JP4771926B2 - Cavitation prevention circuit for construction machinery - Google Patents

Description

  The present invention relates to a cavitation prevention circuit for a construction machine, and in particular, a makeup circuit is provided between driving circuits for supplying and discharging pressure oil to a turning or traveling motor, and suction is performed when the turning or traveling motor is suddenly stopped. The present invention relates to a hydraulic circuit that prevents cavitation from occurring due to negative pressure on the side.

  In a construction machine such as a hydraulic excavator, a turning or traveling motor is driven by operation of a turning or traveling remote control valve, and turning or traveling is enabled by rotation of the turning or traveling motor. When stopping turning or traveling, the turning or traveling remote control valve is returned to the neutral position and the drive circuit is shut off, but in the case of turning, the turning motor keeps rotating due to the inertial force of the upper turning body, and In the case of traveling, particularly when descending a hill, the traveling motor is rotated by inertia due to the inertia force in the downhill direction. As a result, there is a problem in that the suction side circuit of the turning or traveling motor becomes negative pressure and cavitation occurs, and hydraulic equipment such as the turning or traveling motor is damaged by the generation and burst of bubbles.

  Conventionally, a hydraulic circuit as shown in FIG. 5 is generally used as a hydraulic circuit for preventing the occurrence of cavitation when a turning or traveling motor is suddenly stopped. The discharge circuit of the hydraulic pump 50 is connected to a directional control valve 51 for turning or traveling, and pilot pressure is derived from the hydraulic source 68 to the pilot circuit 52a or 52b by operation of the turning or traveling remote control valve 52. Is switched from the neutral position (A) to the turning or traveling position (B) or (C), the hydraulic oil discharged from the hydraulic pump 50 is supplied to the drive circuit 53 or 54. The turning or traveling motor 55 rotates. The drive circuits 53 and 54 are connected with check valves 57 and 58 and a make-up circuit 59 disposed in the opposite directions. The makeup circuit 59 is provided with a check valve 61 that prevents backflow to the tank 60. Further, the drive circuits 53 and 54 are connected via check valves 64 and 65 and cross relief valves 66 and 67 disposed in the opposite directions. Although not shown, the turning or traveling motor 55 brakes the turning or traveling motor 55 when the turning or traveling remote control valve 52 is not operated, and releases the braking when the turning or traveling remote control valve 52 is operated. A brake is provided.

  Now, when the turning or traveling remote control valve 52 is operated to either one, the pilot pressure is generated in either of the pilot circuits 52a and 52b, the pilot pressure is applied to the pilot port 51a or 51b of the direction control valve 51, The direction control valve 51 is switched from the neutral position (A) to the turning or traveling position (B) or (C). For example, when switching to the right turn or forward position (b), the pressure oil discharged from the hydraulic pump 50 passes through the right turn or forward position (b) of the directional control valve 51 and one drive circuit 53. The pressure oil is supplied to the turning or traveling motor 55, and the turning or traveling motor 55 rotates in any one direction. The pressure oil that has passed through the turning or traveling motor 55 is discharged to the other driving circuit 54, and returns to the tank 60 from the right turning or forward position (B) of the direction control valve 51.

  Here, when the turning or traveling remote control valve 52 is returned from the operation position to the neutral position in order to stop the rotating turning or traveling motor 55, the direction control valve 51 is turned to the right or forward position (b). Is switched to the neutral position (A), and the supply and discharge of the pressure oil to the driving circuits 53 and 54 is cut off.

  However, even after the supply and discharge of pressure oil to and from the drive circuits 53 and 54 is interrupted, the turning or traveling motor 55 continues to rotate due to the inertial force of the upper swinging body or the inertial force in the downhill direction of traveling. For this reason, the suction side drive circuit 53 becomes low pressure and tries to generate cavitation. However, the pressure oil is sucked into the suction side drive circuit 53 from the makeup circuit 59 and is replenished. Further, when the blocked discharge side drive circuit 54 becomes higher than the set pressure, the cross relief valve 67 is opened, and the return oil from the drive circuit 54 is sucked in via the cross relief valve 67 and the check valve 64. Into the driving circuit 53. In this way, the occurrence of turning or cavitation of the traveling motor 55 is prevented.

Further, in Patent Document 1, a discharge valve of a hydraulic pump is supplied to and discharged from a drive circuit for a swing motor via a swing direction control valve, and a suction valve capable of sucking in each drive circuit direction is provided between the drive circuits. Connected the suction circuit arranged, branch the oil discharged from the hydraulic pump and lead it from the unload valve to the suction circuit, let it flow into the drive circuit of the swing motor through the suction valve, and decompressed by the unload valve There is known a configuration in which a lift check valve is controlled to be constant with pressure, and a pressure generated between an unload valve and a lift check valve is applied as a back pressure to a drive circuit.
Japanese Patent Laid-Open No. 10-168948

  The conventional cavitation prevention circuit shown in FIG. 5 replenishes the pressure oil from the make-up circuit when the turning or traveling motor is suddenly stopped, and the cross relief valve when the return oil on the discharge side becomes higher than the set pressure. The cavitation is prevented by flowing into the suction side through the. However, this alone may not prevent the occurrence of cavitation.

  Further, the invention described in Patent Document 1 allows the oil discharged from the hydraulic pump to flow into the drive circuit when the direction control valve is in the neutral position and the drive circuit is shut off when the swing motor is stopped, Since the pressure generated between the load valve and the lift check valve is applied as a back pressure to the driving circuit, the driving circuit is controlled so as not to become negative pressure.

  However, in order to supply the oil discharged from the hydraulic pump to the drive circuit, it is necessary to enlarge the make-up circuit, which increases the cost. If the return oil of the driving circuit can be used effectively, cavitation prevention measures can be efficiently performed while saving energy.

  Therefore, technical problems to be solved in order to prevent the occurrence of cavitation by effectively using the return oil of the drive circuit when the suction side becomes negative pressure when the construction machine turns or the traveling motor suddenly stops The present invention aims to solve this problem.

The present invention has been proposed in order to achieve the above object, and the invention according to claim 1 is a makeup circuit between driving circuits for supplying and discharging pressure oil to a turning or traveling motor via a direction control valve. In the hydraulic circuit of construction machinery with
A connection between the driving circuit and the direction control valve, and a connection between the driving circuit and the makeup circuit at a position between the driving circuit and the make-up circuit are connected by a new communication circuit, A normally closed on-off valve is provided in the middle of the communication circuit, a pilot port for switching the on-off valve to an open position is provided at one end of the spool of the on-off valve, and a tank communicates with the other end of the spool of the on-off valve. And a spring that pushes back the opening / closing valve in the closing direction, a secondary port of the switching valve is connected to the pilot port, and a throttle valve is interposed in the circuit that communicates with the tank. Connect the hydraulic source and tank to the primary side,
The switching valve is in the hydraulic pressure source position when there is no operation of the turning or traveling remote control valve, and the pilot pressure of the hydraulic pressure source is led to the pilot port of the on-off valve to bring the on-off valve to the open position. A construction characterized in that when the traveling remote control valve is operated, the switching valve is switched to the tank position, and the pilot pressure of the on-off valve is released to the tank so that the on-off valve is in the closed position. An anti-cavitation circuit for a machine is provided.

  According to this configuration, a new communication circuit is connected between the driving circuits for supplying and discharging pressure oil to the turning or traveling motor, and the normally closed on-off valve is interposed, so that the operation of the machine is stopped. When the hydraulic pump is not driven, the communication circuit between the driving circuits is blocked by the on-off valve. When the operation of the machine is started and the hydraulic pump is driven, the switching valve is in the hydraulic source position when the turning or traveling remote control valve is not operated, so the pilot pressure of the hydraulic source is changed to the hydraulic source of the switching valve. The position is led to a pilot port provided at one end of the spool of the on-off valve, and the on-off valve is switched to the open position. This switching timing is adjusted in advance by a throttle valve provided in a circuit communicating with the tank.

  When the turning or traveling remote control valve is operated, the pilot pressure of the hydraulic pressure source is led to the pilot port of the turning or traveling direction control valve, and the direction control valve is switched to the turning or traveling position. At the same time, the switching valve is switched to the tank position by the pilot pressure of the hydraulic power source, and the pilot pressure of the on-off valve is returned to the tank, so that the opening and closing is performed by the bias of the spring provided at the other end of the spool of the on-off valve. The valve returns to the closed position, and the communication circuit between the driving circuits is shut off. Therefore, the pressure oil discharged from the hydraulic pump is led to one drive circuit through the direction control valve, and this pressure oil is supplied to the turning or traveling motor to rotate the turning or traveling motor in any direction. . The pressure oil that has passed through the turning or traveling motor is discharged to the other driving circuit, and this pressure oil returns to the tank through the direction control valve.

  When the turning or running remote control valve is returned from the turning or running operation position to the neutral position, the pilot pressure of the hydraulic power source is not derived to the pilot port of the turning or running direction control valve, and the direction control valve is in the neutral position. The hydraulic pump and the driving circuit are cut off, and pressure oil is not supplied to the turning or traveling motor. At the same time, since the pilot pressure of the hydraulic source does not act on the switching valve, the switching valve returns to the hydraulic source position, and the pilot pressure of the hydraulic source passes through the hydraulic source position of the switching valve to the pilot port of the on-off valve. Then, the on-off valve is switched to the open position. As described above, the switching timing is adjusted in advance by the throttle valve.

  Even if pressure oil is no longer supplied from the hydraulic pump, the rotation or traveling motor tries to continue to rotate for a while due to the inertia of the machine, so the drive circuit on the suction side becomes low pressure and tries to generate cavitation. Not only replenishment of pressure oil from the conventional make-up circuit to the drive circuit on the suction side, but also the drive circuit communicates by opening the on-off valve, so the pressure difference between the suction side and the discharge side is instantly eliminated. Thus, the occurrence of cavitation is reliably prevented.

  According to the first aspect of the present invention, a communication circuit having an opening / closing valve interposed between the driving circuits is connected, and the opening / closing valve is opened / closed by a switching valve interlocked with the operation of the turning or traveling remote control valve. Since the remote control valve for turning or traveling is returned from the turning or traveling operation position to the neutral position, the on-off valve is opened and the drive circuit is communicated with each other. And the pressure difference on the discharge side is eliminated instantly. The timing at which the on-off valve is switched to the open position can be adjusted in advance by the throttle valve. Therefore, combined with the replenishment of pressure oil from the conventional makeup circuit, the occurrence of cavitation is reliably prevented.

  In this way, by effectively using the return oil of the driving circuit, it is possible to efficiently take cavitation prevention measures while saving energy.

  Hereinafter, a cavitation prevention circuit for a construction machine according to the present invention will be described with reference to preferred embodiments. To achieve the object of preventing the occurrence of cavitation by effectively using the return oil of the drive circuit when the suction side becomes negative pressure when the construction machine turns or the traveling motor is suddenly stopped. Is a hydraulic circuit of a construction machine having a make-up circuit between driving circuits for supplying and discharging pressure oil to a turning or traveling motor, and the driving circuits are connected by a new communication circuit. A normally-closed on-off valve is installed on the way, the secondary port of the switching valve is connected to a pilot port that switches the on-off valve to the open position, and a hydraulic source and a tank are connected to the primary port of the switching valve. The switching valve is in the hydraulic pressure source position when there is no operation of the turning or traveling remote control valve, and the pilot pressure of the hydraulic pressure source is led to the pilot port of the on-off valve to bring the on-off valve to the open position. , This was realized by switching the switching valve to the tank position when the remote control valve for turning or traveling was operated, and releasing the pilot pressure of the on-off valve to the tank to bring the on-off valve to the closed position. .

  FIG. 1 shows a hydraulic excavator 10 as an example of a construction machine, and an upper swing body 13 is mounted on a lower traveling body 11 via a swing mechanism 12 so as to be rotatable. The upper swing body 13 is provided with a cab 14 on one front side thereof, and a boom 15 is attached to the front center portion so as to be able to be raised and lowered. Further, an arm 16 is attached to the tip of the boom 15 so as to be rotatable up and down, and a bucket 17 is attached to the tip of the arm 16.

  FIG. 2 shows a cavitation prevention circuit. The same components as those of the conventional circuit shown in FIG. 5 differs from the conventional circuit shown in FIG. 5 in that the driving circuits 53 and 54 of the turning or traveling motor 55 are connected by a new communication circuit 20, and a normally closed on-off valve 30 is provided in the middle of the communication circuit 20. It is intervening. A pilot port 31 is provided at one end of the spool of the on-off valve 30, and a spring 32 for pushing back the on-off valve 30 in the closing direction and a circuit 33 communicating with the tank 60 are provided at the other end of the spool of the on-off valve 30. A secondary port 41 of the switching valve 40 is connected to the pilot port 31 by a pilot circuit 45, and a throttle valve 34 is interposed in a circuit 33 communicating with the tank. The pilot circuit 45 is provided with a branch circuit 46, and the branch circuit 46 is provided with a brake 48 for braking the turning or traveling motor 55 via a slow return valve 47. The slow return valve 47 includes a throttle valve 47a and a check valve 47b that shuts off the pilot pressure from the switching valve 40 to the brake 48.

  The on-off valve 30 has a closed position (g) and an open position (h), and a check valve is arranged in the reverse direction at the closed position (g) so that pressure oil cannot pass from either direction. is there. Then, the bias of the spring 32 normally closes the communication circuit 20 in the closed position (g) and switches to the open position (h) when a predetermined pilot pressure is applied to the pilot port 31. The communication circuit 20 is opened, and the drive circuits 53 and 54 are communicated. In addition, although illustration is abbreviate | omitted, the said closing position (g) is not limited to the structure which arrange | positions a check valve in the reverse direction, You may form in the interruption | blocking state only so that pressurized oil cannot pass.

  The switching valve 40 has a hydraulic pressure source position (re) and a tank position (nu), and the secondary port 41 of the switching valve 40 is always connected to the pilot port 31 of the on-off valve 30 and a slow return valve. 47 is always connected to the brake 48, and the tank 60 and the hydraulic source 68 are selectively connected to the primary side port 42. A shuttle valve 49 is interposed between the pilot circuits 52 a and 52 b of the turning or traveling remote control valve 52, and the outlet port of the shuttle valve 49 is connected to the pilot port 43 of the switching valve 40.

  The switching valve 40 is normally in a hydraulic pressure source position (re) due to the bias of the spring 44 and connects the primary port 42 to the hydraulic pressure source 68, and the pilot pressure from the hydraulic pressure source 68 is supplied to the pilot circuit. It is led to the pilot port 31 of the on-off valve 30 through 45 and to the brake 48 via a slow return valve 47 provided in the pilot circuit 46. On the other hand, when the shuttle valve 49 selects a pilot pressure in either of the pilot circuits 52a and 52b of the turning or traveling remote control valve 52 and a predetermined pilot pressure is applied to the pilot port 43 of the switching valve 40, When the switching valve 40 is switched to the tank position (n), the primary port 42 is connected to the tank 60, and the pilot pressure applied to the pilot port 31 of the on-off valve 30 and the pilot pressure applied to the brake 48 are applied to the tank 60. It is formed to return.

  Next, the operation of the cavitation prevention circuit of the present invention will be described. When the operation of the excavator 10 is stopped and the hydraulic pump 50 and the hydraulic source 68 are not driven, the pilot pressure from the pilot circuits 52a and 52b is applied to the pilot port 43 of the switching valve 40 as shown in FIG. Since it is not derived, the switching valve 40 is in the hydraulic pressure source position (re). In this state, although the primary port 42 of the switching valve 40 is connected to the hydraulic source 68, no pressure oil is supplied from the hydraulic source 68, so that pilot pressure is derived to the pilot port 31 of the on-off valve 30. Since the on-off valve 30 maintains the closed position (g), the communication circuit 20 between the drive circuits 53 and 54 is shut off.

  In this operation stop state, since the circuits between the drive circuits 53 and 54 are both cut off, no pressure oil flows in and out between the drive circuits 53 and 54, and the turning or traveling motor 55 is operated. The upper revolving unit 13 does not rotate and unexpectedly swivels, or the excavator 10 does not escape.

  When the operation of the hydraulic excavator 10 is started and the hydraulic pump 50 and the hydraulic power source 68 are driven, the switching valve 40 is operated as the hydraulic power source when the turning or traveling remote control valve 52 is not operated as shown in FIG. Therefore, the pilot pressure of the hydraulic power source 68 is led to the pilot port 31 of the on-off valve 30 through the hydraulic power source position (re) of the switching valve 40, and the on-off valve 30 is in the open position (h). Switch to. Accordingly, the communication circuit 20 is opened and the drive circuits 53 and 54 are in communication with each other, but at the same time, the pilot pressure of the hydraulic source 68 passes through the hydraulic source position (re) of the switching valve 40 to the brake 48. Then, the turning or traveling motor 55 is braked, so that the turning or traveling motor 55 does not run idle and the upper turning body 13 performs an unexpected turning operation or the excavator 10 does not escape. The timing at which the on-off valve 30 switches to the open position (h) is adjusted in advance by a throttle valve 34 interposed in a circuit 33 communicating with the tank.

  When the turning or traveling remote control valve 52 is operated to turn the upper swing body 13 or to drive the hydraulic excavator 10, a pilot pressure is generated from the hydraulic source 68 in either of the pilot circuits 52a and 52b. Then, the pilot pressure is led to one of the pilot ports 51a and 51b of the turning or traveling direction control valve 51, and the direction control valve 51 is switched to the turning or traveling position (b) or (c).

  For example, as shown in FIG. 4, when the turning or traveling remote control valve 52 is turned right or forward, a pilot pressure is generated in the pilot circuit 52b and is led to the pilot port 51a of the direction control valve 51. The control valve 51 switches to the right turn or forward position (B). At the same time, the shuttle valve 49 selects the high pilot pressure of the pilot circuit 52b, a predetermined pilot pressure is derived to the pilot port 43 of the switching valve 40, and the switching valve 40 is switched to the tank position (N). Since the pilot pressure applied to the pilot port 31 of the on-off valve 30 returns to the tank 60, the on-off valve 30 is switched to the closed position (g) by the bias of the spring 32. On the other hand, the pilot pressure applied to the brake 48 returns to the tank 60 via the check valve 47b of the slow return valve 47, and the turning or braking of the traveling motor 55 is quickly released.

  Then, the pressure oil discharged from the hydraulic pump 50 is led to one drive circuit 53 through the right turn or forward position (b) of the direction control valve 51, and the pressure oil is supplied to the turn or travel motor 55. Thus, the turning or traveling motor 55 rotates in the right direction. The pressure oil that has passed through the turning or traveling motor 55 is discharged to the other driving circuit 54, and returns to the tank 60 from the right turning or forward position (B) of the direction control valve 51. In this state, the on-off valve 30 blocks the communication circuit 20 at the closed position (g), so that no pressure oil flows in and out between the driving circuits 53 and 54.

  Here, when the turning or traveling remote control valve 52 is returned from the right turning or forward operation position to the neutral position in order to stop the turning or traveling motor 55 rotating, as shown in FIG. The pilot pressure 68 is not led to the pilot port 51a of the directional control valve 51, the directional control valve 51 is switched to the neutral position (A), and the hydraulic pump 50 and the driving circuits 53 and 54 are shut off. At the same time, since the pilot pressure of the hydraulic source 68 does not act on the pilot port 43 of the switching valve 40, the switching valve 40 returns to the hydraulic source position (re) by the bias of the spring 44, and the pilot pressure of the hydraulic source 68 Is led to the pilot port 31 of the on-off valve 30 through the hydraulic pressure source position (re) of the switching valve 40, the on-off valve 30 is switched to the open position (h) and the pilot pressure of the hydraulic source 68 is changed to the switching valve 40. The hydraulic pressure source position (re) and the slow return valve 47 lead to the brake 48. The switching timing of the on / off valve 30 is adjusted in advance by the throttle valve 34 and the throttle valve 47a of the slow return valve 47, while the turning or traveling motor 55 is prevented from being shocked by sudden braking when the turning is stopped or stopped. Then, the brake is gradually braked by the throttle valve 47a of the slow return valve 47.

  Even if pressure oil is not supplied from the hydraulic pump 50, the turning or traveling motor 55 tries to continue to rotate for a while due to the inertial force of the upper swing body 13 or the inertial force in the downhill direction when descending the slope. Therefore, the suction side driving circuit 53 becomes low pressure, and the pressure oil is sucked into the suction side driving circuit 53 from the makeup circuit 59 and replenished.

  Further, the discharge side drive circuit 54 is blocked by the direction control valve 51 so that the pressure becomes high, and the release valve 30 is in the open position (h), so that the high pressure return oil passes through the communication circuit 20 and is on the suction side. It flows into the driving circuit 53.

  Thus, not only replenishment of the pressure oil from the makeup circuit 59 to the drive circuit 53 on the suction side, but also the return oil of the drive circuit 54 is effectively used, so that the pressure difference between the suction side and the discharge side is instantaneous. Thus, cavitation prevention measures can be efficiently performed while saving energy.

  It should be noted that the present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

1 is a side view of a hydraulic excavator to which the present invention is applied. Explanatory drawing which shows the cavitation prevention circuit which concerns on this invention. Explanatory drawing which shows operation | movement of the cavitation prevention circuit which concerns on this invention. Explanatory drawing which shows operation | movement of the cavitation prevention circuit which concerns on this invention. Explanatory drawing which shows the conventional cavitation prevention circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Hydraulic excavator 13 Upper turning body 20 Communication circuit 30 On-off valve 31 Pilot port 32 Spring 33 Circuit connected to tank 34 Throttle valve 40 Switching valve 41 Secondary side port 42 Primary side port 43 Pilot port 44 Spring 47 Slow return valve 47a Throttle Valve 47b Check valve 48 Brake 49 Shuttle valve 50 Hydraulic pump 51 Direction control valve 52 Swing remote control valve 53, 54 Drive circuit 55 Swing motor 57, 58 Check valve 59 Make-up circuit 60 Tank 61, 62, 63 Check valve 64, 65 Check valve 66, 67 Cross relief valve 68 Hydraulic source

Claims (1)

In a hydraulic circuit of a construction machine having a make-up circuit between drive circuits for supplying and discharging pressure oil to a turning or traveling motor via a direction control valve ,
A connection between the driving circuit and the direction control valve, and a connection between the driving circuit and the makeup circuit at a position between the driving circuit and the make-up circuit are connected by a new communication circuit, A normally closed on-off valve is provided in the middle of the communication circuit, a pilot port for switching the on-off valve to an open position is provided at one end of the spool of the on-off valve, and a tank communicates with the other end of the spool of the on-off valve. And a spring that pushes back the opening / closing valve in the closing direction, a secondary port of the switching valve is connected to the pilot port, and a throttle valve is interposed in the circuit that communicates with the tank. Connect the hydraulic source and tank to the primary side,
The switching valve is in the hydraulic pressure source position when there is no operation of the turning or traveling remote control valve, and the pilot pressure of the hydraulic pressure source is led to the pilot port of the on-off valve to bring the on-off valve to the open position. A construction characterized in that when the traveling remote control valve is operated, the switching valve is switched to the tank position, and the pilot pressure of the on-off valve is released to the tank so that the on-off valve is in the closed position. Machine cavitation prevention circuit.

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