JPH0352279Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a hydraulic system for earthmoving vehicles such as wheel loaders.

<Prior Art> A conventional hydraulic system for an earthmoving vehicle such as a wheel loader is shown in FIG.

In Fig. 5, 1 is a fixed capacity gear pump, 2
3 is a steering cylinder, 3 is a steering control valve, 4 is a boom cylinder, 5 is a bucket cylinder, 6 is a cargo handling circuit control valve, and 7 is a carryover pipe.

<Problem that the invention aims to solve> Generally, earthmoving vehicles such as wheel loaders divide the engine output mainly into traction force and hydraulic pressure.
Hydraulic energy is consumed by power steering equipment and cargo handling equipment.

However, since the hydraulic pump used in this system is a fixed capacity gear pump, even when a high pressure and small flow rate is required during vehicle operation, a high pressure and large flow rate is generated, resulting in a loss of much of the hydraulic energy.

Furthermore, in the case of a wheel loader, since the operator controls the engine speed and the vehicle speed, the performance of the steering device and cargo handling device may not be satisfactory. For example, the disadvantage is that the steering speed decreases at low engine speeds.

In view of the above, an object of the present invention is to provide a hydraulic system for an earthmoving vehicle such as a wheel loader that can prevent wasteful energy consumption.

<Means for Solving the Problems> As shown in FIGS. 1 to 4, the means for solving the problems according to the present invention is as shown in FIGS. A displacement pump 9 and a steering side detection device 1 that detects the load applied to the steering device 9.
0, a second variable displacement pump 12 that is driven via the output shaft 29 of the engine 28 and supplies pressure oil to the cargo handling device 11, a cargo handling device side detection device 13 that detects the load applied to the cargo handling device 11, and engine 2
8, and a control device 14 that controls the pressure oil capacity of the two pumps based on signals from the rotation speed detector 30 and both the detection devices 10 and 13. The steering device 8 includes a steering cylinder 15, a first control valve 16 that switches the direction of pressure oil in the steering cylinder 15, and a first pilot control that controls the operation of the first control valve 16 according to the steering operation speed. and a valve 17, the steering side detection device 1
0 consists of a first detector 19 that detects the discharge pressure of the first variable displacement pump 9 and a second detector 20 that detects the pilot pressure of the first pilot control valve 17.
These include cargo handling cylinders 21 and 22, a second control valve 23 that switches the direction of pressure oil in the cargo handling cylinders 21 and 22, and a second pilot that controls the operation of the second control valve 23 in accordance with the cargo handling operation speed. It consists of a control valve 24,
The cargo handling device side detection device 13 includes a third detector 2 that detects the discharge pressure of the second variable displacement pump 12.
6, and the second pilot control valve 2.
The control device 14 includes the rotation speed detector 30 and the first to fourth detectors 19, 20,
Based on the signals from 26 and 27, the engine 2
Changes in the performance of the steering device 8 and cargo handling device 11 caused by fluctuations in the flow rates of both pumps 9 and 12 due to fluctuations in the rotational speed of pumps 8 are detected, and the capacities of both pumps 9 and 12 are calculated accordingly. ,1
The system is configured to control the pressure oil capacity of No. 2.

<Operation> In the problem solving means described above, the rotation speed of the engine 28 during driving is detected by the control device 14, and
The pilot pressure of the second pilot control valve 24 is detected by a fourth detector 27, and the discharge pressure of the second variable displacement pump 12 is detected by a third detector 26, and the signals are sent to the control device 14. Further, the pilot pressure of the first pilot control valve 17 is detected by the second detector 20, and the discharge pressure of the first variable displacement pump 9 is detected by the first detector 19, and these are output to the control device 14.

The control device 14 calculates the capacities of the first variable displacement pump 9 and the second variable displacement pump 12 based on the rotational speed of the engine 28 and the output signals of the respective detectors 19, 20, 26, and 27. Controls 12 hydraulic oil capacities.

<Example> Hereinafter, an example of the present invention will be described based on the drawings.

As shown in FIGS. 1 and 2, the hydraulic system of an earthmoving vehicle such as a power shovel according to this embodiment is driven by an output shaft 29 of an engine 28 and a steering device 8.
a first variable displacement pump 9 that supplies pressure oil to the steering device 8; a steering side detection device 10 that detects the load applied to the steering device 8; the second variable displacement pump 12 and the cargo handling device 11
Cargo handling equipment side detection device 13 that detects the load applied to
a rotation speed detector 30 that detects the rotation speed of the engine 28; and a control device 14 that controls the driving of the pumps 9 and 12 based on signals from the rotation speed detector 30 and the detection devices 10 and 13. is provided.

The steering device 8 includes a steering cylinder 15 and a first control valve 1 that switches the direction of pressure oil in the steering cylinder 15.
6, and a first pilot control valve 17 that controls the operation of the first control valve 16 in accordance with the steering operation speed.

The steering side detection device 10 includes a first detector 19 that detects the discharge pressure of the first variable displacement pump 9, and a second detector 2 that detects the pilot pressure of the first pilot control valve 17.
Consists of 0.

The cargo handling device 11 includes a boom cylinder 21;
Bucket cylinder 22 and each cylinder 21, 2
The second control valve 23 is configured to switch the direction of the pressure oil in the second control valve 2, and the second pilot control valve 24 is configured to control the operation of the second control valve 23 in accordance with the cargo handling speed.

The cargo handling equipment side detection device 13 includes a third detector 26 that detects the discharge pressure of the second variable displacement pump 12 and a fourth detector 27 that detects the pilot pressure of the second pilot control valve 24.
It consists of

The control device 14 controls each of the detectors 19 and 2.
0, 26, 27, 30, the troll actuator 1 of both pumps 9, 12
It consists of a microcomputer that controls the operation of 8 and 25, and has internal program ROM, data RAM,
It has a CPU and is driven by a reference clock oscillation circuit.

As shown in FIG. 3, the control device 14 controls the engine 28 based on the signal from the rotation speed detector 30.
means for inputting the rotation speed of the second detector 20;
means for inputting the steering pilot pressure (steering operation speed) according to a signal from the first detector 19; means for inputting the discharge pressure of the steering pump (first variable displacement pump) 9 according to a signal from the first detector 19; Means for inputting the cargo handling equipment pilot pressure (loading operation speed) based on the signal from the detector 27; and means for inputting the discharge pressure of the cargo handling equipment pump (second variable displacement pump) 12 based on the signal from the third detector 26. and means for determining the presence or absence of steering operation by detecting changes in steering pilot pressure based on the signal from the second detector 20;
means for determining the presence or absence of a cargo handling operation by detecting changes in the pilot pressure of the cargo handling equipment based on the signal from the fourth detector 27;
Based on the signals from the detectors 19, 20, 26, and 27, changes in performance of the steering device 8 and the cargo handling device 11 caused by fluctuations in the flow rates of both pumps 9, 12 due to fluctuations in the rotational speed of the engine 28 are detected. The system is configured to calculate the capacities of both the pumps 9 and 12 in accordance with the above-described conditions, and to control the pressure oil capacity of both the pumps 9 and 12.

In the above configuration, the control device 14 detects the rotational speed of the engine 28 during driving, the fourth detector 27 detects the pilot pressure of the second pilot control valve 24, and the third detects the discharge pressure of the second variable displacement pump 12. The detector 26 detects each and sends the signal to the control device 14. Further, the pilot pressure of the first pilot control valve 17 is detected by the second detector 20, and the discharge pressure of the first variable displacement pump 9 is detected by the first detector 19, and these are output to the control device 14.

The control device 14 calculates the capacities of the first variable displacement pump 9 and the second variable displacement pump 12 based on the rotation speed of the engine 28 and the output signals of the respective detectors 19, 20, 26, and 27, and calculates the capacities of the first variable displacement pump 9 and the second variable displacement pump 12. A control signal is output to the motors 18 and 25 to control the amount of pressurized oil.

The control characteristics of the control device 14 are as follows: positive control that makes the pump discharge flow rate proportional to the pilot pressure (Fig. 4 a), negative control that keeps the absorbed energy constant at high pressure (Fig. 4 b), and Fig. 4 c. The relationship between the high pressure cut-off control (H, P, C, O control) which makes the discharge flow rate zero at the time of relief as shown in FIG.

The 100% flow rate line in Figure 2 is the flow rate necessary for vehicle performance characteristics, and the broken line is the unnecessary flow rate that occurs as the engine speed increases when using a conventional fixed capacity pump. It shows. Therefore, the rotation speed of the engine 28 and each detector 1
Control the pressure oil capacity of the variable displacement pumps 9, 12 based on the output signals of 9, 20, 26, 27 (positive control, negative control, H, P, C, O control)
This eliminates unnecessary flow that occurs as the engine speed increases. For example, in positive control, the flow rate of 100% in FIG. 4a is a line diagonally connecting the flow rate of 100% in FIG. 2 and the flow rate of 0 to 100%. In other words, the thick line corresponds to 100% flow rate in FIG. 4a. Negative control shown in Figures 4b and c,
The same applies to H, P, C, and O control.

Here, the above control characteristics will be explained in detail based on the flowchart of FIG.

As described above, after the engine 28 is started, the control device 14 controls the engine 28 rotational speed, the pilot pressure (steering operation speed) of the steering device 8, the discharge pressure of the steering pump (first variable displacement pump) 9, and the cargo handling device. The pilot pressure (cargo handling operation speed) of 11 and the discharge pressure of the cargo handling device pump (second variable displacement pump) 12 are respectively input.

Then, in Step 1, it is determined from the output of the second detector 20 whether or not there is a steering operation. That is,
Since the pilot pressure of the first pilot control valve 17 changes depending on the steering operation speed, by detecting this change with the second detector 20, it can be determined whether or not the steering operation is being performed. When a steering operation is performed, positive control is performed to make the discharge flow rate of the steering pump 9 proportional to the pilot pressure of the steering device 8, as shown in FIG. 4a.

Thereafter, in Step 2, the steering pressure, that is, the discharge pressure of the steering pump 9 is determined from the signal of the first detector 19. When the steering pressure becomes high pressure, that is, above a certain pressure, the discharge amount of the steering pump 9 is negatively controlled in order to keep the absorbed energy constant, as shown in FIG. Diagram c
As shown, H, P, C, O control is performed to make the discharge amount of the steering pump 9 zero. Note that if the steering pressure has not reached the pressure for performing negative control, positive control is continued.

In Step 3, it is determined from the output of the fourth detector 27 whether there is a cargo handling operation or not. That is, since the pilot pressure of the second pilot control valve 24 changes depending on the speed of the cargo handling operation, by detecting this change with the fourth detector 27, the presence or absence of the cargo handling operation can be determined. When a cargo handling operation is performed, positive control is performed to make the discharge flow rate of the cargo handling device pump 12 proportional to the pilot pressure of the cargo handling device 11, as shown in FIG. 4a.

Thereafter, in Step 4, the cargo handling device pressure, that is, the discharge pressure of the cargo handling device pump 12 is checked from the signal of the third detector 26. When the pressure of the cargo handling device becomes high pressure, that is, above a certain pressure, the discharge amount of the cargo handling device pump 12 is negatively controlled in order to keep the absorbed energy constant, as shown in FIG. 4b, and when the pressure of the cargo handling device reaches the relief pressure. , as shown in FIG. 4c, H, P, C, O control is performed to make the discharge amount of the cargo handling device pump 12 zero. Note that if the steering pressure has not reached the pressure for performing negative control, positive control is continued.

As described above, changes in the performance of the steering device 8 and cargo handling device 11 due to the rotation of the engine 28 are detected based on the signals from the detectors 19, 20, 26, and 27, and the pressure oil of both pumps 9 and 12 is detected accordingly. Since the capacity is controlled, fluctuations in the flow rates of both pumps 9 and 12 due to fluctuations in the rotational speed of the engine 28 can be compensated by combining positive control, negative control, and H, P, C, and O control. Therefore, it is possible to provide an energy system that discharges the required amount of pressurized oil at the required time.

<Effects> As is clear from the above explanation, according to the present invention, changes in the performance of the steering device or cargo handling device due to engine rotation are detected based on signals from the steering side detection device or the cargo handling device side detection device, and Since the pressure oil capacities of the first variable displacement pump and the second variable displacement pump are controlled by the pump, it is possible to control and correct fluctuations in the flow rates of both pumps due to fluctuations in engine speed.

Therefore, the required amount of oil is discharged at the required time, and there is an excellent effect that a hydraulic system for an earthwork vehicle such as a wheel loader can be provided, which can prevent wasteful energy consumption.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a hydraulic system according to an embodiment of the present invention.
Figure 2 is the same engine rotation vs. flow rate characteristic graph, Figure 3 is
The figure is a flowchart showing the control characteristics of the control device.
Figures 4a, b, and c are graphs representing positive control, negative control, and HPCO control, respectively, and Figure 5 is a block diagram of a hydraulic system in a conventional earthmoving vehicle. 8... Steering device, 9... First variable displacement pump, 10... Steering side detection device, 11
...Cargo handling device, 12...Second variable displacement pump, 1
3... Cargo handling equipment side detection device, 14... Control device,
15... Steering cylinder, 16, 23...
Control valve, 17, 24... Pilot control valve, 19, 20, 26, 27...
...Detector, 21, 22...Cargo handling cylinder, 28...
...Engine, 29...Output shaft, 30...Revolution speed detector.

Claims (1)

[Claims for Utility Model Registration] A first variable displacement pump 9 that is driven via the output shaft 29 of the engine 28 and supplies pressure oil to the steering device 8, and a steering side detection device that detects the load applied to the steering device 8. 10, a second variable displacement pump 12 that is driven via the output shaft 29 of the engine 28 and supplies pressure oil to the cargo handling device 11; a cargo handling device side detection device 13 that detects the load applied to the cargo handling device 11; a rotation speed detector 30 that detects the rotation speed of the engine 28; the rotation speed detector 30 and both detection devices 10, 1;
3, the steering device 8 is provided with a control device 14 that controls the pressure oil capacity of both the pumps according to a signal from the steering cylinder 15, and a first control device that switches the direction of the pressure oil in the steering cylinder 15. It consists of a valve 16 and a first pilot control valve 17 that controls the operation of the first control valve 16 according to the steering operation speed, and the steering side detection device 10 detects the discharge pressure of the first variable displacement pump 9. and a second detector 20 that detects the pilot pressure of the first pilot control valve 17.
It consists of a second control valve 23 that switches the direction of the pressure oil in the cargo handling equipment 1 and 22, and a second pilot control valve 24 that controls the operation of the second control valve 23 according to the cargo handling operation speed. The device 13 includes a third detector 26 that detects the discharge pressure of the second variable displacement pump 12 and a fourth detector 27 that detects the pilot pressure of the second pilot control valve 24. Based on the signals from the rotation speed detector 30 and the first to fourth detectors 19, 20, 26, 27, the steering is determined based on the fluctuation in the flow rate of both pumps 9, 12 due to the fluctuation in the rotation speed of the engine 28. Capturing changes in performance of equipment 8 and cargo handling equipment 11,
A hydraulic system for an earthmoving vehicle, characterized in that the hydraulic system for an earthmoving vehicle is configured to calculate the capacities of the pumps 9 and 12 in accordance with this and control the pressure oil capacities of the pumps 9 and 12.