JP2006177402A - Hydraulic circuit of construction machinery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain a downward movement of a heavy burden caused by its own weight, heighten an action velocity of a cylinder as well as reducing power losses of a prime mover for driving a hydraulic pump, ensure a cylinder action even in a low-power condition of the prime mover, and further to permit an opening control action of a variable open nozzle to perform more surely. <P>SOLUTION: In a meter out pipe line 7 which is branched from a rod side pipe line 5b communicating with a rod side oil chamber 6b of a hydraulic cylinder 6 to be connected to a tank 4, a pilot variable open nozzle 8 is intervened. Thereby, an opening degree in the pilot variable open nozzle 8 is controlled in response to a pilot control pressure output from a proportional decompression solenoid valve 13. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydraulic circuit of a construction machine, and in particular, when applied to a hydraulic excavator, can suppress a weight load drop, reduce power loss of a prime mover, increase a cylinder operating speed, and The present invention relates to a hydraulic circuit of a construction machine that can ensure cylinder operation even when a prime mover is in a low output state.

  As a conventional technique related to a hydraulic circuit of a construction machine, for example, the following hydraulic drive circuit is known. This prior art is arranged between a variable displacement hydraulic pump driven by a prime mover, a hydraulic cylinder connected to the variable displacement hydraulic pump, and between the variable displacement hydraulic pump and the hydraulic cylinder, and controls driving of the hydraulic cylinder. An electromagnetic proportional flow rate adjusting valve having a direction switching function and a flow meter for detecting a load flow rate adjusted by the flow rate adjusting valve. The flow rate adjusting valve is operated by a drive signal output from the valve control device based on a flow rate command value from the flow rate command means.

  Further, a branch point is provided in the main pipeline that forms the meter-out side pipeline between the flow rate adjusting valve and the hydraulic cylinder, and a branch pipeline that connects the branch point and the tank is provided. In the branch pipe, there is provided a variable adjustment valve including an electromagnetic switching valve capable of secondarily finely adjusting the flow rate adjusted by the flow rate adjustment valve. When the flow rate command value from the flow rate command means is smaller than a reference value, the variable adjustment valve operates according to the drive signal output from the external command means according to the magnitude of the flow rate command value.

When the hydraulic cylinder is finely operated, the opening of the variable adjustment valve is controlled in accordance with the magnitude of the flow rate command value, so that a part of the flow rate guided to the main line passes through the branch line to the tank. The supply flow rate to the hydraulic cylinder during the fine operation can be finely adjusted well (see, for example, Patent Document 1).
JP-A-8-4705 (pages 5-7, FIG. 1).

  In the prior art described in Patent Document 1, a variable adjustment valve that can secondarily finely adjust the flow rate adjusted by the flow rate adjustment valve is provided in the branch pipeline from the main pipeline. The variable adjustment valve is operated by a drive signal output from the external command means to enable fine operation of the hydraulic cylinder.

  By the way, a hydraulic circuit including a hydraulic cylinder is often used for operating an arm cylinder, a bucket cylinder, and the like in a hydraulic excavator. In this application example, arms, buckets, etc. are a significant weight load for the hydraulic cylinder. For this reason, a hydraulic circuit that can suppress the weight drop of the heavy load and increase the operating speed of the cylinder is desired in order to improve work accuracy and workability.In addition, in order to save energy, the power loss of the prime mover is reduced. What can be reduced and can ensure cylinder operation even when the prime mover is in a low output state is desired.

  Therefore, the weight drop of the weight load is suppressed, the power loss of the prime mover is reduced, the operating speed of the cylinder is increased, the cylinder operation is secured even when the prime mover is in a low output state, and the opening control operation of the variable opening valve is further improved. The technical problem which should be solved arises in order to make it perform reliably, and this invention aims at solving this problem.

  The present invention has been proposed to achieve the above object, and the invention according to claim 1 includes a hydraulic pump that is rotationally driven by a prime mover, and a hydraulic cylinder including a rod side oil chamber and a head side oil chamber. A directional control valve that controls supply and discharge of pressure oil from the hydraulic pump to the hydraulic cylinder via a rod side conduit communicating with the rod side oil chamber and a head side conduit communicating with the head side oil chamber. A pilot variable opening valve is interposed in a meter-out pipe branched from the rod side pipe and connected to the tank, and the pilot is controlled according to a pilot control pressure from an electromagnetic proportional pressure reducing valve. Provided is a hydraulic circuit for a construction machine configured to control the width of an opening in a variable opening valve.

  According to this configuration, the hydraulic circuit of the construction machine is applied to an operating hydraulic circuit such as an arm cylinder or a bucket cylinder in a hydraulic excavator. Due to the weight of the arm and the bucket, which is a heavy load for the hydraulic cylinder, a tendency to drop its weight occurs. At this time, by reducing the opening of the pilot variable opening valve controlled by the electromagnetic proportional pressure reducing valve to prevent the holding pressure of the rod side oil chamber from being lowered, the drop in its own weight can be suppressed. In addition, when the hydraulic cylinder is operated by supplying pressure oil at the time of high rotation of the prime mover to the head side oil chamber, the opening of the pilot variable opening valve controlled by the electromagnetic proportional pressure reducing valve is appropriately widened. The occurrence of boost pressure in the rod side oil chamber is suppressed.

  The invention according to claim 2 is a pressure sensor that detects a holding pressure of the rod side oil chamber in the hydraulic cylinder, a rotation speed sensor that detects a rotation speed of the prime mover, and the rod side that is detected by the pressure sensor. When the holding pressure of the oil chamber is lower than a predetermined pressure, the opening of the pilot variable opening valve is expanded through the electromagnetic proportional pressure reducing valve, and when the holding pressure is higher than the predetermined pressure, the rotation speed sensor detects the rotation speed sensor. There is provided a hydraulic circuit for a construction machine having control means for controlling so as to narrow the opening of the pilot variable opening valve via the electromagnetic proportional pressure reducing valve as the rotation speed of the prime mover is lower than a predetermined rotation speed.

  According to this configuration, when the holding pressure of the rod-side oil chamber is lower than a predetermined pressure in the state of supplying pressure oil to the head-side oil chamber, it is determined that the excavating operation is being performed by the bucket of the hydraulic shovel. At this time, the back pressure of the rod side oil chamber is further reduced by widening the opening of the pilot variable opening valve controlled by the electromagnetic proportional pressure reducing valve. Further, when the holding pressure of the rod-side oil chamber is higher than a predetermined pressure when the pressure oil is supplied to the rod-side oil chamber, the pilot variable that is controlled by the electromagnetic proportional pressure reducing valve as the number of rotations of the prime mover is lower than the predetermined number of rotations By narrowing the opening of the opening valve, the operation of the hydraulic cylinder is ensured even when the prime mover is in a low output state.

  According to the first aspect of the present invention, a pilot variable opening valve is interposed in a meter-out pipe branched from the rod side pipe and connected to the tank, and the pilot variable opening valve according to the pilot control pressure from the electromagnetic proportional pressure reducing valve. Since the opening of the pilot variable opening valve controlled by the electromagnetic proportional pressure reducing valve is throttled, the weight drop of the arm, bucket, etc., which is a heavy load, can be suppressed. Also, when pressure oil is supplied to the head side oil chamber at the time of high rotation of the prime mover, boost pressure is generated in the rod side oil chamber by appropriately widening the opening of the pilot variable opening valve controlled by the electromagnetic proportional pressure reducing valve. This can suppress the loss of power of the prime mover and increase the operating speed of the hydraulic cylinder. Furthermore, there is an advantage that the opening control operation can be performed more reliably by controlling the width of the opening of the pilot variable opening valve in accordance with the pilot control pressure from the electromagnetic proportional pressure reducing valve.

The invention according to claim 2 is a pressure sensor that detects a holding pressure of the rod side oil chamber in the hydraulic cylinder, a rotation speed sensor that detects a rotation speed of the prime mover, and the rod side that is detected by the pressure sensor. When the holding pressure of the oil chamber is lower than a predetermined pressure, the opening of the pilot variable opening valve is expanded through the electromagnetic proportional pressure reducing valve, and when the holding pressure is higher than the predetermined pressure, the rotation speed sensor detects the rotation speed sensor. And a control means for controlling the opening of the pilot variable opening valve via the electromagnetic proportional pressure reducing valve as the number of revolutions of the prime mover is lower than a predetermined number of revolutions. When the holding pressure of the rod-side oil chamber is lower than the predetermined pressure in the supply state, the back pressure of the rod-side oil chamber is further reduced by widening the opening of the pilot variable opening valve controlled by the electromagnetic proportional pressure reducing valve. It is possible to increase the operating speed of the hydraulic cylinder makes it possible to reduce the power loss of the machine. Further, when the holding pressure of the rod-side oil chamber is higher than a predetermined pressure when the pressure oil is supplied to the rod-side oil chamber, the pilot variable that is controlled by the electromagnetic proportional pressure reducing valve as the number of rotations of the prime mover is lower than the predetermined number of rotations. By narrowing down the opening of the opening valve, there is an advantage that the operation of the hydraulic cylinder can be secured even when the prime mover is in a low output state and the operation speed can be increased.

  Reduces the weight drop of the heavy load, reduces the power loss of the prime mover, increases the cylinder operating speed, ensures the cylinder operation even when the prime mover is in a low output state, and more reliably performs the opening control operation of the variable opening valve A hydraulic pump that is rotationally driven by a prime mover, a hydraulic cylinder that includes a rod-side oil chamber and a head-side oil chamber, a rod-side conduit that communicates with the rod-side oil chamber, and the head-side oil chamber In a hydraulic circuit of a construction machine having a directional control valve for controlling supply and discharge of pressure oil from the hydraulic pump to the hydraulic cylinder via a head side pipe communicating with the tank, a tank branched from the rod side pipe A pilot variable opening valve interposed in a meter-out conduit communicated with the solenoid, and an electromagnetic for controlling the width of the opening in the pilot variable opening valve in accordance with the pilot control pressure An example pressure reducing valve, a pressure sensor for detecting a holding pressure of the rod side oil chamber in the hydraulic cylinder, a rotation speed sensor for detecting the rotation speed of the prime mover, and the rod side oil chamber detected by the pressure sensor When the holding pressure is lower than a predetermined pressure, the opening of the pilot variable opening valve is expanded through the electromagnetic proportional pressure reducing valve, and when the holding pressure is higher than the predetermined pressure, the rotation of the prime mover detected by the rotation speed sensor This is realized by including control means for controlling the pilot variable opening valve to narrow the opening through the electromagnetic proportional pressure reducing valve as the number is lower than the predetermined rotation number.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a hydraulic circuit diagram, and FIG. 2 is a diagram showing an opening characteristic of a pilot variable opening valve. The present embodiment is applied to an operating hydraulic circuit such as an arm cylinder or a bucket cylinder in a hydraulic excavator.

  First, the configuration of the hydraulic circuit of the construction machine according to the present embodiment will be described with reference to FIG. A discharge port of a variable displacement hydraulic pump 2 that is rotationally driven by an engine 1 as a prime mover is communicated with an oil supply port of a direction control valve 3. The oil discharge port of the directional control valve 3 communicates with the tank 4. The direction control valve 3 is a four-port three-position valve, and includes a neutral position 3a, an extension side position 3b, and a reduction side position 3c.

  One output port of the directional control valve 3 communicates with the head side oil chamber 6a in the hydraulic cylinder 6 via the head side conduit 5a, and the other output port of the directional control valve 3 is connected to the rod side conduit 5b. And communicates with the rod-side oil chamber 6b in the hydraulic cylinder 6. The hydraulic cylinder 6 functions as an arm cylinder or a bucket cylinder in a hydraulic excavator.

The directional control valve 3 is normally switched to the neutral position 3a, but when switched to the expansion side position 3b, the pressure oil from the variable displacement hydraulic pump 2 passes through the head side line 5a. While being supplied to the head side oil chamber 6a, the oil discharged from the rod side oil chamber 6b is discharged to the tank 4 via the rod side pipe line 5b, and the rod 6c advances. When switched to the reduction side position 3c, the pressure oil from the variable displacement hydraulic pump 2 is supplied to the rod side oil chamber 6b via the rod side pipe line 5b and discharged oil from the head side oil chamber 6a. Is discharged to the tank 4 via the head side pipe line 5a, and the rod 6c moves backward. As described above, the direction control valve 3 is configured to control the supply and discharge of the pressure oil from the variable displacement hydraulic pump 2 with respect to the hydraulic cylinder 6.

  In this embodiment, in addition to the above configuration, a meter-out pipe 7 branched from the rod-side pipe 5 b and connected to the tank 4 is provided, and a pilot variable opening valve 8 is provided in the meter-out pipe 7. Intervened. As shown in FIG. 2, the pilot variable opening valve 8 has an opening characteristic in which the opening area increases exponentially according to the spool stroke.

  On the other hand, a rotational speed sensor 9 that detects the rotational speed of the engine 1, a holding pressure sensor 10 that detects a holding pressure of the rod-side oil chamber 6 b in the hydraulic cylinder 6, and a discharge pressure of the variable displacement hydraulic pump 2 are detected. A discharge pressure sensor 11 is provided. And each detection signal from these rotation speed sensors 9 and both the pressure sensors 10 and 11 is input into the controller 12 as a control means.

  The controller 12 outputs a control signal corresponding to each input detection signal, and the control signal is input to the drive unit 13 a in the electromagnetic proportional pressure reducing valve 13. The electromagnetic proportional pressure reducing valve 13 outputs a pilot control pressure obtained by reducing the pressure oil from the auxiliary hydraulic power source 14 in accordance with a control signal level input to the drive unit 13a, and the pilot control pressure is the pilot variable opening valve 8. Is input to the pilot port 8a. The pilot variable opening valve 8 is configured such that the opening and closing thereof are controlled according to the level of the pilot control pressure input to the pilot port 8a. The controller 12 not only outputs a control signal corresponding to each detection signal, but also outputs a control signal of a level corresponding to the arbitrary operation when an arbitrary operation is performed on the controller 12.

  Next, the operation of the hydraulic circuit of the construction machine configured as described above will be described. When the weight of the arm and bucket, which is a heavy load for the hydraulic cylinder 6, tends to drop due to its own weight, the controller 12 performs a required operation and opens the pilot variable opening valve 8 with the pilot control pressure from the electromagnetic proportional pressure reducing valve 13. Squeeze. Thereby, the fall of the holding pressure of the rod side oil chamber 6b is prevented, and the fall of its own weight is suppressed.

  Further, when the directional control valve 3 is switched to the extension side position 3b, pressure oil at the time of high rotation of the engine 1 is supplied to the head side oil chamber 6a, and the rod 6c is moved forward, the electromagnetic proportional pressure reducing valve 13 By appropriately widening the opening of the pilot variable opening valve 8 with the pilot control pressure, the occurrence of boost pressure in the rod side oil chamber 6b can be suppressed.

  Similar to the above, when the directional control valve 3 is switched to the extension side position 3b and the rod 6c is moved forward with pressure oil supplied to the head side oil chamber 6a, the holding pressure of the rod side oil chamber 6b is low. When it is determined that the excavation operation is being performed by the bucket of the excavator. At this time, by expanding the opening of the pilot variable opening valve 8 with the pilot control pressure from the electromagnetic proportional pressure reducing valve 13, the back pressure of the rod side oil chamber 6b is further reduced and the power loss of the engine 1 is reduced.

  Further, when the directional control valve 3 is switched to the reduction side position 3c, the pilot variable opening valve 8 is switched to the cutoff position, and all of the pressure oil from the variable displacement hydraulic pump 2 flows into the rod side oil chamber 6b, The hydraulic cylinder 6 is quickly reduced.

As described above, in the hydraulic circuit of the construction machine according to the present embodiment, the holding pressure of the rod-side oil chamber 6b is prevented from being lowered by restricting the opening of the pilot variable opening valve 8, and the arm which is a heavy load In addition, the weight drop of the bucket and the like can be suppressed.

  Further, when pressure oil is supplied to the head side oil chamber 6a at the time of high rotation of the engine 1, the opening of the pilot variable opening valve 8 is appropriately widened to suppress the generation of boost pressure in the rod side oil chamber 6b. Thus, the power loss of the engine 1 can be reduced, and the forward speed of the rod 6c in the hydraulic cylinder 6 can be increased.

  Furthermore, by controlling the width of the opening of the pilot variable opening valve 8 according to the pilot control pressure from the electromagnetic proportional pressure reducing valve 13, the opening control operation can be performed more reliably.

  When the holding pressure of the rod-side oil chamber 6b is low when the pressure oil is supplied to the head-side oil chamber 6a, the back pressure of the rod-side oil chamber 6b is further reduced by widening the opening of the pilot variable opening valve 8 and the engine. 1 can be reduced, and the forward speed of the rod 6c in the hydraulic cylinder 6 can be increased.

  Further, in the pressure oil supply state to the rod side oil chamber 6b, the pilot variable opening valve 8 is switched to the shut-off position, and all of the pressure oil from the variable displacement hydraulic pump 2 flows into the rod side oil chamber 6b. The cylinder 6 can be quickly reduced.

  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.

The hydraulic circuit diagram of the construction machine which concerns on a present Example. The figure which shows the opening characteristic of the pilot variable opening valve in FIG.

Explanation of symbols

1 engine (motor)
2 Variable displacement hydraulic pump 3 Directional control valve 3b Expansion side position 3c Reduction side position 4 Tank 5a Head side line 5b Rod side line 6 Hydraulic cylinder 6a Head side oil chamber 6b Rod side oil chamber 7 Meter-out line 8 Pilot variable Opening valve 9 Rotational speed sensor 10 Holding pressure sensor 12 Controller (control means)
13 Electromagnetic proportional pressure reducing valve

Claims (2)

A hydraulic pump that is rotationally driven by a prime mover, a hydraulic cylinder having a rod-side oil chamber and a head-side oil chamber, a rod-side conduit that communicates with the rod-side oil chamber, and a head-side tube that communicates with the head-side oil chamber In a hydraulic circuit of a construction machine having a directional control valve that controls supply and discharge of pressure oil from the hydraulic pump to the hydraulic cylinder via a path,
A pilot variable opening valve is interposed in the meter-out pipe branched from the rod side pipe and connected to the tank, and the opening and closing of the pilot variable opening valve is controlled according to the pilot control pressure from the electromagnetic proportional pressure reducing valve. A hydraulic circuit for a construction machine, characterized by being configured as described above. The pressure sensor for detecting the holding pressure of the rod-side oil chamber in the hydraulic cylinder, the rotation speed sensor for detecting the rotation speed of the prime mover, and the holding pressure of the rod-side oil chamber detected by the pressure sensor are a predetermined pressure. When the pressure is lower, the opening of the pilot variable opening valve is expanded through the electromagnetic proportional pressure reducing valve. When the holding pressure is higher than the predetermined pressure, the rotational speed of the prime mover detected by the rotational speed sensor is a predetermined rotational speed. 2. The hydraulic circuit for a construction machine according to claim 1, further comprising a control unit that performs control so as to narrow the opening of the pilot variable opening valve via the electromagnetic proportional pressure reducing valve as it is lower.

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