JP2006064110A - Hydraulic circuit of construction equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent cavitation from generating by detecting pressure variation at a rotation operating part and adding back pressure by controlling with a controller only at the stopping period of a hydraulic motor. <P>SOLUTION: A variable back pressure valve 9 is provided in a returning oil line 8 from the hydraulic motor (a rotation motor 2) to a tank 7 and a pressure sensor 13 is provided in an oil route 12 for connecting an operation valve (a rotation operation valve 10) for issuing a driving command of the hydraulic motor and a main valve 3 and a pressure signal by the pressure sensor 13 is input to the controller 14. On/off of the variable back pressure valve 9 is controlled by the controller 14 via an electromagnetic valve 15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydraulic circuit for a construction machine that prevents cavitation from occurring during a stop operation of a hydraulic actuator that rotates in a construction machine such as a hydraulic excavator.

  In general, in a construction machine that includes a work machine such as a hydraulic excavator or a crawler crane and in which an upper turning body performs a turning operation, the upper turning body is configured to be driven to turn on a lower traveling body. The swing drive is performed by a hydraulic swing motor (hereinafter simply referred to as a swing motor), and when the operator returns the operation lever from the swing operation position to the neutral position, the direction control valve is closed and the main valve is switched to the swing motor. The supply of pressure oil is stopped and rotation is stopped.

  However, even if refueling to the turning motor is stopped by this turning stop operation, the upper turning body rotates due to inertia, so the turning motor does not stop immediately but rotates. For this reason, pressure oil is rotated without being supplied until the swing motor is completely stopped, so that the pressure oil supply line is negatively pressured, cavitation occurs, and the swing motor and oil supply line are damaged. There is a problem. In order to solve such a problem, for example, the back pressure of the main valve return oil is increased to a predetermined pressure or higher by the back pressure compensation valve, and the main valve return oil is caused to flow into the pressure oil supply line of the swing motor. Is added. However, in such a cavitation prevention means, a pressure exceeding a certain level is applied to the pressure oil supply line by the back pressure compensation valve at all times other than when the swing motor is stopped. In addition, heat is generated.

  As a means for preventing the occurrence of cavitation that can prevent such energy loss and heat generation, for example, a back pressure check valve is provided in the return path from the hydraulic actuator to the tank, and the liquid is liquidated by the back pressure generated by the back pressure check valve. It is known from Patent Document 1 that the fluid is guided to the low pressure side of the hydraulic actuator through the supply passage. In this, a bypass passage is provided in parallel with the back pressure check valve, and a bypass valve for opening and closing control is provided in the bypass passage. Then, only when the hydraulic actuator is stopped, the bypass valve is closed and back pressure is generated by the back pressure check valve, and liquid is supplied to the low pressure side of the hydraulic actuator through the liquid supply passage to prevent cavitation. It prevents energy loss and heat generation due to unnecessary pressure generation in the check valve.

  In addition to this, the discharge oil of the hydraulic pump is allowed to flow from the unload valve through the suction line to the pressure oil supply line of the swing motor through the suction valve, and at the pressure reduced by the unload valve It is known from Patent Document 2 that the pressure is controlled to be constant and the pressure generated between the unload valve and the lift check valve is applied to the pressure oil supply line as a back pressure.

JP 2002-089505 A Japanese Patent Laid-Open No. 10-168948

  However, in the cavitation prevention means known from Patent Document 1, a back pressure check valve is used to check the back pressure at the time of turning stop in the return passage from the actuator to the tank and to replenish pressure oil to the low pressure side of the actuator. The bypass passage is provided in the door, and the opening and closing thereof are performed by the bypass valve, and the bypass passage and the bypass valve are required. Also, the device controls the application of back pressure. In short, it functions only under the set conditions, and there is no degree of freedom to change the set conditions, so that there is a problem that it is not possible to respond to work situations and operator preferences.

  Further, in the cavitation prevention means according to Patent Document 2, control is performed such that the back pressure is applied to the pressure oil supply line by controlling the lift check valve with the pressure reduced by the unload valve. It functions only under certain conditions. Therefore, there is no degree of freedom to change the setting conditions. There is also a problem of requiring a plurality of devices.

  The present invention has been made to solve such problems. Only when the hydraulic motor is stopped, the pressure change in the rotary operation unit is detected and controlled by the controller to add back pressure, and cavitation. It is an object of the present invention to provide a hydraulic circuit for a construction machine that prevents the occurrence of the above-mentioned.

In order to achieve the above object, a hydraulic circuit for a construction machine according to the present invention comprises:
In a hydraulic circuit of a construction machine in which pressure oil from a hydraulic pump drives a hydraulic motor through a main valve,
A variable pressure compensation valve is provided in the return oil pipeline from the hydraulic motor to the tank, a pressure sensor is connected to the oil passage connecting the operation valve that issues a drive command for the hydraulic motor and the main valve, and a controller that inputs a pressure signal from the pressure sensor And the controller controls on / off of the variable pressure compensation valve via an electromagnetic valve.

  According to the present invention, the pilot oil passage that connects the operation valve that issues a drive command (forward / reverse rotation, stop) of the hydraulic motor and the operation portion of the direction switching valve provided in the pressure oil supply conduit to the hydraulic motor is provided. The pressure sensor detects the change in the pressure in the pilot oil passage when the drive of the hydraulic motor stops and transmits it to the controller. The variable pressure provided in the return oil line of the main valve via the solenoid valve is determined by the controller. The on / off control of the compensation valve (variable back pressure valve) is controlled so that the back pressure is applied quickly only when the hydraulic motor stops. Therefore, not only the stop state of the hydraulic motor but also the back pressure does not act at the time of driving, so there is no loss of hydraulic pressure, and the effect of preventing the occurrence of cavitation during the stop operation can be achieved. In addition, the condition for applying the back pressure can be set by control by the controller, so that it is possible to cope with the work situation and the preference of the operator. In addition, an economic effect that the object can be achieved with a small number of devices can be obtained.

  Next, a specific embodiment of a hydraulic circuit for a construction machine according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic diagram of a hydraulic circuit of a construction machine according to the present invention. FIG. 2 shows a flowchart of the back pressure application operation by the controller.

  The hydraulic circuit shown in FIG. 1 is a hydraulic circuit that controls a swing motor that swings an upper swing body (not shown) in a hydraulic excavator. Pressure oil supply pipes 4 and 4 ′ are connected to the turning motor 2 from the main pump 1 through the main valve 3 (turning direction switching valve) to the forward rotation side and the reverse rotation side. A back pressure applying pipe 6 for applying a back pressure to the return oil is provided on the oil supply pipes 4 and 4 ′ via check valves 5 and 5. In addition, a variable back pressure valve 9 (corresponding to the variable pressure compensation valve of the present invention) is disposed in the return oil line 8 from the main valve 3 to the tank 7, and the back pressure application line 6 is disposed upstream thereof. It is connected.

  On the other hand, the pilot oil passages 12 and 12 ′ that connect the turning operation valve 10 that operates the turning motor “right turn-neutral-left turn” and the switching operation portion of the main valve 3 by the operation lever 11 are provided on the left and right sides. Pressure sensors 13 and 13 ′ for detecting a change in hydraulic pressure during the turning operation are provided, and the pressure sensors 13 and 13 ′ are electrically connected to the controller 14. The controller 14 receives the signals detected by the pressure sensors 13 and 13 ', compares them with preset data, operates or stops the electromagnetic valve 15 for turning the variable back pressure valve 9 on and off, and turns the motor. 2 can be applied or released.

  The hydraulic circuit configured as described above operates the swing operation lever 11 to operate the swing motor 2 and stop the drive thereof (returns the operation lever 11 to the neutral position). Pressure sensors 13 and 13 'provided in pilot oil passages 12 and 12' connecting the operation portion of the direction switching valve (main valve 3) provided in the pressure oil supply pipe 4 (4 ') to the swing motor 2. Thus, the pressure change in the pilot oil passages 12 and 12 ′ is detected and transmitted to the controller 14. The controller 14 compares the data set in advance with the data from the pressure sensors 13 and 13 ′ and makes a determination (described later) to operate the electromagnetic valve 15 to change the variable valve provided in the return oil line 8 of the main valve 3. Only when the back pressure valve 9 is operated and the turning motor 2 is stopped, the variable back pressure valve 9 is switched to the throttle side port 9a to return the back pressure to the back pressure applying line 6 from the oil line 8.

  Thus, when the turning motor 2 stops turning, the stop operation is quickly detected, and the back pressure is applied in the normal operation by determining that the supply of the pressure oil to the turning motor has stopped. Does not work. Therefore, it is possible to prevent damage to the piping system such as hydraulic loss due to the constant back pressure and heat generation in the pipeline, and to save energy.

  Next, the control during the turning operation of the turning motor by the controller 14 will be described based on the flowchart shown in FIG. Reference symbol S represents a step.

S1: When the turning operation lever 11 is operated in a required turning direction and the turning operation valve 10 is operated so as to correspond thereto, the pilot connecting the turning operation valve 10 and the operation part of the main valve 3 (direction switching valve). Pressure sensors 13, 13 'provided in the oil passages 12, 12' detect pressure fluctuations. It is determined whether or not the pressure signal from the pressure sensors 13 and 13 ′ is, for example, 15 kg / cm ² or more. When it is less than 15 kg / cm ^{2, the process} proceeds to step S2. If it is 15 kg / cm ² or more, the process proceeds to step S3.

  S2: The solenoid valve 15 is turned on. That is, the variable back pressure valve 9 is operated to the throttle side port 9a so as to be equal to or higher than the set pressure, and the process returns to step S1.

  S3: The solenoid valve 15 is turned off. That is, the return oil pipe 8 is opened with the variable back pressure valve 9 on the open port 9b side. Therefore, back pressure does not stand.

S4: When the turning operation lever 11 is returned to the neutral position and the turning motor 2 is stopped, it is provided in the pilot oil passage 12 (12 ') that connects the turning operation valve 10 and the operation part of the main valve 3 (direction switching valve). The pressure sensor 13 (13 ') detects the pressure fluctuation. It is determined whether or not the pressure signal from the pressure sensor 13 (13 ′) is, for example, 15 kg / cm ² or less. If it exceeds 15 Kg / cm ² , the process proceeds to step S5. If it is 15 kg / cm ² or less, the process proceeds to step S6.

  S5: The solenoid valve 15 is turned off. That is, since the main valve 3 (direction switching valve) has not stopped supply of pressure oil to the swing motor 2, the return oil pipe 8 is opened and the process returns to step S4.

  S6 to S7: It is determined whether or not the elapsed time after stopping the pressure oil supply is, for example, 1 second or longer. If the elapsed time is within 1 second, the process returns to step S5, the electromagnetic valve 15 is turned off, and the process returns to step S4. If it is determined that the elapsed time is 1 second or longer, the process proceeds to step S7 and the solenoid valve 15 is turned on. The variable back pressure valve 9 is operated to the throttle side port 9 a, the return oil pipe 8 from the main valve 3 to the tank 7 is throttled, and the back pressure by the return oil is applied through the back pressure applying pipe 6. As a result, the rotation stop operation is performed and the pressure oil is sent to the negative pressure side of the swing motor 2 during the swing stop operation so that the negative pressure can be eliminated, so that the occurrence of cavitation can be prevented.

  As described above, when the behavior of the swing motor 2 is detected quickly by transmitting the change of the pilot pressure to the controller 14 by the pressure sensor 13 (13 ') and controlling it by the controller 14 to drive / stop the swing motor 2 as described above. Depending on the back pressure can be given. That is, it is possible to freely set the threshold value of the pressure sensor for operating the solenoid valve and the timing for operating the solenoid valve according to the work situation and the preference of the operator. In addition, it is possible to obtain a degree of freedom of control for applying the back pressure only when stopping.

  In the above description, the swivel motor of the hydraulic excavator has been described. However, the present invention can be applied to other machines configured to swivel by a hydraulic motor. In addition, a drive hydraulic motor of a drive unit having inertia when stopped, for example, a travel motor It can also be applied.

Outline diagram of hydraulic circuit of construction machine according to the present invention Flow chart of back pressure application operation by controller

Explanation of symbols

1 Main pump 2 Swing motor 3 Main valve (Direction switching valve)
4, 4 'Pressure oil supply line 6 Back pressure application line 7 Tank 8 Return oil line 9 Variable back pressure valve 10 Swing operation valve 11 Operation lever 12, 12' Pilot oil path 13, 13 'Pressure sensor 14 Controller 15 Variable back Solenoid valve to operate the pressure valve

Claims (1)

In a hydraulic circuit of a construction machine in which pressure oil from a hydraulic pump drives a hydraulic motor through a main valve,
A variable pressure compensation valve is provided in the return oil pipeline from the hydraulic motor to the tank, a pressure sensor is connected to the oil passage connecting the operation valve that issues a drive command for the hydraulic motor and the main valve, and a controller that inputs a pressure signal from the pressure sensor And the controller controls the on / off of the variable pressure compensation valve via an electromagnetic valve.

Images