Working machine

Abstract

To improve responsiveness of a hydraulic actuator to operations and suppress malfunctions of a hydraulic actuator.SOLUTION: A work machine comprises: a directional control valve that is driven by pilot pressure acting on first and second pilot chambers to control pressure oil to a hydraulic actuator; first and second solenoid valves generating the pilot pressure for the first and second pilot chambers; and a controller that sets a target pilot pressure based on an operation amount of an electric lever and controls the first and second solenoid valves. The controller, when the operation amount is within a dead band range, calculates a preset standby pressure as the target pilot pressure and outputs a command signal according to the standby pressure to both the first and second solenoid valves. And when the operation amount exceeds a dead band range, the controller calculates pressures corresponding to a command pressure and a tank pressure according to the operation amount as the target pilot pressure and outputs a command signal according to the command pressure to one of the first and second solenoid valves and a command signal according to the tank pressure to the other.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a working machine such as a hydraulic excavator.

Background Art

[0002] The pressure oil supplied from a hydraulic pump to a direction control valve is output from an actuator port through a notch of a spool. The spool of the direction control valve moves by a pilot pressure acting on a pilot chamber in response to a lever operation of an operator, and switches the supply direction of fluid to a hydraulic actuator. The pilot pressure is generated by reducing the pressure of the pressure oil discharged from a pilot pump.

[0003] In recent years, the electrification of working machines has advanced, and in many cases, an electric lever is used as an operation lever device as described in Patent Document 1. When an electric lever is applied, the operation amount of the lever is calculated by a controller, and a solenoid valve is driven by a command signal from the controller. Thereby, the pressure oil discharged from the pilot pump is decompressed by the solenoid valve, and a pilot pressure corresponding to the lever operation amount acts on the pilot chamber of the direction control valve.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When controlling the pressure in the pilot chamber with a solenoid valve, power is consumed according to the magnitude of the command signal (e.g., current) applied to the solenoid of the solenoid valve. This power consumption can be suppressed by setting a small value for the command signal (hereinafter referred to as the "standby value") applied to the solenoid valve during non-operation (when the lever operation amount is within the dead band range). However, in this case, when the lever is operated, it takes time for the command signal to reach the value corresponding to the operation amount from the standby value, and the responsiveness of the operation of the hydraulic actuator to the lever operation deteriorates accordingly.

[0006] The operation delay of the hydraulic actuator with respect to the lever operation can be suppressed by making the standby value setting closer to the value of the command signal to the solenoid valve when the pilot pressure at which the direction change valve starts to move is output. However, in this case, due to the influence of disturbances such as electromagnetic pulses, the current flowing through the solenoid of the solenoid valve may exceed the standby value, and there is a possibility that the hydraulic actuator may operate even though the operator has no intention of operating.

[0007] An object of the present invention is to provide a working machine that can improve the responsiveness of the operation of the hydraulic actuator to the lever operation and suppress the malfunction of the hydraulic actuator due to disturbances acting on the solenoid valve.

Means for Solving the Problems

[0008] To achieve the above object, the present invention provides a working machine comprising a hydraulic pump, a pilot pump, a hydraulic actuator driven by pressure oil discharged from the hydraulic pump, a direction control valve having a first pilot chamber and a second pilot chamber and controlling the flow of pressure oil supplied to the hydraulic actuator by being driven by pilot pressures acting on the first pilot chamber and the second pilot chamber, a first solenoid valve for reducing the discharge oil of the pilot pump and generating a pilot pressure acting on the first pilot chamber of the direction control valve, a second solenoid valve for reducing the discharge oil of the pilot pump and generating a pilot pressure acting on the second pilot chamber of the direction control valve, an electric lever for operating the hydraulic actuator, and a controller for setting a target pilot pressure based on an operation amount of the electric lever and controlling the first solenoid valve and the second solenoid valve according to the target pilot pressure. In the working machine, when the operation amount of the electric lever is within a predetermined dead zone range, the controller calculates a preset standby pressure equal to or lower than a required pressure for driving the direction control valve as the target pilot pressure, outputs command signals corresponding to the standby pressure to both the first solenoid valve and the second solenoid valve, and when the operation amount of the electric lever exceeds the dead zone, the controller calculates a command pressure corresponding to the operation amount and a pressure corresponding to a tank pressure as the target pilot pressure, outputs a command signal corresponding to the command pressure to one of the first solenoid valve and the second solenoid valve corresponding to the lever operation direction, and outputs a command signal corresponding to the pressure corresponding to the tank pressure to the other solenoid valve of the first solenoid valve and the second solenoid valve.

Advantages of the Invention

[0009] According to the present invention, it is possible to improve the responsiveness of the operation of the hydraulic actuator to the lever operation and suppress the malfunction of the hydraulic actuator due to disturbance acting on the solenoid valve.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0012] <First Embodiment> -Working Machine- The present invention is applicable not only to hydraulic excavators but also to other types of working machines such as cranes. However, hereinafter, the case where the present invention is applied to a hydraulic excavator will be described as an example.

[0013] FIG. 1 is a left side view of a hydraulic excavator which is an example of a working machine according to the first embodiment of the present invention. In this embodiment, the left and right in FIG. 1 are regarded as the front and rear of the hydraulic excavator. The hydraulic excavator shown in the figure includes a traveling body 1, a slewing body 2 provided on the traveling body 1, and a front working machine 3 attached to the slewing body 2.

[0014] The traveling body 1 is the base structure of the hydraulic excavator and is a crawler-type traveling body that travels by means of left and right crawlers 4. However, a wheel-type traveling body may also be used. The traveling body 1 is driven to travel by driving the left and right crawlers 4 by left and right traveling motors (not shown).

[0015] The slewing body 2 is provided on the upper part of the traveling body 1 via a slewing ring 6 and is equipped with a cab 7 for an operator to board at the front left. A slewing motor (not shown) is attached to the slewing frame which is the base frame of the slewing body 2. The slewing motor may use an electric motor, a hydraulic motor, or both. A power unit 9 is provided on the rear side of the cab 7 in the slewing body 2, and a counterweight 10 is provided at the rearmost part. The cab 7 is provided with a driver's seat (not shown) for the operator to sit on.

[0016] On the left and right of the driver's seat, there are left and right electric levers 16 (only one is shown in FIG. 2) for instructing the slewing operation of the slewing body 2 and the operation of the front work implement 3. The power unit 9 houses a hydraulic pump 32 (FIG. 2) that discharges pressure oil for driving a hydraulic actuator, a prime mover 31 (FIG. 2) that drives the hydraulic pump 32, a control valve device (direction change valves 34, 35, etc. in FIG. 2) that controls the flow of the pressure oil supplied to the hydraulic actuator, etc. The prime mover is an engine (internal combustion engine) in this embodiment, but an electric motor may also be used as the prime mover. The slewing body 2 is also equipped with a controller 50 (FIG. 2) for controlling each operating device including the prime mover.

[0017] The front work implement 3 is connected to the front part of the slewing body 2 (on the right side of the cab 7 in this embodiment). The front work implement 3 is a multi-joint type front work device including a boom 21, an arm 22, and an attachment 23 (a bucket in this embodiment). The boom 21 is directly connected to the slewing frame so as to be rotatable up and down, and is also connected to the slewing body frame via a boom cylinder 24. The arm 22 is directly connected to the tip of the boom 21 so as to be rotatable, and is also connected to the boom 21 via an arm cylinder 25. The attachment 23 is directly connected to the tip of the arm 22 so as to be rotatable, and is also connected to the arm 22 via an attachment cylinder 26. The boom cylinder 24, the arm cylinder 25, and the attachment cylinder 26 are hydraulic actuators.

[0018] In the hydraulic excavator shown in Fig. 1, the pressure oil discharged from the hydraulic pump 32 (Fig. 2) is supplied to the swing motor (not shown), boom cylinder 24, arm cylinder 25, and attachment cylinder 26 according to the operation of the left and right electric levers 16 (Fig. 2). When the swing motor is driven, the swing body 2 swings. When the boom cylinder 24, arm cylinder 25, and attachment cylinder 26 are driven, the boom 21, arm 22, and attachment 23 rotate respectively, and the position and posture of the attachment 23 change. The traveling body 1 is operated by a lever with a pedal for traveling operation (not shown) arranged in front of the driver's seat.

[0019] -Hydraulic System- Fig. 2 is a hydraulic circuit diagram of a part of the hydraulic system of the hydraulic excavator shown in Fig. 1, and Fig. 3 is a cross-sectional view of a direction switching valve described later. In Fig. 2, the hydraulic circuit for driving the boom cylinder 24 and the attachment cylinder 26 is extracted and shown, but the same circuit can also be applied to the hydraulic circuits of the swing motor and the arm cylinder 25.

[0020] In Fig. 2, the electric lever 16 is, for example, a cross-operating type operation lever arranged on the right side of the driver's seat. For example, when the electric lever 16 is tilted forward in the driver's seat, the boom is lowered, when tilted backward, the boom is raised, when tilted left, the bucket crowd is instructed, and when tilted right, the bucket dump is instructed. The electric lever 16 is provided with a plurality of sensors (for example, potentiometers, angle sensors) for detecting the lever tilt angle corresponding to the lever tilt direction. The outputs of these sensors are input to the controller 50, and the operation direction and operation amount of the electric lever 16 are calculated by the controller 50. Note that the relationship between the operation directions of the left and right electric levers 16 and the operation targets (swing motor, boom cylinder 24, arm cylinder 25, attachment cylinder 26) can be changed as appropriate.

[0021] The hydraulic system shown in Fig. 2 is composed of an engine 31, a hydraulic pump 32, a pilot pump 33, direction switching valves 34, 35, solenoid valves 36, 37, 38, 39, a controller 50, etc.

[0022] The hydraulic pump 32 is a variable displacement pump that discharges pressurized oil for driving hydraulic actuators such as the boom cylinder 24. A fixed displacement pump can also be used as the hydraulic pump 32. The pilot pump 33 is a fixed displacement pump that discharges pressurized oil for driving the direction control valves 34, 35, etc. These hydraulic pump 32 and pilot pump 33 are driven by the prime mover 31 to suck hydraulic oil from the tank TK and discharge pressurized oil into the center bypass oil passage 32a and the primary pressure oil passage 33a, respectively.

[0023] The direction control valve 34 is a proportional hydraulically driven three-position switching valve that controls the flow (direction and flow rate) of the pressurized oil supplied from the hydraulic pump 32 to the boom cylinder 24. This direction control valve 34 has pilot chambers (pressure receiving chambers) 34a, 34b, and the spool 34c is moved and driven by the differential pressure of the pilot pressure acting on the pilot chambers 34a, 34b.

[0024] As shown in FIG. 3, the spool 34c is provided with notches N1, N2, N3, N4. The valve body of the direction control valve 34 is provided with an A port, a B port, a P port, and a T port. The A port and the B port are actuator ports, the A port is connected to the rod chamber of the boom cylinder 24, and the B port is connected to the bottom chamber of the boom cylinder 24, respectively. The P port is a pump port and is connected to the discharge port of the hydraulic pump 32 via the parallel oil passage 32b. The T port is a tank port and is connected to the tank TK via the tank oil passage Tb.

[0025] When the spool 34c is in the position (neutral position) shown in FIG. 3, the connections of the A port and the B port to both the P port and the T port are blocked.

[0026] When the spool 34c moves to the left in Fig. 3, the direction switching valve 34 switches to the switching position on the right side in Fig. 2. As a result, while the center bypass passage 32a is narrowed, the connection between the P port and the A port by the notch N1 (PA opening), and the connection between the B port and the T port by the notch N3 (BT opening) are opened. The areas of the PA opening and the BT opening change according to the amount of movement of the spool 34c.

[0027] Conversely, when the spool 34c moves to the right in Fig. 3, the direction switching valve 34 switches to the switching position on the left side in Fig. 2. As a result, while the center bypass passage 32a is narrowed, the connection between the P port and the B port by the notch N2 (PB opening), and the connection between the A port and the T port by the notch N3 (AT opening) are opened. The areas of the PB opening and the AT opening also change according to the amount of movement of the spool 34c.

[0028] The direction switching valve 35 is a proportional hydraulic drive three-position switching valve that controls the flow (direction and flow rate) of the pressure oil supplied from the hydraulic pump 32 to the attachment cylinder 26. This direction switching valve 35 also has pilot chambers (pressure receiving chambers) 35a, 35b similar to the direction switching valve 34, and the spool 35c is moved and driven by the differential pressure of the pilot pressure acting on the pilot chambers 35a, 35b.

[0029] The solenoid valves 36 - 39 are proportional electromagnetic drive type pressure reducing valves provided in the primary pressure oil passage 33a, and are provided corresponding to the pilot chambers 34a, 34b, 35a, 35b of the direction switching valves 34, 35 individually. These solenoid valves 36 - 39 are driven by exciting the solenoid with a command signal (for example, current) output from the controller 50 according to the operation amount of the electric lever 16. The discharge oil of the pilot pump 33 flowing through the primary pressure oil passage 33a is reduced in pressure in the solenoid valves 36 - 39 according to the magnitude of the command signal, thereby generating a pilot pressure acting on the corresponding pilot chamber.

[0030] For example, the solenoid valve 36 is configured to connect the pilot chamber 34a of the direction switching valve 34 to the primary pressure oil passage 33a (pilot pump 33) and the tank oil passage Ta (tank TK). When the spool position of the solenoid valve 36 changes, the ratio of the opening area connecting the pilot chamber 34a to the primary pressure oil passage 33a and the opening area connecting the pilot chamber 34a to the tank oil passage Ta changes, and the pilot pressure acting on the pilot chamber 34a changes. The solenoid valves 37 - 39 also have the same configuration as the solenoid valve 36, and change the pilot pressure acting on the corresponding pilot chambers 34b, 35a, 35b according to the spool position.

[0031] Note that the spools of the solenoid valves 36 - 39 are pressed by springs in the direction in which the pilot pressure to the pilot chambers 34a, 34b, 35a, 35b decreases, and are configured such that the higher the command signal (current) received by the solenoid, the higher the pilot pressure. Specifically, as shown in FIG. 4, in the region where the command signal is equal to or greater than the minimum value A0 (>0), the pilot pressure generated by the solenoid valves 36 - 39 increases monotonically from the tank pressure P0 (minimum value) to the maximum value as the command signal increases (increases linearly in the example of FIG. 4). In the region where the command signal is less than the minimum value A0 (>0), the pilot pressure generated by the solenoid valves 36 - 39 is constant (tank pressure P0). Note that an air breather circuit (not shown) serving as an air inlet / outlet is provided on the upper surface of the tank TK, and the interior of the tank TK is configured to be maintained at a pressure within a certain range (e.g., atmospheric pressure) (preventing the pressure from exceeding a certain level and preventing a negative pressure when the pump sucks the hydraulic oil from the tank TK). The tank pressure P0 is a pressure corresponding to the set pressure of this air breather circuit and is a slight pressure with a predetermined width.

[0032] In the above configuration, for example, when there is no differential pressure in the pilot pressures generated by the solenoid valves 36 and 37, the spool 34c of the direction switching valve 34 is maintained at the neutral position (Figure 2) by the spring force. In this case, the center bypass oil passage 32a is connected to the tank oil passage Tb via the direction switching valve 34, and the pressure oil discharged from the hydraulic pump 32 is returned to the tank TK without being supplied to the boom cylinder 24. Also, as described above, the circuit of the boom cylinder 24 is closed.

[0033] When the pilot pressure generated by the solenoid valve 36 is greater than the pilot pressure generated by the solenoid valve 37, the spool 34c moves to the left side in the figure against the spring force, and the direction switching valve 34 switches to the switching position on the right side in the figure. In this case, the center bypass oil passage 32a is narrowed, and the pressure oil discharged from the hydraulic pump 32 flows into the parallel oil passage 32b that branches off from the center bypass oil passage 32a. The pressure oil guided to the parallel oil passage 32b flows into the rod chamber of the boom cylinder 24 via the check valve 34d and the direction switching valve 34, contracting the boom cylinder 24. Along with this, the pressure oil pushed out from the bottom chamber of the boom cylinder 24 is returned to the tank TK via the direction switching valve 34 and the tank oil passage Tb.

[0034] Conversely, when the pilot pressure generated by the solenoid valve 37 is greater than the pilot pressure generated by the solenoid valve 36, the direction switching valve 34 switches to the switching position on the left side in the figure. In this case, the center bypass oil passage 32a is narrowed, and the pressure oil discharged from the hydraulic pump 32 flows into the bottom chamber of the boom cylinder 24 via the parallel oil passage 32b, the check valve 34d, and the direction switching valve 34, extending the boom cylinder 24. Along with this, the pressure oil pushed out from the rod chamber of the boom cylinder 24 is returned to the tank TK via the direction switching valve 34 and the tank oil passage Tb.

[0035] The operation of the direction switching valve 35 is the same as that of the direction switching valve 34. For example, when there is no differential pressure in the pilot pressures generated by the solenoid valves 38 and 39, the pressurized oil discharged from the hydraulic pump 32 is returned to the tank TK without being supplied to the attachment cylinder 26. When there is a differential pressure in the pilot pressures generated by the solenoid valves 38 and 39, the center bypass oil passage 32a is narrowed, and the discharged oil of the hydraulic pump 32 flows into the parallel oil passage 32b. The pressurized oil flowing into the parallel oil passage 32b flows into the bottom chamber or the rod chamber of the attachment cylinder 26 via the check valve 35d and the direction switching valve 35, and expands and contracts the attachment cylinder 26. Along with this, the pressurized oil discharged from the attachment cylinder 26 is returned to the tank TK via the direction switching valve 35 and the tank oil passage Tb.

[0036] In addition, a pilot relief valve RV and a solenoid valve SV are provided in the primary pressure oil passage 33a. The pilot relief valve RV defines the pressure of the primary pressure oil passage 33a (the original pressure of the pilot pressure). The solenoid valve SV is driven by a command signal output from the controller according to the operation amount of the electric lever 16 and the discharge pressure of the hydraulic pump 32 detected by the pressure sensor PS, and controls the regulator PR of the hydraulic pump 32.

[0037] In addition, overload relief valves R1, R2, R3, and R4 are provided in each circuit connected to the rod chambers and the bottom chambers of the boom cylinder 24 and the attachment cylinder 26, respectively. When an abnormal load is applied to the boom cylinder 24 and the attachment cylinder 26, the pressurized oil escapes to the tank oil passage Tb via the overload relief valves R1 - R4, and the circuits of the boom cylinder 24 and the attachment cylinder 26 are protected. Also, when each circuit of the boom cylinder 24 and the attachment cylinder 26 becomes negative pressure depending on the working conditions, pressurized oil is supplied from the tank oil passage Tb via the overload relief valves R1 - R4 (make-up operation). Thereby, it is suppressed that each circuit of the boom cylinder 24 and the attachment cylinder 26 becomes negative pressure.

[0038] At this time, a back pressure relief valve R5 and a makeup valve MV are provided in parallel in the tank oil passage Tb. The back pressure relief valve R5 and the makeup valve MV constitute the same mechanism as the overload relief valves R1-R4 as a set. The back pressure relief valve R5 maintains the pressure in the tank oil passage Tb at the set pressure so that the makeup operation can be easily performed. The makeup valve MV operates in a situation where the tank oil passage Tb may become negative pressure when any one of the overload relief valves R1-R4 performs a makeup operation, and supplies pressure oil from the tank TK to the tank oil passage Tb to suppress the tank oil passage Tb from becoming negative pressure.

[0039] -Operating Characteristics of Directional Control Valve- FIG. 5 is a diagram showing the operating characteristics of the pilot pressures of the directional control valves 34 and 35. P0 in FIG. 5 is the same tank pressure as P0 in FIG. 4. Here, the directional control valve 34 will be taken as an example for explanation, but the operating characteristics are the same for the directional control valve 35. The horizontal axis in FIG. 5 represents, for example, the pilot pressure acting on the pilot chamber 34a of the directional control valve 34, and it is assumed that the pilot pressure acting on the opposite pilot chamber 34b is constant at P0 (for example, 0 MPa).

[0040] First, in the range where the pilot pressure acting on the pilot chamber 34a is from P0 to P1 (for example, 0.7 MPa), the driving force of the spool 34c due to the differential pressure between the pilot chambers 34a and 34b does not exceed the spring force, and the spool 34c does not move from the neutral position. P1 is the required pressure required to drive the directional control valve. In the range where the pilot pressure acting on the pilot chamber 34a is P1 or more, the movement amount of the spool 34c increases in proportion to the increase in the pilot pressure acting on the pilot chamber 34a. During this period, when the pilot pressure acting on the pilot chamber 34a reaches from P1 to P2 (for example, 1 MPa), the PA opening and the BT opening due to the notches N1 and N3 (FIG. 4) open. In the range where the pilot pressure acting on the pilot chamber 34a is from P2 to the maximum value P4 (for example, 3 MPa), the opening areas of the PA opening and the BT opening increase monotonically with the increase in the pilot pressure.

[0041] That is, when the differential pressure in the pilot chambers 34a and 34b rises from P0 to P1, the spool 34c starts to move. When the differential pressure rises to P2, the PA port and the BT port open, and as the differential pressure increases from P2, the opening areas of the PA port and the BT port increase. Between when the pilot pressure reaches P1 and the spool 34c starts to move until the pilot pressure rises to P2, the PA port and the BT port are designed not to open, and the direction switching valve 34 is designed so that unexpected operations due to shock or vibration in the fine operation range are suppressed.

[0042] When the pilot pressure acting on the pilot chamber 34a decreases from P4 to P0, it shows the opposite behavior to the above.

[0043] -Direction Switching Valve Control- FIG. 6 is a functional block diagram of the controller 50. P0, P1, and P4 in FIG. 6 have the same values as P0, P1, and P4 in FIG. 5, and A0 in FIG. 6 has the same value as A0 in FIG. 4. The controller 50 is an in-vehicle computer including a control arithmetic device such as a CPU, an input / output interface, in addition to a storage device such as a ROM, a RAM, an HDD, and an SSD, and executes various control and arithmetic processes by executing a program stored in the storage device.

[0044] In particular, the controller 50 of the present embodiment is provided with functions for executing a target pilot pressure setting process F1 and solenoid valve control processes F2a and F2b. The target pilot pressure setting process F1 and the solenoid valve control processes F2a and F2b will be sequentially described below. Note that a series of processes of the target pilot pressure setting process F1 and the solenoid valve control processes F2a and F2b are independently and similarly executed for each operation direction (hydraulic actuator to be operated) of the electric lever 16. In the following description, the operation of the boom cylinder 24 will be taken as an example for explanation.

[0045] ·Target Pilot Pressure Setting Process The target pilot pressure setting process F1 is a process of setting the target pilot pressure for driving a direction switching valve (here, the direction switching valve 34 is taken as an example) based on the operation amount of the electric lever 16. In the present embodiment, the controller 50 stores in the storage device a characteristic curve preset for the relationship between the operation amount and the target pilot pressure. This characteristic curve may be optimized for each direction switching valve, or may be common to all direction switching valves. The characteristic curve for the direction switching valve 34 is shown in the functional block of the target pilot pressure setting process F1. In FIG. 6, the solid line represents the characteristic curve of the target pilot pressure for the pilot chamber 35a, and the broken line represents the characteristic curve of the target pilot pressure for the pilot chamber 35b. The controller 50 uses this characteristic curve to calculate the target pilot pressures for the pilot chambers 34a and 34b on both sides of the direction switching valve 34 based on the operation amount of the electric lever 16 for the boom operation.

[0046] An inoperative zone, a dead zone, and an operative zone are set for the operation amount of the electric lever 16. The inoperative zone is a range of the operation amount for determining that the electric lever 16 is substantially at the neutral position (operation amount = 0), and is set as an extremely small range on the boom raising side and the boom lowering side with the neutral position in between. The dead zone is a range of the operation amount in which the corresponding direction switching valve does not operate even when the electric lever 16 is tilted, and has a predetermined range (the same amount on both sides in this example) on the boom raising side and the boom lowering side with the neutral position (operation amount = 0) of the electric lever 16 in between. The range of the dead zone is wider than the range of the inoperative zone. Hereinafter, the pilot pressure applied to the pilot chambers 34a and 34b in the range of the dead zone will be appropriately described as the standby pressure, and the pilot pressure applied to the pilot chamber corresponding to the lever operation direction in the range of the operative zone will be described as the command pressure.

[0047] When the electric lever 16 is tilted within the dead zone range, both the standby pressure on the boom lowering side (i.e., the pressure acting on the pilot chamber 35a) and the standby pressure on the boom raising side (i.e., the pressure acting on the pilot chamber 35b) are set to the required pressure P1 (for example, 0.7 MPa). However, in the case of this embodiment, even within the dead zone range, when the operation amount is within a certain range or less, as the operation amount approaches 0, the target pilot pressure decreases from the standby pressure for both sides, and when the operation amount is 0, the target pilot pressure for both sides is set to the tank pressure P0 (for example, 0 MPa).

[0048] When the electric lever 16 is operated beyond the dead zone (i.e., within the operating range), the target pilot pressure (i.e., the command pressure) corresponding to the operation direction increases from P1 to the maximum value P4 as the operation amount increases (proportionally in this example). On the other hand, the setting of the pilot pressure on the opposite side switches stepwise from P1 to P0 when the operation amount exceeds the dead zone and is constantly set to a constant value (P0) within the dead zone range. In FIG. 6, the characteristic that the target pilot pressure increases linearly in proportion to the operation amount in the operating range is illustrated, but the slope and shape of the characteristic line of the target pilot pressure in the operating range can be adjusted.

[0049] In the target pilot pressure setting process F1, the controller 50 refers to the above characteristic line and calculates the two target pilot pressures to be applied to the pilot chambers 34a and 34b of the direction switching valve 34 according to the operation amount of the electric lever 16.

[0050] · Solenoid valve control process The electromagnetic valve control processes F2a and F2b are processes that control the corresponding electromagnetic valves 36 and 37 according to the respective target pilot pressures for the pilot chambers 34a and 34b set in the target pilot pressure setting process F1. In the present embodiment, the controller 50 stores a characteristic curve set in advance regarding the relationship between the target pilot pressure and the command signal to the electromagnetic valve in the storage device. This characteristic curve may be optimized for each electromagnetic valve or may be common to all electromagnetic valves. What is shown in the functional blocks of the electromagnetic valve control processes F2a and F2b are the characteristic curves for the electromagnetic valves 36 and 37. The controller 50 calculates command signals for the electromagnetic valves 36 and 37 from the two target pilot pressures set in the target pilot pressure setting process F1 using these characteristic curves.

[0051] The characteristic curve of the command signal with respect to the target pilot pressure takes the minimum value A0 (>0) when the target pilot pressure is P0, and as the target pilot pressure rises from P0 (proportional to the target pilot pressure in this example), the command signal rises from A0 to the maximum value A4. In the range where the target pilot pressure is above a certain level, the command signal becomes constant (A4).

[0052] In the electromagnetic valve control process F2a, the controller 50 refers to the characteristic curve, calculates and generates (analog-converts to current) a command signal for the electromagnetic valve 36 based on the target pilot pressure for the pilot chamber 34a, and outputs it to the electromagnetic valve 36. At the same time, in the electromagnetic valve control process F2b, the controller 50 refers to the characteristic curve, calculates and generates a command signal for the electromagnetic valve 37 based on the target pilot pressure for the pilot chamber 34b, and outputs it to the electromagnetic valve 37.

[0053] -Operation- Here, taking the boom lowering operation as an example, the output operation of the command signals to the electromagnetic valves 36 and 36 by the controller 50 will be described.

[0054] First, for example, when the operator is not touching the electric lever 16, the electric lever 16 is in the neutral position. When the electromagnetic lever 16 is in the neutral position in this way, the controller 50 calculates P0 as the target pilot pressure for each of the pilot chambers 34a and 34b of the direction switching valve 34. In this case, a command signal of the minimum value A1 corresponding to P0 is output for both of the electromagnetic valves 36 and 37, and the pilot pressure of P0 acts on the pilot chambers 34a and 34b of the direction switching valve 34 (the pilot pressure does not act on both of the pilot chambers 34a and 34b). Therefore, the spool 34c of the direction switching valve 34 does not move from the neutral position, and the boom cylinder 24 does not move and is held.

[0055] Next, assume a situation where the operator touches the electric lever and the electric lever 16 falls in the boom lowering direction beyond the non-operation zone and within the dead zone. When the operation amount of the electric lever 16 is within the dead zone, the controller 50 calculates P1 as the target pilot pressure for both of the pilot chambers 34a and 34b of the direction switching valve 34. In this case, a command signal of a value A1 corresponding to P1 is output for both of the electromagnetic valves 36 and 37, and the pilot pressure (standby pressure) of P1 acts on the pilot chambers 34a and 34b of the direction switching valve 34. Therefore, no differential pressure is generated in the pilot chambers 34a and 34b, and the effective value of the pilot pressure driving the direction switching valve 34 becomes P0. Accordingly, the spool 34c of the direction switching valve 34 does not move from the neutral position, and the boom cylinder 24 also does not expand or contract and is held.

[0056] And when the boom lowering operation is performed beyond the dead zone, the controller 50 calculates a command pressure Px corresponding to the operation amount as the pilot pressure for the pilot chamber 34a, and calculates the tank pressure P0 as the pilot pressure for the pilot chamber 34b. As a result, a command signal with a value Ax (>A1) corresponding to the command pressure Px is output to the solenoid valve 36, and at the same time, a command signal with a value A0 corresponding to P0 is output to the other solenoid valve 37. In this case, while the pilot pressure of Px acts on the pilot chamber 34a of the direction switching valve 34, the pilot pressure of P0 acts on the pilot chamber 34b (no pilot pressure acts on the pilot chamber 34b). Therefore, a differential pressure corresponding to Px is generated between the pilot chambers 34a and 34b, and the effective value of the pilot pressure driving the direction switching valve 34 becomes Px. As a result, the spool 34c moves leftward in FIG. 2 from the neutral position, and the direction switching valve 34 switches to the switching position on the right side, causing the boom cylinder 24 to contract.

[0057] When the operation amount of boom lowering becomes small, the operation is reverse to the above. Also, regarding the boom raising operation and the operation of other hydraulic actuators (arm cylinder 25, attachment cylinder 26, swing motor), the operation is the same.

[0058] -Effect- (1) According to the present embodiment, when the operation amount is within the dead zone, a standby pressure of P1 (for example, 0.7 MPa) is applied to both pilot chambers (for example, pilot chambers 34a and 34b) of the direction switching valve (for example, direction switching valve 34) to cancel each other out. And when the operation amount exceeds the dead zone, while applying a command pressure Px corresponding to the operation amount to the pilot chamber (for example, pilot chamber 34a) corresponding to the operation direction, the pressure in the pilot chamber on the opposite side (for example, pilot chamber 34b) is reduced to the tank pressure P0 (for example, 0 MPa).

[0059] If the pilot pressure is not applied to the pilot chambers 34a and 34b in the dead zone, for example, when the boom lowering operation is performed and the command pressure Px (e.g., 2 MPa) is applied to the pilot chamber 34a, it is necessary to increase the pressure in the pilot chamber 34a from P0 to Px. In this case, the pressure increase range in the pilot chamber 34a is Px - P0 (e.g., 2 MPa), and the command signal to the solenoid valve 36 also needs to be significantly increased from A0 to Ax.

[0060] On the other hand, in the case of this embodiment, when the boom lowering operation is similarly performed and the command pressure Px (e.g., 2 MPa) is applied to the pilot chamber 34a, it is sufficient to increase the pilot pressure applied to the pilot chamber 34a from P1 to Px. In this case, the pressure increase range in the pilot chamber 34a can be suppressed to Px - P1 (e.g., 1.3 MPa). It is only necessary to increase the command signal to the solenoid valve 36 from A1 to Ax, and the increase range of the command signal can be shortened by only A1 - A0. Although it is necessary to reduce the pilot pressure applied to the pilot chamber 34b from P1 to P0, the decrease speed is faster than the increase speed, and the situation where the decrease of the pilot pressure on the opposite side to P0 becomes the bottleneck is limited. Therefore, the responsiveness of the operation of the hydraulic actuator to the lever operation can be improved.

[0061] Also, assume that in a state where the electric lever 16 is tilted, for example, to the boom lowering side within the dead zone range, a pilot pressure Pe (e.g., 1.2 MPa) greater than P1 acts on the pilot chamber 34a of the direction switching valve 34 due to the influence of an electromagnetic pulse on the solenoid valve 36. In this case, if it is assumed that the pilot pressure of only P1 is applied to only the pilot chamber 34a and the system is in a standby state according to the operation direction, when the pilot pressure Pe is applied due to the influence of an external disturbance on the solenoid valve 36, the direction switching valve 34 may operate even though the operation amount is within the dead zone range.

[0062] In contrast, in the case of this embodiment, in the dead zone, not only the pilot chamber 34a but also the pilot chamber 34b on the opposite side is applied with the pilot pressure of P1, and the pilot pressures of each other cancel each other out, and the effective value of the pilot pressure acting on the direction switching valve 34 becomes P0. As a result, even if an unintended pilot pressure Pe is applied to the pilot chamber 34a as described above, the pilot pressure Pe is partially canceled out, and the effective pilot pressure acting on the direction switching valve 34 stops at Pe - P1 (for example, 0.5 MPa). As described with reference to FIG. 5, the direction switching valve 34 does not operate with a pilot pressure having an effective value of 0.5 MPa (<P1 = 0.7 MPa).

[0063] In this way, while applying the pilot pressure of P1 in the dead zone to improve the responsiveness, both pilot chambers are pressurized in the dead zone to suppress the effective value of the pilot pressure to P0 (for example, 0 MPa), and it is also possible to suppress the malfunction of the hydraulic actuator due to the action of disturbance on the solenoid valve.

[0064] (2) When the operator touches the electric lever 16, even when there is no intention of operation, the electric lever 16 has a strong tendency to tilt within the dead zone. In other words, when the operation amount of the electric lever 16 is 0, it is estimated that the operator has released his hand from the electric lever 16. In such a scene where there is no need for such standby (operation preparation), by setting the target pilot pressure to both pilot chambers of the direction switching valve (for example, the direction switching valve 34) to the tank pressure P0 and minimizing the command signal to the solenoid valve, energy consumption can be suppressed.

[0065] <Second Embodiment> FIG. 7 is a functional block diagram of a controller 50 provided in a working machine according to the second embodiment of the present invention. FIG. 7 corresponds to FIG. 6 of the first embodiment.

[0066] The difference between this embodiment and the first embodiment is that the electric lever 16 (for example, the grip portion) is provided with a pressure sensor 17, and the output of the pressure sensor 17 is input to the controller 50. When the output of the pressure sensor 17 exceeds the set value, the controller 50 calculates P1 as the target pilot pressure even if the operation amount of the electric lever 16 is 0, and outputs command signals of value A1 corresponding to P1 to both of the solenoid valves 36, 37 and both of the solenoid valves 38, 39.

[0067] In this embodiment, when the output of the pressure sensor 17 exceeds the set value, the characteristic line of the target pilot pressure is set so that the target pilot pressure remains constant at P1 regardless of the operation amount in the entire dead zone including the non-operation zone, as shown by the dashed-dotted line L in FIG. 7. However, when the output of the pressure sensor 17 is below the set value, if the operation amount is 0, the target pilot pressure becomes P0 as in the first embodiment.

[0068] In other respects, this embodiment is the same as the first embodiment, and the same effects as the first embodiment can be obtained in this embodiment.

[0069] In addition, in the case of the first embodiment, the operator's state of releasing the hand from the electric lever 16 was estimated based on the angle of the electric lever 16. However, even when the operator is holding the electric lever 16, the operation amount may become 0. In this case, for example, when the operation amount increases from a state where no pilot pressure is applied to either of the pilot chambers 34a, 34b of the direction switching valve 34 with the operation amount being 0 to the operation range, a delay may be felt in the operation of the boom cylinder 24.

[0070] On the other hand, in the case of this embodiment, when the pressure sensor 17 detects that the operator is holding the electric lever 16, by applying pilot pressure to both of the pilot chambers 34a, 34b even when the operation amount is 0 to set it in the standby state, the above-mentioned response delay can be suppressed.

[0071] <Third Embodiment> FIG. 8 is a functional block diagram of a controller 50 provided in a working machine according to the third embodiment of the present invention. FIG. 8 corresponds to FIG. 6 of the first embodiment.

[0072] The difference between this embodiment and the first embodiment is that a difference is provided in the pilot pressure (standby pressure) that acts on and cancels out two pilot chambers of the same direction switching valve in the dead zone. Specifically, when the electric lever 16 tilts within the dead zone range, the standby pressure calculated corresponding to the tilt direction of the electric lever 16 is set to be larger than the standby pressure on the other side. In this embodiment, the target pilot pressure that is the basis of the command signal to one solenoid valve (for example, solenoid valve 36) corresponding to the lever operation direction in the dead zone is set as P1, and the target pilot pressure that is the basis of the command signal to the other solenoid valve (for example, solenoid valve 37) is set as P1' (<P1).

[0073] Regarding other points, this embodiment is the same as the first embodiment.

[0074] When applying the pilot pressure of P1 to both pilot chambers of the direction switching valve in the dead zone, for example, during the boom lowering operation, in the fine operation range near the dead zone, it may take more time for the pressure in pilot chamber 34b to drop from P1 to P0 than for the pressure in pilot chamber 34a to increase from P1 to Px. In contrast, in this embodiment, since the pilot pressure (P1') on the opposite side is lower than the pilot pressure (P1) corresponding to the lever operation direction in the dead zone, the pressure drop time of the pilot pressure can be shortened by the difference between P1 and P1'. Thereby, the responsiveness in the fine operation range can be improved compared to the first embodiment.

[0075] <Modification Example> Although the representative embodiments have been described above, the embodiments can be appropriately modified without departing from the technical idea of the invention. In the first or third embodiment, an example in which the operation amount for the target pilot pressure to reach P0 to P1 or P1' when the electric lever 16 inclines in the boom lowering direction in the dead zone is set equally for both of the pilot chambers 34a and 34b has been described. In this regard, as shown in FIG. 9, for example, it is also conceivable to delay (set a larger operation amount) the timing for the pilot pressure in the pilot chamber on the side opposite to the lever operation direction to reach P1 or P1' by Δ. That is, for example, when performing a boom lowering operation, the target pilot pressure for the pilot chamber 34a reaches P1 in the dead zone, and the target pilot pressure for the pilot chamber 34b reaches P1 or P1' with a slight delay (with a larger operation amount by Δ). In this case, compared with the first embodiment, there is almost no influence on the operability, and the command time for the solenoid valve 37 is shortened by the amount of delay in the timing for raising the target pilot pressure in the pilot chamber 34b on the side opposite to the lever operation direction, and an energy saving effect is expected.

[0076] Also, an example has been described by taking as an example the case where the target pilot pressure (standby pressure) applied to the pilot chambers 34a, 34b, 35a, and 35b of the direction switching valves 34 and 35 in the dead zone is set to the required pressure P1 (FIG. 5) required to move the spools 34c and 35c of the direction switching valves 34 and 35. However, for example, a value lower than P1 (>P0) may be set as the standby pressure.

[0077] Also, in the above embodiment, an example in which the target pilot pressure for the pilot pressure of both of the direction switching valves is set to P0 under the condition of an operation amount of 0 has been described, but the value of the operation amount for setting the target pilot pressure to P0 may have a width. For example, it may be a characteristic in which the pilot pressure of both of the direction switching valves is set to P0 throughout the non-operation zone.

Explanation of Reference Numerals

[0078] 16…Electric lever, 17…Pressure sensor, 24…Boom cylinder (hydraulic actuator), 25…Arm cylinder (hydraulic actuator), 26…Attachment cylinder (hydraulic actuator), 32…Hydraulic pump, 33…Pilot pump, 34, 35…Direction control valve, 34a, 34b, 35a, 35b…Pilot chamber, 36 - 39…Solenoid valve, 50…Controller, P0…Tank pressure, P1…Required pressure

Claims

1. A hydraulic pump, a pilot pump, a hydraulic actuator driven by the pressure oil discharged from the hydraulic pump, a direction switching valve having a first pilot chamber and a second pilot chamber, and controlling the flow of the pressure oil supplied to the hydraulic actuator by being driven by the pilot pressure acting on the first pilot chamber and the second pilot chamber, a first electromagnetic valve that reduces the discharged oil of the pilot pump and generates a pilot pressure acting on the first pilot chamber of the direction switching valve, a second electromagnetic valve that reduces the discharged oil of the pilot pump and generates a pilot pressure acting on the second pilot chamber of the direction switching valve, an electric lever for operating the hydraulic actuator, a controller that sets a target pilot pressure based on the operation amount of the electric lever and controls the first electromagnetic valve and the second electromagnetic valve according to the target pilot pressure In a working machine equipped with the controller When the operation amount of the electric lever is within the range of a predetermined dead zone, calculates a preset standby pressure that is equal to or lower than the required pressure required to drive the direction switching valve as the target pilot pressure, and outputs a command signal corresponding to the standby pressure to both the first electromagnetic valve and the second electromagnetic valve, When the operation amount of the electric lever exceeds the dead zone, calculates a command pressure corresponding to the operation amount and a pressure corresponding to the tank pressure as the target pilot pressure, and outputs a command signal corresponding to the command pressure to one of the first electromagnetic valve and the second electromagnetic valve corresponding to the lever operation direction, and outputs a command signal corresponding to the pressure corresponding to the tank pressure to the other electromagnetic valve of the first electromagnetic valve and the second electromagnetic valve A working machine characterized by this.

2. In the working machine according to Claim 1, When the operation amount of the electric lever is 0, calculates a pressure corresponding to the tank pressure as the target pilot pressure, and outputs a command signal corresponding to the pressure corresponding to the tank pressure to both the first electromagnetic valve and the second electromagnetic valve. A working machine characterized by this.

3. In the working machine according to Claim 2, The electric lever is provided with a pressure sensor, When the output of the pressure sensor exceeds a set value, the controller calculates the standby pressure as the target pilot pressure even if the operation amount of the electric lever is 0, and outputs a command signal corresponding to the standby pressure to both the first electromagnetic valve and the second electromagnetic valve A working machine characterized by this.

4. In the working machine according to claim 1, When the electric lever tilts within the dead zone, the standby pressure calculated corresponding to the tilting direction of the electric lever is set to be larger than the standby pressure on the other side. A working machine characterized by this.

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