JP2010112494A - Cavitation prevention circuit for working machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more surely prevent cavitation while achieving energy saving at low cost without enlarging apparatuses. <P>SOLUTION: This device includes a negative control circuit generating negative control pressure by providing a negative control restriction 14 in an oil passage passing through a turning control valve 20A for controlling a turning motor 22 and applying the negative control pressure on a regulator 16 for controlling delivery quantity of the pump 18. When speed reduction of the turning motor 22 is detected, (low) false negative control pressure is applied on the regulator 16 by a negative control pressure change over valve 58 and delivery quantity of the pump 18 is increased, and foot release valve (unload valve) 60 is unloaded. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cavitation prevention circuit for a work machine.

  When a hydraulic actuator such as a swing motor, a traveling motor or various hydraulic cylinders of a construction machine or the like is suddenly stopped, the suction side circuit of the hydraulic actuator becomes negative pressure due to the inertia of the hydraulic actuator, so-called cavitation occurs. It tends to occur.

  FIG. 2 is an example of a hydraulic control circuit of a hydraulic excavator described in Patent Document 1 as a hydraulic circuit for preventing the occurrence of cavitation. This hydraulic control circuit is referred to as a negative control system. A negative control throttle 14 is provided downstream of the center bypass oil passage 12 to generate a pressure called negative control pressure, which is applied to the regulator 16 and pumped. 18 discharge amount is negatively controlled.

  Now, for example, when a turning control lever (not shown) is operated, the turning control valve 20A is switched, and the discharge oil of the pump 18 is supplied to the turning motor 22 via the supply oil passage 24 (26). The swivel body starts turning. When the turning operation lever is returned, the turning control valve 20A returns to the neutral position. As a result, the supply oil passage 24 (26) of the pump 18 and the communication oil passage 26 (24) of the tank T are closed, and the swing motor 22 is decelerated by the relief valve 28. At the time of deceleration, the swing motor 22 needs to suck in oil immediately after the start of deceleration due to the pump action. In this circuit, the makeup oil path 30 is connected to the drain oil path 26 and the downstream of the drain oil path 26. Cavitation is prevented by providing back pressure check valves 32 and 34 at the part to increase the circuit pressure and making the swing motor 22 easily suck oil. Reference numeral 36 denotes an oil cooler.

  However, in the hydraulic control circuit shown in FIG. 2, since the back pressure is always generated by the back pressure check valves 32 and 34, the discharge pressure of the pump 18 is increased by the back pressure in every state. The energy consumption of 18 increased, and the fuel consumption of the engine and the like deteriorated.

  Therefore, in Patent Document 1, as shown in FIG. 3, the back pressure check valve 32 in FIG. 2 is changed to a variable check valve (variable differential pressure valve) 40, and the deceleration state of the swing motor 22 is changed via the shuttle valve 43. An improved technique has been proposed in which the pressure of the pilot pump 50 is applied to the pilot port 40A of the variable check valve 40 only during deceleration by the controller 46 via the switching valve 48 and detected by the pressure switch 44 or the like. As a result, back pressure is generated in the drain oil passage 26 only during turning deceleration to prevent cavitation. According to this technique, since it is possible to prevent the back pressure from being generated in the drain oil passage 26 at times other than during turning deceleration, energy saving can be realized.

  On the other hand, in Patent Document 2, as a hydraulic control circuit for solving the same problem, a bypass valve is provided in a bypass passage provided in parallel with the back pressure check valve (32), and the bypass valve is closed only when the hydraulic actuator is stopped. It proposes an improved technology that generates back pressure.

JP 2003-120603 A JP 2002-89505 A

  However, with the improved technology described in Patent Document 1, although an energy saving effect is certainly recognized, the cost of the equipment increases and the device tends to be large, which is difficult to say as a practical technology. was there.

  Further, in the improved technology described in Patent Document 2, since the negative control pressure is used to close the bypass valve, and the operation of closing the bypass valve does not function unless all the actuators are stopped. Even if the turning operation is simultaneously performed and the turning operation is stopped first, there is a problem that the bypass valve cannot be closed because the negative control pressure does not increase. That is, the back pressure does not increase unless all the actuators are stopped and the turning is stopped at the end. As a result, in many situations, the turning motor does not suck oil well and cavitation occurs. There was a case.

  The present invention has been made in view of such a conventional situation, and is a work machine that can prevent cavitation more reliably while realizing energy saving, without increasing the size of the device and at low cost. It is an object of the present invention to provide a cavitation prevention circuit.

  According to the present invention, in a cavitation prevention circuit for a work machine having a make-up oil passage in a drive circuit for supplying and discharging pressure oil to and from a hydraulic actuator, a negative constriction is provided in the oil passage that passes through a control valve that controls the hydraulic actuator. The negative control circuit that generates the negative control pressure and applies the negative control pressure to the regulator that controls the discharge amount of the pump, and the regulator can be applied by switching to the pseudo negative control pressure in which the negative control pressure is artificially reduced. A negative control pressure switching valve, an unload valve provided in parallel with the negative control throttle, and a deceleration detection means for detecting deceleration of the hydraulic actuator, and when the deceleration of the hydraulic actuator is detected, the negative control pressure The pseudo negative control pressure is applied to the regulator by a switching valve. Ri with increasing displacement of said pump, by unloading the unloading valve, in which the above-mentioned problems are eliminated.

  In the present invention, in order to prevent cavitation, the characteristics of the negative control circuit itself are basically used (rather than increasing the back pressure of the drain oil passage). That is, when the deceleration of the hydraulic actuator is detected, the discharge amount of the pump is increased by applying the pseudo negative control pressure reduced to the regulator by the negative control pressure switching valve, thereby preventing cavitation. At the same time, an unloader valve is disposed with respect to the negative control throttle, and when the pseudo negative control pressure is applied, the unloader valve is unloaded. As a result, the back pressure load of the pump can be reduced. For example, even in a situation where turning and stopping are frequently repeated, the pump discharge amount frequently becomes the maximum discharge amount and the fuel efficiency is deteriorated. Can be prevented.

  In the present invention, the unloading valve is an electromagnetic pilot type variable relief valve, and when the deceleration of the hydraulic actuator is detected, the variable relief valve is driven to the unloading side. Can obtain an unloading action accurately linked with the switching to the pseudo negative control pressure.

  Further, in the present invention, the unload valve is configured to include a relief valve and a communication valve in parallel, and when the deceleration of the hydraulic actuator is detected, the communication valve switches to the communication side. Even in this case, similarly, an unloading action accurately linked with the switching to the pseudo negative control pressure can be obtained.

  Since the present invention prevents cavitation by increasing the discharge rate of the pump by utilizing the characteristics of the negative control circuit, the drain pressure downstream of the negative control throttle has a conventional back pressure for generating back pressure. The check valve circuit is not necessarily provided. However, in the present invention, it is not prohibited to provide this back pressure check valve circuit. By providing this back pressure check valve circuit, the effect of preventing cavitation can be further enhanced.

  According to the present invention, it is possible to prevent cavitation while reducing the cost and achieving energy saving without increasing the size of the hydraulic control device of the work machine.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an overall configuration of a hydraulic control circuit for a work machine according to an example of an embodiment to which the present invention is applied. The same components as those of the conventional apparatus (FIGS. 2 and 3) are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

  In FIG. 1, a control valve group 20 (20A to 20D in the illustrated example) is connected to the center bypass oil passage 12 of the pump 18. In this example, the control valve 20A corresponds to a turning control valve (control valve) to which the present invention is applied. A negative control (a negative feedback control throttle) 14 is disposed downstream of the center bypass oil passage 12 and can generate a so-called negative control pressure. The negative control pressure acts on the regulator 16 that controls the discharge amount of the pump 18 via the feedback oil passage 56, and a “negative control circuit” is configured in which the discharge amount of the pump 18 is adjusted according to the negative control pressure.

  A makeup oil passage 30 is connected downstream of the negative control aperture 14 and further branches into oil passages 52 and 54. The branch oil passage 52 is connected to the tank T via the check valve 32 and the oil cooler 36, and the branch oil passage 54 is connected to the tank T via the check valve 34. The relief pressures of the check valves 32 and 34 are determined in consideration of the pipeline resistance of the oil cooler 36, the flow rate ratio of each oil passage, the back pressure necessary for preventing cavitation, and the like. In this embodiment, the prevention of cavitation is basically performed by increasing the discharge amount of the pump 18. Therefore, the relief pressure of the check valves 32 and 34 can be made smaller than the conventional relief pressure that has prevented cavitation by this alone, and the fuel consumption can be prevented from deteriorating accordingly (may be omitted in some cases) Is).

  The makeup oil passage 30 is connected between the drive circuits P1 of the turning motor 22. If the amount of oil that can flow into the make-up oil passage 30 can be secured to a certain extent or more (the oil pressure in either the oil passage 24 or the oil passage 26 is reduced, and the gas in the oil passage is bubbled as it is. (Even in a situation where cavitation occurs), the oil flows from the makeup oil passage 30 into the oil passage 24 or the oil passage 25 at a low pressure, and the decrease in hydraulic pressure is alleviated, thereby preventing the occurrence of cavitation. This is the basic technical principle of cavitation prevention in this embodiment.

  Here, a negative control pressure switching valve (electromagnetic valve) 58 is disposed in the negative control pressure feedback oil passage 56. A foot relief valve (unload valve) 60 is disposed in parallel with the negative control throttle 14. The foot relief valve 60 is a pilot-type relief valve. When the pilot pressure of the solenoid valve 62 is applied to the pilot port 60A, the oil relief state is established and the negative control throttle 14 can function. When it does not act on the pilot port 60A, it is driven to the unload side. The negative control pressure switching valve 58 and the solenoid valve 62 of the foot relief valve 60 are driven by control signals S 1 and S 2 from the controller 64. The generation of the control signals S1 and S2 will be described in detail later.

  On the other hand, a pressure switch (deceleration detection means) 44 is connected to the input side of the controller 64. The pressure switch 44 is connected to the output side oil passage of the turning operation lever 42 via the shuttle valve 43. The output of the turning control lever 42 is connected to pilot ports 20A1 and 20A2 of the turning control valve 20A.

  The controller 64 detects and stores the ON state of the pressure switch 44 (a state in which the pilot pressure is acting). The moment when the state is switched from this state to the off state (state where the pilot pressure does not act) is detected (deceleration of the swing motor 22 as a hydraulic actuator is detected), and the control signals S1 and S2 are output for a predetermined time.

  When the control signal S 1 is output from the controller 64, the negative control pressure switching valve 58 is switched from the state “A” to the state “B” in the figure, and the extremely low pressure pseudo negative control pressure is applied to the regulator 16. Yes. When the control signal S2 is output from the controller 64, the electromagnetic valve 62 is switched from the state “A” to the state “B” in the figure, and the pilot port 60A of the foot relief valve 60 (which has been applied so far) is switched. The pressure is no longer applied and the foot relief valve 60 is in an unloaded state.

  In this embodiment, the control signals S1 and S2 are configured to be generated “simultaneously” in conjunction with the switching of the pressure switch 44. However, in the actual hydraulic control circuit design, Considering a response delay due to the oil path length, etc., a slight time difference may be provided in the generation of the control signals S1 and S2. For example, first, after generating the control signal S1 for switching the negative control pressure switching valve 58 and securing the oil amount in the pump 18, the control signal S2 is generated (slightly behind) and the foot relief valve 60 is turned on. A configuration for unloading may be adopted. As a result, the influence on other operating hydraulic actuators can be minimized. Further, if the effect of preventing cavitation is higher when the control signal S2 is issued earlier due to the arrangement position of the makeup oil passage 30 in the hydraulic control circuit, the control signal S2 is issued earlier. May be.

  This embodiment functions as follows by the above configuration.

  That is, when the turning operation lever 42 is operated, the pilot hydraulic pressure acts on the pilot port 20A1 or 20A2 of the turning control valve 20A, and the pump 18 rotates in the operation direction. At this time, the pressure switch 44 detects this pilot oil pressure and is turned on. The controller 64 stores the ON state in the memory. In this state, the controller 64 sets the control signal to zero and does not output the control signals S1 and S2. Next, when the turning operation lever 42 is operated from this state to the stop state (neutral state), the pilot hydraulic pressure is lowered. At this time, the pressure switch 44 is switched to the off state, and the off state is input to the controller 64. The controller 64 outputs the control signals S1 and S2 at the same time for the time necessary to prevent cavitation, and after the elapse of this time, both the control signals S1 and S2 are set to zero and the memory storage is cleared.

  When the control signal S <b> 1 is output from the controller 64, the negative control pressure switching valve 58 is switched from the state “A” to the state “B” in the figure, and an extremely low pseudo negative control pressure acts on the regulator 16. As a result, the discharge amount of the pump 18 is increased to the maximum by the function of the regulator 16. In other cases, the controller 64 sets the control signal S1 to zero, and maintains the negative control pressure switching valve 58 in the state “A”. It is desirable that the pressure switch 44 be turned on / off at a relatively high pressure, thereby increasing the response speed of the oil amount increase in the makeup oil passage 30.

  On the other hand, when the control signal S2 is output from the controller 64, the electromagnetic valve 62 is switched from the state “A” to the state “B” in the figure, and the pilot pressure that has been applied to the pilot port 60A of the foot relief valve 60 so far is changed. No longer works. As a result, the foot relief valve 60 is unloaded, and the presence of the check valves 32, 34, coupled with the occurrence of back pressure in the drain oil passage to the tank T, causes the oil in the center bypass oil passage 12. Regardless of the presence of the negative control throttle 14, a large amount can flow into the makeup oil passage 30 in an unloaded state. Since the oil in the center bypass oil passage 12 is supplied by the pump 18 with the maximum discharge amount, there is no fear of exhaustion. In other cases, the controller 64 sets the control signal S2 to zero and maintains the electromagnetic valve 62 in the state “A”.

  The pump 18 discharges oil at the maximum discharge amount, but since the foot relief valve 60 is in an unloaded state, the load on the pump 18 is extremely small (even if the pump is frequently turned and stopped, Energy saving operation is possible (even in situations where the discharge rate increases frequently at 18).

  As described above, the present invention has been described in detail based on the embodiment in which the present invention is applied to a swing motor, but the scope of application of the present invention is not limited to this. For example, the present invention effectively functions not only for a swing motor but also for a hydraulic actuator such as a traveling motor or a hydraulic cylinder such as a boom or an arm.

  Further, the configuration of the unload valve is not limited to the configuration of the above embodiment. For example, even when the unloading valve is configured to include a relief valve and a communication valve in parallel, and when the deceleration of the hydraulic actuator is detected, the communication valve is switched to the communication side. A similar effect can be obtained.

  Furthermore, in the above-described embodiment, the back pressure check valve circuit for generating back pressure similar to the conventional one is arranged downstream of the negative control, but the present invention basically uses the characteristics of the negative control circuit. Since the cavitation is prevented by increasing the discharge amount of the pump, it is not always necessary to provide a back pressure check valve circuit for generating back pressure in the drain oil passage downstream of the negative control throttle. When the back pressure check valve circuit for generating back pressure is saved, it is possible to further reduce the cost and further energy saving operation. On the other hand, when the back pressure check valve circuit is provided, the cavitation Can be further enhanced.

  In a working machine such as a construction machine, it can be suitably used for a hydraulic actuator that generates cavitation when suddenly decelerated.

1 is an overall configuration diagram of a hydraulic control circuit for a work machine to which a cavitation prevention circuit for a work machine according to an embodiment of the present invention is applied. 1 is an overall configuration diagram corresponding to FIG. 1 showing an example of a cavitation prevention circuit of a conventional work machine Partial circuit diagram showing an improved example of a conventional cavitation prevention circuit for work machines

Explanation of symbols

12 ... Center bypass oil passage 14 ... Negative control throttle 16 ... Regulator 18 ... Pump 20A ... Swing control valve (control valve)
22 ... Swivel motor (hydraulic actuator)
26 ... Drain oil passage 30 ... Make-up oil passage 42 ... Swivel operation lever 43 ... Shuttle valve 44 ... Pressure switch (deceleration detection means)
58 ... Negative control pressure switching valve 60 ... Foot relief valve (unload valve)
62 ... Solenoid valve 64 ... Controller

Claims (4)

In a cavitation prevention circuit for a work machine having a make-up oil passage in a drive circuit for supplying and discharging pressure oil to and from a hydraulic actuator,
A negative control circuit that generates a negative control pressure by providing a negative control throttle in an oil passage that has passed through a control valve that controls the hydraulic actuator, and applies the negative control pressure to a regulator that controls the discharge amount of the pump;
A negative control pressure switching valve that can be applied to the regulator by switching to a pseudo negative control pressure obtained by quasi-depressing the negative control pressure;
An unloading valve provided in parallel with the negative control throttle,
A deceleration detecting means for detecting deceleration of the hydraulic actuator,
When the deceleration of the hydraulic actuator is detected, the negative control pressure is applied to the regulator by the negative control pressure switching valve to increase the discharge amount of the pump and unload the unload valve. A cavitation prevention circuit for work machines. In claim 1,
The unloading valve is an electromagnetic pilot type variable relief valve, and when the deceleration of the hydraulic actuator is detected, the variable relief valve is driven to the unloading side. circuit. In claim 1,
The unloading valve is configured to include a relief valve and a communication valve in parallel, and when the deceleration of the hydraulic actuator is detected, the communication valve is switched to the communication side. Cavitation prevention circuit. The work pressure cavitation prevention circuit according to any one of claims 1 to 3, further comprising a back pressure check valve circuit capable of generating back pressure in an oil passage to a tank downstream of the negative control throttle.

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