means 10 is connected to the controller 9 and detects the lift cylinder 3 detected by the load detecting means 10.
Is input to the controller 9.

The controller 9 is connected to a lift operation lever 11 installed in the cab of the vehicle body,
An operation amount of the lift operation lever 11 is input, and a signal based on the input operation amount of the lift operation lever 11 and taking into account a load coefficient corresponding to the load pressure of the lift cylinder 3 detected by the load detection means 10 is proportionally calculated. The output is output to the solenoid A or the solenoid B of the solenoid valve 8, and by controlling the proportional solenoid valve 8, lift lifting, lift stop, and lift lowering of the lift cylinder 3 are controlled.

In the hydraulic circuit 4, a relief valve 12 is provided between the proportional solenoid valve 8 and the hydraulic pump 6.
The pressure in the hydraulic circuit 4 is maintained at a set pressure. Note that the relief valve 12 may be built in the proportional solenoid valve 8.

In the lift cylinder control device as described above, the controller 9 includes the lift cylinder 3
The load pressure of the lift cylinder 3 detected by the load detection means 10 at the time of lifting of the lift in the above is stored in advance, and when the lift of the lift cylinder 3 is lowered, the load pressure of the lift cylinder 3 detected by the load detection means 10 is stored in the relief valve 12. When the lift exceeds a certain value that can be regarded as the set pressure, specifically, exceeds a predetermined value (exceeds a value slightly lower than the relief pressure), the lift stored in advance is increased. And outputs a signal to the proportional solenoid valve 8 based on the operation amount of the lift operation lever 11 taking into account a load coefficient corresponding to the load pressure of the lift cylinder 3.

In general, the controller 9 calculates a command value based on the input operation amount of the lift operation lever 11 as described above, and calculates the load value of the lift cylinder 3 from the input load pressure of the lift cylinder 3. A load coefficient corresponding to the pressure is calculated, and a final command value is calculated by adding a load coefficient corresponding to the load pressure of the lift cylinder 3 to a command value based on the operation amount of the lift operation lever 11 calculated earlier. Proportional solenoid valve 8 with final command value as signal
Will be output to On the other hand, when the lift of the lift cylinder 3 rises, the controller 9 always stores the load pressure of the lift cylinder 3 input from the load detection means 10 from the present time to a time before the predetermined time t1, and this is always repeated. Then, as shown in FIG. 2, when the load pressure of the lift cylinder 3 detected by the load detecting means 10 becomes equal to or more than a certain value which can be regarded as the set pressure of the relief valve 12, the controller moves the lift cylinder 3 to the upper end. And a predetermined time t from the present time (when the set pressure is reached).
The load pressure of the lift cylinder 3 (at the time of lifting the lift) input from the load detection means 10 just before is stored as the final load pressure. From this state, when the lift of the lift cylinder 3 is lowered, a command value based on the input operation amount of the lift operation lever 11 is calculated, and the load of the lift cylinder 3 detected by the current load detection means 10 which is normally performed at the time is described. Without using the pressure (in this case, the set pressure of the relief valve 12), a load coefficient corresponding to the load pressure of the lift cylinder 3 is calculated from the pre-stored final load pressure (when the lift is raised). A final command value is calculated by adding a load coefficient corresponding to the load pressure of the lift cylinder 3 calculated from the pre-stored final load pressure to the command value based on the operated amount of the lift operation lever 11 and the calculated final command. The value is output to the proportional solenoid valve 8 as a signal.

Thus, when the lift in the lift cylinder 3 is lifted and the lift is lowered from the state in which the lift cylinder 3 has reached the upper end, for example, the pressure increases in the hydraulic circuit 4 and the set pressure is set by the relief valve 12. Even if the load pressure is held at the predetermined time t1, the load pressure of the lift cylinder 3 input from the load detection means 10 (at the time of lift rise) input from the load detection means 10 a predetermined time t1 before the present time (when the set pressure is reached) is accurately stored. The load state can be detected, a load coefficient corresponding to the load pressure of the lift cylinder 3 at the time of the lift rise is calculated, and a signal taking this into account is output to the proportional solenoid valve 8. Even when the lift is lowered from the upper end, it is possible to control the lift cylinder 3 optimally according to the load condition.

Next, another embodiment of the control apparatus for a lift cylinder of a forklift truck according to the present invention will be described. Each configuration is the same as that of the above-described embodiment, but the load pressure of the lift cylinder 3 detected by the load detecting means at the time of lift lifting stored in the controller 9 in advance is different from that of the above-described embodiment.

When the lift of the lift cylinder 3 is lifted, the controller 9 stores the load pressure of the lift cylinder 3 input from the load detecting means 10 after a predetermined time t2 has elapsed since the start of the lift. Is rewritten each time is repeated. Then, as shown in FIG. 3, the lift cylinder 3
Controller 9 determines that the lift cylinder 3 has reached the upper end when the load pressure of the relief valve 12 reaches the set pressure of the relief valve 12, and the lift cylinder 3 input from the load detection means 10 at a lapse of a predetermined time t2 from the start of rising. Is stored as the final load pressure (when the lift is raised). In this state, when the lift of the lift cylinder 3 is lowered, a command value based on the input operation amount of the lift operation lever 11 is calculated, and the current load detection means 1 which is normally performed at the normal time is used.
Without using the load pressure of the lift cylinder 3 detected at 0 (in this case, the set pressure of the relief valve 12), the load pressure of the lift cylinder 3 is changed from the previously stored final load pressure (at the time of lifting the lift). Command value based on the operation amount of the lift operation lever 11 calculated previously, and a final command value in which a load coefficient corresponding to the load pressure of the lift cylinder 3 calculated from the previously stored final load pressure is added to the command value based on the operation amount of the lift operation lever 11 calculated previously. And outputs the calculated final command value to the proportional solenoid valve 8 as a signal.

Thus, when the lift in the lift cylinder 3 is lifted and the lift is lowered from the state in which it reaches the upper end of the lift cylinder 3, the pressure rises in the hydraulic circuit 4, and the set pressure is set by the relief valve 12. Even if it is held, the load state of the lift cylinder 3 (at the time of lift rise) input from the load detection means 10 at the lapse of the predetermined time t2 from the rise start time stored in advance, and the accurate load state is detected. Calculate the load coefficient according to the load pressure of the lift cylinder 3 at the time of lifting the lift,
By outputting a signal taking this into account to the proportional solenoid valve 8,
Even when the lift is lowered from the upper end of the lift cylinder 3, it is possible to optimally control the lift cylinder 3 according to the load state.

[0022]

When the lift in the lift cylinder is lifted and the lift is lowered from the state in which the lift cylinder reaches the upper end, the pressure increases in the hydraulic circuit, for example.
Even if the pressure is held at the set pressure by the relief valve, the load state of the lift cylinder at the time of lift lift stored in advance can accurately detect the load state, and the load pressure of the lift cylinder at the time of lift lift can be detected. By outputting a signal taking into account the corresponding load coefficient to the proportional solenoid valve, even when performing a lift down from the upper end of the lift cylinder, it is possible to control the lift cylinder optimally according to the load condition,
Workability and operability can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a control device of a lift cylinder of a forklift truck.

FIG. 2 is a chart for explaining control by a controller in the lift cylinder control device of the present invention.

FIG. 3 is a table illustrating another control by the controller in the control device for the lift cylinder of the present invention.

[Description of Signs] 1 ... Fork, 2 ... Chain, 3 ... Lift Cylinder, 4
... Hydraulic circuit, 5 ... Hydraulic tank, 6 ... Hydraulic pump, 7 ... Pump motor, 8 ... Proportional solenoid valve, 9 ... Controller, 10
... load detection means, 11 ... lift operation lever, 12 ... relief valve.

Claims (1)

[Claims] 1. A hydraulic pump 5 for discharging hydraulic oil,
By regulating the flow rate of the hydraulic oil discharged from the hydraulic pump 5 and supplying a desired flow rate to the lift cylinder 3, the lift
It is provided with a proportional solenoid valve 8 for lowering the lift, and a load detecting means 10 for detecting the load pressure of the lift cylinder 3.
A lift cylinder of a forklift truck including a controller 9 for controlling the operation of the proportional solenoid valve 8 by outputting a signal based on the amount of operation of the lift operating lever 11 taking into account a load coefficient corresponding to the load pressure of the lift valve to the proportional solenoid valve 8 The controller 9 stores in advance the load pressure of the lift cylinder 3 detected by the load detecting means 10 when the lift in the lift cylinder 3 is lifted, and the load detecting means 10 when the lift in the lift cylinder 3 is lowered. When the load pressure of the lift cylinder 3 detected in the step (c) becomes the set pressure of the relief valve 12, the lift cylinder
A signal based on the amount of operation of the lift operation lever 11 in consideration of a load coefficient corresponding to the load pressure of the forklift truck is output to the proportional solenoid valve 8.