JP2007298137A - Hydraulic system of construction machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic system of a construction machine, which prevents generation of cavitation caused by intake of a hydraulic pump in a hydraulic circuit in simple constitution, and is free to adapt to the hydraulic pump in either type of variable capacity type and fixed capacity type. <P>SOLUTION: The hydraulic system of the construction machine is furnished with: an electronic governor 3 to change engine speed of an engine 2 by a signal from a controller 4; a hydraulic pump 1 driven by the engine 2; and a pressure sensor 5 to detect intake pressure (circuit pressure P) of the hydraulic pump 1 by connecting it to the controller 4, and controls the engine speed of the engine 2 so as to be reduced to predetermined engine speed when the intake pressure (circuit pressure P) of the hydraulic pump 1 becomes lower than specified pressure (standard pressure Ps). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technology of a hydraulic device for a construction machine, and more particularly to a hydraulic device for a construction machine that prevents the occurrence of cavitation caused by suction of a hydraulic pump.

2. Description of the Related Art Conventionally, a technique related to a hydraulic device for a construction machine that prevents cavitation caused by suction of a hydraulic pump is known. In the case of a hydraulic circuit, it is known that reducing the suction amount of the hydraulic pump (that is, reducing the discharge amount of the hydraulic pump) is effective in preventing the occurrence of cavitation. For example, Patent Document 1 discloses a method for preventing cavitation by detecting the temperature of hydraulic oil using a temperature sensor and adjusting the swash plate angle of the hydraulic pump when the hydraulic oil temperature is equal to or lower than a predetermined temperature. Proposed.
In Patent Document 1, oil temperature detection means is provided upstream of a hydraulic pump for supplying hydraulic oil to various actuators to detect the oil temperature of the hydraulic oil, and the hydraulic pressure is detected based on the detected value of the oil temperature detection means. There is disclosed a hydraulic circuit provided with a controller for adjusting the discharge flow rate of the pump. According to the conventional invention, the temperature of the hydraulic oil upstream of the hydraulic pump and the pressure of the hydraulic oil upstream of the oil cooler are detected, and when the oil temperature is lower than a predetermined value, the discharge flow rate of the hydraulic pump is minimized. Thus, cavitation caused by the low temperature of the hydraulic oil can be prevented.
JP 2001-41204 A

  However, the hydraulic circuit disclosed in Patent Document 1 detects the oil temperature of the hydraulic oil with a temperature sensor, and adjusts the swash plate angle of the hydraulic pump when the oil temperature of the hydraulic oil is lower than a predetermined temperature. This is a method to prevent cavitation. Cannot be specified. Further, in this method of controlling the swash plate angle of the hydraulic pump, it is necessary to install a regulator for controlling the swash plate of the hydraulic pump, so that the configuration of the hydraulic circuit becomes complicated. Further, it cannot be applied to a fixed displacement hydraulic pump that does not have a variable displacement mechanism.

  In view of the above situation, the present invention can prevent the occurrence of cavitation due to suction of a hydraulic pump with a simple hydraulic circuit, and can be applied to either a variable displacement type or a fixed displacement type hydraulic pump. An object is to provide a hydraulic device for a machine.

  The problems to be solved by the present invention are as described above. Next, means for solving the problems will be described.

That is, in claim 1,
A rotation speed changing means for changing the rotation speed of the engine according to a signal from the controller;
A hydraulic pump driven by the engine;
Pressure detecting means connected to the controller for detecting the suction pressure of the hydraulic pump;
When the suction pressure of the hydraulic pump becomes equal to or lower than a predetermined pressure, the engine speed is controlled to be decreased to a predetermined engine speed by the engine speed changing means.

In claim 2,
The rotation speed changing means is an electronic governor.

  As effects of the present invention, the following effects can be obtained.

  According to the first aspect of the present invention, when the suction pressure of the hydraulic pump becomes equal to or lower than the predetermined pressure, the engine speed is controlled to be reduced to the predetermined engine speed by the engine speed changing means. Occurrence of cavitation due to inhalation can be prevented. And by reducing the number of rotations of the engine, it is possible to efficiently operate while suppressing fuel consumption. Further, it can be applied to either a variable displacement type or a fixed displacement type hydraulic pump.

  According to the second aspect of the present invention, since the engine speed is changed by the electronic governor, the responsiveness is fast, the fuel injection amount is adjusted, the engine speed can be easily changed, and the engine can be operated efficiently.

Next, the best mode for carrying out the invention will be described.
FIG. 1 is a hydraulic circuit diagram of a hydraulic device for a construction machine according to an embodiment of the present invention, and FIG. 2 is a control block diagram.

  As shown in FIG. 1, the hydraulic apparatus for a construction machine according to the present embodiment includes a controller 4, an engine 2, an electronic governor 3, a hydraulic pump 1, a relief valve 6, a pressure sensor 5, and the like. It is configured.

  The engine 2 is an electronically controlled governor type engine having an electronic governor 3 serving as a rotational speed control means, and the rotational speed is controlled by a signal from the controller 4. Although details will be described later, the engine 2 has its rotation speed adjusted according to an accelerator lever, a load, and the like (not shown), and a signal is input from the controller 4 to the electronic governor 3 based on the detection value of the pressure sensor 5. The rotational speed is controlled. In this embodiment, the rotation of the diesel engine is controlled by an electronic governor, and the rotational speed is controlled by operating a rack actuator such as a solenoid. The rotational speed changing means is not limited to the electronic governor 3, and the fuel injection amount is changed by controlling the opening and closing of the valve, or the rotational speed is changed by rotating the accelerator lever with a motor, a cylinder or the like. It can also be set as a structure to. The output shaft of the engine 2 is connected to the input shaft (pump shaft) of the hydraulic pump 1.

The hydraulic pump 1 is a variable displacement hydraulic pump, and an input shaft (pump shaft) is connected to an output shaft of the engine 2 so that the driving force of the engine 2 is transmitted and driven. In the present embodiment, the hydraulic pump 1 is a variable displacement hydraulic pump, but may be a fixed displacement hydraulic pump.
The hydraulic pump 1 sucks hydraulic oil from a reservoir tank 9 in which the hydraulic oil is stored, and pumps the hydraulic oil, and the hydraulic fluid (hereinafter referred to as pressure oil) that is pumped is discharged into a discharge circuit (hydraulic pump). The oil passage 8 connected to one discharge port) 10 and the direction switching valve 7 are supplied to the hydraulic actuator 8 to drive the hydraulic actuator 8. Then, the pressure oil supplied to the hydraulic actuator 8 is returned to the reservoir tank 9 via the direction switching valve 7 and then pumped again by the hydraulic pump 1 and circulated. Note that the hydraulic circuit of the present invention can be used for construction machines, agricultural machines, and the like, and in this embodiment, a case where it is applied to a hydraulic excavator will be described. In this case, the hydraulic actuator 8 is a hydraulic cylinder such as a boom cylinder, an arm cylinder, a bucket cylinder, or a swing cylinder, or a hydraulic motor such as a traveling hydraulic motor or a swing hydraulic motor, and is connected in parallel to the discharge side of the hydraulic pump 1. In this embodiment, one directional switching valve 7 and a hydraulic cylinder 8 (hydraulic actuator) are shown.

The direction switching valve 7 is a switching valve, is connected to the discharge circuit 10 of the hydraulic pump 1, and controls the amount and direction of pressure oil supplied from the hydraulic pump 1 to the hydraulic actuator 8. The direction switching valve 7 is configured such that the pilot hydraulic pressure is sent to the operation portion and switched by operating an operation lever (not shown) that operates the hydraulic actuator 8.
Specifically, the operation lever is connected to a pilot type control valve, and by operating this operation lever, the pilot type control valve is switched, and the pilot hydraulic pressure is changed to the spool operation portion 7a ( Or the oil is fed to 7b), the spool is slid, and the direction switching valve 7 is switched. For example, when the pilot hydraulic pressure is guided to the spool operation portion 7a (or 7b) by operating the operation lever, the direction switching valve 7 is switched from the central neutral position 7C to the right switching position 7A (or the left switching position) in FIG. Switch to position 7B). Thereby, pressure oil is supplied to the rod chamber side of the boom cylinder, and the boom is rotated in the raising direction (or the lowering direction) from the stopped state. When the operation lever is returned to the original position, the pilot hydraulic pressure is not fed, the direction switching valve 7 returns the spool to the neutral position by the spring force, the oil passage communicating with the hydraulic cylinder 8 is blocked, and the expansion and contraction is stopped. The pressure oil from the hydraulic pump 1 is returned to the reservoir tank 9 via the relief valve 6.

  The relief valve 6 determines the maximum pressure for supplying hydraulic oil discharged to the discharge circuit 10 of the hydraulic pump 1 to the hydraulic actuator 8. The relief valve 6 connects the discharge port of the hydraulic pump 1 and the pump port of the direction switching valve 7. It is branched from the middle of the communicating oil passage (discharge circuit 10) and connected in parallel.

  The pressure sensor 5 is pressure detection means for detecting the suction pressure of the hydraulic pump 1 and is connected to the upstream side of the hydraulic pump 1 and in the middle of the suction circuit 11, and the pressure of the suction circuit 11 (hereinafter, circuit pressure). P). As shown in FIG. 2, the pressure sensor 5 is connected to a controller 4 serving as a control means, and the controller 4 indicates a pressure for reducing the engine speed (reference pressure Ps described later) and an engine speed at the time of reduction. The setting device 12 to be set is connected to the electronic governor 3 of the engine 2.

  And in the hydraulic apparatus of the construction machine of a present Example, control for preventing generation | occurrence | production of the cavitation resulting from the suction | inhalation of the hydraulic pump 1 is performed as follows.

First, a detection signal (circuit pressure P) of the pressure sensor 5 is input to the controller 4 (see FIG. 2).
The controller 4 converts the detection signal from the pressure sensor 5 into a circuit pressure P and compares it with the reference pressure Ps. When the circuit pressure P is larger than the reference pressure Ps, the state is maintained. When the circuit pressure P reaches the reference pressure Ps, an operation signal S for decreasing the rotational speed of the engine 2 is output to the electronic governor 3. Here, a predetermined pressure (hereinafter referred to as a reference pressure Ps) equal to or lower than the atmospheric pressure (1 atm = 101325 Pa) is input from the setting device 12 to the controller 4. Note that the reference pressure Ps is set to a value lower than the atmospheric pressure by an amount that adds a margin to the maximum width of variation due to a temperature change or the like.

When the circuit pressure P input to the controller 4 is higher than the reference pressure Ps (the pressure is higher than the reference pressure Ps), the controller 4 sends an operation signal S for reducing the rotational speed of the engine 2 to the electronic governor. Do not output to 3. Therefore, since the rotational speed of the engine 2 is not reduced, the intake amount of the hydraulic pump 1 is not reduced.
On the other hand, when the circuit pressure P becomes equal to or lower than the reference pressure Ps (the pressure is lower than the reference pressure Ps), the controller 4 electronically sends an operation signal S for decreasing the rotational speed of the engine 2 according to the pressure. Output to governor 3. Therefore, the engine 2 is reduced to a predetermined rotational speed at which the suction pressure of the hydraulic pump 1 is reduced, the suction amount of the hydraulic pump 1 is reduced, and the discharge amount is also reduced, thereby preventing the occurrence of cavitation.
When the circuit pressure P rises and returns until it exceeds the reference pressure Ps, the controller 4 does not output the operation signal S for reducing the rotational speed of the engine 2 to the electronic governor 3, but the rotational speed of the engine 2. Return to the original speed.

As described above, the hydraulic device for the construction machine according to the present embodiment is connected to the electronic governor 3 that changes the rotational speed of the engine 2 by the signal from the controller 4, the hydraulic pump 1 that is driven by the engine 2, and the controller 4. And a pressure sensor 5 for detecting the suction pressure (circuit pressure P) of the hydraulic pump 1, and when the suction pressure (circuit pressure P) of the hydraulic pump 1 falls below a predetermined pressure (reference pressure Ps). The electronic governor 3 controls the rotational speed of the engine 2 to be reduced to a predetermined rotational speed.
With such a configuration, when the suction pressure (circuit pressure P) of the hydraulic pump 1 becomes equal to or lower than a predetermined pressure (reference pressure Ps), the electronic governor 3 sets the rotation speed of the engine 2 to a predetermined rotation. By controlling so as to decrease to the number, cavitation caused by suction of the hydraulic pump 1 can be prevented. And by reducing the rotation speed of the engine 2, fuel consumption is suppressed and it can drive | operate efficiently. Further, the present invention can be applied to either a variable displacement type or a fixed displacement type hydraulic pump 1.

  In the construction machine hydraulic device of the present embodiment, since the rotation speed changing means is the electronic governor 3, the rotation speed of the engine 2 is changed by the electronic governor 3, so the responsiveness is fast and the fuel injection amount is adjusted. Thus, it can be easily changed to a predetermined number of revolutions and can be operated efficiently.

1 is a hydraulic circuit diagram of a hydraulic device for construction machinery according to an embodiment of the present invention. The control block diagram.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydraulic pump 2 Engine 3 Electronic governor 4 Controller 5 Pressure sensor 6 Relief valve 7 Directional switching valve 7A Switching position 7B Switching position 7C Neutral position 7a Spool operation part 7b Spool operation part 8 Hydraulic actuator 9 Reservoir tank 10 Discharge circuit 11 Suction circuit 12 Setter P Circuit pressure Ps Reference pressure S Operation signal

Claims (2)

A rotation speed changing means for changing the rotation speed of the engine according to a signal from the controller;
A hydraulic pump driven by the engine;
Pressure detecting means connected to the controller for detecting the suction pressure of the hydraulic pump;
The hydraulic pressure of a construction machine, wherein when the suction pressure of the hydraulic pump becomes equal to or lower than a predetermined pressure, the engine speed is controlled to be decreased to a predetermined engine speed by the engine speed changing means. apparatus. The hydraulic device for a construction machine according to claim 1, wherein the rotation speed changing means is an electronic governor.

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