JP2006105324A - Pilot pressure adjusting device of construction machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power loss of a pilot pump of a construction machine in which a relief valve is arranged in a discharge oil path of the pilot pump. <P>SOLUTION: An accumulator 29 which accumulates pilot pressure is arranged in the discharge oil path 27 of the pilot pump 23. A check valve 30 which prevents backflow from the accumulator 29 is provided between the accumulator 29 and the pilot pump 23. Further, there is provided a branch oil path 32 which branches from the discharge oil path 27 of the pilot pump 23 to a tank 31. The branch oil path 32 is provided with a change-over valve 33 which is retained at a throttle position A when the pressure of the accumulator is lower than a predetermined pressure and which is changed to an opening position B when the pressure of the accumulator is equal to or higher than the predetermined pressure. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pilot pressure adjusting device for a construction machine, and more particularly to a pilot pressure adjusting device that reduces power loss in a discharge oil passage of a pilot pump.

  Conventionally, in this type of construction machine, a hydraulic actuator that drives an attachment attached to the fuselage, a main pump and a pilot pump that are driven by an engine, a control valve that supplies and discharges oil discharged from the main pump to the hydraulic actuator, An apparatus having operation means for receiving a pilot oil discharged from a pilot pump and switching a control valve is widely known. In such a configuration, the pilot oil discharged from the pilot pump is maintained at a constant pressure by the relief valve. However, when the control valve is in the neutral position, power loss is caused by discharging a wasteful flow rate from the relief valve to the tank. It has become. In addition, there is a problem in that a device such as a pilot pump generates heat and a high load is applied to shorten the life of the device.

In order to solve this problem, a variable relief valve in which the maximum set pressure is larger than the relief valve and the minimum set pressure is set to the tank pressure is provided in parallel with the relief valve provided in the discharge oil passage of the pilot pump. A switching valve is provided in a pipe line connecting the drive part of the variable relief valve and the tank, and when the operation lever is neutral, the switching valve is switched to a position communicating with the pipe line and discharged from the pilot pump. There has been proposed a hydraulic circuit including a relief pressure reducing device configured to return the pilot oil from the variable relief valve to the tank (see, for example, Patent Document 1).
JP-A 63-186005

  The invention described in Patent Document 1 is provided with a signal generator for detecting the operation of the operation lever, and drives a solenoid valve provided at the spool end of the control valve in accordance with an electric signal output from the signal generator. The spool of the control valve is switched by controlling the flow rate of pilot oil discharged from the pilot pump. For this reason, a plurality of solenoid valves are required for each control valve, and the cost may increase due to an increase in the number of parts and a complicated circuit configuration.

  Therefore, in construction machinery provided with a relief valve in the discharge oil passage of the pilot pump, a technical problem to be solved in order to reduce the power loss of the pilot pump arises, and the present invention solves this problem. With the goal.

  The present invention has been proposed to achieve the above object, and the invention according to claim 1 includes a hydraulic actuator for driving an attachment attached to the airframe, a main pump and a pilot pump driven by an engine, A control valve that supplies and discharges the oil discharged from the main pump to the hydraulic actuator, a relief valve that holds the pilot oil discharged from the pilot pump at a constant pressure, and an operating means that receives the pilot oil and switches the control valve And an accumulator for accumulating pilot pressure in the discharge oil passage of the pilot pump, and a check valve for preventing a backflow from the accumulator is interposed between the accumulator and the pilot pump, and , Branch from pilot pump discharge oil passage to tank A branch oil passage is provided, and a switching valve that holds the throttle position when the accumulator pressure is less than a predetermined pressure and switches to the opening position when the accumulator pressure is higher than the predetermined pressure is provided in the branch oil passage. A pilot pressure adjusting device for a construction machine is provided.

  According to this configuration, the pilot oil discharged from the pilot pump is accumulated in the accumulator. When the accumulator pressure is equal to or higher than the predetermined pressure, the switching valve switches to the open position, and the pilot pump discharge oil passage communicates with the tank through the open position of the switch valve. Become.

  When the control valve is switched to the operating position by the operating means and the accumulator pressure falls below a predetermined pressure, the switching valve is switched to the throttle position and the communication with the tank is throttled. The oil is controlled by a relief valve to return to high pressure.

  According to a second aspect of the present invention, there is provided a pilot pressure adjusting device for a construction machine in which a heat exchanger for oil cooling is interposed between the switching valve and a tank. .

  According to this configuration, when the pilot oil passes through the opening position of the switching valve and communicates with the tank, the oil temperature is cooled by the heat exchanger.

  According to the first aspect of the present invention, a branch oil passage that branches from the discharge oil passage of the pilot pump to the tank is provided, and in this branch oil passage, when the accumulator pressure is less than a predetermined pressure, the throttle position is maintained, and the accumulator pressure is predetermined. When the pressure is higher than the pressure, a switching valve that switches to the opening position is provided, so if the accumulator pressure exceeds the specified pressure, the pilot oil communicates with the tank and becomes low pressure, so a wasteful flow rate is discharged from the relief valve to the tank. Therefore, power loss can be reduced.

  In the invention according to claim 2, since the heat exchanger for oil cooling is interposed between the switching valve and the tank, the heat exchanger can be used at low oil pressure, and the oil temperature is efficiently cooled.

  Hereinafter, a pilot pressure adjusting device for a construction machine according to the present invention will be described with reference to preferred embodiments. In construction machinery provided with a relief valve in the discharge oil passage of the pilot pump, an accumulator for accumulating pilot pressure is provided in the discharge oil passage of the pilot pump for the purpose of reducing the power loss of the pilot pump, and the accumulator and the pilot pump In addition, a check valve that prevents backflow from the accumulator is interposed between the pipe and the branch oil passage that branches from the discharge oil passage of the pilot pump to the tank, and the accumulator pressure is less than the predetermined pressure in the branch oil passage. This is realized by interposing a switching valve that maintains the throttle position when the accumulator pressure exceeds a predetermined pressure.

  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.

  A boom cylinder 18, an arm cylinder 19, and a bucket cylinder 20 are provided as hydraulic actuators for driving attachments such as the boom 15, the arm 16, and the bucket 17, and a hydraulic pump is provided by an engine 21 provided on the upper swing body. 22 is driven to supply / discharge pressure oil to / from each hydraulic actuator.

  FIG. 2 is a circuit diagram of the pilot pressure adjusting device, and shows a hydraulic circuit of a boom cylinder 18 as an example of a hydraulic actuator. A hydraulic pump (hereinafter referred to as a main pump) 22 and a pilot pump 23 are driven by the power of the engine 21. The discharge oil passage 24 of the main pump 22 is provided with a relief valve 25 for adjusting the pressure oil discharged from the main pump 22 to a constant pressure, and this pressure oil is supplied to and discharged from the boom cylinder 18 via the control valve 26. The

  On the other hand, the discharge oil passage 27 of the pilot pump 23 is provided with a relief valve 28 for adjusting the pilot oil discharged from the pilot pump 23 to a constant pressure, an accumulator 29 for accumulating the pilot pressure, and the accumulator A check valve 30 for preventing a backflow from the accumulator 29 is interposed between the pilot pump 23 and the pilot pump 23.

  Further, a branch oil passage 32 that branches from the discharge oil passage 27 of the pilot pump 23 to the tank 31 is provided, and a switching valve 33 is interposed in the branch oil passage 32. The switching valve 33 has a throttle position A and an opening position B, and a port 33 a provided at the end of the spool on the opening position B side is connected to a position near the accumulator 29 of the discharge oil passage 27. Accordingly, the switching valve 33 maintains the throttle position a when the accumulator pressure of the accumulator 29 is less than a predetermined pressure, and switches to the opening position B when the accumulator pressure is higher than the predetermined pressure.

  A remote control valve 35 having an operation lever 34 is provided as an operation means for switching the control valve 26, and a discharge oil passage 27 of the pilot pump 23 and a tank 31 are connected to the remote control valve 35. Then, by operating the operation lever 34 in either the right or left direction in the figure, the pilot oil discharged from the pilot pump 23 or the pilot oil accumulated in the accumulator 29 is supplied to the pilot oil passage 36 or 37 to the pilot port 38a or 38b of the control valve 26.

  Next, the operation of the pilot pressure adjusting device will be described. When the operation lever 34 is not operated and is in the neutral position, the pilot oil discharged from the pilot pump 23 passes through the check valve 30 provided in the discharge circuit 27 and is accumulated in the accumulator 29. When the accumulator pressure is less than the predetermined pressure, the switching valve 33 maintains the throttle position a as shown in FIG. 2, and when the accumulator pressure becomes equal to or higher than the predetermined pressure, as shown in FIG. 33 switches to the opening position b.

  When the switching valve 33 is switched to the opening position B, the branch oil passage 32 of the pilot pump 23 communicates with the tank 31 via the opening position B of the switching valve 33, so that the pilot oil discharged from the pilot pump 23 Decreases to the tank pressure and becomes low pressure.

  As shown in FIG. 4, when the operation lever 34 is operated in any one direction, the pilot oil accumulated in the accumulator 29 passes through one pilot oil passage 37 via the remote control valve 35 and passes through one of the control valves 26. To the pilot port 38b, the control valve 26 is switched to the operating position.

  When the pilot oil in the accumulator 29 decreases and the accumulator pressure falls below a predetermined pressure, as shown in FIG. 5, the switching valve 33 is switched to the throttle position a and the communication with the tank 31 is throttled. Therefore, the pilot oil discharged from the pilot pump 23 is controlled by the relief valve 28 to return to a high pressure, and the pilot oil is accumulated in the accumulator 29 provided in the discharge oil passage 27.

  FIG. 6 shows a modification, in which a heat exchanger 40 for oil cooling is interposed between the switching valve 33 provided in the branch oil passage 32 and the tank 31. The pilot oil passing from the pilot pump 23 through the branch oil passage 32 has a low pressure, and the heat exchanger 40 can be used at a low oil pressure, so that the oil temperature is efficiently cooled.

  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. 1 is a circuit diagram of a pilot pressure adjusting device according to the present invention. FIG. 3 is a circuit diagram when the switching valve shown in FIG. 2 is in an open state. FIG. 4 is a circuit diagram when the operation lever illustrated in FIG. 3 is in an operation state. FIG. 5 is a circuit diagram when the switching valve shown in FIG. 4 is in a throttle state. The circuit diagram which shows the modification of FIG.

Explanation of symbols

18 Boom cylinder 22 Hydraulic pump (main pump)
23 Pilot pump 26 Control valve 27 Discharge circuit 28 Relief valve 29 Accumulator 30 Check valve 31 Tank 32 Branch oil passage 33 Switching valve 34 Operation lever 35 Remote control valve

Claims (2)

A hydraulic actuator for driving an attachment attached to the airframe, a main pump and a pilot pump driven by an engine, a control valve for supplying and discharging the discharge oil of the main pump to and from the hydraulic actuator, and a pilot oil discharged from the pilot pump In a construction machine comprising a relief valve that maintains a constant pressure, and an operation means that receives the pilot oil and performs a switching operation of the control valve,
An accumulator for accumulating pilot pressure is provided in the discharge oil passage of the pilot pump, and a check valve for preventing a backflow from the accumulator is interposed between the accumulator and the pilot pump, and further from the discharge oil passage of the pilot pump. A branch oil passage that branches to the tank is provided, and this branch oil passage is provided with a switching valve that holds the throttle position when the accumulator pressure is lower than the predetermined pressure, and switches to the open position when the accumulator pressure is higher than the predetermined pressure. A pilot pressure adjusting device for a construction machine characterized by the above. 2. The pilot pressure adjusting device for a construction machine according to claim 1, wherein a heat exchanger for oil cooling is interposed between the switching valve and the tank.

Images